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Evaluation model of policy scenarios for basin-wide water resources and quality management in the tone river, japan
e>
Pergamon
Wal. Sci. T~ch. Vol. 38. No. II. pp. .5~7. 1998. ~
1998IAWQ
Published by Elsevier Science Ud. Printed in Great Britain. AU righll reserved
po: S0273-1223(98)00640-4
0273-1223/98 $19'00 + ()OOO
EVALUATION MODEL OF POLICY SCENARIOS FOR BASIN-WIDE WATER RESOURCES AND QUALITY MANAGEMENT IN THE.. TONE RIVER, JAPAN T. Aramaki and T. Matsuo Department 0/ Urban Engineering. The University o/Tokyo. 7-3-1 Hongo. Bunkyo-ku, Tokyo 113-8656. Japan
ABSTRACf The objective of this study is to evaluate the conceptual scenarios of various water resources and quality management on the same level of policy decisions for optimizing river basin management First, the water and pollutants balance model in the upper reaches of the Tone River is proposed. This model has the following characteristics: (1) Water quantity and quality at various target points of the rivers are estimated simultaneously. with a statistical evaluation for the uncertainty of hydrological events; (2) The management scenarios include selection of water savings in domestic use. reservoir construction. the expansion of sewerage coverage and so on. Several interesting results supporting policy making arc obtained as follows: (I) Fifteen percent reduction in domestic use is sufficient as a substitute for new reservoir; (2) the expansion of sewage coverage in the upper reaches has large effects on reduction of BOD and COD. but the nutrient removal process should be introduced in sewage treatment plants for reduction of TN and TP.
KEYWORDS River basin management; statistical evaluation; the Tone River; water quality; water resources. INTRODUCTION In order to keep the stability and the safety of water resources, and to prevent the degradation of water environment, various river basin management measures are carried out, such as reservoir construction, water savings by users, construction of sewerage systems and so on. These management measures cause large impacts to the environment and are expensive, so these impacts have to be evaluated quantitatively on the Same level of policy decisions, for investigating their optimum scope and combination. However, quantitative evaluation of river basin management is very difficult for some issues, because of insufficient knowledge about water movement, uncertainty of hydrological events and the variety of management goals. In this study, the water and pollutants balance model in the upper reaches of the Tone River, which is the main water resource of the Tokyo Metropolitan area, is proposed and the various policy scenarios of basin 59
T. ARAMAKI and T. MATSUO
60
management are evaluated. for example water savings. new reservoir. the expansion of sewage systems and so on. In this model. water quantity and quality at various target points in the Tone River are estimated simultaneously. with a statistical evaluation for the uncertainty of their flow rate in the river. METHODS Out!ine of the Tone Riyer Basjn The Tone River flows across the Kanto Area of Japan. and its length is 322 km and its catchment area is 16.840 km2• The Tokyo Metropolitan area is influenced by the drought of this river once for every two or three years. because it depend for almost 80% of domestic water supply on this river.
_
River Reservoir. operated in 1990
c:J
Reservoir. newly completed after 1990
o
Main target points for the flow rate and water quality
Tone Waterway Figure 1. Map of object area.
The map of the is shown in Figure 1. This area is the upper reaches of Kuri~ashi ~n the Ton7Rive~. and its area was 8.588 km2 and its population was 3.9 million in 1990. There were SIX major reservOirs. whlc~ wer~ managed and controlled under the unified criteria of keeping the predetermined target flow rate at Kunhashl.
Basin-wide water resources and quality management
61
This target flow rate was determined by the requirements for water demands in the lower reaches including the Tokyo Metropolitan area, for water resources, water quality and environmental preservation. The total capacity of six reservoirs for water resources was 350 million-m 3. Two additional reservoirs, named Watarase and Naramata, were newly completed in early 1990s. Through the Tone Waterway which is about 25 km upstream of Kurihashi, 22% of total discharge from this area was diverted to the other river for use in the Tokyo Metropolitan area. There were 88 public water works in this area, and the ratio of coverage based on population was 88%. They depended for almost half their water resources on groundwater. There were 31 sewage treatment plants and the ratio of sewage coverage was about 20% in 1990. Water demand in this area was about 3 billion-m 3 and almost 70% was for agricultural use. Structure of the model The area consists of 23 small basins, and the simulation of water and pollutants movement are carried from the upper basin to the lower one a the time step of 5-day average. Target pollutants are BOD, COD, TN and
TP.
Simulated water movement in each small basin is shown schematically in Figure 2. The data sets of 5-day river discharge from rainfall for a thousand years are generated from the monthly stochastic distribution of discharge estimated by statistical data in the last 10 years. The uncertainty of hydrological events is thought to be reproduced in these data sets, for the stochastic evaluation of river flow rate, volume of water use, water level of reservoir and water qUality.
CtmosPh~ ~
Figure 2. Simulated water movement in the small basin.
Three types of water usage, such as domestic, industrial and agricultural use, are considered in each basin. Water demand in each use is calculated from the empirical relationships with population, production and the regional characteristics (Japan Sewage Works Association, 1993). The planned volume of water use is allocated to water intake from river, groundwater and discharge from rainfall as determined beforehand. All reservoirs are managed and controlled in an unified way to ensure the target flow rate at Kurihashi, and water withdrawals from the river are regulated in accordance with the water level of the reservoirs. The relationships between the reduction ratio of withdrawals and the water level are determined empirically.
62
T. ARAMAKI and T. MATSUO
Houses, offices, industries and Iivestocks are considered as point sources of pollutants, and cultivated land, forests and urbanized area are considered as non-point sources. Estimations of pollutant load, except for houses and offices, are carried out using the empirical relationships with population, production and the regional characteristics (Japan Sewage Works Association, 1993). Four typical measures of treatment of domestic wastewater (houses and offices) are considered, such as public sewerage systems, local and individual treatment systems, individual treatment systems only for toilet flush, and the treatment systems of collected night soil. Estimations of pollutants load are carried out using observed effluent water quality data in each sewage treatment plants for public sewerage systems, and pollutants load per capita for individual systems and collected night soil treatments. Indices for eyaluation criteria Many indices for evaluation criteria are calculated from the stochastic distribution of river flow rate, volume of water use, volume of reservoir and water quality every 5-day time step. Among these indices, the definition of indices used in the following analysis are shown below.
Vulnerability Scale of Drought (%-day/yr): Hashimoto et al. (1982) discussed three drought indices, in which the uncertainty of hydrological events were taken into consideration. These indices describe how likely a system is to fail (reliability), how quickly it recovers from failure (resiliency), and how severe the consequences of failure may be (vulnerability). Among them, the concept of vulnerability is adopted in this index. This is calculated as follows: Vulnerability Scale of Drought = L( L ,
,(,)<,.(,)
prob[q(t)]X(q * (t!-q(t»)x
q (t)
100)
where q(t) is the volume of water at time t in simulation and q*(t) is the target volume at t. Prob[q(t)] is the probability that the volume of water is q. This index is calculated for each usag~ type in the small basin, for the flow rate at Kurihashi and for the volume of the Tone Waterway. Because the water demand in the Tokyo Metropolitan area is included in the target flow rate at Kurihashi and the planned volume of the Tone Waterway, the influence on the Tokyo Metropolitan area can be evaluated. Scale of drought in the object area is averaged with the values of small basins. weighted with water demand in each basin.
Drought Damage (billion-yen/yr): This index represents the cost of drought and is calculated as follows; Drought Damage
= LP(S)x(q *(t)-q(t»), ,
where S is the shortage ratio, and P(S) is the cost of drought per unit volume of shortage. This P(S) is the empirical quadratic equation of the shortage ratio, determined for eacb type of use.
Water Balance of Groundwater (million-m 3/yr): In the relationships between surface water and groundwater, water withdrawal and artificial recharge, such as permeation from agricultural field and leakage of water from water works, are considered. This index is calculated by subtracting artificial recharge from groundwater intake. Exceedance Value of 25% Events per Year for BOD, COD. TN and TP (mg/L): In this model, averages of water quality are much influenced by abnormal high value in drought condition. Therefore, the value which is exceeded by 25% of events in the series of water quality for one year is adopted as the representation of water quality indices.
Exceedance Ratio over the Environmental Standard of BOD (%): At Kurihashi in the Tone River, 2 mgIL is the environmental standard of BOD. This index is the probability that the simulated BOD value is over 2 mgIL.
Basin-wide water resources and quality management
63
RESULTS AND DISCUSSION model should be examined. Before evaluating various management policy programs, the validity of this l and empirical data for statistica using n, validatio the f?r d simulate are 0 !herefore, ~ituations in 1~80-199 es the observed reproduc i Inputs of thIS model. In Ftgure 3, the average of sImulated flow rate at Kurihash for BOD at events 25% of values excess d average. For water quality, the results of observed and simulate such as area the in points upper the in value d simulate The 1. Table four river points are summarized in the than higher is i as Kurihash Gunma-ohashi is lower than the observed value, but in the lower points such of son compari the for applied be can model observed value. It is, however, reasonably confirmed that this various scenarios.
~~~~~~ -------Average of simulated I ~~~ ~ '"~ 50r--------Average of observed
~
40
]
30
~,f~
;'I
~
------
Target flow rate
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Figure 3. Comparison between observed and simulated flow rate at Kurihashi.
for BOD Table 1. Observed and Simulated exceedance values of 25% events per year Sakawada Takamatsu Gunma-ohashi 3.7 3.7 0.6 Simulated Observed
0.8 - 1.3
2.2 -4.7
2.9 -4.2
at four river points Kurihashi 3.1 1.1 - 1.9
policy scenarios are evaluated These simulated results are defined as 'Standard', and the effects of various the following analysis. in ' scenario USing the differences between 'Standard' and 'result of each policy Evaluation of poIicy scenarios on water resources mana~ement ents are as follows: The outlines of four policy scenarios concerned with water resources managem in domestic use, with Scenario I (Water savings in domestic use): Water savings will be achieved In on. this scenario, domestic consciousness of users, reuse of treated wastewater, use of rain water and so of the Tone Waterways volume planned the Water demand in the area, the target flow rate at Kurihashi and to the volume for toilet equal almost is use c domesti in will be equally 15% reduced. 15% of water demand flush water in Japan. ir, which is located in the lower Scenario 2 (Construction of the Watarase Reservoir): The Watarase Reservo 3 will be in operation. m million26 is s resource reach of the area and whose capacity for water ta Reservoir, which is in the lower reach Scenario 3 (Construction of the Naramata Reservoir): The Narama 3 will be in operation. m millionof the area and which capacity for water resources is 85
64
T. ARAMAKI and T. MATSUO
Scenario 4 (Prevention of leakage in water works) : The average ratio of effective water to total water distributed at 88 public water works in the area was 81 % in 1990. In this scenario, this ratio of all water works in the area will improve by more than 90% by repairing the distribution pipes. Evaluation indices in 'Standard', and their difference between 'Standard' and 'results for the above scenarios' are su~marized in Table 2. Minus si~ in difference means that the index will be reduced for introducing the scenano. In the aspect of total reduction of damage, water savings in domestic use gives about 142 billion• yen reduction and shows the most effective performance among these scenarios. Table 2. Evaluation indices of 'Standard' and the difference between 'Standard' and 'the simulated for policy scenarios on water resources management' Difference Standard Vulnerabilitl scal~ of drought (%·daX/Xr) Domestic use in the object area Industrial use in the object area Agricultural use in the object area Volume at Kurihashi Volume at the Tone Waterway
364 1,864 3,194
of dmught (l:!illion-~nlxr) Water use in the the object area Volume at Kurihashi Volume at the Tone Waterway Total
l2arnag~
of grQundwater (million-m'lYr.)
Wat~r l:!alanc~
Excess valu~ of 25% ~vents ~[ xear [or BOD at Kurihashi (mglL)
300
Water Watarase Naramata Prevention savings Reservoir Reservoir of leakage
-461
-76 +38 -768
-65 -10 -116 -175 -758
-66 -3 -9 -302 -174
14.5 255.9 247.4 517.8
-2.2 -64.4 -75.3 -141.9
-1.9 -73.9 -43.3 -119.1
-3.4 -54.0 -50.6 -108.0
-1.4 -31.3 -60.6 -93.3
-65
-18
-14
-18
+23
3.11
-0.02
-0.03
0.00
-0.04
46
-73 -5 -35 -461
-78
-11
Reduction of drought damage at Kurihashi and the Tone Waterway is estimated to be 64 and 75 billion-yen for the scenario of water savings, 74 and 43 billion-yen for construction of the Watarase reservoir, S4 and S1 billion-yen for construction of the Naramata reservoir, 31 and 61 billion-yen for prevention of leakage. Reduction for construction of new reservoirs is larger at Kurihashi than at the Tone Waterway, while reduction for water savings and prevention of water leakage is larger at the Tone Waterway. This result indicates that the evaluation of management policies is highly dependent on local water use. Furthermore, reductions of Vulnerability Scale for new reservoirs are larger at the Tone Waterway than at Kurihashi. Thus, the evaluation of management policies is also dependent on the indices applied. Water savings and construction of the Naramata Reservoir decrease 18 miIlion-m 3 of water balance of groundwater, so these are the most effective for the conservation of groundwater. On the other hand, the prevention of water leakage has a negative effect on the conservation of groundwater, because the decrease of leakage from the distribution pipes causes decrease in artificial recharge. Compared with the construction of the Watarase Reservoir and the Naramata Reservoir, the capacity of the Naramata Reservoir is about three times larger than that of the Watarase Reservoir. However, reduction of Damage and Vulnerability Scale of Drought are almost the same. The estimated effects for construction of new reservoirs are varied, depending not only on capacity, but also on location. Therefore, this type of simulation is useful for the assessment of reservoir's construction in advance.
Basin-wIde water resources and quality management
65
Evaluation of policy scenarios on water Quality mana~ement Figure 4 shows the ratio of pollutant load for each source to the total load for the river, esttmated under the 'Stan.dard' condition. Main sources of BOD, COD emissions are the domestic wastewater, not collected by p~b!lc sewerage systems. For TN and TP emissions, main sources are pubhc sewerage systems and livestock ralsmg, respecti vely. Domestic (except for sewerage)
o
20 40 60 80 Ratio of pollutants load from each source, %
100
Figure 4 RallO of pollutants load from each source to the total load for the river. estimated from the sImulatIOn of 'Standard'.
For water quality management, the reduction of pollutant emissions at main source IS the effective measure. Therefore, the following four scenarios, concerned with domestic wastewater and live~tock raising, are evaluated for water quality management. The outline of four policy scenarios are as follow~: Scenario 5 (Expansions of sewage coverage): In this scenario, the covered area of pubhc sewerage systems will expand to the area, where sewerage systems are being planned or constructed. Users of public ~ewerage systems will increase by more than one million, and the ratio of sewage coverage Will become about 40% m this scenario. Scenario 6 (Improvement of effluent water quality to sewage treatment plants): In the 'Standard' ~imulation, the observed values are used as effluent water quality of BOD and COD in each sewage treatment plant. In this scenario, it is assumed that advanced treatment systems Will be installed at all plants. Thus, effluent water quality of BOD and COD for all plants Will be improved less than \0 mgIL. Furthermore, two thirds of TN and TP loads from all plants will be reduced against the Simulation of 'Standard'. Scenario 7 (Introduction of local and individual treatment systems): In this model, it is a~sumed that I % of total population in the area introduces this system. In this scenario, 4% of total population who have used priVate treatment systems only for toilet flush Will convert to this system. Users of this system will increase from 48 thousand to 240 thousand. Scenario 8 (Reduction of pollutants from livestock raising): In thiS model, pollutants from livestock raislOg are calculated by pollutant UOlts per cattle or pig. In this scenario, these UOlts decrease by 10% and the pollutants from livestock raising are reduced. Evaluation indices at Kurihashi in 'Standard', and their difference between 'Standard' and 'results for the above scenarios' are summarized in Table 3. Minus sign in difference means that the IOdex will be reduced for introducing the scenario.
66
T. ARAMAKJ and T. MATSUO
Table 3. Evaluation indices of 'St~dard' and the di.fference between 'Standard' and 'the simulated for policy scenarIos on water qualIty management', at Kurihashi Difference Standard Exceedance value of25% events per year (mgIL) BOD COD TN TP Exceedance ratio for environmental standard of BOD (%)
3.11
Sewage Improvement Individual Expansion in sewage systems
Livestock raising
2.31 0.23
-0.20 -0.16 +0.39 +0.02
-0.02 -0.05 -0.56 -0.03
-0.08 -0.08 -0.02 -0.00
-0.03 -0.06 -0.04 -0.02
48.8
-3.4
-0.3
-1.3
-0.5
4.60
All scenarios have favorable effects for BOD and COD reduction. Expansions of public sewerage systems are the most effective. On the other hand, the improvement of effluent quality in sewage treatment plants is the most effective for TN and TP reduction. Reduction of pollutants from livestock raising is also effective on TP reduction. The expansion of sewage systems results in increasing the values of TN and TP, because it is assumed in the 'Standard' situation that conventional activated sludge systems, which are not good for removing TN and TP, are installed in sewage treatment plants. On the other hand., as the collected night soil is treated by very advanced technology in Japan, the discharge from this system is very small compared with the conventional activated sludge systems. Thus, the nutrient removal process should be introduced in sewage treatment plants for reduction of TN and TP. Reductions of Exceedance value of 25% events per year for BOD of Watarase Reservoir and the prevention of leakage water in Table 2 are as almost same as those of improvement of sewage treatment and reduction from livestock raising in Table 3. Some of water resources management have an effect on the reduction of water pollution, because of stabilizing the flow rate of the river. CONCLUSIONS
In order to evaluate various policy scenarios for water resources and quality managements, the water and pollutants balance model in the upper reaches of the Tone River is proposed and examined. In this model, water quantity and quality can be calculated simultaneously, the uncertainty of hydrological events can be taken into consideration and the evaluation can be carried by stochastic indices. Furthermore, the effects of eight policy scenarios in the Tone River Basin are evaluated using this model. The adopted policy scenarios are as follows: water savings in domestic use, reservoir's construction, the prevention of leakage in water works, the expansion of sewage coverage, the improvement of effluent water quality in sewage treatment plants, the introduction of local and individual treatment systems, the reduction of pollutants from livestock raising. The following recommendations for water resources managements and water quality control are proposed: (I) 15% water savings in domestic use has much effect on the drought damage compared with reservoir construction, (2) the evaluation of management policies has to be executed using several indices, because they are highly dependent on the indices applied and local conditions of water use, (3) the expansion of sewage coverage in the upper reaches has considerable effects on reduction of BOD and COD, but the nutrient removal process should be introduced in sewage treatment plants for reduction of TN and TP, and soon.
Basin-wide water resources and quality management
67
Using this model. various scenarios of water resources and quality management can be quantitatively evaluated. considering the uncertainty of hydrological events. Further analysis with this model are necessary for increasing the accuracy of this model. because the actual phenomena, such as pollutants' transformation and recharge and discharge of groundwater. are not fully expressed in this model. REFERENCES Hashimoto, T., Stedinger, 1. R. and Loucks, D. P. (1982). Reliability, resiliency and vulnerability criteria for water resource system performance evaluation. Water Resources Research, 18(1), 14-20. Japan Sewage Works Association (1993). Guideline and Commentary for Comprehensive Basin-wide Planning of Sewerage Systems.
Pergamon
Wal. Sci. T~ch. Vol. 38. No. II. pp. .5~7. 1998. ~
1998IAWQ
Published by Elsevier Science Ud. Printed in Great Britain. AU righll reserved
po: S0273-1223(98)00640-4
0273-1223/98 $19'00 + ()OOO
EVALUATION MODEL OF POLICY SCENARIOS FOR BASIN-WIDE WATER RESOURCES AND QUALITY MANAGEMENT IN THE.. TONE RIVER, JAPAN T. Aramaki and T. Matsuo Department 0/ Urban Engineering. The University o/Tokyo. 7-3-1 Hongo. Bunkyo-ku, Tokyo 113-8656. Japan
ABSTRACf The objective of this study is to evaluate the conceptual scenarios of various water resources and quality management on the same level of policy decisions for optimizing river basin management First, the water and pollutants balance model in the upper reaches of the Tone River is proposed. This model has the following characteristics: (1) Water quantity and quality at various target points of the rivers are estimated simultaneously. with a statistical evaluation for the uncertainty of hydrological events; (2) The management scenarios include selection of water savings in domestic use. reservoir construction. the expansion of sewerage coverage and so on. Several interesting results supporting policy making arc obtained as follows: (I) Fifteen percent reduction in domestic use is sufficient as a substitute for new reservoir; (2) the expansion of sewage coverage in the upper reaches has large effects on reduction of BOD and COD. but the nutrient removal process should be introduced in sewage treatment plants for reduction of TN and TP.
KEYWORDS River basin management; statistical evaluation; the Tone River; water quality; water resources. INTRODUCTION In order to keep the stability and the safety of water resources, and to prevent the degradation of water environment, various river basin management measures are carried out, such as reservoir construction, water savings by users, construction of sewerage systems and so on. These management measures cause large impacts to the environment and are expensive, so these impacts have to be evaluated quantitatively on the Same level of policy decisions, for investigating their optimum scope and combination. However, quantitative evaluation of river basin management is very difficult for some issues, because of insufficient knowledge about water movement, uncertainty of hydrological events and the variety of management goals. In this study, the water and pollutants balance model in the upper reaches of the Tone River, which is the main water resource of the Tokyo Metropolitan area, is proposed and the various policy scenarios of basin 59
T. ARAMAKI and T. MATSUO
60
management are evaluated. for example water savings. new reservoir. the expansion of sewage systems and so on. In this model. water quantity and quality at various target points in the Tone River are estimated simultaneously. with a statistical evaluation for the uncertainty of their flow rate in the river. METHODS Out!ine of the Tone Riyer Basjn The Tone River flows across the Kanto Area of Japan. and its length is 322 km and its catchment area is 16.840 km2• The Tokyo Metropolitan area is influenced by the drought of this river once for every two or three years. because it depend for almost 80% of domestic water supply on this river.
_
River Reservoir. operated in 1990
c:J
Reservoir. newly completed after 1990
o
Main target points for the flow rate and water quality
Tone Waterway Figure 1. Map of object area.
The map of the is shown in Figure 1. This area is the upper reaches of Kuri~ashi ~n the Ton7Rive~. and its area was 8.588 km2 and its population was 3.9 million in 1990. There were SIX major reservOirs. whlc~ wer~ managed and controlled under the unified criteria of keeping the predetermined target flow rate at Kunhashl.
Basin-wide water resources and quality management
61
This target flow rate was determined by the requirements for water demands in the lower reaches including the Tokyo Metropolitan area, for water resources, water quality and environmental preservation. The total capacity of six reservoirs for water resources was 350 million-m 3. Two additional reservoirs, named Watarase and Naramata, were newly completed in early 1990s. Through the Tone Waterway which is about 25 km upstream of Kurihashi, 22% of total discharge from this area was diverted to the other river for use in the Tokyo Metropolitan area. There were 88 public water works in this area, and the ratio of coverage based on population was 88%. They depended for almost half their water resources on groundwater. There were 31 sewage treatment plants and the ratio of sewage coverage was about 20% in 1990. Water demand in this area was about 3 billion-m 3 and almost 70% was for agricultural use. Structure of the model The area consists of 23 small basins, and the simulation of water and pollutants movement are carried from the upper basin to the lower one a the time step of 5-day average. Target pollutants are BOD, COD, TN and
TP.
Simulated water movement in each small basin is shown schematically in Figure 2. The data sets of 5-day river discharge from rainfall for a thousand years are generated from the monthly stochastic distribution of discharge estimated by statistical data in the last 10 years. The uncertainty of hydrological events is thought to be reproduced in these data sets, for the stochastic evaluation of river flow rate, volume of water use, water level of reservoir and water qUality.
CtmosPh~ ~
Figure 2. Simulated water movement in the small basin.
Three types of water usage, such as domestic, industrial and agricultural use, are considered in each basin. Water demand in each use is calculated from the empirical relationships with population, production and the regional characteristics (Japan Sewage Works Association, 1993). The planned volume of water use is allocated to water intake from river, groundwater and discharge from rainfall as determined beforehand. All reservoirs are managed and controlled in an unified way to ensure the target flow rate at Kurihashi, and water withdrawals from the river are regulated in accordance with the water level of the reservoirs. The relationships between the reduction ratio of withdrawals and the water level are determined empirically.
62
T. ARAMAKI and T. MATSUO
Houses, offices, industries and Iivestocks are considered as point sources of pollutants, and cultivated land, forests and urbanized area are considered as non-point sources. Estimations of pollutant load, except for houses and offices, are carried out using the empirical relationships with population, production and the regional characteristics (Japan Sewage Works Association, 1993). Four typical measures of treatment of domestic wastewater (houses and offices) are considered, such as public sewerage systems, local and individual treatment systems, individual treatment systems only for toilet flush, and the treatment systems of collected night soil. Estimations of pollutants load are carried out using observed effluent water quality data in each sewage treatment plants for public sewerage systems, and pollutants load per capita for individual systems and collected night soil treatments. Indices for eyaluation criteria Many indices for evaluation criteria are calculated from the stochastic distribution of river flow rate, volume of water use, volume of reservoir and water quality every 5-day time step. Among these indices, the definition of indices used in the following analysis are shown below.
Vulnerability Scale of Drought (%-day/yr): Hashimoto et al. (1982) discussed three drought indices, in which the uncertainty of hydrological events were taken into consideration. These indices describe how likely a system is to fail (reliability), how quickly it recovers from failure (resiliency), and how severe the consequences of failure may be (vulnerability). Among them, the concept of vulnerability is adopted in this index. This is calculated as follows: Vulnerability Scale of Drought = L( L ,
,(,)<,.(,)
prob[q(t)]X(q * (t!-q(t»)x
q (t)
100)
where q(t) is the volume of water at time t in simulation and q*(t) is the target volume at t. Prob[q(t)] is the probability that the volume of water is q. This index is calculated for each usag~ type in the small basin, for the flow rate at Kurihashi and for the volume of the Tone Waterway. Because the water demand in the Tokyo Metropolitan area is included in the target flow rate at Kurihashi and the planned volume of the Tone Waterway, the influence on the Tokyo Metropolitan area can be evaluated. Scale of drought in the object area is averaged with the values of small basins. weighted with water demand in each basin.
Drought Damage (billion-yen/yr): This index represents the cost of drought and is calculated as follows; Drought Damage
= LP(S)x(q *(t)-q(t»), ,
where S is the shortage ratio, and P(S) is the cost of drought per unit volume of shortage. This P(S) is the empirical quadratic equation of the shortage ratio, determined for eacb type of use.
Water Balance of Groundwater (million-m 3/yr): In the relationships between surface water and groundwater, water withdrawal and artificial recharge, such as permeation from agricultural field and leakage of water from water works, are considered. This index is calculated by subtracting artificial recharge from groundwater intake. Exceedance Value of 25% Events per Year for BOD, COD. TN and TP (mg/L): In this model, averages of water quality are much influenced by abnormal high value in drought condition. Therefore, the value which is exceeded by 25% of events in the series of water quality for one year is adopted as the representation of water quality indices.
Exceedance Ratio over the Environmental Standard of BOD (%): At Kurihashi in the Tone River, 2 mgIL is the environmental standard of BOD. This index is the probability that the simulated BOD value is over 2 mgIL.
Basin-wide water resources and quality management
63
RESULTS AND DISCUSSION model should be examined. Before evaluating various management policy programs, the validity of this l and empirical data for statistica using n, validatio the f?r d simulate are 0 !herefore, ~ituations in 1~80-199 es the observed reproduc i Inputs of thIS model. In Ftgure 3, the average of sImulated flow rate at Kurihash for BOD at events 25% of values excess d average. For water quality, the results of observed and simulate such as area the in points upper the in value d simulate The 1. Table four river points are summarized in the than higher is i as Kurihash Gunma-ohashi is lower than the observed value, but in the lower points such of son compari the for applied be can model observed value. It is, however, reasonably confirmed that this various scenarios.
~~~~~~ -------Average of simulated I ~~~ ~ '"~ 50r--------Average of observed
~
40
]
30
~,f~
;'I
~
------
Target flow rate
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Figure 3. Comparison between observed and simulated flow rate at Kurihashi.
for BOD Table 1. Observed and Simulated exceedance values of 25% events per year Sakawada Takamatsu Gunma-ohashi 3.7 3.7 0.6 Simulated Observed
0.8 - 1.3
2.2 -4.7
2.9 -4.2
at four river points Kurihashi 3.1 1.1 - 1.9
policy scenarios are evaluated These simulated results are defined as 'Standard', and the effects of various the following analysis. in ' scenario USing the differences between 'Standard' and 'result of each policy Evaluation of poIicy scenarios on water resources mana~ement ents are as follows: The outlines of four policy scenarios concerned with water resources managem in domestic use, with Scenario I (Water savings in domestic use): Water savings will be achieved In on. this scenario, domestic consciousness of users, reuse of treated wastewater, use of rain water and so of the Tone Waterways volume planned the Water demand in the area, the target flow rate at Kurihashi and to the volume for toilet equal almost is use c domesti in will be equally 15% reduced. 15% of water demand flush water in Japan. ir, which is located in the lower Scenario 2 (Construction of the Watarase Reservoir): The Watarase Reservo 3 will be in operation. m million26 is s resource reach of the area and whose capacity for water ta Reservoir, which is in the lower reach Scenario 3 (Construction of the Naramata Reservoir): The Narama 3 will be in operation. m millionof the area and which capacity for water resources is 85
64
T. ARAMAKI and T. MATSUO
Scenario 4 (Prevention of leakage in water works) : The average ratio of effective water to total water distributed at 88 public water works in the area was 81 % in 1990. In this scenario, this ratio of all water works in the area will improve by more than 90% by repairing the distribution pipes. Evaluation indices in 'Standard', and their difference between 'Standard' and 'results for the above scenarios' are su~marized in Table 2. Minus si~ in difference means that the index will be reduced for introducing the scenano. In the aspect of total reduction of damage, water savings in domestic use gives about 142 billion• yen reduction and shows the most effective performance among these scenarios. Table 2. Evaluation indices of 'Standard' and the difference between 'Standard' and 'the simulated for policy scenarios on water resources management' Difference Standard Vulnerabilitl scal~ of drought (%·daX/Xr) Domestic use in the object area Industrial use in the object area Agricultural use in the object area Volume at Kurihashi Volume at the Tone Waterway
364 1,864 3,194
of dmught (l:!illion-~nlxr) Water use in the the object area Volume at Kurihashi Volume at the Tone Waterway Total
l2arnag~
of grQundwater (million-m'lYr.)
Wat~r l:!alanc~
Excess valu~ of 25% ~vents ~[ xear [or BOD at Kurihashi (mglL)
300
Water Watarase Naramata Prevention savings Reservoir Reservoir of leakage
-461
-76 +38 -768
-65 -10 -116 -175 -758
-66 -3 -9 -302 -174
14.5 255.9 247.4 517.8
-2.2 -64.4 -75.3 -141.9
-1.9 -73.9 -43.3 -119.1
-3.4 -54.0 -50.6 -108.0
-1.4 -31.3 -60.6 -93.3
-65
-18
-14
-18
+23
3.11
-0.02
-0.03
0.00
-0.04
46
-73 -5 -35 -461
-78
-11
Reduction of drought damage at Kurihashi and the Tone Waterway is estimated to be 64 and 75 billion-yen for the scenario of water savings, 74 and 43 billion-yen for construction of the Watarase reservoir, S4 and S1 billion-yen for construction of the Naramata reservoir, 31 and 61 billion-yen for prevention of leakage. Reduction for construction of new reservoirs is larger at Kurihashi than at the Tone Waterway, while reduction for water savings and prevention of water leakage is larger at the Tone Waterway. This result indicates that the evaluation of management policies is highly dependent on local water use. Furthermore, reductions of Vulnerability Scale for new reservoirs are larger at the Tone Waterway than at Kurihashi. Thus, the evaluation of management policies is also dependent on the indices applied. Water savings and construction of the Naramata Reservoir decrease 18 miIlion-m 3 of water balance of groundwater, so these are the most effective for the conservation of groundwater. On the other hand, the prevention of water leakage has a negative effect on the conservation of groundwater, because the decrease of leakage from the distribution pipes causes decrease in artificial recharge. Compared with the construction of the Watarase Reservoir and the Naramata Reservoir, the capacity of the Naramata Reservoir is about three times larger than that of the Watarase Reservoir. However, reduction of Damage and Vulnerability Scale of Drought are almost the same. The estimated effects for construction of new reservoirs are varied, depending not only on capacity, but also on location. Therefore, this type of simulation is useful for the assessment of reservoir's construction in advance.
Basin-wIde water resources and quality management
65
Evaluation of policy scenarios on water Quality mana~ement Figure 4 shows the ratio of pollutant load for each source to the total load for the river, esttmated under the 'Stan.dard' condition. Main sources of BOD, COD emissions are the domestic wastewater, not collected by p~b!lc sewerage systems. For TN and TP emissions, main sources are pubhc sewerage systems and livestock ralsmg, respecti vely. Domestic (except for sewerage)
o
20 40 60 80 Ratio of pollutants load from each source, %
100
Figure 4 RallO of pollutants load from each source to the total load for the river. estimated from the sImulatIOn of 'Standard'.
For water quality management, the reduction of pollutant emissions at main source IS the effective measure. Therefore, the following four scenarios, concerned with domestic wastewater and live~tock raising, are evaluated for water quality management. The outline of four policy scenarios are as follow~: Scenario 5 (Expansions of sewage coverage): In this scenario, the covered area of pubhc sewerage systems will expand to the area, where sewerage systems are being planned or constructed. Users of public ~ewerage systems will increase by more than one million, and the ratio of sewage coverage Will become about 40% m this scenario. Scenario 6 (Improvement of effluent water quality to sewage treatment plants): In the 'Standard' ~imulation, the observed values are used as effluent water quality of BOD and COD in each sewage treatment plant. In this scenario, it is assumed that advanced treatment systems Will be installed at all plants. Thus, effluent water quality of BOD and COD for all plants Will be improved less than \0 mgIL. Furthermore, two thirds of TN and TP loads from all plants will be reduced against the Simulation of 'Standard'. Scenario 7 (Introduction of local and individual treatment systems): In this model, it is a~sumed that I % of total population in the area introduces this system. In this scenario, 4% of total population who have used priVate treatment systems only for toilet flush Will convert to this system. Users of this system will increase from 48 thousand to 240 thousand. Scenario 8 (Reduction of pollutants from livestock raising): In thiS model, pollutants from livestock raislOg are calculated by pollutant UOlts per cattle or pig. In this scenario, these UOlts decrease by 10% and the pollutants from livestock raising are reduced. Evaluation indices at Kurihashi in 'Standard', and their difference between 'Standard' and 'results for the above scenarios' are summarized in Table 3. Minus sign in difference means that the IOdex will be reduced for introducing the scenario.
66
T. ARAMAKJ and T. MATSUO
Table 3. Evaluation indices of 'St~dard' and the di.fference between 'Standard' and 'the simulated for policy scenarIos on water qualIty management', at Kurihashi Difference Standard Exceedance value of25% events per year (mgIL) BOD COD TN TP Exceedance ratio for environmental standard of BOD (%)
3.11
Sewage Improvement Individual Expansion in sewage systems
Livestock raising
2.31 0.23
-0.20 -0.16 +0.39 +0.02
-0.02 -0.05 -0.56 -0.03
-0.08 -0.08 -0.02 -0.00
-0.03 -0.06 -0.04 -0.02
48.8
-3.4
-0.3
-1.3
-0.5
4.60
All scenarios have favorable effects for BOD and COD reduction. Expansions of public sewerage systems are the most effective. On the other hand, the improvement of effluent quality in sewage treatment plants is the most effective for TN and TP reduction. Reduction of pollutants from livestock raising is also effective on TP reduction. The expansion of sewage systems results in increasing the values of TN and TP, because it is assumed in the 'Standard' situation that conventional activated sludge systems, which are not good for removing TN and TP, are installed in sewage treatment plants. On the other hand., as the collected night soil is treated by very advanced technology in Japan, the discharge from this system is very small compared with the conventional activated sludge systems. Thus, the nutrient removal process should be introduced in sewage treatment plants for reduction of TN and TP. Reductions of Exceedance value of 25% events per year for BOD of Watarase Reservoir and the prevention of leakage water in Table 2 are as almost same as those of improvement of sewage treatment and reduction from livestock raising in Table 3. Some of water resources management have an effect on the reduction of water pollution, because of stabilizing the flow rate of the river. CONCLUSIONS
In order to evaluate various policy scenarios for water resources and quality managements, the water and pollutants balance model in the upper reaches of the Tone River is proposed and examined. In this model, water quantity and quality can be calculated simultaneously, the uncertainty of hydrological events can be taken into consideration and the evaluation can be carried by stochastic indices. Furthermore, the effects of eight policy scenarios in the Tone River Basin are evaluated using this model. The adopted policy scenarios are as follows: water savings in domestic use, reservoir's construction, the prevention of leakage in water works, the expansion of sewage coverage, the improvement of effluent water quality in sewage treatment plants, the introduction of local and individual treatment systems, the reduction of pollutants from livestock raising. The following recommendations for water resources managements and water quality control are proposed: (I) 15% water savings in domestic use has much effect on the drought damage compared with reservoir construction, (2) the evaluation of management policies has to be executed using several indices, because they are highly dependent on the indices applied and local conditions of water use, (3) the expansion of sewage coverage in the upper reaches has considerable effects on reduction of BOD and COD, but the nutrient removal process should be introduced in sewage treatment plants for reduction of TN and TP, and soon.
Basin-wide water resources and quality management
67
Using this model. various scenarios of water resources and quality management can be quantitatively evaluated. considering the uncertainty of hydrological events. Further analysis with this model are necessary for increasing the accuracy of this model. because the actual phenomena, such as pollutants' transformation and recharge and discharge of groundwater. are not fully expressed in this model. REFERENCES Hashimoto, T., Stedinger, 1. R. and Loucks, D. P. (1982). Reliability, resiliency and vulnerability criteria for water resource system performance evaluation. Water Resources Research, 18(1), 14-20. Japan Sewage Works Association (1993). Guideline and Commentary for Comprehensive Basin-wide Planning of Sewerage Systems.