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Hydro-geomorphological characterization of Dhidhessa River Basin, Ethiopia
Author’s Accepted Manuscript Hydro-geomorphological characterization Dhidhessa River Basin, Ethiopia
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Gizachew Kabite, Berhan Gesesse
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S2095-6339(17)30249-6 https://doi.org/10.1016/j.iswcr.2018.02.003 ISWCR131
To appear in: International Soil and Water Conservation Research Received date: 17 October 2017 Revised date: 3 February 2018 Accepted date: 15 February 2018 Cite this article as: Gizachew Kabite and Berhan Gesesse, Hydrogeomorphological characterization of Dhidhessa River Basin, Ethiopia, International Soil and Water Conservation Research, https://doi.org/10.1016/j.iswcr.2018.02.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Hydro-geomorphological characterization of Dhidhessa River Basin, Ethiopia Gizachew Kabite1, 2, Berhan Gesesse2, 3 1
Department of Earth Science, Wollega University, P.O.Box 395, Nekemte, Ethiopia
2
Earth Observation Research Division, Entoto Observatory and Research Center, P.O.Box
33679, Addis Ababa, Ethiopia 3
Department of Geography and Environmental Studies, Kotebe University Collega, Addis
Ababa, Ethiopia
Correspondence to: [email protected]
Cell Phone: +251-911-951952
Abstract Dhidhessa River Basin is physio-graphically and hydrologically important in the Blue Nile basin, however, its morphometry and hydrology are not well known. This study aimed to characterize hydro-geomorphology of the basin via basin morphometry analysis. SRTM DEM, geological and hydrological maps of the area were used in ArcGIS 10.3 environment for this analysis. Results showed that a 33,468km total stream length of all orders was found distributed within 28,637km2 drainage area in a dendritic pattern. According to morphometric parameter classification, total stream length and stream order of the basin were high whereas stream length ratio, bifurcation ratio and hydrologic storage coefficient were low. Furthermore, drainage area was large, drainage frequency was coarse, basin shape was more elongated, drainage density was medium, infiltration number was low, overland flow was long and constant
of channel maintenance was high. Moreover, the basin’s relief, relief ratio, ruggedness number, gradient ratio and slope was high. In general, the study asserted that the basin was underlain by uniform resistant rocks, less prone to flooding, with high water resources potential and susceptible to soil erosion. The morphometric analysis approach pursued in this study was costand time-effective for basin characterization. Keywords:
Dhidhessa
River
Basin,
hydro-geomorphology,
hydrological
processes,
morphometric parameters, water resource potential.
1. Introduction
Digital Elevation Model (DEM) is the major dataset for various applications including hydrology and morphometry studies (Patel et al., 2016; Jensen, 1991; Wise, 2000). Hydrological analysis in particular relies heavily on DEM data (Moore et al., 1991; Li & Wong, 2010; Bastawesy et al., 2013). Drainage basin morphometric analysis is one of the typical hydrological applications of DEM data. According to Clarke (1966), morphometry is the measurement and mathematical analysis of Earth’s surface configuration, shape and dimension. Extracting drainage parameters from DEM is efficient, precise and economical (Moore et al., 1991).
Morphometric characteristics of drainage basins provide evidences to describe the topographical, geological and hydrological behavior of a basin (Angillieri, 2012). Morphometric characteristics influence basin processes (Garde, 2005; Mohd et al., 2013, Singh et al., 2014); describe geomorphology and hydrogeology features (Bloomfield et al., 2011; Soni, 2016) and provide valuable information on water resources potential assessment and management (Chandrashekar et al., 2015).
Quantitative morphometric analysis requires measurement of linear aspects of drainage network (e.g., stream order, stream length, stream number and bifurcation ratio), areal aspects of the drainage basin (e.g., length of overland flow, drainage density and basin shape) and relief aspects (e.g., basin relief, relief ratio, ruggedness number, gradient ratio, basin slope and relative relief) of the channel network and contributing ground slope (Miller, 1953; Schmm, 1956; Melton, 1957; Strahler, 1964). Such morphometric parameters can be readily determined from DEM using GIS than in conventional methods (Samal et al., 2015). GIS is ideal for morphometric analysis because of its strength in visualizing, processing and quantifying topographic attributes (Altaf et al., 2013).
The hydrological processes in a river basin strongly control the spatio-temporal distribution of water resources (i.e., surface and groundwater) and consequently potential water resource related developments in the basin. In the Dhidhessa River Basin, the study area, there are two ongoing major water resources development projects (i.e., Arjo-Dhidhessa Irrigation Dam project and the Grand Ethiopian Renaissance Dam project). The long-term success of these projects mainly depends on hydrologic characteristics of the river basin. As such, proper planning and management of water resources in the basin, requires good understanding of hydrologic processes and behaviors. However, hydro-meteorological data are not readily available as the basin is generally ungauged. In addition, reliability of watershed characteristics data such as soil, topography, land cover, and geology is questionable. These means, hydrogeomorphological characteristics of the Dhidhessa River Basin is also not well known. On the other hand, Dhidhessa River Basin is hydrological and physiographical importance for the Nile River Basin.
In the absence of observed hydrologic data, numerical morphometric analysis can provide valuable information about hydrologic characteristics (Perucca & Angillieri, 2011; Angillieri, 2012; Altaf et al., 2013; Soni, 2016) and physiographic and geologic information of basins. Despite the importance of morphometric analysis for planning and management of ungauged basins, only limited researches were conducted on the topic in Ethiopia, where most watersheds are poorly gauged. Even, globally, there is very limited research that quantified all the drainage morphometric parameters and characterized hydro-geomorphology of a basin in a comprehensive way. Only very few studies were done so far in Ethiopia on drainage morphometric analysis and characterization (Tesfaye & Wondimu, 2014; Girma & Vijaya, 2015). Both studies used Advanced Spaceborne Thermal Emission and Reflection radiometer Digital Elevation Model (ASTER DEM); however, several studies revealed that Shuttle Radar Topography Mission Digital Elevation (SRTM DEM) is much better than ASTER DEM in providing relatively accurate data to characterize drainage basin morphometry (Farr et al., 2007; Forkuor & Maathuis, 2012). Moreover, valuable morphometric parameters such as hydrologic storage (Rho) coefficient, length of overland flow, constant of channel maintenance, shape index, infiltration number, gradient ratio, Melton ruggedness number, channel gradient, and basin slope were not computed in the previous studies. Besides, the implication of the parameters on hydrological processes as well as on geomorphology in the respective watersheds were not discussed.
This research tried to fill these research gaps through quantifying valuable drainage morphometric parameters and characterize the hydro-geomorphology of the basin using the computed parameters. Therefore, the aim of the study was: i) to quantify morphometric parameters of the Dhidhessa River Basin from SRTM derived DEM data using ArcGIS 10.3 software and ii) to characterize the hydrology, geology, and topography of the basin from the
computed morphometric parameters (linear, areal and relief aspects). This valuable information could help guide with soil and water resource planning and management of the ungauged, but very important, river basin.
2. Materials and methods 2.1. Description of the study area
The Dhidhessa River is the largest among the 14 major rivers in the Blue Nile basin interms of its annual discharge. Among others, from hydrological and physiographical prospective, the Dhidhessa River is the most important basin in the Blue Nile Basin (Yohannes, 2008). The Nile Basin which supports millions of inhabitants since prehistoric times (Bastawesy et al., 2013) receives about 60% of its annual discharge from Blue Nile River (Williams, 2009a) of which about 25% comes from Dhidhessa River alone (Yohannes, 2008). This river receives the highest rainfall (>1800 mm/year) (Gamachu, 1977; Conway, 2000) among the Blue Nile basins and is covered with vegetation that promote high infiltration and increase base flow during dry season. As such, the river contributes the most flow to the Blue Nile River among the tributaries in the basin. Dhidhessa River Basin is located between 07040’ N and 10000’N Latitude and 35030’E and 37015’E Longitude whereas elevations in the basin ranges from 619 m to 3,213 m a.m.s.l (Figure 1). The Dhidhessa River Basin originate from Sigmo mountain ranges in southwestern Ethiopia and flows towards the easterly direction for about 75 km, and then turning rather sharply to the north until it joins the Blue Nile River near the junction of Wenbara and Yaso districts of Ethiopia. The outlet considered for this study is at about 76 km downstream of the confluence of Angar River with main Dhidhessa River, which covers a total drainage area of
28,637 km2. The Dhidhessa River basin is composed of five main watersheds such as Upper Dhidhessa, Wama, Dabana, Anger, and Lower Dhidhessa. Mean annual rainfall in the Dhidhessa River Basin ranges from 1509 mm (e.g., at Alibo and Sibu Sire stations) to 2322 mm (e.g., at Nekemte and Dembi stations). The majority of the basin is characterized by a humid tropical climate with heavy rainfall. Most of the total annual rainfall is received from June to August but the rainy season in the area ranges from May to October. Mean annual temperature of the basin ranges from 160c to 300c. The area is known for its dense vegetation cover and cash crop plantations such as coffee and Tea.
Figure 1. Location Map of Dhidhessa River Basin with their DEM and major streams
Most part of the Dhidhessa River Basin is mountainous, highly rugged and dissected topography with steep slopes while the valley floor with flat to gentle slopes characterizes the lower part of the basin (Figure 1). The major soil types in the basin includes Acrisols (36.7%), Cambisols (21.5%), Nitosols (20.6%), Lixisols (12.7%), Vertisols (4.8%), Leptosols (3. 4%), Fluvisols (0.22%), and Luvisols (0.12%) (OWWDSE, 2014).
The geology of western Ethiopia, where the study basin is found, is characterized by a variety of rock types ranging in age from Precambrian to Quaternary. Precambrian rocks, Tertiary volcanic, and Quaternary Sedimentary formations underlain Dhidhessa River Basin. The Tertiary volcanic formation (Lower basalt, Middle basalt and Upper basalt) occupy the largest proportion of the area (~50%) and it is one of the good aquifers in the area with varying yield and water quality (GSE, 2006). There are numerous fractures and joints forming various trending lineaments in the Proterozoic crystalline basement rocks of the River basin. Most of the lineaments are steeply dipping to vertical fractures.
Figure 2. Terrain Profile of Dhidhessa River basin from the headwater to the outlet
2.2. Data sources and processing
SRTM derived DEM data sampled over 1 arc-second by 1 arc-second (resampled to approximately 30-m resolution) was obtained from United State Geological Survey (USGS) website free of charge. The morphometric analysis reported in this study used the DEM dataset. SRTM DEM data is preferred to ASTER DEM due to its higher vertical and horizontal accuracy (Sun et al., 2003; Forkuor & Maathuis, 2012; Patel et al., 2016). The SRTM DEM is derived from radar system, which is less affected by weather condition compared to DEM derived from optical ASTER. However, irrespective of data source and the method used to process the data, all DEMs are subjected to errors (Forkuor & Maathuis, 2012). In this study, patching missing data via interpolation techniques and sink fill algorithm were applied as pre-processing of DEM for minimizing errors. In addition, geological and hydrogeological maps of the study area with 1: 250,000 scales were used as supplementary during the analysis.
The pre-processed DEM was used to determine the morphometric parameters including linear, areal and relief aspects using ArcGIS 10.3 software. In this study, a threshold value of 0.36km2 was used for extracting stream network as proposed by Tarboton et al. (1992). The parameters analyzed, the method used to quantify each parameter along with references for each method are summarized in Table 1. Finally, the computed drainage morphometric parameters were used to examine hydrological, geologic and topographic characteristics of the basin.
Table 1. Standard Methods of Morphometric parameters Morphometric Parameters
Methods and Descriptions
Stream order (u)
Hierarchical ordering
Strahler (1957)
Stream length (Lu)
Length of the stream
Horton (1945)
s
aspect
r
Linea
Morphometric Aspects
References
Mean stream length (Lm)
Lm = Lu/Nu
Horton (1945)
Stream length ratio (RI)
RI=Lu/L(u-1); Lu is stream Horton (1945) length of order u and L(u-1) is stream of the next lower order
Bifurcation ratio (Rb)
Rb=Nu/N(u+1); Nu is number Horton (1945) of streams of any given order and N(u+1) is the next higher order
Rho coefficient (??)
?? = RI/Rb
Drainage density (Dd)
Dd = L/A; L is total stream Horton (1945)
Horton (1945)
length, A is area of watershed Stream frequency (Fs)
Fs = N/A; N is total number of Horton (1945) streams
Areal aspects
Drainage texture (Dt)
T = Dd*Fs
Smith (1950)
Length of overland flow (Lg) Lg = ½*Dd
Horton (1945)
Constant of channel
Schumm
C = 1/Dd
maintenance (C)
(1956)
Form factor (Ff)
Ff = A/Lb2; Lb is basin length
Circularity ratio (Rc)
Rc = 4πA/P2; P is perimeter of Miller (1953)
Horton (1945)
basin Elongation ratio (Re)
Re=2/Lb* (A/ π)1/2
Schumm (1956)
Shape index (Sw)
Sw = 1/Fs
Horton (1932)
Infiltration Number (If)
If = Dd*Fs
Zavoiance (1985)
Relief aspects
Basin relief (R)
R=H-h;
H
is
maximum Schumm
elevation and h is minimum (1956) elevation within the basin Relief ratio (Rr)
Rr= R/Lb
Schumm (1956)
Ruggedness number (Rn)
Rn = R*Dd/1000
Schumm (1956)
Gradient ratio (Rg)
Rg = Es-Em/Lb; Es is the Sreedevi et al., elevation at the source, Em is (2009) the elevation at the mouth
Melton ruggedness number MRn = R/A1/2
Melton (1965)
(MRn) Cg = R/ {(π/2*Lb}
Channel Gradient (Cg)
Singh et al., (2008)
Basin Slope (Sb)
Sb = H/Lb
Miller (1953)
3. Results and discussions 3.1. Linear, areal and relief aspects of Dhidhessa River Basin
Figure 1 and 3 show the Dhidhessa River Basin boundary and streams generated using the technique recommended by Strahler (1957), respectively. The major linear morphometric parameters quantified for the basin including total stream length, mean stream length, stream length ratio, bifurcation ratio and Rho coefficient ratio of each stream order are summarized in Table 2. The basin has dendritic drainage pattern and has up to 8th order streams (Figure 3).
Table 2. Linear Aspects of Dhidhessa River Basin Parameters
Stream Orders 1
Total Stream Length in
16742.9
2
3
4
5
6
7
8
8251.3
4438.8
2212.8
905.9
291.9
344.4
280.1
km (TLu) Total Stream Length of all order (km) Mean Stream Length in
33468
0.8
0.9
0.9
9.0
17.4
26.5
114.8
280.1
19986
9097
5190
246
52
11
3
1
km (Lm) Total number of streams
Stream Length Ratio (RI) 0.5
0.5
0.5
0.4
0.3
1.2
0.2
0.8
Bifurcation Ratio (Rb)
2.2
1.8
1.9
2.1
3.0
0.7
1.3
-
Rho Coefficient (??)
-
0.3
0.3
0.2
0.1
0.4
0.9
-
Mean Bifurcation
1.8
Figure 3. Drainage Pattern of Dhidhessa River Basin
Similarly, major areal morphometric parameters of Dhidhessa River Basin which include area, perimeter, drainage density, stream frequency, drainage texture, length of overland flow, constant of channel maintenance, form factor, circularity ratio, elongation ratio, shape index and infiltration number are presented in Table 3.
Table 3. Areal Aspects of Dhidhessa River Basin Basin Name Dhidhessa River Basin Area (A) in km2
28637.2
Perimeter (P) in km Drainage density (Dd) in km/km
1571.2 2
1.2
Stream frequency (Fs) in km-2
1.4
Drainage texture (Dt)
1.7
Shape index (Sw)
0.7
Infiltration Number (If)
1.7
Length of overland flow (Lg)
0.6
Constant of channel maintenance (C) km2/km
0.7
Form factor (Ff)
0.1
Circularity ratio (Rc)
0.1
Elongation ratio (Re)
0.4
On the other hand, major Morphometric relief aspect parameters of Dhidhessa River Basin including basin relief, basin length, relief ratio, ruggedness number, gradient ratio, Melton ruggedness number, channel gradient and basin slope are presented in Table 4.
Table 4. Relief aspects of Dhidhessa River Basin Basin Name
Dhidhessa River Basin
Basin relief (R) in meter
2594
Basin length (Lb) in km
437
Relief ratio (Rr)
5.9
Ruggedness number (Rn)
3.1
Gradient ratio (Rg)
4.9
Melton Ruggedness number (MRn)
15.3
Channel Gradient (Cg) m/km
3.8
Basin Slope (Sb)
7.4
The dendritic drainage pattern and up to 8th order streams implies that the basin is composed of homogenous resistant lithology and can produce large quantity of streamflow, respectively. In the light of this, Withanage et al. (2014) noted that dendritic drainage pattern as irregular branching of streams at angle less than 900 that can be developed in area where the underlying geology has uniform resistance, and no structural control. Such drainage pattern is likely to exist on nearly horizontal sedimentary rocks, on areas of massive igneous rocks or on complex metamorphosed rocks (Garde, 2005). The inference is in line with the study conducted by Geological Survey of Ethiopia (2000, 2006 & 2007), which reported that the basin is underlain by sedimentary, igneous and complex metamorphic rocks. However, most of the igneous rocks in the study area are less massive, weathered and fractured. The study further revealed that the fractures and joints that form various trending lineament in the basin, mostly in the Proterozoic crystalline basement rocks, are steeply dipping to vertical fractures, which leads to less control surface runoff, groundwater recharge and base-flow. The total stream length is longest for the 1st order streams in the basin (i.e., 16,742.9 km) and shortest for the 8th order (i.e., 280 km). As shown in Figure 4a and Table 2, total stream
length is inversely proportional to stream order, which is consistent with findings reported by the existing literature (Horton, 1945; Singh et al., 2014). On the other hand, the mean stream length increases from 1st order to the 8th order (Figure 4b) which indicate that 1st order streams are short but numerous in number while 8th order streams are few in number but longer in length as described by Strahler (1964). This could be due to the decreasing slope of the basin from the divide line to the outlet of the basin, and indicate that the basin is still in its youthful stage of development. Moreover, short stream length describe steep slopes while longer lengths indicate flatter gradient (Withanage et al., 2014). The stream length and stream length ratio can depict clue information about hydrologic characteristics of the basin. The variability of those values from one stream order to the other (Table 2) revealed difference in the infiltration capacity at different stream orders which could be due to change in slope and topography (Bharadwaj et al., 2014). Dhidhessa River Basin has the lowest (i.e., 0.3) stream length ratio in the 6th order and the highest (i.e., 1.2) in 7th order with mean value of 0.6.
Figure 4. Relationship between mean stream length and stream order (a) and total stream length and stream order (b). Similarly, the Bifurcation ratio (Rb) and Rho coefficient (??) of the basin are different for different stream orders. The Bifurcation ratio of the basin ranges from 0.7 to 2.2 with 1.8 mean value while the Rho coefficient ranges from 0.1 for 5th order streams to 0.9 for 7th order streams with mean value of 0.4. Such irregularities in Rb values between stream orders revealed variation
in geological and lithological development of the drainage basin (Strahler, 1964). The Bifurcation ratio could be used to infer whether geological structure of the basin is controlling the drainage pattern or not (Singh et al., 2014) while Rho coefficient represents storage capacity of the drainage network during a rainfall event (Soni, 2016). Bifurcation ratio less than 5 indicates that: i) the drainage basin is underlain by rocks of uniform resistance; ii) streams are branched systematically with large number of first, second and third order streams (Chandrashekar et al., 2015); and iii) there is less structural disturbance that control drainage pattern in the basin (Strahler, 1964; Nag, 1998). Low Rho coefficient for 5th order streams confirmed the susceptibility to soil erosion and flooding than the 7th order, which has high runoff storage capacity during flooding. Generally, the linear morphometric analysis shown that stream length and stream orders of the basin are high while stream length ratio, Bifurcation ratio and Rho coefficient values are low (Table 2). Drainage area and perimeter of the basin are 28,637.2 km2 and 1,571.2 km, respectively, which indicate the study area is large. On the other hand, drainage density, stream frequency, drainage texture and infiltration number of the basin are 1.2 km/km2, 1.4, 1.7 and 1.7, respectively characterizing the basin as medium drainage density and coarse textured indicating the basin is underlain with highly permeable lithology (Table 3). According to Geological Survey of Ethiopia (2007), large portion of the basin is underlain with Tertiary volcanic formation (igneous rocks) (~50%), which are weathered, fractured and faulted by SE and NE lineaments. However, the lineaments have less control on drainage patterns. Generally, the basin’s drainage density, stream frequency and drainage texture are strongly correlated (Horton, 1945) showing its permeability and infiltration capacity. Furthermore, the length of overland
flow is 0.6 km/km2 for the basin indicating longer flow path with high infiltration and minimum runoff as argued by Chandrashekar et al. (2015).
In addition, the computed areal morphometric analysis showed that the elongation ratio, shape index, form factor and circulatory ratio of the basin are 0.4, 0.7, 0.1 and 0.1, respectively. These parameters are strongly correlated with each other and are used to describe the basin configuration (Soni, 2016). Elongation ratio values less than 0.8 are considered elongated and usually associated with high relief and deep ground slope (Strahler, 1964). Generally, the configuration of the Dhidhessa River Basin is more elongated (0.4) indicating longer lag time and low risk of soil erosion and flooding compared to other basins of similar size (Miller, 1953; Strahler, 1964; Singh & Singh, 1997; Soni, 2016). Erosion risk could still be high in the headwaters as the elongation ratio of the upper Dhidhessa River Basin is higher (i.e., 0.7).
The low circularity ratio (i.e., 0.1) of the basin indicates that the basin is elongated in shape, and may has low runoff potential resulted from the presence of highly permeable subsoil conditions (Singh et al., 2014). The low infiltration number of the basin further revealed the high infiltration and lower runoff potential (Strahler, 1964) of the basin. Constant of channel maintenance implies how much drainage area is required to maintain a unit length of channel and it is determined by the degree of resistance of the underlain material, vegetation cover and topography (Altaf et al., 2013). It is a measure of basin erodibility (Bharadwaj et al., 2014) which in the case of Dhidhessa River Basin with 0.7. This means 0.7 km2 basin is required to sustain 1 km length of drainage channel.
Relief aspect parameters provide information about denudation characteristics of a basin (Oruonye et al., 2016), morphological characteristics of a terrain (Hadley & Schumm, 1961), and
overall steepness of basin and intensity of erosional process (Tejpal, 2013). The basin relief and basin length of Dhidhessa River Basin are 2594 m. a. s. l and 494 km, respectively which show that the river flows longer distance in rugged topography. The longer the basin length and the steeper the topography, the higher the erosive power of the runoff will be. The basin slope of the study basin is 7.4, which is highly related with basin relief indicating that Dhidhessa River Basin is steep slope with high potential for surface run-off production and soil erosion. Moreover, relief ratio of the basin is 5.9 revealing that the area has steep slope that creates high potential energy for transporting water and sediment down slope per unit length. The ruggedness number combines the slope steepness and length indicating the extent of instability of land surface (Strahler, 1957). In the case of the study basin, the ruggedness number is 3.1 which is considered high showing the area has a rugged topography, susceptible to soil erosion and structurally complex.
Other important relief characteristics quantified in this study is Melton ruggedness number (MRn) which is a slope index that provides particular representation of relief ruggedness within the watershed (Melton, 1965). Melton ruggedness number for Dhidhessa River Basin is 15.3 indicating that sediment transport is dominated by bed loads according to Wilfordet et al (2004) classification. Gradient ratio (Rg) is used to assess runoff volume and it is an indicator of channel slope (Sreedevi et al., 2004). Rg of the study basin is 4.9 indicating that the basin has high relief and is mountainous in nature.
Some of the morphometric parameters of the Dhidhessa catchments have generally similar pattern with that of the main Dhidhessa River Basin. However, the catchments are different in most parameters particularly in their relief aspect (Table 5). For example, Anger and
Dabena catchments have higher constant of channel maintenance value (i.e., 0.9) than the main Dhidhessa (i.e., 0.7) while the Upper Dhidhessa is less elongated (i.e., 0.7) compared to the main Dhidhessa (i.e., 0.4). Dabena catchment have relatively with less basin relief (i.e., 1328) and ruggedness number (i.e., 1.5). However, Anger and Upper Dhidhessa catchments are with higher relief and gradient ratios compared to the main Dhidhessa. The Melton ruggedness number and channel gradient is higher in the Anger catchment compared to the other Dhidhessa catchments while basin slope is higher in the Upper Dhidhessa catchment (i.e., 20.1).
Table 5. Morphometric Parameters of Main Dhidhessa and its watersheds Parameters A Dd Fs Dt Sw If Lg C Ff Rc Re R Lb Rr Rn Rg MRn Cg Sb Rb (mean) RI (mean) Rho (mean)
Main Dhidhessa Anger Dabena Upper Dhidhessa Lower Dhidhessa 28637.2 7766 3209.4 8946.1 8716 1.2 1.1 1.1 1.2 1.2 1.4 1.3 1.4 1.4 1.4 1.7 1.5 1.5 1.6 1.7 0.7 0.8 0.7 0.7 0.7 1.7 1.5 1.5 1.6 1.7 0.6 0.5 0.6 0.6 0.6 0.7 0.9 0.9 0.8 0.8 0.1 0.2 0.1 0.4 0.1 0.1 0.2 0.1 0.2 0.1 0.4 0.5 0.4 0.7 0.4 2594 2343 1328 1849 1985 490 200 161 157 280 5.9 11.7 8.2 11.8 7.1 3.1 2.6 1.5 2.2 2.4 4.9 7.8 7.4 9.3 2.2 15.3 26.6 23.4 19.5 21.3 7.5 4.5 3.8 7.8 5.3 7.4 16.7 15.4 20.1 9.3 1.8 2.4 1.9 0.8 2.6 0.6 0.9 0.7 1.9 4.7 0.4 0.3 0.3 0.3 1.8
3.2. Hydro-geomorphologic characteristics of Dhidhessa River Basin
As previously described, several studies have revealed that basin morphometry is strongly correlated with basin physio-geographic and hydrological processes making it possible to infer major hydrological behavior of a basin such as flooding, soil erosion, topography, groundwater recharge, and geologic and lithologic formation of a basin from quantitative morphometric analysis.
3.2.1. The relationship between drainage morphology and topography of the basin
Relief aspect parameters such as basin relief, relief ratio, gradient ratio, ruggedness number, Melton ruggedness number and basin slope are indicators of topographic characteristics of a basin (Hadley & Schumm, 1961; Tejpal, 2013; Oruonye et al., 2016). Accordingly, the relief morphometric analysis revealed that the Dhidhessa River Basin is characterized by high relief with steep slope, mountainous and topographically rugged (Figure 1 and 2). Such characteristics resulted in high drainage density, frequency and texture (Rekha et al., 2011). Contrary to this, drainage density, frequency, and texture of the area are low to medium revealing that there are other controlling factors like soil type, vegetation cover and permeability of the underlain lithology coupled by high rainfall.
3.2.2. Morphometric parameters nexus underlined geology of the basin
The underlined geology of a given basin can be inferred from morphometric parameters like drainage pattern, mean stream length, bifurcation ratio and constant of channel maintenance (Strahler, 1964; Nag, 1998; Garde, 2005; Altaf et al., 2013; Withanage et al., 2014). According to the study, geology of the Dhidhessa River Basin is likely a horizontal sedimentary rock,
igneous rocks or complex metamorphosed rocks underlain with uniformly resistant rocks that lacks structural control. Furthermore, the variation of mean stream length and bifurcation ratio between stream orders indicates that the basin is still at its youthful stage of development and hence the geological and lithological development of the drainage basin varies spatially. Similarly, geological map of the Dhidhessa River Basin showed similar results. According to Geological Survey of Ethiopia (2000), the geology of the basin is underlain by crystalline Precambrian basement rocks, Tertiary volcanic rocks and Quaternary sedimentary formation where most part of the area is covered by tertiary volcanic rocks (~50%). Furthermore, the study revealed the presence of complex structures specifically in the Proterozoic crystalline basement rocks of the basin. However, since most of the lineaments are steeply dipping to vertical fractures, they have less control over the drainage pattern and groundwater recharge conditions (GSE, 2006).
3.2.3. Morphometric parameters nexus flood status of the basin
The flood status of a given watershed could be inferred from morphometric parameters like area, basin length, basin configurations (elongation ratio, circularity ratio and forma factor), drainage density and drainage frequency. Generally, elongated, and medium drainage density and medium frequency of the river basin is expected to produce minimum peak runoff (Miller, 1953; Strahler, 1964; Singh & Singh, 1997; Soni, 2016). The values of the parameters revealed that the lag time is high in the area resulting in less chance for flooding to occur as the conditions promote more infiltration than peak runoff formation. Furthermore, high infiltration capacity of the area, inferred from low infiltration number and physical properties of the geologic formation of the area supports the absence of severe flooding. However, low to medium Rho coefficient
indicates the possibility of flooding during heavy rainfall as the drainage channels have less capacity to store much runoff. The high permeability of the basin is compensated by high rainfall with longer wet season and larger drainage area (~29,000 km2). Generally, the Dhidhessa River Basin has high annual mean runoff quantity (13 km3/year) (Conway, 2000), but with less flooding hazard that could occur in the lowland areas of the basin. The upper Dhidhessa catchment is less prone to flooding compared to the rest catchment (Table 5).
3.2.4. Soil erosion and drainage morphometric characteristics of the basin
Soil erosion potential and its intensity in a given basin could be obtained from relief aspect (Tejpal, 2013), which includes basin relief, relief ratio, channel gradients, ruggedness number, basin length and Melton ruggedness number. The value of those parameters indicate that the basin is characterized by steep slope and is topographically rough which allows easy sediment production and transportation that dominated by bed loads (Wilfordet et al., 2004). The study, thus, showed Dhidhessa River Basin is susceptible to sever soil erosion, which is higher in the Anger and the Upper Dhidhessa catchment.
On the other hand, the more elongated basin configuration and drainage characteristics (medium density, coarse texture and low frequency) of the Dhidhessa River Basin may counterbalance the high soil erosion status that could result from topographic effect. However, the basin is still susceptible to headwater erosion. In addition to the steep slope of the area, the presence of less resistant underlying material could result in sever soil erosion (Altaf et al., 2013). However, the susceptibility of the basin to sever soil erosion could be modified further by vegetation cover and soil type.
3.2.5. Groundwater recharge potential and the basin morphometry
Groundwater recharge of a given basin is influenced by stream frequency, infiltration number, drainage density, drainage texture, length of overland flow, basin configuration and basin length. Those parameters depict information about infiltration capacity of the area and runoff generation (Singh et al., 2014; Soni, 2016). From the values of those parameters, Dhidhessa River Basin could be with high infiltration capacity, which shows high groundwater recharge. According to the study, Anger catchment have high groundwater potential compared to the other catchments.
Furthermore, the morphometric analysis indicate that runoff formation and transportation is slow in the basin. Runoff gets extended time to infiltrate during such slow movement. This could be due to the presence of permeable underlying materials, which is inferred from drainage characteristics of the basin and the geological and hydrogeological map of the river basin. Despite high infiltration rate, runoff volume could be high for the basin due to high rainfall, large drainage area, and high stream order. The mean annual discharge of Dhidhessa River Basin is estimated to be 13 km3/year with fairly higher dry season flow compared to other Blue Nile basins (Conway, 2000). The high dry season flow of the basin is another indicator of high groundwater recharge during the wet season and base-flow during dry season. Furthermore, hydrogeological study of the basin revealed that most parts of the basin are underlain with very productive fractured aquifers (i.e., 6.2 l/s to 27 l/s), highly productive fracture aquifers (i.e., 5 l/s to 13.5l/s) and moderately productive fractures aquifers (i.e., 2.1 l/s to 2.8 l/s)(GSE, 2006). This implies that the Dhidhessa River Basin has ample surface water and groundwater resources.
According to the study, Dabena catchment seems to have high groundwater potential compared to the other catchments.
Conclusions
GIS based drainage morphometric quantification and analysis is found to be a cost-and time-effective approach to characterize poorly gauged basins as an alternative and complementary source of information. Accordingly, the stream length and stream order of the basin is higher while stream length ratio, bifurcation ratio and Rho coefficient values are low. On the other hand, large drainage area, coarse drainage frequency and texture, more elongated shape, medium drainage density, high infiltration capacity, longer overland flow and high constant of channel maintenance are the characteristics of the Dhidhessa River Basin. Similarly, high relief, longer basin length, high relief ratio, high ruggedness number, high gradient ratio and high basin slope are the relief characteristics of the Dhidhessa River Basin.
From the morphometric analysis, the characteristics of Dhidhessa River Basin can be inferred as the underlying geology is with uniform resistance and lack of structural disturbance, the geological and lithological developments of the basin are spatially variable and the basin is less prone to flooding except in the lowland parts of the basin during heavy rainfall.
Moreover, Dhidhessa River Basin is very susceptible to soil erosion due to topographic factors like slope steepness and topographic roughness that aggravate the erosive capability of rainfall for both detachment and transportation. According to the morphometric analysis, the Anger and Upper Dhidhessa catchments seems to be more susceptible to soil erosion. However, susceptibility to soil erosion could be minimized by dense vegetation cover and/or deep soil
depth of the area that could reduce the erosive energy of rainfall and runoff. Moreover, more elongated basin configuration and the longer basin length could further minimize the topographic effect on soil erosion. Quantitative morphometric analysis of the basin further indicates high potential of both surface and groundwater resources in the basin. Despite the high relief, rugged topography and steep slope of the basin, its drainage characteristics are low to medium revealing that there are other controlling factors in addition to terrain parameters. Further research is needed to investigate these issues.
Generally, this study shows that quantitative morphometric analysis using the-state-of-the-art approach is time- and cost-effective in providing baseline information for characterizing basin hydrologically, physio-graphically and geologically. However, such morphometric analysis should be supported by detailed geophysical, hydrogeological and hydro-metrological studies to use the information for decision-makings.
Acknowledgments We are very gratitude to Ethiopia Geological Survey and Oromia Water Works Design and Supervision Enterprise for providing us data required for the research such as Geological and Hydrological maps, and Soil map of the study area, respectively, free of charge. Moreover, we thank NASA for availing SRTM DEM data freely, which were also used as a main data source for this particular research. We would also thank the anonymous reviewers for their constructive comments.
Disclosure statement There is no potential conflict of interest.
Funding There is no direct fund for conducting this research.
References
Altaf, F., Meraj, G., & Romshoo, A. Sh. (2013). Morphometric Analysis to Infer Hydrological Behavior of Lidder Watershed, Western Himalaya, India. Geography Journal, 2013, 114. Angillieri, E. Y. M. (2012). Morphometric characterization of the Carrizal basin applied to the evaluation of flash floods hazards, San Juan, Argentina. Quaternary International, 253 (2012), 74-79. Bastawesy, E. l. M, Gabr, S., & White, K. (2013). Hydrology and geomorphology of the Upper White Nile lakes and their relevance for water resources management in the Nile basin. Hydrological processes, 27,196-205. Bharadwaj, K. A., Pradeep, C., Thirumalaivasan, D., Shankar, P. C., & Madhavan, N. (2014). Morphometric Analysis of Adyar Watershed. Journal of Mechanical and Civil Engineering, 2320-334X, 71-77. Bloomfield, J. P., Bricker, S. H., & Newell, A. J. (2011). Some relationships between lithology, basin form and hydrology: a case study from the Thames basin, UK. Hydrological processes, 25 (16), 2518-2530. Chandrashekar, H., Lokesh, V. K., Sameena, M., Roopa, J., & Ranganna, G. (2015). GIS-Based Morphometric Analysis of Two Reservoir Catchments of Arkavati River, Ramanagaram District, Karnataka. International Conference on water resources, Coastal and Ocean Engineering (ICWCOE2015). Aquatic Procedia, 4(2015), 1345-1353.
Clarke, J. I. (1966). Morphometry from Maps. Essays in geomorphology. Elsevier Publication Corporation, India, Delhi. Conway, D. (2000). Climate and Hydrology of the upper Blue Nile River Basin. The Geographical Journal, 166(1): 49–62. Farr, T., Rosen, P. A., Caro, E., Crippen, R., Duren, R., & Hensley, S. (2007). The shuttle radar topography mission. Reviews of Geophysics 45, RG2004. Forkuor, G., & Maathuis, B. (2012). Chapter 9: Comparison of SRTM and ASTER Derived Digital
Elevation Models over Two Regions in Ghana-Implications for Hydrological and Environmental Modeling. In Studies on Environmental and Applied Geomorphology, Dr.Tommaso Piacentini (ed.), InTech, 219-240.
Gamachu, D. (1977). Aspects of climate and water budget in Ethiopia. Addis Ababa, Addis Ababa University Press. Garde, R. J. (2005). River Morphology, New Age International (Pvt) Ltd. Publishers, New Delhi.
Geological Survey of Ethiopia (GSE). (2000). Geology of the Nekemte and Gimbi Area. Sheet Number: NC-37-9 and NC-36-12, respectively. Unpublished.
Geological Survey of Ethiopia (GSE). (2006/7). Hydrogeology and Hydrochemisry of Nekemte and Arjo area. Sheet Number: NC37-9 and NC37-13, respectively. Unpublished.
Girma, M., & Vijaya, B. (2015). Morphometric Characteristics and the Relation of Stream Orders to Hydraulic Parameters of River Goro: An Ephemeral River in Dire-dawa, Ethiopia. Universal Journal of Geoscience, 3(1), 13-27. Hadley, R. F, & Schumm, S. A. (1961). Sediment Sources and Drainage Basin Characteristics in Upper Cheyenne River Basin. USGS Water-Supply Paper, 1531-B, 1-198.
Horton, R. E. (1945). Erosional Development of Streams and Their Drainage Basins. Geological Society of America Bulletin, 56 (3), 275-370. Horton, E. R. (1932). Drainage basin characteristics. Transactions American Geophysical Union 13, 350-361. Jensen, S. K. (1991). Applications of hydrologic information automatically extracted from digital elevation models. Hydrological Processes, 5(1), 31-44. Li, J., Wong, W. D. (2010). Effects of DEM sources on hydrologic applications. Computers, Environment and Urban Systems, 34, 251-261. Melton, M. A. (1965). The geomorphic and paleo-climatic significance of alluvial deposits in Southern Arizona. Journal of Geology, 73, 1-3. Melton, M. A. (1957). An Analysis of the relations among elements of climate, Surface properties
and geomorphology. Technical Report Number 11, Department of Geology,
Columbia
University.
Miller, V. C. (1953). A quantitative geomorphic study of drainage basin characteristics in the Clinch Mountain area, Virginia and Tennessee, Project NR 389042, Tech. Rept. 3., Columbia University, Department of Geology, ONR, Geography Branch, New York. Mohd, I., Haroon, S., & Bhat, F. A. (2013). Morphometric Analysis of Shaliganga Subcatchment,
Kashmir Valley, India Using Geographical Information System. International
Journal of
Engineering Trends and Technology, 4(1), 10-21.
Moore, I. D, Grayson, R. B, & Ladspm, A. R. (1991). Digital terrain modeling: A review of hydrological, geomorphological and biological applications. Hydrological Processes, 5, 3-
30.
Nag, S. K. (1998). Morphometric analysis using remote sensing techniques in the Chaka sub basin, Purulia district, West Bengal. Journal of Indian Society of Remote sensing, 26 (1 & 2), 69 - 76.
Oromia Water Works Design and Supervision Enterprise (OWWDSE). (2014). Dhidhessa SubBasin Soil Survey Report. Dhidhessa-Dabus Integrated Land Use Planning Study Project. Unpublished. Oruonye, D. E., Ezekiel, B. B, Atiku, G. H., Baba, E., Musa, I. N. (2016). Drainage Basin Morphometric Parameters of River Lamurde: Implication for Hydrologic and Geomorphic
Processes. Journal of Agriculture and Ecology Research International, 5(2), 1-11.
Patel, A., Katiyar, K. S., & Prasad, V. (2016). Performances evaluation of different open source DEM using Differential Global Positioning System (DGPS). The Egyptian Journal of Remote Sensing and Space Sciences. Article in press. Perucca, P. L., & Angilieri, E. Y. (2011). Morphometric characterization of Del Molle Basin applied to the evaluation of flash floods hazard, Iglesia Department, San Juan, Argentina. Quaternary International, 233 (2011), 81-86. Rekha, B. V., George, V. A., & Rita, M. (2011). Morphometric Analysis and Micro-watershed Prioritization of Peruvanthanam Sub-watershed, the Manimala River Basin, Kerala, South India. Environmental Research, Engineering and Management, 3(57), 6-14. Samal, R. D., Gedam, S. Sh., & Nagarajan, R. (2015). GIS based drainage morphometry and its influence on hydrology in parts of Western Ghats region, Maharashtra, India. Geocarto International, 30(7), 755-778. Schumm, S. A. (1956). The Evolution of drainage systems and slopes in badlands at Perth Amboi,
New Jersey. Geological Society of America Bulletins, 67(5).
Singh, S., Singh, M. C. (1997). Morphometric analysis of Kanhar river basin. National Geographical Journal of India, 43(1), 31-43. Singh, P., Gupta, A., & Singh, M. (2014). Hydrological inferences from watershed analysis for water resource management using remote sensing and GIS techniques. The Egyptian Journal of Remote Sensing and Space Sciences, 17,111-121.
Smith, K. G. (1950). Standards for grading texture of erosional topography. American Journal Science, 248:655-668. Soni, S. (2016). Assessment of morphometric characteristics of Chakrar watershed in Madhya Pradesh India using geospatial technique. Applied Water Science. Sreedevi P. D., Subrahmanyam, K., & Ahmed S. (2004). The significance of morphometric analysis for obtaining groundwater potential zones in a structurally controlled terrain. Environmental Geology, 47, 412-420. Sreedevi, P. D., Owais, S., Khan, H. H., & Ahmed, S. (2009). Morphometric analysis of a watershed of South India using SRTM data and GIS. Journal of Geological Society of India 73(4), 543-552. Strahler, A. N. (1964). Quantitative Geomorphology of drainage basins and channel networks. Chow VT. (ed). Handbook of Applied Hydrology, McGraw-Hill, New York, 439-476. Strahler, A. N. (1957). Quantitative analysis of watershed geomorphology. Transactions American
Geophysical Union, 38,913-920.
Sun, G., Ranson, K. J., Kharuk, V. I., & Kovacs, K. (2003). Validation of surface height from shuttle radar topography mission using shuttle laser altimeter. Remote Sensing of Environment, 88 (4), 401-411. Tarboton, D. G., Bras, R. L., & Rodriguez-Iturbe, I. (1992). A physical basis for drainage density. Geomorphology, 5(1/2), 59-76. Tejpal. (2013). Relief Analysis of the Tangri Watershed in the Lower Shivalik and Piedmont Zone of Haryana and Punjab. Indian Journal of Spatial Science, 4(1), 9-20. Tesfaye, M., & Wondimu M. 2014. Morphometric Analysis of Didessa River Catchment in Blue Nile Basin, Western Ethiopia. Science, Technology and Arts Research Journal, 3(3), 191197.
Wise, S. (2000). Assessing the quality for hydrological applications of digital elevation models derived from contours. Hydrological Processes, 14(11 and 12), 1909-1929. Withanage, S. N., Dayawansa, K. D. N., & De Silva, P. R. (2014). Morphometric Analysis of the Gal Oya River Basin Using Spatial Data Derived from GIS. Tropical Agricultural Research, 26(1), 175-188. Yohannes, O. (2008). Water Resources and Inter-Riparian Relations in the Nile Basin; the Search for an Integrative Discourse. State University of New York Press, Alhany. ISBN 978-07914-431-0. Zavoianu, I. (1985). Morphometry of Drainage basin (Developments in Water Science, 20). Amsterdam: Elsevier.
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To appear in: International Soil and Water Conservation Research Received date: 17 October 2017 Revised date: 3 February 2018 Accepted date: 15 February 2018 Cite this article as: Gizachew Kabite and Berhan Gesesse, Hydrogeomorphological characterization of Dhidhessa River Basin, Ethiopia, International Soil and Water Conservation Research, https://doi.org/10.1016/j.iswcr.2018.02.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Hydro-geomorphological characterization of Dhidhessa River Basin, Ethiopia Gizachew Kabite1, 2, Berhan Gesesse2, 3 1
Department of Earth Science, Wollega University, P.O.Box 395, Nekemte, Ethiopia
2
Earth Observation Research Division, Entoto Observatory and Research Center, P.O.Box
33679, Addis Ababa, Ethiopia 3
Department of Geography and Environmental Studies, Kotebe University Collega, Addis
Ababa, Ethiopia
Correspondence to: [email protected]
Cell Phone: +251-911-951952
Abstract Dhidhessa River Basin is physio-graphically and hydrologically important in the Blue Nile basin, however, its morphometry and hydrology are not well known. This study aimed to characterize hydro-geomorphology of the basin via basin morphometry analysis. SRTM DEM, geological and hydrological maps of the area were used in ArcGIS 10.3 environment for this analysis. Results showed that a 33,468km total stream length of all orders was found distributed within 28,637km2 drainage area in a dendritic pattern. According to morphometric parameter classification, total stream length and stream order of the basin were high whereas stream length ratio, bifurcation ratio and hydrologic storage coefficient were low. Furthermore, drainage area was large, drainage frequency was coarse, basin shape was more elongated, drainage density was medium, infiltration number was low, overland flow was long and constant
of channel maintenance was high. Moreover, the basin’s relief, relief ratio, ruggedness number, gradient ratio and slope was high. In general, the study asserted that the basin was underlain by uniform resistant rocks, less prone to flooding, with high water resources potential and susceptible to soil erosion. The morphometric analysis approach pursued in this study was costand time-effective for basin characterization. Keywords:
Dhidhessa
River
Basin,
hydro-geomorphology,
hydrological
processes,
morphometric parameters, water resource potential.
1. Introduction
Digital Elevation Model (DEM) is the major dataset for various applications including hydrology and morphometry studies (Patel et al., 2016; Jensen, 1991; Wise, 2000). Hydrological analysis in particular relies heavily on DEM data (Moore et al., 1991; Li & Wong, 2010; Bastawesy et al., 2013). Drainage basin morphometric analysis is one of the typical hydrological applications of DEM data. According to Clarke (1966), morphometry is the measurement and mathematical analysis of Earth’s surface configuration, shape and dimension. Extracting drainage parameters from DEM is efficient, precise and economical (Moore et al., 1991).
Morphometric characteristics of drainage basins provide evidences to describe the topographical, geological and hydrological behavior of a basin (Angillieri, 2012). Morphometric characteristics influence basin processes (Garde, 2005; Mohd et al., 2013, Singh et al., 2014); describe geomorphology and hydrogeology features (Bloomfield et al., 2011; Soni, 2016) and provide valuable information on water resources potential assessment and management (Chandrashekar et al., 2015).
Quantitative morphometric analysis requires measurement of linear aspects of drainage network (e.g., stream order, stream length, stream number and bifurcation ratio), areal aspects of the drainage basin (e.g., length of overland flow, drainage density and basin shape) and relief aspects (e.g., basin relief, relief ratio, ruggedness number, gradient ratio, basin slope and relative relief) of the channel network and contributing ground slope (Miller, 1953; Schmm, 1956; Melton, 1957; Strahler, 1964). Such morphometric parameters can be readily determined from DEM using GIS than in conventional methods (Samal et al., 2015). GIS is ideal for morphometric analysis because of its strength in visualizing, processing and quantifying topographic attributes (Altaf et al., 2013).
The hydrological processes in a river basin strongly control the spatio-temporal distribution of water resources (i.e., surface and groundwater) and consequently potential water resource related developments in the basin. In the Dhidhessa River Basin, the study area, there are two ongoing major water resources development projects (i.e., Arjo-Dhidhessa Irrigation Dam project and the Grand Ethiopian Renaissance Dam project). The long-term success of these projects mainly depends on hydrologic characteristics of the river basin. As such, proper planning and management of water resources in the basin, requires good understanding of hydrologic processes and behaviors. However, hydro-meteorological data are not readily available as the basin is generally ungauged. In addition, reliability of watershed characteristics data such as soil, topography, land cover, and geology is questionable. These means, hydrogeomorphological characteristics of the Dhidhessa River Basin is also not well known. On the other hand, Dhidhessa River Basin is hydrological and physiographical importance for the Nile River Basin.
In the absence of observed hydrologic data, numerical morphometric analysis can provide valuable information about hydrologic characteristics (Perucca & Angillieri, 2011; Angillieri, 2012; Altaf et al., 2013; Soni, 2016) and physiographic and geologic information of basins. Despite the importance of morphometric analysis for planning and management of ungauged basins, only limited researches were conducted on the topic in Ethiopia, where most watersheds are poorly gauged. Even, globally, there is very limited research that quantified all the drainage morphometric parameters and characterized hydro-geomorphology of a basin in a comprehensive way. Only very few studies were done so far in Ethiopia on drainage morphometric analysis and characterization (Tesfaye & Wondimu, 2014; Girma & Vijaya, 2015). Both studies used Advanced Spaceborne Thermal Emission and Reflection radiometer Digital Elevation Model (ASTER DEM); however, several studies revealed that Shuttle Radar Topography Mission Digital Elevation (SRTM DEM) is much better than ASTER DEM in providing relatively accurate data to characterize drainage basin morphometry (Farr et al., 2007; Forkuor & Maathuis, 2012). Moreover, valuable morphometric parameters such as hydrologic storage (Rho) coefficient, length of overland flow, constant of channel maintenance, shape index, infiltration number, gradient ratio, Melton ruggedness number, channel gradient, and basin slope were not computed in the previous studies. Besides, the implication of the parameters on hydrological processes as well as on geomorphology in the respective watersheds were not discussed.
This research tried to fill these research gaps through quantifying valuable drainage morphometric parameters and characterize the hydro-geomorphology of the basin using the computed parameters. Therefore, the aim of the study was: i) to quantify morphometric parameters of the Dhidhessa River Basin from SRTM derived DEM data using ArcGIS 10.3 software and ii) to characterize the hydrology, geology, and topography of the basin from the
computed morphometric parameters (linear, areal and relief aspects). This valuable information could help guide with soil and water resource planning and management of the ungauged, but very important, river basin.
2. Materials and methods 2.1. Description of the study area
The Dhidhessa River is the largest among the 14 major rivers in the Blue Nile basin interms of its annual discharge. Among others, from hydrological and physiographical prospective, the Dhidhessa River is the most important basin in the Blue Nile Basin (Yohannes, 2008). The Nile Basin which supports millions of inhabitants since prehistoric times (Bastawesy et al., 2013) receives about 60% of its annual discharge from Blue Nile River (Williams, 2009a) of which about 25% comes from Dhidhessa River alone (Yohannes, 2008). This river receives the highest rainfall (>1800 mm/year) (Gamachu, 1977; Conway, 2000) among the Blue Nile basins and is covered with vegetation that promote high infiltration and increase base flow during dry season. As such, the river contributes the most flow to the Blue Nile River among the tributaries in the basin. Dhidhessa River Basin is located between 07040’ N and 10000’N Latitude and 35030’E and 37015’E Longitude whereas elevations in the basin ranges from 619 m to 3,213 m a.m.s.l (Figure 1). The Dhidhessa River Basin originate from Sigmo mountain ranges in southwestern Ethiopia and flows towards the easterly direction for about 75 km, and then turning rather sharply to the north until it joins the Blue Nile River near the junction of Wenbara and Yaso districts of Ethiopia. The outlet considered for this study is at about 76 km downstream of the confluence of Angar River with main Dhidhessa River, which covers a total drainage area of
28,637 km2. The Dhidhessa River basin is composed of five main watersheds such as Upper Dhidhessa, Wama, Dabana, Anger, and Lower Dhidhessa. Mean annual rainfall in the Dhidhessa River Basin ranges from 1509 mm (e.g., at Alibo and Sibu Sire stations) to 2322 mm (e.g., at Nekemte and Dembi stations). The majority of the basin is characterized by a humid tropical climate with heavy rainfall. Most of the total annual rainfall is received from June to August but the rainy season in the area ranges from May to October. Mean annual temperature of the basin ranges from 160c to 300c. The area is known for its dense vegetation cover and cash crop plantations such as coffee and Tea.
Figure 1. Location Map of Dhidhessa River Basin with their DEM and major streams
Most part of the Dhidhessa River Basin is mountainous, highly rugged and dissected topography with steep slopes while the valley floor with flat to gentle slopes characterizes the lower part of the basin (Figure 1). The major soil types in the basin includes Acrisols (36.7%), Cambisols (21.5%), Nitosols (20.6%), Lixisols (12.7%), Vertisols (4.8%), Leptosols (3. 4%), Fluvisols (0.22%), and Luvisols (0.12%) (OWWDSE, 2014).
The geology of western Ethiopia, where the study basin is found, is characterized by a variety of rock types ranging in age from Precambrian to Quaternary. Precambrian rocks, Tertiary volcanic, and Quaternary Sedimentary formations underlain Dhidhessa River Basin. The Tertiary volcanic formation (Lower basalt, Middle basalt and Upper basalt) occupy the largest proportion of the area (~50%) and it is one of the good aquifers in the area with varying yield and water quality (GSE, 2006). There are numerous fractures and joints forming various trending lineaments in the Proterozoic crystalline basement rocks of the River basin. Most of the lineaments are steeply dipping to vertical fractures.
Figure 2. Terrain Profile of Dhidhessa River basin from the headwater to the outlet
2.2. Data sources and processing
SRTM derived DEM data sampled over 1 arc-second by 1 arc-second (resampled to approximately 30-m resolution) was obtained from United State Geological Survey (USGS) website free of charge. The morphometric analysis reported in this study used the DEM dataset. SRTM DEM data is preferred to ASTER DEM due to its higher vertical and horizontal accuracy (Sun et al., 2003; Forkuor & Maathuis, 2012; Patel et al., 2016). The SRTM DEM is derived from radar system, which is less affected by weather condition compared to DEM derived from optical ASTER. However, irrespective of data source and the method used to process the data, all DEMs are subjected to errors (Forkuor & Maathuis, 2012). In this study, patching missing data via interpolation techniques and sink fill algorithm were applied as pre-processing of DEM for minimizing errors. In addition, geological and hydrogeological maps of the study area with 1: 250,000 scales were used as supplementary during the analysis.
The pre-processed DEM was used to determine the morphometric parameters including linear, areal and relief aspects using ArcGIS 10.3 software. In this study, a threshold value of 0.36km2 was used for extracting stream network as proposed by Tarboton et al. (1992). The parameters analyzed, the method used to quantify each parameter along with references for each method are summarized in Table 1. Finally, the computed drainage morphometric parameters were used to examine hydrological, geologic and topographic characteristics of the basin.
Table 1. Standard Methods of Morphometric parameters Morphometric Parameters
Methods and Descriptions
Stream order (u)
Hierarchical ordering
Strahler (1957)
Stream length (Lu)
Length of the stream
Horton (1945)
s
aspect
r
Linea
Morphometric Aspects
References
Mean stream length (Lm)
Lm = Lu/Nu
Horton (1945)
Stream length ratio (RI)
RI=Lu/L(u-1); Lu is stream Horton (1945) length of order u and L(u-1) is stream of the next lower order
Bifurcation ratio (Rb)
Rb=Nu/N(u+1); Nu is number Horton (1945) of streams of any given order and N(u+1) is the next higher order
Rho coefficient (??)
?? = RI/Rb
Drainage density (Dd)
Dd = L/A; L is total stream Horton (1945)
Horton (1945)
length, A is area of watershed Stream frequency (Fs)
Fs = N/A; N is total number of Horton (1945) streams
Areal aspects
Drainage texture (Dt)
T = Dd*Fs
Smith (1950)
Length of overland flow (Lg) Lg = ½*Dd
Horton (1945)
Constant of channel
Schumm
C = 1/Dd
maintenance (C)
(1956)
Form factor (Ff)
Ff = A/Lb2; Lb is basin length
Circularity ratio (Rc)
Rc = 4πA/P2; P is perimeter of Miller (1953)
Horton (1945)
basin Elongation ratio (Re)
Re=2/Lb* (A/ π)1/2
Schumm (1956)
Shape index (Sw)
Sw = 1/Fs
Horton (1932)
Infiltration Number (If)
If = Dd*Fs
Zavoiance (1985)
Relief aspects
Basin relief (R)
R=H-h;
H
is
maximum Schumm
elevation and h is minimum (1956) elevation within the basin Relief ratio (Rr)
Rr= R/Lb
Schumm (1956)
Ruggedness number (Rn)
Rn = R*Dd/1000
Schumm (1956)
Gradient ratio (Rg)
Rg = Es-Em/Lb; Es is the Sreedevi et al., elevation at the source, Em is (2009) the elevation at the mouth
Melton ruggedness number MRn = R/A1/2
Melton (1965)
(MRn) Cg = R/ {(π/2*Lb}
Channel Gradient (Cg)
Singh et al., (2008)
Basin Slope (Sb)
Sb = H/Lb
Miller (1953)
3. Results and discussions 3.1. Linear, areal and relief aspects of Dhidhessa River Basin
Figure 1 and 3 show the Dhidhessa River Basin boundary and streams generated using the technique recommended by Strahler (1957), respectively. The major linear morphometric parameters quantified for the basin including total stream length, mean stream length, stream length ratio, bifurcation ratio and Rho coefficient ratio of each stream order are summarized in Table 2. The basin has dendritic drainage pattern and has up to 8th order streams (Figure 3).
Table 2. Linear Aspects of Dhidhessa River Basin Parameters
Stream Orders 1
Total Stream Length in
16742.9
2
3
4
5
6
7
8
8251.3
4438.8
2212.8
905.9
291.9
344.4
280.1
km (TLu) Total Stream Length of all order (km) Mean Stream Length in
33468
0.8
0.9
0.9
9.0
17.4
26.5
114.8
280.1
19986
9097
5190
246
52
11
3
1
km (Lm) Total number of streams
Stream Length Ratio (RI) 0.5
0.5
0.5
0.4
0.3
1.2
0.2
0.8
Bifurcation Ratio (Rb)
2.2
1.8
1.9
2.1
3.0
0.7
1.3
-
Rho Coefficient (??)
-
0.3
0.3
0.2
0.1
0.4
0.9
-
Mean Bifurcation
1.8
Figure 3. Drainage Pattern of Dhidhessa River Basin
Similarly, major areal morphometric parameters of Dhidhessa River Basin which include area, perimeter, drainage density, stream frequency, drainage texture, length of overland flow, constant of channel maintenance, form factor, circularity ratio, elongation ratio, shape index and infiltration number are presented in Table 3.
Table 3. Areal Aspects of Dhidhessa River Basin Basin Name Dhidhessa River Basin Area (A) in km2
28637.2
Perimeter (P) in km Drainage density (Dd) in km/km
1571.2 2
1.2
Stream frequency (Fs) in km-2
1.4
Drainage texture (Dt)
1.7
Shape index (Sw)
0.7
Infiltration Number (If)
1.7
Length of overland flow (Lg)
0.6
Constant of channel maintenance (C) km2/km
0.7
Form factor (Ff)
0.1
Circularity ratio (Rc)
0.1
Elongation ratio (Re)
0.4
On the other hand, major Morphometric relief aspect parameters of Dhidhessa River Basin including basin relief, basin length, relief ratio, ruggedness number, gradient ratio, Melton ruggedness number, channel gradient and basin slope are presented in Table 4.
Table 4. Relief aspects of Dhidhessa River Basin Basin Name
Dhidhessa River Basin
Basin relief (R) in meter
2594
Basin length (Lb) in km
437
Relief ratio (Rr)
5.9
Ruggedness number (Rn)
3.1
Gradient ratio (Rg)
4.9
Melton Ruggedness number (MRn)
15.3
Channel Gradient (Cg) m/km
3.8
Basin Slope (Sb)
7.4
The dendritic drainage pattern and up to 8th order streams implies that the basin is composed of homogenous resistant lithology and can produce large quantity of streamflow, respectively. In the light of this, Withanage et al. (2014) noted that dendritic drainage pattern as irregular branching of streams at angle less than 900 that can be developed in area where the underlying geology has uniform resistance, and no structural control. Such drainage pattern is likely to exist on nearly horizontal sedimentary rocks, on areas of massive igneous rocks or on complex metamorphosed rocks (Garde, 2005). The inference is in line with the study conducted by Geological Survey of Ethiopia (2000, 2006 & 2007), which reported that the basin is underlain by sedimentary, igneous and complex metamorphic rocks. However, most of the igneous rocks in the study area are less massive, weathered and fractured. The study further revealed that the fractures and joints that form various trending lineament in the basin, mostly in the Proterozoic crystalline basement rocks, are steeply dipping to vertical fractures, which leads to less control surface runoff, groundwater recharge and base-flow. The total stream length is longest for the 1st order streams in the basin (i.e., 16,742.9 km) and shortest for the 8th order (i.e., 280 km). As shown in Figure 4a and Table 2, total stream
length is inversely proportional to stream order, which is consistent with findings reported by the existing literature (Horton, 1945; Singh et al., 2014). On the other hand, the mean stream length increases from 1st order to the 8th order (Figure 4b) which indicate that 1st order streams are short but numerous in number while 8th order streams are few in number but longer in length as described by Strahler (1964). This could be due to the decreasing slope of the basin from the divide line to the outlet of the basin, and indicate that the basin is still in its youthful stage of development. Moreover, short stream length describe steep slopes while longer lengths indicate flatter gradient (Withanage et al., 2014). The stream length and stream length ratio can depict clue information about hydrologic characteristics of the basin. The variability of those values from one stream order to the other (Table 2) revealed difference in the infiltration capacity at different stream orders which could be due to change in slope and topography (Bharadwaj et al., 2014). Dhidhessa River Basin has the lowest (i.e., 0.3) stream length ratio in the 6th order and the highest (i.e., 1.2) in 7th order with mean value of 0.6.
Figure 4. Relationship between mean stream length and stream order (a) and total stream length and stream order (b). Similarly, the Bifurcation ratio (Rb) and Rho coefficient (??) of the basin are different for different stream orders. The Bifurcation ratio of the basin ranges from 0.7 to 2.2 with 1.8 mean value while the Rho coefficient ranges from 0.1 for 5th order streams to 0.9 for 7th order streams with mean value of 0.4. Such irregularities in Rb values between stream orders revealed variation
in geological and lithological development of the drainage basin (Strahler, 1964). The Bifurcation ratio could be used to infer whether geological structure of the basin is controlling the drainage pattern or not (Singh et al., 2014) while Rho coefficient represents storage capacity of the drainage network during a rainfall event (Soni, 2016). Bifurcation ratio less than 5 indicates that: i) the drainage basin is underlain by rocks of uniform resistance; ii) streams are branched systematically with large number of first, second and third order streams (Chandrashekar et al., 2015); and iii) there is less structural disturbance that control drainage pattern in the basin (Strahler, 1964; Nag, 1998). Low Rho coefficient for 5th order streams confirmed the susceptibility to soil erosion and flooding than the 7th order, which has high runoff storage capacity during flooding. Generally, the linear morphometric analysis shown that stream length and stream orders of the basin are high while stream length ratio, Bifurcation ratio and Rho coefficient values are low (Table 2). Drainage area and perimeter of the basin are 28,637.2 km2 and 1,571.2 km, respectively, which indicate the study area is large. On the other hand, drainage density, stream frequency, drainage texture and infiltration number of the basin are 1.2 km/km2, 1.4, 1.7 and 1.7, respectively characterizing the basin as medium drainage density and coarse textured indicating the basin is underlain with highly permeable lithology (Table 3). According to Geological Survey of Ethiopia (2007), large portion of the basin is underlain with Tertiary volcanic formation (igneous rocks) (~50%), which are weathered, fractured and faulted by SE and NE lineaments. However, the lineaments have less control on drainage patterns. Generally, the basin’s drainage density, stream frequency and drainage texture are strongly correlated (Horton, 1945) showing its permeability and infiltration capacity. Furthermore, the length of overland
flow is 0.6 km/km2 for the basin indicating longer flow path with high infiltration and minimum runoff as argued by Chandrashekar et al. (2015).
In addition, the computed areal morphometric analysis showed that the elongation ratio, shape index, form factor and circulatory ratio of the basin are 0.4, 0.7, 0.1 and 0.1, respectively. These parameters are strongly correlated with each other and are used to describe the basin configuration (Soni, 2016). Elongation ratio values less than 0.8 are considered elongated and usually associated with high relief and deep ground slope (Strahler, 1964). Generally, the configuration of the Dhidhessa River Basin is more elongated (0.4) indicating longer lag time and low risk of soil erosion and flooding compared to other basins of similar size (Miller, 1953; Strahler, 1964; Singh & Singh, 1997; Soni, 2016). Erosion risk could still be high in the headwaters as the elongation ratio of the upper Dhidhessa River Basin is higher (i.e., 0.7).
The low circularity ratio (i.e., 0.1) of the basin indicates that the basin is elongated in shape, and may has low runoff potential resulted from the presence of highly permeable subsoil conditions (Singh et al., 2014). The low infiltration number of the basin further revealed the high infiltration and lower runoff potential (Strahler, 1964) of the basin. Constant of channel maintenance implies how much drainage area is required to maintain a unit length of channel and it is determined by the degree of resistance of the underlain material, vegetation cover and topography (Altaf et al., 2013). It is a measure of basin erodibility (Bharadwaj et al., 2014) which in the case of Dhidhessa River Basin with 0.7. This means 0.7 km2 basin is required to sustain 1 km length of drainage channel.
Relief aspect parameters provide information about denudation characteristics of a basin (Oruonye et al., 2016), morphological characteristics of a terrain (Hadley & Schumm, 1961), and
overall steepness of basin and intensity of erosional process (Tejpal, 2013). The basin relief and basin length of Dhidhessa River Basin are 2594 m. a. s. l and 494 km, respectively which show that the river flows longer distance in rugged topography. The longer the basin length and the steeper the topography, the higher the erosive power of the runoff will be. The basin slope of the study basin is 7.4, which is highly related with basin relief indicating that Dhidhessa River Basin is steep slope with high potential for surface run-off production and soil erosion. Moreover, relief ratio of the basin is 5.9 revealing that the area has steep slope that creates high potential energy for transporting water and sediment down slope per unit length. The ruggedness number combines the slope steepness and length indicating the extent of instability of land surface (Strahler, 1957). In the case of the study basin, the ruggedness number is 3.1 which is considered high showing the area has a rugged topography, susceptible to soil erosion and structurally complex.
Other important relief characteristics quantified in this study is Melton ruggedness number (MRn) which is a slope index that provides particular representation of relief ruggedness within the watershed (Melton, 1965). Melton ruggedness number for Dhidhessa River Basin is 15.3 indicating that sediment transport is dominated by bed loads according to Wilfordet et al (2004) classification. Gradient ratio (Rg) is used to assess runoff volume and it is an indicator of channel slope (Sreedevi et al., 2004). Rg of the study basin is 4.9 indicating that the basin has high relief and is mountainous in nature.
Some of the morphometric parameters of the Dhidhessa catchments have generally similar pattern with that of the main Dhidhessa River Basin. However, the catchments are different in most parameters particularly in their relief aspect (Table 5). For example, Anger and
Dabena catchments have higher constant of channel maintenance value (i.e., 0.9) than the main Dhidhessa (i.e., 0.7) while the Upper Dhidhessa is less elongated (i.e., 0.7) compared to the main Dhidhessa (i.e., 0.4). Dabena catchment have relatively with less basin relief (i.e., 1328) and ruggedness number (i.e., 1.5). However, Anger and Upper Dhidhessa catchments are with higher relief and gradient ratios compared to the main Dhidhessa. The Melton ruggedness number and channel gradient is higher in the Anger catchment compared to the other Dhidhessa catchments while basin slope is higher in the Upper Dhidhessa catchment (i.e., 20.1).
Table 5. Morphometric Parameters of Main Dhidhessa and its watersheds Parameters A Dd Fs Dt Sw If Lg C Ff Rc Re R Lb Rr Rn Rg MRn Cg Sb Rb (mean) RI (mean) Rho (mean)
Main Dhidhessa Anger Dabena Upper Dhidhessa Lower Dhidhessa 28637.2 7766 3209.4 8946.1 8716 1.2 1.1 1.1 1.2 1.2 1.4 1.3 1.4 1.4 1.4 1.7 1.5 1.5 1.6 1.7 0.7 0.8 0.7 0.7 0.7 1.7 1.5 1.5 1.6 1.7 0.6 0.5 0.6 0.6 0.6 0.7 0.9 0.9 0.8 0.8 0.1 0.2 0.1 0.4 0.1 0.1 0.2 0.1 0.2 0.1 0.4 0.5 0.4 0.7 0.4 2594 2343 1328 1849 1985 490 200 161 157 280 5.9 11.7 8.2 11.8 7.1 3.1 2.6 1.5 2.2 2.4 4.9 7.8 7.4 9.3 2.2 15.3 26.6 23.4 19.5 21.3 7.5 4.5 3.8 7.8 5.3 7.4 16.7 15.4 20.1 9.3 1.8 2.4 1.9 0.8 2.6 0.6 0.9 0.7 1.9 4.7 0.4 0.3 0.3 0.3 1.8
3.2. Hydro-geomorphologic characteristics of Dhidhessa River Basin
As previously described, several studies have revealed that basin morphometry is strongly correlated with basin physio-geographic and hydrological processes making it possible to infer major hydrological behavior of a basin such as flooding, soil erosion, topography, groundwater recharge, and geologic and lithologic formation of a basin from quantitative morphometric analysis.
3.2.1. The relationship between drainage morphology and topography of the basin
Relief aspect parameters such as basin relief, relief ratio, gradient ratio, ruggedness number, Melton ruggedness number and basin slope are indicators of topographic characteristics of a basin (Hadley & Schumm, 1961; Tejpal, 2013; Oruonye et al., 2016). Accordingly, the relief morphometric analysis revealed that the Dhidhessa River Basin is characterized by high relief with steep slope, mountainous and topographically rugged (Figure 1 and 2). Such characteristics resulted in high drainage density, frequency and texture (Rekha et al., 2011). Contrary to this, drainage density, frequency, and texture of the area are low to medium revealing that there are other controlling factors like soil type, vegetation cover and permeability of the underlain lithology coupled by high rainfall.
3.2.2. Morphometric parameters nexus underlined geology of the basin
The underlined geology of a given basin can be inferred from morphometric parameters like drainage pattern, mean stream length, bifurcation ratio and constant of channel maintenance (Strahler, 1964; Nag, 1998; Garde, 2005; Altaf et al., 2013; Withanage et al., 2014). According to the study, geology of the Dhidhessa River Basin is likely a horizontal sedimentary rock,
igneous rocks or complex metamorphosed rocks underlain with uniformly resistant rocks that lacks structural control. Furthermore, the variation of mean stream length and bifurcation ratio between stream orders indicates that the basin is still at its youthful stage of development and hence the geological and lithological development of the drainage basin varies spatially. Similarly, geological map of the Dhidhessa River Basin showed similar results. According to Geological Survey of Ethiopia (2000), the geology of the basin is underlain by crystalline Precambrian basement rocks, Tertiary volcanic rocks and Quaternary sedimentary formation where most part of the area is covered by tertiary volcanic rocks (~50%). Furthermore, the study revealed the presence of complex structures specifically in the Proterozoic crystalline basement rocks of the basin. However, since most of the lineaments are steeply dipping to vertical fractures, they have less control over the drainage pattern and groundwater recharge conditions (GSE, 2006).
3.2.3. Morphometric parameters nexus flood status of the basin
The flood status of a given watershed could be inferred from morphometric parameters like area, basin length, basin configurations (elongation ratio, circularity ratio and forma factor), drainage density and drainage frequency. Generally, elongated, and medium drainage density and medium frequency of the river basin is expected to produce minimum peak runoff (Miller, 1953; Strahler, 1964; Singh & Singh, 1997; Soni, 2016). The values of the parameters revealed that the lag time is high in the area resulting in less chance for flooding to occur as the conditions promote more infiltration than peak runoff formation. Furthermore, high infiltration capacity of the area, inferred from low infiltration number and physical properties of the geologic formation of the area supports the absence of severe flooding. However, low to medium Rho coefficient
indicates the possibility of flooding during heavy rainfall as the drainage channels have less capacity to store much runoff. The high permeability of the basin is compensated by high rainfall with longer wet season and larger drainage area (~29,000 km2). Generally, the Dhidhessa River Basin has high annual mean runoff quantity (13 km3/year) (Conway, 2000), but with less flooding hazard that could occur in the lowland areas of the basin. The upper Dhidhessa catchment is less prone to flooding compared to the rest catchment (Table 5).
3.2.4. Soil erosion and drainage morphometric characteristics of the basin
Soil erosion potential and its intensity in a given basin could be obtained from relief aspect (Tejpal, 2013), which includes basin relief, relief ratio, channel gradients, ruggedness number, basin length and Melton ruggedness number. The value of those parameters indicate that the basin is characterized by steep slope and is topographically rough which allows easy sediment production and transportation that dominated by bed loads (Wilfordet et al., 2004). The study, thus, showed Dhidhessa River Basin is susceptible to sever soil erosion, which is higher in the Anger and the Upper Dhidhessa catchment.
On the other hand, the more elongated basin configuration and drainage characteristics (medium density, coarse texture and low frequency) of the Dhidhessa River Basin may counterbalance the high soil erosion status that could result from topographic effect. However, the basin is still susceptible to headwater erosion. In addition to the steep slope of the area, the presence of less resistant underlying material could result in sever soil erosion (Altaf et al., 2013). However, the susceptibility of the basin to sever soil erosion could be modified further by vegetation cover and soil type.
3.2.5. Groundwater recharge potential and the basin morphometry
Groundwater recharge of a given basin is influenced by stream frequency, infiltration number, drainage density, drainage texture, length of overland flow, basin configuration and basin length. Those parameters depict information about infiltration capacity of the area and runoff generation (Singh et al., 2014; Soni, 2016). From the values of those parameters, Dhidhessa River Basin could be with high infiltration capacity, which shows high groundwater recharge. According to the study, Anger catchment have high groundwater potential compared to the other catchments.
Furthermore, the morphometric analysis indicate that runoff formation and transportation is slow in the basin. Runoff gets extended time to infiltrate during such slow movement. This could be due to the presence of permeable underlying materials, which is inferred from drainage characteristics of the basin and the geological and hydrogeological map of the river basin. Despite high infiltration rate, runoff volume could be high for the basin due to high rainfall, large drainage area, and high stream order. The mean annual discharge of Dhidhessa River Basin is estimated to be 13 km3/year with fairly higher dry season flow compared to other Blue Nile basins (Conway, 2000). The high dry season flow of the basin is another indicator of high groundwater recharge during the wet season and base-flow during dry season. Furthermore, hydrogeological study of the basin revealed that most parts of the basin are underlain with very productive fractured aquifers (i.e., 6.2 l/s to 27 l/s), highly productive fracture aquifers (i.e., 5 l/s to 13.5l/s) and moderately productive fractures aquifers (i.e., 2.1 l/s to 2.8 l/s)(GSE, 2006). This implies that the Dhidhessa River Basin has ample surface water and groundwater resources.
According to the study, Dabena catchment seems to have high groundwater potential compared to the other catchments.
Conclusions
GIS based drainage morphometric quantification and analysis is found to be a cost-and time-effective approach to characterize poorly gauged basins as an alternative and complementary source of information. Accordingly, the stream length and stream order of the basin is higher while stream length ratio, bifurcation ratio and Rho coefficient values are low. On the other hand, large drainage area, coarse drainage frequency and texture, more elongated shape, medium drainage density, high infiltration capacity, longer overland flow and high constant of channel maintenance are the characteristics of the Dhidhessa River Basin. Similarly, high relief, longer basin length, high relief ratio, high ruggedness number, high gradient ratio and high basin slope are the relief characteristics of the Dhidhessa River Basin.
From the morphometric analysis, the characteristics of Dhidhessa River Basin can be inferred as the underlying geology is with uniform resistance and lack of structural disturbance, the geological and lithological developments of the basin are spatially variable and the basin is less prone to flooding except in the lowland parts of the basin during heavy rainfall.
Moreover, Dhidhessa River Basin is very susceptible to soil erosion due to topographic factors like slope steepness and topographic roughness that aggravate the erosive capability of rainfall for both detachment and transportation. According to the morphometric analysis, the Anger and Upper Dhidhessa catchments seems to be more susceptible to soil erosion. However, susceptibility to soil erosion could be minimized by dense vegetation cover and/or deep soil
depth of the area that could reduce the erosive energy of rainfall and runoff. Moreover, more elongated basin configuration and the longer basin length could further minimize the topographic effect on soil erosion. Quantitative morphometric analysis of the basin further indicates high potential of both surface and groundwater resources in the basin. Despite the high relief, rugged topography and steep slope of the basin, its drainage characteristics are low to medium revealing that there are other controlling factors in addition to terrain parameters. Further research is needed to investigate these issues.
Generally, this study shows that quantitative morphometric analysis using the-state-of-the-art approach is time- and cost-effective in providing baseline information for characterizing basin hydrologically, physio-graphically and geologically. However, such morphometric analysis should be supported by detailed geophysical, hydrogeological and hydro-metrological studies to use the information for decision-makings.
Acknowledgments We are very gratitude to Ethiopia Geological Survey and Oromia Water Works Design and Supervision Enterprise for providing us data required for the research such as Geological and Hydrological maps, and Soil map of the study area, respectively, free of charge. Moreover, we thank NASA for availing SRTM DEM data freely, which were also used as a main data source for this particular research. We would also thank the anonymous reviewers for their constructive comments.
Disclosure statement There is no potential conflict of interest.
Funding There is no direct fund for conducting this research.
References
Altaf, F., Meraj, G., & Romshoo, A. Sh. (2013). Morphometric Analysis to Infer Hydrological Behavior of Lidder Watershed, Western Himalaya, India. Geography Journal, 2013, 114. Angillieri, E. Y. M. (2012). Morphometric characterization of the Carrizal basin applied to the evaluation of flash floods hazards, San Juan, Argentina. Quaternary International, 253 (2012), 74-79. Bastawesy, E. l. M, Gabr, S., & White, K. (2013). Hydrology and geomorphology of the Upper White Nile lakes and their relevance for water resources management in the Nile basin. Hydrological processes, 27,196-205. Bharadwaj, K. A., Pradeep, C., Thirumalaivasan, D., Shankar, P. C., & Madhavan, N. (2014). Morphometric Analysis of Adyar Watershed. Journal of Mechanical and Civil Engineering, 2320-334X, 71-77. Bloomfield, J. P., Bricker, S. H., & Newell, A. J. (2011). Some relationships between lithology, basin form and hydrology: a case study from the Thames basin, UK. Hydrological processes, 25 (16), 2518-2530. Chandrashekar, H., Lokesh, V. K., Sameena, M., Roopa, J., & Ranganna, G. (2015). GIS-Based Morphometric Analysis of Two Reservoir Catchments of Arkavati River, Ramanagaram District, Karnataka. International Conference on water resources, Coastal and Ocean Engineering (ICWCOE2015). Aquatic Procedia, 4(2015), 1345-1353.
Clarke, J. I. (1966). Morphometry from Maps. Essays in geomorphology. Elsevier Publication Corporation, India, Delhi. Conway, D. (2000). Climate and Hydrology of the upper Blue Nile River Basin. The Geographical Journal, 166(1): 49–62. Farr, T., Rosen, P. A., Caro, E., Crippen, R., Duren, R., & Hensley, S. (2007). The shuttle radar topography mission. Reviews of Geophysics 45, RG2004. Forkuor, G., & Maathuis, B. (2012). Chapter 9: Comparison of SRTM and ASTER Derived Digital
Elevation Models over Two Regions in Ghana-Implications for Hydrological and Environmental Modeling. In Studies on Environmental and Applied Geomorphology, Dr.Tommaso Piacentini (ed.), InTech, 219-240.
Gamachu, D. (1977). Aspects of climate and water budget in Ethiopia. Addis Ababa, Addis Ababa University Press. Garde, R. J. (2005). River Morphology, New Age International (Pvt) Ltd. Publishers, New Delhi.
Geological Survey of Ethiopia (GSE). (2000). Geology of the Nekemte and Gimbi Area. Sheet Number: NC-37-9 and NC-36-12, respectively. Unpublished.
Geological Survey of Ethiopia (GSE). (2006/7). Hydrogeology and Hydrochemisry of Nekemte and Arjo area. Sheet Number: NC37-9 and NC37-13, respectively. Unpublished.
Girma, M., & Vijaya, B. (2015). Morphometric Characteristics and the Relation of Stream Orders to Hydraulic Parameters of River Goro: An Ephemeral River in Dire-dawa, Ethiopia. Universal Journal of Geoscience, 3(1), 13-27. Hadley, R. F, & Schumm, S. A. (1961). Sediment Sources and Drainage Basin Characteristics in Upper Cheyenne River Basin. USGS Water-Supply Paper, 1531-B, 1-198.
Horton, R. E. (1945). Erosional Development of Streams and Their Drainage Basins. Geological Society of America Bulletin, 56 (3), 275-370. Horton, E. R. (1932). Drainage basin characteristics. Transactions American Geophysical Union 13, 350-361. Jensen, S. K. (1991). Applications of hydrologic information automatically extracted from digital elevation models. Hydrological Processes, 5(1), 31-44. Li, J., Wong, W. D. (2010). Effects of DEM sources on hydrologic applications. Computers, Environment and Urban Systems, 34, 251-261. Melton, M. A. (1965). The geomorphic and paleo-climatic significance of alluvial deposits in Southern Arizona. Journal of Geology, 73, 1-3. Melton, M. A. (1957). An Analysis of the relations among elements of climate, Surface properties
and geomorphology. Technical Report Number 11, Department of Geology,
Columbia
University.
Miller, V. C. (1953). A quantitative geomorphic study of drainage basin characteristics in the Clinch Mountain area, Virginia and Tennessee, Project NR 389042, Tech. Rept. 3., Columbia University, Department of Geology, ONR, Geography Branch, New York. Mohd, I., Haroon, S., & Bhat, F. A. (2013). Morphometric Analysis of Shaliganga Subcatchment,
Kashmir Valley, India Using Geographical Information System. International
Journal of
Engineering Trends and Technology, 4(1), 10-21.
Moore, I. D, Grayson, R. B, & Ladspm, A. R. (1991). Digital terrain modeling: A review of hydrological, geomorphological and biological applications. Hydrological Processes, 5, 3-
30.
Nag, S. K. (1998). Morphometric analysis using remote sensing techniques in the Chaka sub basin, Purulia district, West Bengal. Journal of Indian Society of Remote sensing, 26 (1 & 2), 69 - 76.
Oromia Water Works Design and Supervision Enterprise (OWWDSE). (2014). Dhidhessa SubBasin Soil Survey Report. Dhidhessa-Dabus Integrated Land Use Planning Study Project. Unpublished. Oruonye, D. E., Ezekiel, B. B, Atiku, G. H., Baba, E., Musa, I. N. (2016). Drainage Basin Morphometric Parameters of River Lamurde: Implication for Hydrologic and Geomorphic
Processes. Journal of Agriculture and Ecology Research International, 5(2), 1-11.
Patel, A., Katiyar, K. S., & Prasad, V. (2016). Performances evaluation of different open source DEM using Differential Global Positioning System (DGPS). The Egyptian Journal of Remote Sensing and Space Sciences. Article in press. Perucca, P. L., & Angilieri, E. Y. (2011). Morphometric characterization of Del Molle Basin applied to the evaluation of flash floods hazard, Iglesia Department, San Juan, Argentina. Quaternary International, 233 (2011), 81-86. Rekha, B. V., George, V. A., & Rita, M. (2011). Morphometric Analysis and Micro-watershed Prioritization of Peruvanthanam Sub-watershed, the Manimala River Basin, Kerala, South India. Environmental Research, Engineering and Management, 3(57), 6-14. Samal, R. D., Gedam, S. Sh., & Nagarajan, R. (2015). GIS based drainage morphometry and its influence on hydrology in parts of Western Ghats region, Maharashtra, India. Geocarto International, 30(7), 755-778. Schumm, S. A. (1956). The Evolution of drainage systems and slopes in badlands at Perth Amboi,
New Jersey. Geological Society of America Bulletins, 67(5).
Singh, S., Singh, M. C. (1997). Morphometric analysis of Kanhar river basin. National Geographical Journal of India, 43(1), 31-43. Singh, P., Gupta, A., & Singh, M. (2014). Hydrological inferences from watershed analysis for water resource management using remote sensing and GIS techniques. The Egyptian Journal of Remote Sensing and Space Sciences, 17,111-121.
Smith, K. G. (1950). Standards for grading texture of erosional topography. American Journal Science, 248:655-668. Soni, S. (2016). Assessment of morphometric characteristics of Chakrar watershed in Madhya Pradesh India using geospatial technique. Applied Water Science. Sreedevi P. D., Subrahmanyam, K., & Ahmed S. (2004). The significance of morphometric analysis for obtaining groundwater potential zones in a structurally controlled terrain. Environmental Geology, 47, 412-420. Sreedevi, P. D., Owais, S., Khan, H. H., & Ahmed, S. (2009). Morphometric analysis of a watershed of South India using SRTM data and GIS. Journal of Geological Society of India 73(4), 543-552. Strahler, A. N. (1964). Quantitative Geomorphology of drainage basins and channel networks. Chow VT. (ed). Handbook of Applied Hydrology, McGraw-Hill, New York, 439-476. Strahler, A. N. (1957). Quantitative analysis of watershed geomorphology. Transactions American
Geophysical Union, 38,913-920.
Sun, G., Ranson, K. J., Kharuk, V. I., & Kovacs, K. (2003). Validation of surface height from shuttle radar topography mission using shuttle laser altimeter. Remote Sensing of Environment, 88 (4), 401-411. Tarboton, D. G., Bras, R. L., & Rodriguez-Iturbe, I. (1992). A physical basis for drainage density. Geomorphology, 5(1/2), 59-76. Tejpal. (2013). Relief Analysis of the Tangri Watershed in the Lower Shivalik and Piedmont Zone of Haryana and Punjab. Indian Journal of Spatial Science, 4(1), 9-20. Tesfaye, M., & Wondimu M. 2014. Morphometric Analysis of Didessa River Catchment in Blue Nile Basin, Western Ethiopia. Science, Technology and Arts Research Journal, 3(3), 191197.
Wise, S. (2000). Assessing the quality for hydrological applications of digital elevation models derived from contours. Hydrological Processes, 14(11 and 12), 1909-1929. Withanage, S. N., Dayawansa, K. D. N., & De Silva, P. R. (2014). Morphometric Analysis of the Gal Oya River Basin Using Spatial Data Derived from GIS. Tropical Agricultural Research, 26(1), 175-188. Yohannes, O. (2008). Water Resources and Inter-Riparian Relations in the Nile Basin; the Search for an Integrative Discourse. State University of New York Press, Alhany. ISBN 978-07914-431-0. Zavoianu, I. (1985). Morphometry of Drainage basin (Developments in Water Science, 20). Amsterdam: Elsevier.