Sediment budget of high mountain stream channels in an arid zone (High Atlas mountains, Morocco)

Catena 190 (2020) 104530

Contents lists available at ScienceDirect

Catena journal homepage: www.elsevier.com/locate/catena

Sediment budget of high mountain stream channels in an arid zone (High Atlas mountains, Morocco)

T

Elżbieta Rojana,⁎, Maciej Dłużewskia, Kazimierz Krzemieńb a b

Faculty of Geography and Regional Studies, University of Warsaw, Krakowskie Przedmieście 30, 00-927 Warszawa, Poland Faculty of Geography and Geology, Jagiellonian University in Cracow, Gronostajowa 7, 30-387 Kraków, Poland

ARTICLE INFO

ABSTRACT

Keywords: Channel sediment budget Discharge Rainfall typology Catchments morphology High mountains Arid zone

In an arid zone the sediment budget is predominantly dependent on runoff, which is controlled mainly by the type of rainfall. Sediment budget calculation is one of the indirect methods of estimating channel morphodynamics. This method is advised here since it is not possible to directly measure this important hydrological indicator of environmental dynamics. This is because in small mountain catchments of an arid zone it is impossible to obtain flow rates due to factors such as the amount and size of transported rock debris, as well as the episodic and sudden nature of precipitation events. The research was conducted in 3 catchments (2.95 km2, 7.39 km2, 22.73 km2) situated within the boundaries of the basin of the upper Dades, on the southern slopes of the High Atlas in Morocco. The rivers of these catchments, tributaries to a trunk river Dades, are ephemeral and mostly bedrock depending on lithology of the geology. Three automatic weather stations were installed there. Precipitation events ≥ 10 mm (51 rains in 3 catchments) were used in the analysis. Simple rainfall typology (3 types) was devised for these events. During the research period seasonally repeated (6 times) measurements of topography were obtained from 21 cross-section profiles of streams of different order. These measurements formed a basis for calculating both the intensity of flow in ephemeral rivers (max 69,6 m/s) and the sediment budget. In 70% of analysed channel cross-sections erosion was dominant. The average change of the surface area of the cross-section profile is −82%. The maximum seasonal (between measurements) enlargement of the surface cross-section (erosion) is as high as 128%. The lower catchment, which is predominantly composed of conglomerates, distinctly shows the slightest changes of the cross-section profile surfaces, max 24%. The average volume of channel material displaced at the measurement point is 1.07 m3 (max 9.81 m3). There is evidence that not only high intensity rains, but also less intense but longer lasting rains, amounting to high precipitation totals (type C), may result in the highest channel sediment budgets. Differences between a catchment lithology composed of limestones and marlstones and that composed of conglomerates have only a minor impact on sediment budgets in the first and second order channels, whereas in the channels of the third and fourth order this impact is much higher. It was found that sediment budgets calculated for individual channels were higher for the catchments composed of limestones and marlstones, than for those composed of conglomerates, even though the catchments of different lithology may have had the same number of tributaries. This suggests that the sediment supply from slopes is comparatively larger in the catchments dominated by limestones and marlstones.

1. Introduction Sediment budgets provide a useful framework for understanding dominant erosion and sedimentation processes, and can offer detailed insight into internal watershed sediment dynamics across a range of scales (Nichols et al., 2013). Sediment budget also provides a simplification of the interaction between geomorphological processes that transfer sediments from their points of origin, down slopes and through the fluvial network, to their deposit in the catchment or its exit, which

⁎

was first highlighted by Dietrich and Dunne (1978). Since that time, (as well as before, among others by Rapp, 1960), other studies following the same approach have been carried out. Some of them were conducted in the Mediterranean, in the semi-arid and arid zone (e.g., Batalla et al., 1995, Trimble, 1997, Rovira, et al., 2005, Mather and Stokes, 2016). Sediment budget is defined as difference between accumulation (m2) and erosion (m2) computed for the same cross-sections (Rovira et al. 2005). We have also employed the term total sediment budget as the sum of accumulation (m2) and erosion (m2) computed for

Corresponding author. E-mail address: [email protected] (E. Rojan).

https://doi.org/10.1016/j.catena.2020.104530 Received 12 December 2018; Received in revised form 15 February 2020; Accepted 23 February 2020 Available online 05 March 2020 0341-8162/ © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).

Catena 190 (2020) 104530

E. Rojan, et al.

the cross-sections in a 1 m wide band (for each cross-sections profile), which provides volume calculated in m3. Nichols et al. (2013) define total sediment discharge (t, t/ha/yr, m3) as difference between total erosion and total deposition. Their calculation is based on measurements made in a small semi-arid watershed in south-eastern Arizona, where channel erosion was estimated based on the difference between outflow and combined hillslope erosion and landscape deposition. Sediment budget mostly depends on runoff, which is controlled by climate, mainly rainfall (e.g., Abrahams and Parsons, 1991, Nicolau et al., 1996, Calvo-Cases et al., 2003, Ochoa et al., 2016). In an arid zone, a considerable variation in the sediment budget is the result of

short-term rainfall of high intensity, which is characterized by a rapid concentration of overland flow (Schick, 1988, Laronne and Reid, 1993). However, sediment budget also depends on factors such as catchment topography and channels, bedrock lithology and structure, soil thickness and permeability, as well as vegetation, which are determining runoff persistence (e.g., Yair and Kossovsky, 2002, Yair and Raz-Yassif, 2004, Puigdefábregas, 2005, Ziadat and Taimeh, 2013). The scarcity of vegetation cover in combination with relatively steep topography and a dense channel network creates geomorphic conditions that support high rates of erosion and efficient sediment transport in response to discontinuous rainfall and runoff (Graf, 1988).

Fig. 1. Study area: A – location of the study area, B – upper Dades catchment, C – catchments subject to detailed studies: 1 – DAD1, 2 – DAD2, 3 – DAD3, D – catchment lithology (based on Carte Géologique du Maroc, 1993): a – conglomerates, Hamadien, continental Neogene; b - oolitic and oncolitic limestones, sometimes sandstones and marls, the Bin El Ouidane formation 3, middle Jurassic; c – marlstones, the Bin El Ouidane formation 2, middle Jurassic; d - oolitic limestones and blue marlstones, the Bin El Ouidane formation 1b, middle Jurassic; e – limestones interbedded with marlstones, Ouchbis formation, lower Jurassic; f – undulated black limestones interbedded with marlstones, Aberdouz formation, lower Jurassic; g – massive limestones and dolomites, lower Jurassic. 2

Catena 190 (2020) 104530

E. Rojan, et al.

It is slopes that are mainly responsible for producing and supplying detritus and rock material, especially in the arid zone. The functioning of stream channels, especially the lower order, is to a large degree driven by slopes (Golden and Springer, 2015). As an example, the share of slope material in channel sediments in the south-western Arizona is 72–86% (Nichols et al., 2013). Material transported down the channels is in part deposited in the form of alluvial fans, which are also conditioned by lithology and tectonic structure of the bedrock (Mather et al., 2017). The material deposited in the channels reflects the degree of intensity of slope and fluvial processes. Therefore, it is important to calculate the sediment budget. However, interactions between factors controlling the sediment budget are poorly understood. This is true particularly for small catchments located in high mountain regions of semi-arid and arid zones (Hrachowitz et al., 2011). In such catchments it is not possible to obtain direct measurements of flow rate, which would directly demonstrate the energy of the slope-fluvial system. This is due to the amount and size of transported rock debris, and due to the episodic nature and suddenness of these events (Laronne and Reid, 1993). Recreating of the flow conditions, even during historic events, is also possible by applying field measurements in situ according to either Mannings indicators or the maximum boulder size determination, the method used by Mather and Stokes (2016) in the research of the Rio Aguas river catchment in SE Spain. This paper aims to determine the impact of precipitation events on the morphodynamics of stream channels in high mountains of the arid zone. It has been achieved by way of calculating channel sediment budgets that result from slope and fluvial processes. Our initial objectives have been to determine litho-structural features and to calculate morphometric parameters of the studied catchments and their stream channels. It was very important to determine the types of morphogenetic precipitation. Once the sediment budgets were developed, it was also possible to calculate the flow rate of ephemeral watercourses. The study area – the Dades Valley in the High Atlas in Morocco – provides a very good testing ground for investigations for the purpose of this study. This is due to high efficiency of geomorphological processes (both slope and fluvial), varied terrain relief (conditioned mainly by lithology, structure and tectonics), hydrometeorological events of high intensity and relatively poor vegetation (the latter is to some degree due to human activity). The upper Dades valley has in recent years been an area of research into fluvial relief. Studies have been carried out predominantly in the fields of geology, tectonics and geomorphology of river channels, including gorges, river terraces and alluvial fans (Stokes et al., 2008, 2017, Dłużewski et al., 2013b,c, Boulton et al., 2014, Stokes and Mather, 2015, Mather et al., 2017, Boulton and Stokes, 2018, Mather and Stokes, 2018, Rojan et al., 2019). It needs to be emphasised, that it is the meteorological data concerning precipitation that forms the key element of the study. As pointed out by Knippertz et al. (2003), there is lack of such data concerning Atlas, particularly for the areas above 1600 m a.s.l., where one of the factors is the relatively high frequency of formation of convective clouds over the mountains compared to the surroundings, a factor, which probably favours significantly higher precipitation amounts.

the less resistant – withdrawn in relation to the former) of slopes and channel walls. Marlstones, as a weak rock (Carte Géologique du Maroc, 1993, Stokes and Mather, 2015) are prone to faster denudation, and this causes niches and lowerings being formed below the limestone strata. This in turn leads to the latter falling or sliding off. In the layers of resistant rock, vertical fluvial incision has dominated, forming narrow and deeply incised canyons, including Dades Gorges (Stokes et al., 2008). Jurassic rock strata are undulated, dipping at various angles (as much as 90°). The grain skeleton of metamorphic rocks consists of smooth and very smooth clasts of various types of limestone. Both matrix and cement are formed of carbonate rock. The relatively low resistance of these types of rock to physical weathering and morphogenetic processes, especially where flowing water is involved, facilitates the erosion of the material, thereby causing rock disintegration. This, to a large degree, results in the detritus layers, the smoother parts of which are easily transported. Active tectonics for the Dades catchment is very low (Stokes et al., 2017) but the passive tectonics linked to Mesozoic extension and Cenozoic compression give the rock masses a structure (discontinuities, tilting etc.) which enhances / suppresses erodibility, evident for example in the formation of river gorges (such as Dades Gorges) and in the ways the channels have been shaped. Above all, in most cases, the geography of the valleys is related to the bedrock structure. Contemporary seismic activity in this area is insignificant (Stokes and Mather, 2015), therefore its impact on the relief transformation is low. Slides caused by earthquakes occur infrequently (Hughes et al., 2014). In the highest parts of the upper Dades valley (above 3000 m a.s.l.), landforms such as cirques, troughs and moraines are found. These landforms provide evidence of glacial and periglacial activity within the south-central High Atlas region (Hughes et al., 2014). The catchment is characterised by broad plateaus. In its upper part, the slope gradient is low (1015°), while in its lower part it is high (3050°) and even includes vertical canyon walls. This is largely conditioned by lithology and bedrock structure of the catchment area. This in turn determines the gradient and shape of riverbeds, especially these of lower orders. They differ in their depth and development. Some tributary catchments are dominated by alluvial reaches, while the other are predominantly bedrock, suggesting that either the sediment supply is limited, or that sediment generated is efficiently transported into the trunk drainage (Stokes and Mather, 2015). There are fluvial forms such as: Quaternary river terraces, Quaternary and modern fans, gorges and wide open valleys on this area (Stockes et al., 2017, Mather et al., 2017). In its section situated within the study area boundaries, the river Dades is 132 km long and forms a perennial river almost along this entire section. Only in its uppermost part, the river is intermittent, supplied by rainfall and snowmelt. When rainfall or snowfall is low, the river is fed by ground waters. The groundwater system is karstic and has been formed thanks to the dominance of carbonate bedrock geology. The north-central part of the study area, which falls within the boundaries of the Aı¨t Abdi Plateau in the central High Atlas (between Zaouite Ahansal, Msemrir and Ait Hani), is situated in the zone of a major underground water reservoir in the area (Akdim, 2015). The groundwater supply presents a high variability in quality and is highly mineralized. It derives solely from the leaching of evaporitic minerals (gypsum, halite and sylvite) that are naturally present in the various geological formations (including Trias, Cretaceous) (Cappy, 2007). The tributaries of the river Dades are ephemeral, flowing several times a year on average, mainly during the periods of SeptemberOctober and February-April (Dłużewski et al., 2013b). The drainage area is on average between 3.5 and 4.5 l/s/km (Fink and Knippertz, 2003). The upper Dades catchment lies in the arid climate zone with elements of the mountain climate zone according to the Köppen climate classification, modified, among others, by Trewartha (Trewartha, 1954 as cited in Kalma and Franks, 2003). It is based on monthly average air

2. Study site The study was conducted in the 3 catchments of ephemeral streams in the valley of upper Dades (1525 km2), situated on the southern slopes of High Atlas in Morocco (Fig. 1A). The lowest part of this valley, above the town of Boumalne, has elevation of 1,526 m above the sea level, while the highest part has elevation of 3313 m (Fig. 1B). Upper and middle sections of the upper Dades catchment area is mainly composed of Jurassic carbonate rocks: limestone, marlstone and mudstone, while the lower section is composed of Neogene conglomerates (Fig. 1D) (Carte Géologique du Maroc, 1993). These rocks are of differing resistance. This causes the development of the, rib” structure (alternate layering of rock strata: the more resistant - protruding and 3

Catena 190 (2020) 104530

E. Rojan, et al.

temperatures, as well as on the volume and pattern of annual precipitation totals, relative to latitude. According to the above classification, the study area falls within the arid zone, although in some years values above 300 mm - that is, values typical for the semi-arid zone. It is possible to annually determine the drier months: January, February, June, July, August, December and more humid months: March, April, May, September, October, November on the basis of the average monthly precipitation amounts recorded at the three weather stations (see Chapter 3) for the period of 5 years. These amounts vary by as much as 100 mm. The mean annual rainfall total for the period 1962–2006 at the weather station located in Msemrir (1942 m a.s.l., the middle section of catchment) is 203 mm (Schulz et al., 2008, Dłużewski et al., 2013a). At the Boumalne weather station (1526 m a.s.l., the lowest part of the catchment) the mean total is 150 mm/year. Snowfall sometimes occurs during winter in the upper parts of the catchment. At altitudes of 2000–3000 m above sea level, the snow cover remains on average for periods of 10–20 days a year. At altitudes above 3,000 m a.s.l. it tends to remain longer. The depth of the snow cover can periodically reach several metres (Schulz and de Jong, 2004). The vegetation of the upper Dades catchment is relatively sparse, which is due to the climatic conditions and also due to high degree of anthropopressure (by grazing and subsistence use for firewood). The slopes are predominantly covered by sparse low shrub vegetation, mainly of specimens of Lamiaceae, Asteraceae and Fabaceae families. Studies were carried out in 3 catchments of ephemeral streams (Fig. 1C) of respective areas: DAD1 – 22.73 km2 (situated in the lower part of the upper Dades catchment), DAD2 – 2.95 km2 (situated in the middle part of the upper Dades catchment), and DAD3 – 7.39 km2 (situated in the upper part of the upper Dades catchment). Relative elevation of these catchments is 591 m, 735 m and 832 m respectively. These catchments have a number of features in common, for example, similar geology of DAD2 and DAD3, the same exposition of DAD1 and DAD2, while others share similar elevation. The DAD1 catchment is composed of continental Neogene rocks, mainly massive conglomerates (Fig. 1D) (Carte Géologique du Maroc, 1993). Their grain framework is composed of different types of wellrounded limestones embedded in calcareous matrix and cemented by calcium carbonate. Only the upper part of this catchment is composed of lower Jurassic massive pelitic limestones interbedded with marlstones. This causes the development of irregular slope and channel profiles. In most of this area, rock layers lie horizontally or are slightly inclined. The catchment DAD2 is composed of lower Jurassic massive dark grey to black pelitic limestones, less than one metre thick, interbedded with marlstones, which are weak (Fig. 1D) (Carte Géologique du Maroc, 1993, Stokes and Mather, 2015). The rocks are fractured due to a joint system consisting of two joint sets perpendicular to each other and to the bedding causing blocky disintegration of rocks (Rojan et al., 2019). The DAD3 catchment is composed of different types of middle Jurassic dark grey limestones: oolitic, oncolitic, bioclastic, and pelitic (Fig. 1D) (Carte Géologique du Maroc, 1993). Beds are folded and monoclinally inclined.

(Kamykowska et al., 1999) - effective width – Rb (km) – relationship of catchment surface area and its length - form factor – Ff (–) – quotient of catchment surface area and its squared length (Horton 1932):

Ff = A/L2 - shape factor – Rs (–) – the ratio of width to depth - elongation ratio – Re (–) – quotient of the diameter of a circle of the same surface area as the catchment (A) and length of the catchment (L):

R e = 2r/ L= 1, 13

A /L

The landform and morphometry of catchment was shown through: -

R=

maximum elevation – Hmax (m n.p.m.) minimum elevation – Hmin (m n.p.m.) relative elevation – ΔH (m) average slope – R (˚), that is the average slope of the catchment (Horton, 1932)

H/ A The main channels of episodic streams were characterised by:

- total streams length – Ls (km) – length of all channels in the catchment - length of main channel – Lk (km) - drainage density – D (km/km2) - gradient of main channel – Rk - tributaries per 1 km of main channel (–). These data were subsequently verified in the course of the field survey. The hierarchical classification of the stream channels network was carried out according to the Strahler’s stream order (Strahler, 1952). For the purpose of this work, the classification was extended to a “0″ order, that represented very numerous initial streams (the channels are not developed, but function during rainfall discharging rainwater in concentrated downpours). The river channel networks were mapped out for each catchment and, subsequently, the order of each section was determined. During the period from November 2012 to November 2015, that is, during the period where meteorological variables were also measured (1.07.2012–30.06.2017) a number of seasonally repeated topographic measurements were conducted in the catchments chosen for detailed studies, consisting of 21 cross-section profiles of stream of different order (8 in DAD1, 6 in DAD2 and 7 in DAD3) (Fig. 2). The measurements were conducted on six occasions, immediately following a major hydro-meteorological event. Due to either high intensity of these events or snow deposits in the upper sections of the catchment, it was not always possible to conduct measurements in all profiles. A total of 107 cross-sections were measured (21 × 5–6 measurements). The depth and width of channels was measured with the tape measure, against permanent benchmarks at cross-section profiles. The depth measurements were typically carried out at 10 cm intervals, with the exception of narrow channels with microforms present, where they were taken at 5 cm intervals. The measurements took place at least twice a year. Longitudinal profiles of the channels, in which cross-section profiles had been installed, were also created. Cross-sections of the channels were used to calculate their surface area (m2). The data obtained for each measurement point were compared with values obtained from earlier readings, which enabled us to calculate accumulation (m2) and erosion (m2) areas. These respective areas were then compared (calculating the difference), a concept termed sediment budget by Rovira et al. (2005). The degree of change

3. Methods The standard morphological parameters of the catchments and stream channels, including channels order (Horton, 1945, Lambor, 1971, Waikar and Nilawar, 2014) and catchments lithology, which influence slope and fluvial processes, thus impacting on sediment budgets, were determined on the basis of topographical and geological maps in scales 1:50000 and 1:100000, as well as on the basis of LANDSAT-8 and Google Earth images with the use of ArcGIS tools. The catchment geometry was demonstrated by the following parameters: - drainage area – A (km2) - length – L (km) – distance in straight line between the closure of catchment (channel mouth) and the farthest point of the watershed 4

Catena 190 (2020) 104530

E. Rojan, et al.

dynamic in high mountains of the arid zone. Data from the topographic survey of channel cross-sections, together with data concerning maximum water levels, determined in each profile for a given event, have enabled us to calculate maximum flow intensity (Qmax) for a given event (Kubrak and Nachlik, 2003; Acrement and Schneider, 1990 as cited in Mul et al., 2009) in

Q max = n 1A R2/3 I1/2 where: A – cross-section area of flow (m2) R – hydraulic radius (m) I – hydraulic gradient (-) n – Manning’s roughness coefficient (ms−1/3) Manning’s roughness coefficient (n) was determined through an inventory of material on the bottom and banks of the channels (Hakiel, 2014). The average value of the coefficient for small mountain streams with gravel beds, in which sparse boulders are found, is 0.04, and in streams with rocky beds with large boulders present – 0.05. Specific peak discharge (SPQ) was also calculated for each measurement point in each channel, representing the ratio between discharge and area of catchment (m3/s per km2). Finally, correlation between the sediment budget and flow intensity was determined for all events in each catchment. Based on this correlation, the influence of catchment morphology and catchment lithology on the stream channel sediment budget was determined. The significance of each type of precipitation episode in relation to the sediment budget was then analysed, separately in channels of given order.

Fig. 2. Location of measurement points in ephemeral channel streams in catchments: DAD1, DAD2 and DAD3.

to these areas were calculated in %. Subsequently, the total sediment budget (m3) was calculated, interpreted as the sum of eroded and accumulated areas of the cross-section within the band 1 m wide of each channel for each measurement point for the 3-year period, during which the measurements were taken. This model better reflects the energy of flows, especially in gravel-bed sections of the channels. This method has also been applied in other high energy environments, for example in the eolian environment (Delgado-Fernandez, 2010). In addition, the mean value of total sediment budget for channels of 1st to 4th order was calculated, which made comparisons possible among respective orders within the three catchments. The rainfall magnitude and intensity was evaluated based on data obtained from 3 weather stations installed in the lower part of each of the studied catchment, at elevation, respectively: in the catchment DAD1 – in the lower part of the slope, at elevation of 1618 m a.s.l., in the catchment DAD2 – at the flattened area of the slope, at elevation of 1750 m a.s.l., and in the catchment DAD3 – the base of the slope at elevation of 2064 m a.s.l. for the period 1.07.2012–30.06.2017 (5 years). Each station is an automatic weather station designed to carry out meteorological and pluviometric measurements. Precipitation was recorded by tipping bucket rain gauges, while the data was recorded by unmanned data loggers. In addition, the station located in the DAD3 catchment has been fitted with an electric heater, which switches on when air temperature falls below 0 °C, enabling turning frozen forms of precipitation into water. According to the principle applied in the Universal Soil Loss Equation empirical model – USLE, a single precipitation episode was defined as an event separated from the next by a 6 h period without precipitation or with precipitation <1.3 mm (in system SI) (Wischmeier and Smith, 1958). The analysis has involved rains ≥ 10 mm, which are potentially erosive and are therefore valid, for example, in predicting hydrological phenomena (Lorenc, 1991). The value taken into consideration was slightly lower than that for erosive rains classified according to the USLE criteria (layer ≥ 12.7 mm or maximum intensity ≥ 6.3 mm/ 15 min). This assumption has enabled us to analyse a slightly higher number of precipitation events. Total of 51 rainfall events were identified (in all three catchments). For each precipitation episode the following variables were evaluated: total time of occurrence, the total of precipitation, mean intensity of each episode, and the maximum intensity for various time units, from 1 min to 24 h. This, together with the analysis of the amount of sediment budget, has made it possible to create simple rainfall typology concerning the effects for channels

4. Results 4.1. Morphometric parameters of catchments and stream channels The relief, morphometry and geometry of the investigated catchments and their channels were characterised through selected parameters listed in Table 1. The gradients of analysed channels are diverse. Given the mountainous area, the gradient of the investigated channel of DAD1 catchment is relatively small – 0.073; the gradient of the channel of DAD3 catchment is almost double – 0.128; and that of the DAD2 catchment is almost 3.5 times steeper than DAD1 – 0.254 (Tab. 1). The higher values of gradients, as in the latter example, can clearly translate into high values of intensity of episodic flows and the resultant increased effectiveness of fluvial processes. This in turn affects the sediment budget. In the investigated catchments, it is the short channels, up to 1 km long and situated in the steep sections of the High Atlas, which Table 1 Catchments and stream channels morphology (Rojan et al., 2019). parameter, indicator CATCHMENTS drainage area maximum elevation minimum elevation relative elevation length effective width form factor shape factor elongation ratio average slope CHANNELS total streams length drainage density length of main channel gradient of main channel tributaries per 1 km of main channel

5

symbol

DAD1

DAD2

DAD3

A (km2) Hmax (m a.s.l.) Hmin (m a.s.l.) ΔH (m) Lp (km) Rb (km) Ff (–) Rs (–) Re (–) R (˚)

22.73 2164 1573 591 9.23 2.46 0.27 3.75 0.58 3.66

2.95 2455 1720 735 3.46 0.85 0.25 4.06 0.56 11.99

7.39 2887 2055 832 6.11 1.21 0.20 5.05 0.50 7.76

Ls (km) D (km/km2) Lk (km) Rk (–)

198.94 8.75 9.37 0.073 2.05

17.92 6.07 3.38 0.254 0.86

39.38 5.33 7.41 0.128 2.03

Catena 190 (2020) 104530

E. Rojan, et al.

are characterised by the steepest slopes. In some of their parts, the gradient exceeds 0.9, which facilitates transport of sediment into lower parts of the channels. Parameters that influence potential energy of a catchment are factors: form, shape and elongation ratio. Form factor (Ff) indicates time of concentration, amount of culmination and time of flow/discharge of water in the catchment (Horton, 1945). The Ff factor for the studied catchments receives similar values: DAD1 – 0.27, DAD2 – 0.25 and a slightly lower value for DAD3 – 0.20. These values are low and reflect the elongated shape of the catchment. The shape factor (Rs) also indicates elongation of the studied catchments, in particular the DAD3 catchment, for which it is 5.05 (the higher the value, the more elongated the catchment). The above results also confirmed by the values of elongation ratio (Re): DAD 1 – 0.58, DAD 2 – 0.56, DAD3 – 0.50. The more these values fall below 1, the more the shape of the catchment resembles a rectangle or a triangle, and less a square. It can therefore be ascertained, that the shapes of the study catchments of the upper Dades valley constitute a factor, which does not facilitate flows of very high morphogenetic potential. Considering an important role that the channel order of watercourses plays, among others, in the occurrence and performance of the volume of flow, the channels of studied catchments of upper Dades were subjected to hierarchical classification of the drainage networks according to Strahler (1952). These channels (Fig. 3) are characterised by a high rate of length of the lowest order (0.) in the total length of the catchment channels: DAD1 – 47.6%, DAD2 – 44.8% and DAD3 – 43.6%. Of the total length, 26–31% is in the lowest orders. The proportion of channels of the highest orders is the lowest, especially of orders 4. and 5., in DAD1: respectively – 3.3% and 0.7%. These and the above values may indicate a very important role the lowest-order channels play in the morphodynamics of the fluvial processes occurring at the study site. Based on the analysis of density of the river network in the studied channels (DAD1 – 8.75 km/km2, DAD2 – 6.07 km/km2 and DAD3 –

Table 2 Parameters of catchments and stream channels morphology in cross-section profiles (in order from the highest situated profile). Catchment

Crosssection profile

Channel order

Gradient of channel

Area of catchment up to the crosssection profile (km2)

Length of channels above the cross-section profile (km)

DAD1

DAD1d9 DAD1d6 DAD1d4 DAD1d8 DAD1d7 DAD1d3 DAD1d2 DAD1d1 DAD2d9 DAD2d8C DAD2d8E DAD2d6 DAD2d4 DAD2d2 DAD3d14 DAD3d9 DAD3d7 DAD3d4 DAD3d3 DAD3d2 DAD3d1

1 1 2 3 3 4 4 4 1 2 2 3 4 4 1 1 2 3 3 4 4

0.158 0.158 0.158 0.114 0.070 0.045 0.047 0.056 0.344 0.158 0.249 0.141 0.158 0.141 0.105 0.105 0.123 0.087 0.061 0.070 0.063

0.04 0.10 0.70 0.45 0.53 2.83 4.11 5.66 0.10 0.30 0.45 0.92 2.52 2.71 0.32 0.60 2.13 3.52 3.98 5.58 6.63

0.21 0.51 11.70 4.04 4.81 19.83 31.01 45.20 0.53 0.91 1.21 3.37 14.20 15.48 0.53 1.05 4.75 10.19 12.48 22.85 33.82

DAD2

DAD3

5.33 km/km2) it can be assumed that the opportunities for drainage of the studied catchments are at least good. Additional characteristics (including morphometric features) of the channels and cross-section profiles, which have direct impact on the level of flow intensity, are listed in Table 2. (see Table 3).

Fig. 3. Channels of different orders in the catchments DAD1, DAD2 and DAD3 (Dłużewski et al., 2013b, changed).

6

Catena 190 (2020) 104530

E. Rojan, et al.

from widespread precipitation on 20–22 September 2014 with a total of 68.4 mm (max. 8.2 mm/h). Morphometric features of the DAD2 catchment and channels (Tab.1 and 2) have an effect on high values of the flow rates. These features include its a very large gradient (0.254), relatively narrow channels and lithological and structural features, such as limestone rock floors in the bottom parts of the channel sections. Flow rate values at DAD2d2 and DAD2d4 that were significantly higher than those in the sections below them resulted from the supply of a significant amount of water from the third-order channel immediately above DAD2d4. The highest flow rate for the bottom DAD1 catchment (Fig. 6) during the study period took place in November 2014. It occurred at two bottom cross-section profiles: DAD1d1 (gradient – 0.07), 11.6 m3/s (SPQ – 2 m3/s per km2); and DAD1d2 (gradient – 0.07), 11.3 m3/s (SPQ – 2.8 m3/s per km2). It resulted from frontal precipitation of type C totaling 68.4 mm (max. 8.2 mm/h). This precipitation event took place two months after a larger precipitation of 81.8 mm (20–22 September 2014). During the September precipitation, some of the channel sediments were removed from the catchment (to the Dades channel and lower), which could have had an impact on the increased flow during the next event (November). During the September precipitation, the soil of the catchments being studied could have become wet, which would have meant that soil retention during the November precipitation was limited, and, therefore, resulted in an increased supply of rainwater from the slopes to the channels. The smaller flow rates in the largest of the analysed catchments, in relation to the central catchment (the smallest), could be, among other things, the result of the geological structure (86% of the catchment area is made of conglomerates and this causes higher infiltration due to permeability). In the upper DAD3 catchment (Fig. 7), the highest flow rates in the study period were caused by precipitation that occurred on 20–22 September 2014, which totaled 59.2 mm (max. 8.6 mm/h); and 20–22 November 2014, totaling 53.8 mm (max. 4.6 mm/h). The flow rates were as follows: at DAD3d1 – 4.7 m3/s in September 2014 (SPQ – 0.71 m3/s per km2) and 6.19 m3/s in November 2014 (SPQ – 0.93 m3/s per km2); and 5.0 m3/s (SPQ – 0,91 m3/s per km2) at DAD3d2 (November 2014). Compared to the values from the central and lower catchments, the flow rates in the upper catchment were considerably smaller. This may have been due to the morphometric features of the catchment and lower channel density (DAD3 – 5.33 km/km2, DAD1 – 8.75 km/km2) (Tab. 1). These factors, together with the characteristics of precipitation, such as spatial and temporal variability and smaller amounts of rain, had affected the supply of water. The majority of values obtained for flow rates in the channels being studied indicate a general increase for subsequent cross-section profiles (the longer the channels). This is primarily a result of connecting lowlevel lateral tributaries to these channels. A deviation from this principle may be a result of the specific, local characteristics of the channel sections, for example, a change in the metrical characteristics of a channel section after a previous flood event (as in the case of DAD3d7 in September 2014), or a breakthrough section (narrowing) at the DAD1d3 cross-section profile. Very high specific peak discharge values (SPQ) were obtained for the study area. The maximum values for each study catchment are as follows: in DAD1 – 10.7 m3/s per km2 (DAD1d9, 1. order) and 7.9 m3/s per km2 (DAD1d6, 1. order), in DAD2 – 27.6 m3/s per km2 (DAD2d4, 4. order) and 22 m3/s per km2 (DAD2d2, 4. order), in DAD3 – 18.8 m3/s per km2 (DAD3d9, 1. order) and 13.2 m3/s per km2 (DAD3d7, 2. order). As a comparison, SPQ obtained by A.E. Mather and M. Stokes (2018) for the fan at the outlet of the DAD2 catchment was 5.5–8.5 m3/s per km2, and the values for three other fans in the upper Dades valley were between 1 and 9.7 m3/s per km2. High SPQ values presented in this study result from significant discharges relative to the very small catchment area, which in the examples shown above are merely 0.04 to 2.71 km2.

Table 3 Average total sediment budget (m3) for each cross-section profile. Channel order

DAD1

DAD2

DAD3

1 2 3 4

0.06 0.23 0.36 1.12

0.09 0.33 0.44 1.76

0.09 0.34 1.08 1.23

4.2. Precipitation and its types Precipitation occurring at the study site is characterised by high space and time variability. At the 3 weather stations during the study (1.07.2012–31.12.2015) the total of 51 effective precipitation episodes were registered (>10 mm): at the lower station DAD1 – 12, at the middle station DAD2 – 18, and at the upper station DAD3 – 21. The highest precipitation was registered in autumn 2014. The maximum value – 83.6 mm in 64 h 7 min, occurred in November of that year at DAD2. The next value in order from high to low – 81.8 mm in 74 h 24 min, was registered in September 2014 at DAD1 (Fig. 4A and B). During the periods of 20–22 September and 20–23 November 2014, there was continuous rainfall resulting from weather front activity. The next high value of precipitation was recorded during 4–5.03.2013 at DAD1 – 55.6 mm in 26 h 24 min. All these rains were of low average intensity – 1.1–2.1 mm/h (Fig. 4C). On 16.08.2015 the next value in order from high to low was recorded at DAD2 – 43.2 mm in 1 h 31 min. In comparison with the previous rainfall events, this rainfall was of a very different average intensity at 28.8 mm/h (max 40.4 mm/h). These and other effective precipitation episodes for the study site are shown in Fig. 4A-C. Based on precipitation characteristics, such as amount and maximum intensity 1-hour (Imax), three types of precipitation were distinguished: - A – amount of 10–30 mm and (Imax) < 4 mm/h - B – amount of 10–30 mm and (Imax) ≥ 4 mm/h - C – amount of ≥ 30 mm and (Imax) ≥ 4 mm/h. The majority of precipitation events analysed (>10 mm) were of type B, and these constituted 57% of all rains during the research period. The type A rains only constituted 10%, and type C – 33%, respectively. 4.3. The flow rate of ephemeral watercourses Cross-sectional measurements at the points of study were used to calculate the flow rates in the ephemeral river in the upper Dades catchments (Fig. 5). The maximum values for the studied area during the period June 2012 to December 2015 were obtained for flows in the catchment DAD2 At the measurement point DAD2d4 (gradient of channel – 0.158) which was established 2.5 km from the upper border of the catchment and encloses the area of 2.5 km2, a value of 69.6 m3/s (SPQ – 27.6 m3/s per km2) was obtained. A slightly lower value of 59.6 m3/s (SPQ – 22 m3/s per km2) was obtained for the DAD2d2 point (gradient – 0.141) situated nearly 400 m further down the valley and enclosing 2.7 km2 of the catchment and 2.9 km of the channel. The width of the channel between these two points is 8–10 m. The flow obtained from a section of channel nearly 3 km long was approximately twice as high as the average flow in the final section of the upper Dades (for 130 km). The values were calculated as a result of heavy precipitation (type C) totalling 43.2 mm and lasting 1 h 31 min (max. 40.4 mm/ h), which took place on 16 August 2015. For the same section, subsequent flow rates in the studied catchments were also obtained. These were 17.1 m3/s (SPQ – 6.3 m3/s per km2) at DAD2d2, and 11.9 m3/s (SPQ – 4.7 m3/s per km2) at DAD2d4. These results arose 7

24-09-2012 27-09-2012 09-11-2012 11-11-2012 04-03-2013 05-03-2013 29-06-2013 19-01-2014 12-03-2014 19-08-2014 20-09-2014 11-10-2014 20-11-2014 28-11-2014 18-02-2015 19-02-2015 14-04-2015 22-05-2015 23-05-2015 16-08-2015 22-08-2015 28-09-2015 28-09-2015 24-10-2015 04-05-2016 29-09-2016 07-10-2016 24-10-2016 25-10-2016 11-02-2017 29-06-2017

mm/h

C

8

29-06-2017

11-02-2017

25-10-2016

24-10-2016

07-10-2016

29-09-2016

04-05-2016

24-10-2015

28-09-2015

28-09-2015

22-08-2015

16-08-2015

23-05-2015

22-05-2015

14-04-2015

19-02-2015

18-02-2015

28-11-2014

20-11-2014

11-10-2014

20-09-2014

19-08-2014

12-03-2014

19-01-2014

29-06-2013

05-03-2013

04-03-2013

11-11-2012

09-11-2012

27-09-2012

24-09-2012

h

24-09-2012 27-09-2012 09-11-2012 11-11-2012 04-03-2013 05-03-2013 29-06-2013 19-01-2014 12-03-2014 19-08-2014 20-09-2014 11-10-2014 20-11-2014 28-11-2014 18-02-2015 19-02-2015 14-04-2015 22-05-2015 23-05-2015 16-08-2015 22-08-2015 28-09-2015 28-09-2015 24-10-2015 04-05-2016 29-09-2016 07-10-2016 24-10-2016 25-10-2016 11-02-2017 29-06-2017

mm

E. Rojan, et al.

Catena 190 (2020) 104530

A 90

80

70

60

50

40

DAD1

30

DAD2

20

DAD3

10

0

B 80

70

60

50

DAD1

40

DAD2

30

DAD3

20

10

0

30

25

20

15

DAD1

10

DAD2

DAD3

5

0

Fig. 4. Precipitation >10 mm at the weather stations DAD1, DAD2 and DAD3 during the period 1.07.2012–30.06.2017: A – volume (mm), B – duration (h), C – average intensity (mm/h).

Catena 190 (2020) 104530

E. Rojan, et al.

Fig. 5. Catchment DAD2: A – a significant part of the catchment with the visible course of the channel being studied, B – the rock floors in the middle section of the channel, C – cross-section profile DAD2d2 in the lower channel section 2. order, D – the cutting of 140 cm in depth into the channel bottom below DAD2d2 as a result of precipitation on 20–22 September 2014 (68.4 mm). A boulder with a diameter of 36 cm, marked (blue) and dislocated with DADd2.

Fig. 6. Catchment DAD1: A – order 4. channel cutting in conglomerates with a multi-current system and median bars, B – bedrock channel bottom in limestones and marls with a system of steps, 2.order; C – channel sediments in 4. channel order, D – beginning of the flood on 20 November 2014, below DAD1d1.

9

Catena 190 (2020) 104530

E. Rojan, et al.

Fig. 7. Catchment DAD3: A – broad and gentle order 4. Channel, B – order 2. channel with coarse-grained (20–30 cm) slope material, C – cross-section profileDAD3d4 (blue line) 3. order channel, D – cross-section profileDAD3d3 (yellow line) 3. order channel.

4.4. Sediment budget in ephemeral river channels

precipitation event of 68.4 mm (max. 24-hour – 43.2 mm, max. – 8.2 mm/min, precipitation type A) and a flow rate of 17.1 m/s. This resulted in a cutting and deepening of the channel bottom by 1.2 m on average (the difference between the blue and green line), for almost its entire width (9 m) (Fig. 9A). The diversification and undulation in the course of the cross-section line from October 2015 is quite clear (Fig. 9A), where a change in the direction of the sediment budget occurs at six points (from accumulation to erosion and vice versa), in comparison to the previous line. Despite insignificant values for the sediment budget (-3.6% of the surface in total), the course of this crosssection line indicates very large fluvial processes dynamics. These result from a heavy type C precipitation of 43.2 mm (max. 40.4 mm/h) and its duration of 1 h 31 min, which caused a short but very high flow rate of 59.6 m3/s. The maximum accumulation, marked by a reduction of the crosssectional surface area by 86.8% in relation to the surface area from the previous measurement, although clearly smaller than the percentage change in erosion, was observed in the second-order channel of the upper catchment at the DAD3d7 point (Fig. 9B). This resulted from the ephemeral watercourse having a maximum flow rate of 28 m3/s, which, at lower values, led to the transported sediment being deposited and filling in the studied section of the 8 m-wide channel to an average depth of 1 m and creating a new channel that was almost 5 m wider. The results presented above come from study points located in catchments made of limestones and marlstones, and the sections of the channels described are characterised by a similar inclination (gradient 0.12–0.14). The reasons for the differences in the type and size of the changes in the cross-sections, i.e., the predominance of erosion or accumulation, in addition to the flow rate, can be found in the order of channels. In addition to the extreme changes in the values of the channels’ cross-sections (max. erosion and accumulation) described above, the highly dynamic fluvial processes of the area being studied is evidenced

The results obtained during the 3-year study period from calculations of the surface areas of the cross-sections profiles, reveal a predominance of erosion over accumulation. Channel sediments are mainly removed from the catchments of ephemeral watercourses to the upper Dades valley (Fig. 8). In 70% of the analysed cases (107 cases during the period November 2012-October 2015), erosion predominates. In the remaining 30% of cases, accumulation prevails. The average change in the cross-sectional surface area measurements for all the study points analysed during the 3-year study period was −1.23 m2 which is -8.2%. This proves the dominance of erosion over accumulation. In general, larger changes in the channels’ cross-sections occur in the lower parts of the cross-sections, i.e., in the higher orders (thirdorder to fifth-order), where the flow rates are usually higher. Clearly, the DAD1 catchment is characterized by the smallest changes in crosssectional surface areas, a maximum of 24%. Here, the share of cases having a predominance of accumulation, i.e. 35.5%, is larger than in the two other catchments. Such results are affected by, among other things, the geological structure. A significant part of this is made up of Neogene conglomerates, while well-rounded limestones dominate in the channels. Infiltration into the underlying bedrock is greater here, in contrast to the other catchments where the bedrock is impermeable. Moreover, the relatively less resistant conglomerates have an impact on the catchment slope making it less steep, while also making the channels wider in comparison with the other catchments. This results in flows of lower intensity, which in turn produces a lower sediment budget. This end result may also be influenced by the fact, that due to the terrain being less steep, the slope processes are less active. The maximum enlargement of the cross-sectional surface area, i.e., the predominance of erosion between successive charts, is up to 128%. This was observed in the lower section of the fourth-order channel of the DAD2 catchment, at the DAD2d2 study point (Fig. 9A) after a 10

Catena 190 (2020) 104530

E. Rojan, et al.

A DAD1

erosion (m2)

(m a.s.l.) 2200

accumulation (m2) erosion+accumulation (m2)

2100

m2 DAD1d7 2 0,00 0

m2 DAD1d6 2 0,03 0 -0,13 -0,16 -2

2000

-2

-1,60

-1,60 m2 DAD1d2 2 0,76 0 -2 -1,33 -2,09

m2 DAD1d8 2 0,07 0 -0,11 -0,18 -2

1900

1800

m 2

2

m2 DAD1d1 2 0,37 0 -2 -1,00 -1,37

DAD1d3

0,11 0 -0,41 -2 -0,52

1700

1600 1500

0

1

2

4

3

5

6

7

8

B DAD2

9 L (km)

erosion (m2)

(m a.s.l.) 2500

m2 DAD2d9 2 0,01 0 -0,12 -0,13 -2

2400

accumulation (m2) erosion+accumulation (m2)

m2 DAD2d8C 2 0,04 0

2300 2200

-2 -0,69

-0,65

m2 DAD2d6 2 0,06 0

2100

-2 -0,58

2000

m2 DAD2d2 2 0,07 0

-0,52

-2

m2 DAD2d8E 2 0,03 0

1900

-2 -1,01

1800

-4 -6 -8

-0,98 m 2

2

DAD2d4

-7,55

-7,48

0,05 0 -2 -1,16 -1,11

1700 1600 1500

0

2

1

4 L (km)

3

C DAD3

erosion (m2)

(m a.s.l.) 2900

m2 DAD3d14 2 0,01 0 -0,06 -0,07 -2

2800 2700 2600

m 2

2

DAD3d9

accumulation (m2) erosion+accumulation (m2) m2 DAD3d7 6 4,55 4,07 4 2 0 -2 -0,48

0,08 0 -0,34 -2 -0,42

2500

m2 DAD3d4 2 0,04 0 -2

m2 DAD3d2 6 5,28 4 1,50 2

-4 -6 -8 -6,66

2400

-6,62

0 -2

2300 2200 2100 2000

0

1

2

3

-4

-6 -4,64 -8

-4 -3,78

m2 DAD3d3 2 1,09 0 -2 -2,77 -4 -3,86 4

m2 DAD3d1 2 0,14 0 -2

5

6

-4,50

7 L (km)

Fig. 8. Sediment budget (m2) in channels of an ephemeral river during the period 2012–2015.

by high variability in the course of the cross-section lines. This demonstrates a frequent variability of flows, and variability of channel forms for the sections of the channels being analysed, especially their

lower sections. Examples include the wide sections of the fourth-order channels in the catchment made of limestones and marlstones (DAD3, benchmark, cross-section profiles DAD3d1-3, Fig. 9C), and of 11

Catena 190 (2020) 104530

E. Rojan, et al.

DAD2d2

A

0.0 -0.2 -0.4 -0.6 -0.8

m

-1.0 -1.2 -1.4 -1.6 -1.8 -2.0 -2.2

-2.4 0

1

2

3

4

5

6

7

8

9

10

11

m X.2012

IX.2013

XI.2014

B

II.2015

VI.2015

X.2015

DAD3d7 0.0 -0.2 -0.4

m

-0.6 -0.8 -1.0 -1.2 -1.4 0

1

2

3

4

5

6

7

8

II.2015

VI.2015

9

10

11

12

13

m X.2012

C

IX.2013

XI.2014

X.2015

DAD3d1 0.00 -0.05 -0.10 -0.15

m

-0.20 -0.25 -0.30 -0.35 -0.40 -0.45 -0.50

0

5

10

15

20

25

30

m X.2012

IX.2013

XI.2014

II.2015

VI.2015

X.2015

Fig. 9. The channel cross-section profiles: A – DAD2d2 in the DAD2 catchment, B – DAD3d7 in the DAD3 catchment, C – DAD3d7 in the DAD3 catchment.

conglomerates (DAD1, benchmark, cross-section profiles DAD1d1-3). The surface areas of erosion and accumulation obtained from crosssections were used to calculate the volume of elevated and deposited total sediment in cross-section profiles during hydrological events. The average value of all the cross-section profiles was 1.07 m3, which means that this amount of channel material was accumulated and eroded together at each benchmark point during the period between measurements, i.e. slightly > 2 m3/year. The maximum value between successive measurements – 9.81 m3 (erosion + accumulation), was calculated for the DAD3d3 point in the fourth-order channel, which was 28.6 m wide and had a flow rate of 40.3 m3/s for the period June to October 2015. Such intensity and the magnitude of changes in the

channel do not correspond to the precipitation amounts recorded by the DAD3 station during that period. The maximum rain was only 11.8 mm during 3 h (type A). The above results, as well as the results obtained from other points in this catchment during the discussed study period, may suggest an occurrence of a heavier, torrential rain in the higher sections of this catchment, which would be consistent with the very large spatial variation in precipitation, especially of the torrential kind, in high mountains of the arid zone. The total sediment budget for all measuring points for the period October 2012 – October 2015 is shown in Fig. 10. In the DAD3 catchment, high amounts of eroded and accumulated material are discernible when compared with the amounts present in other catchments. To a 12

Catena 190 (2020) 104530

E. Rojan, et al.

Fig. 10. The total sediment budget for the period October 2012-October 2015.

large degree they are an effect of the sudden local hydrometeorological event mentioned above. Nevertheless, the catchment’s topography, including land relief developed in middle Jurassic, less resistant types of rock (oolitic and oncolitic limestones, marlstones), is also of importance here. The channel network is very well developed here, mainly with respect to channels of 3rd and 4th order, which are wide. The number of tributaries per 1 km of main channel (2.03) is the same here as in the catchment composed of conglomerates (2.05), and the gradient of the main channel is almost twice as steep as in DAD1. The data for the total sediment budget obtained at each survey point for each measurement period were used to calculate the average values of this parameter for the channels of various orders (Tab. 3). There is distinct difference between the results obtained for channels of all orders in the catchment composed of conglomerates, and those in the catchment composed of limestones and marlstones. Therefore, an impact of the lithology factor is clearly discernible here. When compared with the results for the lower orders, the analysed parameter increases markedly in the channels of the 4th order in DAD1 and DAD2 catchments, while in DAD3 it even increases in channels of the 3rd order. This in turn provides evidence of a significant role that the stream order and the discharges, which are largely conditioned by it, play here. The sediment budget depends significantly on the flow rate. The results obtained for the study area were compared in order to check such a relationship for each of the studied catchments. The relationships are expressed linearly. Correlation coefficients, although not all very high, are statistically significant at the given level of significance, p < 0.001. The most obvious relationship of sediment budget and flow rates is observed for the upper DAD3 catchment, R2 = 0.91 (Fig. 11). Here, the volume of the displaced (accumulated and eroded) channel

total sediment budget (m3)

12

DAD1 DAD2 DAD3

10

y = 0.1662x + 0.2512 R² = 0.6062 p < 0.001 y = 0.1033x + 0.1886 R² = 0.5421 p < 0.001 y = 0.2146x + 0.1989 R² = 0.9058 p < 0.001

8 6 4 2 0 0

10

20

30

40

50

discharge (m3/s) Fig. 11. Relationship between total sediment budget and flow rates in the channels of ephemeral rivers within the studied catchments of the upper Dades valley.

material is the largest, when compared to two other catchments, but a large part of it was deposited in the channel. The weakest relationship is observed for the central DAD2 catchment, R2 = 0.54 (Fig. 11). This could be influenced by many factors, such as small catchment area or large gradients. Fluvial processes are characterized by high energy (maximum values for flow rates are attributed to the channel studied here), mainly due to the gradient. However, here the channels are relatively narrow, deeply cut, and there are rock floors in the upper and partly, central sections. The clear predominance of erosion processes visible in the cross-sections, with small amounts of accumulation, does 13

Catena 190 (2020) 104530

E. Rojan, et al.

not deliver high sediment budget values. In the case of the DAD1 catchment, the analysed correlation is slightly better than in the central catchment, R2 = 0.61 (Fig. 11). The relatively low flow rates resulting from, among other things, small gradients, wide (up to 30 m) channel sections, and well-shaped alluvium (conglomerates), favour small sediment budget values in comparison to the other two catchments.

are activated. Such features include, among other things, flow rates. The maximum flow rates in the catchment channels of arid areas are higher than for similar size catchments in humid areas. This is primarily the effect of poorly-shaped soils and poor vegetation (Graf, 1988). The values for peak discharges and specific peak discharges (SPQ), obtained through the measurements performed, are very high for the catchments occupying such a small area. The results of research by Mather and Stokes (2018) concerning the alluvial fan of the DAD2 catchment, as well as other alluvial fans from the upper Dades valley, an good opportunity for such comparison. The authors cite peak discharges for the alluvial fan of catchment DAD2 as 16–25 m3/s. The values calculated in this study for the cross-section profiles situated above the fan (DAD2 – 0.7 km, DAD4 – 1.1 km) are approximately 3 times higher – 59.6–69.6 m3/s. This may result from the characteristics of precipitation itself, but also from the morphometric features of the channels sections, where cross-section profiles are located. Here the sections are narrow – 6–10 m, several times more narrow than those at the head of the fan, where they are approx. 50 m wide. This significantly influences the flow density. The peak discharges obtained for DAD3 (surface of 7.4 km2) – 33.1–40.3 m3/s are close to the values obtained for the alluvial fan at the outlet of a slightly smaller catchment (5.3 km2) – 33–51 m3/s. The peak discharges for DAD1 (surface of 22.7 km2) are on the other hand much lower – 11 m3/s than those obtained by Mather and Stokes (2018) for the fan of a catchment of similar surface (7.4 km2) – 77–267 m3/s. These catchments differ significantly in terms of lithology, a factor which influences the morphometric features of individual channels. The DAD3 catchment is in large part built of conglomerate, and the catchment, which it is being compared to, of limestone and marlstones. This has very significant impact on water penetration, width of channels, and the extent of alluvial fill. The last comparison presented demonstrates evidence of a very high impact of lithology on flow intensity. With respect to the comparison of flows from the upper Dades valley, in the Wadi Dhuliel catchment in the north-eastern part of Jordan, that has an average annual precipitation of approximately 123 mm, the flow rate during 1986–92 ranged to 125.2 m3/s. In a 6 m wide channel the flow was 0.47 m3/s, and in a 35.8 m wide channel – 47.4 m3/s (Abushandi and Merkel, 2011). What should be emphasized is that the maximum flow rates obtained from the study catchments are evidently very high, considering factors such as small catchment area and relief, including gradient of catchments and of local slopes and the length of channels. However, these results should be treated with some caution, mainly due to the output data, that is, the geometric dimensions of the channels at the cross-section profiles, these are the result of not only erosion process activity, but also, in places, of accumulation processes. Although the calculation methods used are considered to be the most effective (Kubrak and Nachlik, 2003), the flow rate results may not reflect the maximum flow rates, especially in places where accumulation forms occur in the river channel. The transport of bedload in episodic rivers, especially in the high mountains of the arid zones, is, proportionally, the largest for all types of rivers. For example, the river yield for these types of rivers in Israel is on average 400 times greater than the yield for equivalent rivers in humid zones (Laronne and Reid, 1993). This is a key factor in the development of river channels and valleys. In arid zones that have very scarce vegetation and a huge amount of slope material, erosion is predominant in the channels. This has been confirmed by developing a sediment budget for the channels situated on the southern slopes of High Atlas. There, the average change (for all survey points) to the cross-section surface area was −1.2 m2 during 3 years. By comparison, the results of identical measurements (19 cross-section profiles, research period – 3 years) taken in the channel of Tordera river (basin 894 km2) in the northern part of the Catalan Coastal Ranges situated in Mediterranean climate region, reveal the predominance of accumulation – the average value of sediment budget is 2 m2, despite the fact that

5. Discussion Flows and sediment budgets in channels in semi-arid and arid climate zones are dominated by extreme events that are dependent almost exclusively on precipitation, but are clearly related to the catchment’s characteristics (Zarei et al., 2014). The results of research carried out in the valley of upper Dades in High Atlas also confirm a significant role of precipitation, mainly in relation to its amounts and intensity. The sediment budget in episodic river channels is evidently influenced by heavy rains (≥30 mm and Imax ≥ 4 mm/h) of long duration and low average intensity, as well as by sudden, transient rains of high average intensity. The rainfall data obtained reveal substantial spatial and temporal variations in precipitation. Evidence of this is provided by locally occurring rains (registered by only one of the three meteorological stations, e.g. at DAD3 on 22.08.2015 – 11.4 mm). These variations may cause the slope-fluvial system in each catchment to function differently during a given rainfall event, even in neighbouring catchments. Among other features of the natural environment, it is lithology and strata structure, as well as catchment morphology dependent on them, that play a significant role in the functioning of the fluvial system, including the resultant sediment budget of channel material. This is confirmed by our results, which are similar to the results presented in research papers by: Stokes et al. (2008, 2017), Dłużewski et al. (2013b,c), Stokes and Mather (2015), Mather et al. (2017), Mather and Stokes (2018), Rojan et al., 2019). The channel-courses within the study area clearly reflect the shape and pattern of the valleys, the characteristics that are strongly influenced by bedrock structure and, locally, by tectonics of the area (Stokes et al., 2008, Boulton et al., 2014) and, in some sections, the type of transport of channel material. This, among other factors, causes significant diversification of the channels, which concerns their course, long profile (gradient 0.02–0.9), crosssection (clear differences in the sections of the same order) (Dłużewski et al. 2013b), the number and size of forms. Geology and relief also have an impact on the length of the valley network, which in turn determines density (Goudie, 2013). The values for valley network density, obtained by way of analysing the 256 km combined length of the episodic river channels, are between 5.3 km/ km2 for DAD2 (limestone and marl) and 8.8 km/km2 (mainly conglomerates). These values are quite high comparing to data provided by Goudie (2013) for arid areas (precipitation < 300 mm) – 0.5–0.6 km/km2, or for slightly more humid ones – approx. 1.0 km/km2. It can thus be assumed that, within the study area, such value of this parameter contributes to the occurrence of flows of high morphogenetic potential. Furthermore, erosion channels play an important role in providing energy and material to the stream channels. Their network is very dense, particularly on slopes that are almost vertical and are built of alternate layers rock of varied resistance (e.g. in DAD2). In addition, the fact, that a significant proportion of the study channels (even > 50%) belong to the lowest order, may have significant impact on the increase of values of flow intensity and the resultant increased effectiveness of the fluvial processes. Lithology also plays a significant role, particularly in arid environments, in determining sediment calibre and availability due to weathering (Stokes and Mather, 2015). Determining some of the features of the watercourses in mountainous areas of the arid zone is very difficult, mainly because of their periodic nature and high proportion of floods, during which significant amounts of clastic material 14

Catena 190 (2020) 104530

E. Rojan, et al.

in the 63% of cases erosion was predominant (Rovira et al., 2005). When comparing the parameters of both catchments, it needs to be stressed that small catchments play a crucial role in material supply to the lower situated parts of the channels. This has also been noted by other authors, in reference to other climate zones (Bryndal, 2014). The Tordera catchment study also reveals that zones of higher periodic accumulation of channel material are more frequently found there, than in the high mountains, where nevertheless local deposition zones and numerous alluvial fans are also present. In High Atlas these are particularly well developed at the outlets of ephemeral tributaries to the Dades river. There, alluvial fans are activated by the flows caused by type B or C precipitation. This precipitation is only in the form of either sudden local rains, or long-lasting rains of small amounts (< 50 mm) and low intensity. During periods of less frequent heavy rains of long duration an large amounts (>10 a year), as for example, in September and November 2014, the discharge in the river (Dades) has tended to rework / remove the tributary fans (Stockes and Mather, 2015). The results obtained suggest a very significant relationship between the dynamics of mountain river channels, in terms of sediments budget, and the volume and rate of flow. Besides being influenced by the lithology and morphology features and the channel parameters of a given catchment, the flow depends on the total amount and intensity of precipitation. This is despite the fact that in, the upper Dades catchment, for example, 49% of the water balance is accounted for by evapotranspiration, and only 28% by subsurface drainage, just 3% by surface outflow, and 20% by various forms of retention within the catchment (de Jong et al., 2005). Fig. 12 shows the relationship between the total sediment budget and selected features of the natural environment of High Atlas, such as precipitation type, lithology and stream order. Evidently, it is the type C rains that are the main trigger of morphogenetic change there. Their role in flow efficiency is affected predominantly by the stream order and lithology. The impact of lithology on the sediment budget becomes very significant only for channels of the 3rd and 4th order. Fig. 12 shows the impact of selected features of the natural environment on the total sediment budget in the studied catchments of the upper Dades valley. Evidently, it is the type C rains that are the main trigger of morphogenetic change there. Their role in flow efficiency is affected predominantly by the stream order and lithology. The impact of lithology on the sediment budget becomes very significant only for channels of the 3rd and 4th order. During the entire survey period, the highest average sediment budget for a given catchment was identified in the highest situated catchment (DAD3), which is composed of folded and monoclinally inclined limestone; while a smaller budget was recorded in the lowest catchment (DAD1), which is mainly composedof of massive conglomerates; and the smallest budget was found to be in the middle catchment (DAD2), which consisted of fractured limestone interbedded with marlstone. It can be concluded that the highest sediment budget in the channels of the upper Dades is related to the huge inflow of material from the slopes into the channels. The smallest values of sediment budget, which were noted in the channels of the middle catchment, may result from a smaller flow of water on the slopes due to numerous cracks that are related to the geological structure, which, only after being filled with water, allow for surface flow – only then water is able to transport material from the slopes into the channel. The average sediment budget in the smallest catchment, despite its lack of ground sealing, could also be related to a slightly smaller supply of material from the slopes into the channels. This is associated with the catchment’s morphology, and in particular with its low degree of inclination in the significant parts of the slopes, which is related to the occurrence of extensive flat-topped hills. Only very intense precipitation caused the surface flows and triggered the transport of material across the short sections of slope with significant inclination.

Channel order

Lithology

Type of conglomerate

limestones and marlstones

A 1

B C A

2

B C A

3

B

C

A

4

B

C

type amount (mm) Imax (mm/h) A 10-30 <4 B 10-30 ≥4 C ≥30 ≥4 Average total sediment budget (m3) small ≤0.20

medium 0.20-0.75

large ≥0.75-1.50

very larg ≥1.50

Fig. 12. Impact of precipitation, lithology and channel order on the total sediment budget on the southern slopes of High Atlas.

6. Conclusions 1. A total sediment budget in small channels of high mountains of the arid zone depends on the flow rate, i.e. on the channel order. 2. Rainfall data, combined with the sediment budget calculated, provide evidence that during normal rainfall events characterized by the same total amount, it is rainfall intensity that plays a key role in the channel sediment budget, regardless of the channel order. The highest channel sediment budget may be caused not only by high intensity rains but also by rains of low intensity but long duration, which yield high total amounts of precipitation. This is the effect of low water retention in such areas, which is caused by sparse vegetation and a thin cover of regolith. 3. The results reveal that in channels of the first and second order in the study catchments, the differences in catchment lithology have 15

Catena 190 (2020) 104530

E. Rojan, et al.

4.

5. 6.

7.

only a minor impact on the sediment budgets, whereas in channels of the third and fourth order this impact is much higher. Despite the fact, that the catchments of various lithology may contain the same number of tributaries, the sediment budget in channels within the catchments composed of limestones and marlstones is greater, than in the catchments composed of conglomerates. This suggests that the sediment supply from slopes is greater in the catchments dominated by limestones and marlstones. Numerous slope throughs and channels of 1.-3. orders play an important role in depositing of rubble into the channels of higher order. They are characterised by steep declines. When two extreme rainfall events happen one after the other, the sediment budget resulting from the second event is relatively smaller. This is because the channel material that became eroded during the first event, has since nourished the alluvial fan at the end of the main channel. During precipitation events repeated every 1–3 years, a more gradual process of rubble displacement, that is, slug displacement, takes place. This affects the sediment budget locally, but facilitates forming of uneven longitudinal profiles of channels. During extreme hydrometeorological events repeated every 40–50 years channels material is cleared from the bottoms of 1.-4. order channels, while most of the material is deposited at the valley widenings and in alluvial fans.

terrain. Zeitschrift für Geomorphologie N. F. Suppl. 29, 191–206. Dłużewski, M., Biejat, K., Gierszewski, P., Krzemień, K., Michno, A., Rojan E., SobczakSzelc, K., 2013a, Charakterystyka fizycznogeograficzna zlewni Dades-Draa. [in:] Warsztaty Geograficzne, Afryka Zachodnia 2013”, Środowisko przyrodnicze obszarów suchych a człowiek. 15.11-02.12 2013, Komitet Nauk Geograficznych, WGiSR UW, PTG, 7–22. Dłużewski, M., Krzemień, K., Rojan, E., Biejat, K., 2013Cb. Stream channel development in the southern parts of the high atlas mountains, Morocco. Geografija 49, 10–21. Dłużewski, M., Krzemień, K., Rojan, E., Biejat, K., Kokosiński, Ł., 2013Cc. Morphodynamics of small high-mountain wadis in arid zones (on the examples of the tributaries of the upper Dades River, High Atlas Mountains, Morocco). Landf. Anal. 22, 9–19. Fink, A.H., Knippertz, P., 2003. An extreme precipitation event in Southern Morocco in Spring 2002 and some hydrological implications. Weather 58, 377–387. Golden, L.A., Springer, G.S., 2015. Channel geometry, median grain size, and stream power in small mountain streams. Geomorphology 78, 64–76. Goudie, A.S., 2013. Arid and semi-arid geomorphology. Cambridge University Press 1–454. Graf, W.L., 1988. Fluvial Processes in Dryland Rivers. Springer-Verlag, Berlin, Heidelberg, New York, London, Paris, Tokyo, pp. 1–346. Hakiel, J., 2014. Przepustowość małych cieków powierzchniowych na terenach zurbanizowanych. In: Traczewska, T.M., Kaźmierczak, B. (Eds.), Interdyscyplinarne zagadnienia w inżynierii i ochronie środowiska. Oficyna Wydawnicza Politechniki Wrocławskiej, Wrocław, pp. 310–317. Horton, R.E., 1932. Drainage basin characteristics. Trans. Am. Geophys. Union 13, 350–361. https://doi.org/10.1029/TR013i001p00350. Horton, R.E., 1945. Erosional development of streams and their drainage basins; hydrophysical approach to quantitative morphology. Bull. Am. Geol. Society 56, 275–370. Hrachowitz, M., Bohte, R., Mul, M.L., Bogaard, T.A., Savenije, H.H.G., Uhlenbrook, S., 2011. On the value of combined event runoff and tracer analysis to improve understanding of catchment functioning in a data-scarce semi-arid area. Hydrol. Earth Syst. Sci. 15, 2007–2014. Hughes, P.D., Fink, D., Fletcher, W.J., Hannah, G., 2014. Catastrophic rock avalanches in a glaciated valley of the High Atlas, Morocco:10Be exposure ages reveal a 4.5 ka seismic event. Bull. Geol. Soc. Am. 126, 1093–1104. https://doi.org/10.1130/ B30894.1. Kamykowska, M., Kaszowski, L., Krzemień, K., 1999. River channel mapping instruction. Key to the river channel description. in: Krzemień, K. (Ed.). River Channels-pattern, Structure and Dynamics. Prace Geograficzne 104, 9–25. Kalma, J.D., Franks, S.W., 2003. Rainfall in arid and semi-arid regions, w. In: Simmers, I. (Ed.), Understanding Water in a Dry Environment. Hydrological Processes in Arid and Semi-arid Zones. A.A Balkema Publishers, pp. 15–63. Knippertz, P., Christoph, M., Speth, P., 2003. Long-term precipitation variability in Morocco and the link to the large-scale circulation in recent and future climates. Meteorol. Atmos. Phys. 83 (1), 67–88. Kubrak, J., Nachlik, E. (Eds.), 2003. Hydrauliczne podstawy obliczania przepustowości koryt rzecznych. Wydawnictwo SGGW, Warszawa, pp. 1–317. Laronne, J.B., Reid, I., 1993. Very high rates of bedload sediment transport by ephemeral desert rivers. Nature 366, 148–150. Lambor, J., 1971. Hydrologia inżynierska. Arkady, Warszawa, 1–364. Lorenc, H., 1991. Wpływ urbanizacji Warszawy na zmienność opadów atmosferycznych. Wiad. IMGW 14 (35) 1–4, 109–126. Mather, A., Stokes, M., 2016. Extracting palaeoflood data from coarse-grained Pleistocene river terrace archives: an example from SE Spain. Earth Surf. Proc. Land. 41 (13), 1991–2004. Mather, Anne E., Stokes, Martin, 2018. Bedrock structural control on catchment-scale connectivity and alluvial fan processes, high atlas mountains, morocco geological society. London, Special Publ. 440 (1), 103–128. https://doi.org/10.1144/SP440.15. Mather, A.E., Stokes, M., Whitfield, E., 2017. River terraces and alluvial fans: the case for an integrated Quaternary fluvial archive. Quat. Sci. Rev. 166, 74–90. Mul, M.L., Savenije, H.H.G., Uhlenbrook, S., 2009. Spatial rainfall variability and runoff response during an extreme event in a semi-arid catchment in the South Pare Mountains, Tanzania. Hydrol. Earth Syst. Sci. 13, 1659–1670. https://doi.org/10. 5194/hess-13- 1659-2009. Nichols, M.H., Nearing, M.A., Polyakov, V.O., Stone, J.J., 2013. A sediment budget for a small semiarid watershed in southeastern Arizona, USA. Geomorphology 180–181, 137–145. https://doi.org/10.1016/j.geomorph.2012.10.002. Nicolau, J.M., Solé-Benet, A., Puigdefábregas, J., Gutiérrez, L., 1996. Effects of soil and vegetation on runoff along a catena in semi-arid Spain. Geomorphology 14, 297–309. https://doi.org/10.1016/0169-555X(95)00043-5. Ochoa, P.A., Fries, A., Mejía, D., Burneo, J.I., Ruíz-Sinoga, J.D., Cerdà, A., 2016. Effects of climate, land cover and topography on soil erosion risk in a semiarid basin of the Andes. Catena 140, 31–42. https://doi.org/10.1016/j.catena.2016.01.011. Puigdefábregas, J., 2005. The role of vegetation patterns in structuring runoff and sediment fluxes in drylands. Earth Surf. Process. Landforms 30, 133–147. https://doi. org/10.1002/esp.1181. Rapp, A., 1960. Recent development of mountain slopes in Karkevage and surroundings, Northern Scandinavia. Geogr. Ann. 42, 73–200. Rojan, E., Dluzewski, M., Rotnicka, J., Krzemien, K., Kokosinski, Ł., Niklas, E., 2019. Impact of Catchments Morphology and Lithology on Stream Channels System in High Mountains of Arid Zone (Example of High Atlas, Morocco), in: Boughdiri M., Bádanes B., Selden P., Jaillard E., Bengston P., Granier B. (eds) Paleobiodiversity and TectonoSedimentary Records in the Mediterranean Tethys and Related Eastern Areas. Adbances in Science, Technology & Innovation (IEREK Interdisciplinary Series for Sustainable Development).Springer, Cham, 319–321. Rovira, A., Batalla, R.J., Sala, M., 2005. Fluvial sediment budget of a Mediterranean river:

Acknowledgement This study was financed by the National Science Centre, Poland, project No. UMO-2011/01/B/ST10/07295. The authors are particularly grateful to Łukasz Kokosiński, Katrzyna Biejat and local community (Mohammed, Hamid and Ibrahim) for their help in the field works. Thanks to Joanna Rotnicka-Dłużewska for the consultation and Aleksandra Deręgowska for assistance with the graphics. We appreciate the comments by the journal’s reviewers which significantly improved the paper. References Abrahams, A.D., Parsons, A.J., 1991. Resistance to overland flow on desert pavement and its implications for sediment transport modeling. Water Resour. Res. https://doi.org/ 10.1029/91WR01010. Abushandi, E., Merkel, B., 2011. Rainfall estimation over the Wadi Dhuliel arid catchment, Jordan from GSMaP_MVK+. Hydrol. Earth Syst. Sci. Discuss. 8 (1), 1665–1704. Akdim, B., 2015. Karst landscape and hydrology in Morocco: research trends and perspectives. Environ. Earth Sci. 74, 251–265. Boulton, S.J., Stokes, M., 2018. Which DEM is best for analyzing fluvial landscape development in mountainous terrains? Geomorphology 310, 168–187. Batalla, R.J., Sala, M., Werritty, A., 1995. Sediment budget focused on solid material transport in a subhumid Mediterranean drainage basin. Zeitsch. Geomorphol. 29 (2), 249–264. Boulton, S.J., Stokes, M., Mather, A.E., 2014. Transient fluvial incision as an indicator of active faulting and plio-quaternary uplift of the moroccan high atlas. Tectonophysics 633, 16–33. https://doi.org/10.1016/j.tecto.2014.06.032. Bryndal, T., 2014. A method for identification of small Carpathian catchments more prone to flash flood generation. Based on the example of south-eastern part of the polish carpathians. Carpathian J. Earth Environ. Sci. 9 (3), 109–122. Calvo-Cases, A., Boix-Fayos, C., Imeson, A.C., 2003. Runoff generation, sediment movement and soil water behaviour on calcareous (limestone) slopes of some Mediterranean environments in southeast Spain. Geomorphology 50, 269–291. https://doi.org/10.1016/S0169-555X(02)00218-0. Cappy, S., 2007. Hydrogeological characterization of the Upper Drâa catchment: Morocco. Dissertation zur Erlangung des Doktorgrades der MathematischNaturwissenschaftlichen Fakultät der Rheinischen Friedich-Wilhelm-Universität Bonn, 1–216. http://hss.ulb.uni-bonn.de/2007/0963/0963.htm. Carte Géologique du Maroc, 1993. Tinerhir 1 100,000. de Jong C., Machauer R., Leavesely G., Cappy S., Poete P., Schulz O., 2005. Integrated hydrological modelling concepts for a peripheral mountainous semi-arid basin in southern Morocco. In: R. Escadafal, M.L. Paracchini (eds), Geomatics for Land and Water Management: Achievements and Challenges in the Euromed Context. EC JRC Workshop proceedings: 219–227. Delgado-Fernandez, I., 2010. A review of the application of the fetch effect to modelling sand supply to coastal foredunes. Aeolian Res. 2 (2–3), 61–70. Dietrich, W., Dunne, T., 1978. Sediment budget for a small catchment in mountainous

16

Catena 190 (2020) 104530

E. Rojan, et al. The lower Tordera (Catalan Coastal Ranges, NE Spain). Catena 60, 19–42. https:// doi.org/10.1016/j.catena.2004.11.001. Schick A.P., 1988. Hydrologic Aspects of Floods in Extreme Arid Environments, in: Flood Geomorphology. https://doi.org/10.1007/978-3-662-43492-5. Schulz, O., Busche, H., Benbouziane, A., 2008. Decadal Precipitation Variances and Reservoir Inflow in the Semi-Arid Upper Drâa Basin (South-Eastern-Morocco). In: Zereini, F., Hoetzl, H. (Eds.), Climatic Changes and Water Resources in the Middle East and in North Africa. Springer, Berlin, Heidelberg, pp. 165–178 https://doi.org/ http://dx.doi.org/10.1007/978-3-540-85047-2_13. Schulz, O., de Jong, C., 2004. Snowmelt and sublimation: field experiments and modelling in the High Atlas Mountains of Morocco. Hydrol. Earth Syst. Sci. 8, 1076–1089. https://doi.org/10.5194/hess-8-1076-2004. Stokes, M., Mather, A.E., 2015. Controls on modern tributary-junction alluvial fan occurrence and morphology: High Atlas Mountains, Morocco. Geomorphology 248, 344–362. Stokes, M., Mather, A.E., Belfoul, A., Farik, F., 2008. Active and passive tectonic controls for transverse drainage and river gorge development in a collisional mountain belt (Dades Gorges, High Atlas Mountains, Morocco). Geomorphology 102 (1), 2–20. Stokes, M., Mather, A.E., Belfoul, M., Faik, F., Bouzid, S., Geach, M.R., Cunha, P.P., Boulton, S.J., Thiel, C., 2017. Controls on dryland mountain landscape development along the NW Saharan desert margin: Insights from Quaternary river terrace

sequences (Dadès River, south-central High Atlas, Morocco). Quat. Sci. Rev. 166, 363–379. Strahler, A.N., 1952. Hypsometric (area-altitude) analysis of erosional topography. Geol. Soc. Am, Bull 10.1130/0016-7606(1952) 63[1117:HAAOET]2.0.CO;2. Trimble, S.W., 1997. Contribution of stream channel erosion to sediment yield from an urbanizing watershed. Science 278, 1442–1444. Waikar, M.L., Nilawar, A.P., 2014. Morphometric analysis of a drainage basin using geographical information system: a case study. Int. J. Multidiscipl. Curr. Res. http:// ijmcr.com/wp-content/uploads/2014/02/Paper32179-184.pdf. Wischmeier, W.H., Smith, D.D., 1958. Rainfall energy and its relationship to soil loss. Trans. Am. Geophys. Union 39. https://doi.org/10.1029/TR039i002p00285. Yair, A., Raz-Yassif, N., 2004. Hydrological processes in a small arid catchment: scale effects of rainfall and slope length. Geomorphology 61, 155–169. https://doi.org/10. 1016/j.geomorph.2003.12.003. Zarei, M., Sedehi, F., Raeisi, E., 2014. Hydrogeochemical characterization of major factors affecting the quality of groundwater in southern Iran. Janah Plain. Chemie der ErdeGeochemistry 74 (4), 671–680. Ziadat, F.M., Taimeh, A.Y., 2013. Effect of rainfall intensity, slope, land use and antecedent soil moisture on soil erosion in an arid environment. Land Degrad. Develop. 590, 582–590. https://doi.org/10.1002/ldr.2239.

17