EUROPEAN SIDE WATER RESOURCES MANAGEMENT IN ISTANBUL
Zekai Sen* and Veysel Eroglu**
*Istanbul Technical University, Civil Engineering Faculty, Hydraulics Division, Maslak 80626, İstanbul, Turkey.
**General Director, Istanbul Water and Sewerage Department, Aksaray, Istanbul.
ABSTRACT
Urban water requirement for domestic, industrial and other uses is supported by the existing surface water impoundment around the European part of Istanbul which includes the historical and trade centers of the city. Water problems arise on the most densely populated European side as it has always been in the history. Nineteenth century Durusu (Terkos) dam has become more significant from water management of view for Istanbul city, because out of 11 reservoirs, 7 have to transmit their surface waters first to this dam, and then through the supply pipes to two major water treatment centers before pumping to the city water distribution network. The climate regime of the city has shown from the past records that there are severe droughts almost every 8 to 10 years and if the reservoirs enter such a dry spell in lower fullness ratios then the water shortages to the city are unavoidable.
This paper explains the basic philosophy, logical structure and dynamism of an optimum operation program which is special for the European side water dams of Istanbul. The main purposes of the program are to reduce the spillages especially from the Durusu dam to the Black sea, to keep reservoirs as much full as possible in the beginning of November which corresponds to the start of wet period in Istanbul region. The software named shortly ISTWATER shows which dams should be given priorities under different circumstances. Hence, it is possible to save about 20 million cubic meter of water spillage to the Black sea. Although the software does not have genuine fuzzy system logic but has its imprints through the control of reservoir fullness indices by certain percentages. In this manner flood control, spillage reduction and drought periods are taken into consideration.
KEYWORDS: Demand; fullness ratio; fuzzy; Istanbul; optimization; water management.
INTRODUCTION
If a flexible and effective operation rule is not automatically available then even the surplus water resources might not be transmitted to consumption centers according to timewise or spatial deficiency points. In order to deal with these temporal and/or spatial variabilities, it is necessary to develop efficient management and operation programs in local or regional scales under the prevailing conditions. In recent years, demand on water in Istanbul city have significantly increased due to various factors among which are the local population growth, migration from other localities, industrial growth, expansion, and consequently, a general rise in the living standards. According to the prediction models made by the General Directorate of Istanbul Water and Sewerage Administration (1994) (abbreviated as İSKİ, in Turkish) there will be an increase in city water demands of 730000 million meter cubes per year (Mm3/year) in 2010 whereas it is currently at the level of 492750 Mm3/year. Public tolerance plays an important role in the operation and development of water resources in general, and during drought periods in particular. Therefore, the local public’s level of tolerance should be carefully taken into consideration for water shortages in the determination of timing, and sequencing of water yield amounts from the existing reservoirs all together. The higher is the level of tolerance shown by the society the more flexible will be the timing and sequencing of the water shortages. Short term water shortages can result in social inconvenience. In order not to exploit the sensible tolerance level of public this study proposes a newly developed optimization program for the management of Istanbul European side surface water reservoirs for joint operation during the most critical months starting from March each year up to the beginning of November. This study is based on available current water-resources data as well as the data of future development plants.
The traditional methods of reservoir operation include many alternatives such as the linear, nonlinear, dynamic, chance-constrained dynamic, stochastic, etc., methods (Kessler and Shamir, 1989; Land et al., 1982). All these methods need conventional data, which are measured at a multitude of discrete stations along time axis at equal intervals. The more the data ,the better is the expectation of results to represent the problem investigated. However, for Istanbul the data are not available for the application of these conventional procedures, therefore, it is necessary to develop an operation program on the basis of minimum amount of data. Of course the severity of water shortages affects the management and operation of reservoirs, such as storage requirement and release for a particular period. However, as commented by Hsu (1995) no satisfactory criteria exist that can be used to delineate the characteristics of water shortage from a comprehensive point of view. These indices are based on the average or maximum water-shortage rate proposed by the US Army Corps of Engineers (Hydrologic 1966) and the water deficit per day proposed by the Japan Water Resources Development Public Corp. (1977) are among the typical indices currently being used. But these methods view the shortages from a limited perspective and in the past with the hope of their probable repetition in the future. In this paper, fullness ratio index is considered for the future months based not on the past observations but on the present data. Hence, the future water shortages in the form of deficits are related to normal demand, which is given to the city during wet periods.
In general, water resources are limited but additionally their spatial and temporal variabilities play significant role for right water allocation at right times and places. This is possible only through an efficient and suitable operation rule based management porograms. Such a program was missing for Istanbul and throughout this study a philosophically convenient operation program has been developed by Şen (2000) which will be briefly presented in this paper. For the successful application of this operation program, it is necessary to have sound data basis including rainfall, runoff and evaporation records in addition to the dry and wet period statistics, dam size, dead and active storages, dam surface area, elevation-surface and elevation-volume relationships. Of course, the seasonal variations in the deterministic water demand must be also entered into the program.
It is the main purpose of this paper to present the logical, philosophical, engineering and computational rules of a suitable operation and management program for the European side surface water impoundments with different scenarios and alternatives. The objective from an optimal operation is not to provide solutions without any water shortages but to minimize the duration and intensity of such periods within the limits of curently available water resources.
LOCATION AND WATER RESOURCES OF THE STUDY AREA
Istanbul is located at a point defined by 410 northern latitude and 290 eastern longitude between the two continents, Europa and Asia. These two continents are separated through the Bosphorus straight which connects the Black sea to the southern seas of Marmara. (see Figure 1). This city has its foundation history that goes back to 250 B.C. and since then there are water problems that have been solved according to the water technological facilities of each century.
Figure 1. Location of Istanbul city
It is obvious from this figure that 3 of the Yildiz mountain dams are within Istanbul city boundaries whereas remaining 4 are outside on the European side. Presently there are 5700 m2 land surface and 12 million population which make Istanbul greater than at least 10 European countries administrally. Although general population growth rate is about 2.5 % for the country, İstanbul is distinctive and has about 4.5 % amounting to a medium size city population increment each year by 400.000 individuals. Addition of natural birth rate brings it up to 6 % which means 600.000 individual every year. In the past, inhabitants of the city have suffered from water shortages, droughts, misadministration and mismanagement of the available water resources within and around the city. Although there are significant water resources within the city administrational boundaries, unfortunately their rational, planned and managerial distributions have not been achieved until recently. It is therefore, first step to manage within city water resources in an optimal manner so that the deficiencies can be imported from other nearby alternatives. After the completion of 7 Yıldız mountain dams and regulators in addition to the Sazlıdere dam, İstanbul-European water supply system configuration has been updated and consequently, a new operation program is needed. On the other hand, a new and large scale treatment plant has been also constructed on the European side for water treatment and supply to the city water distribution system. Now there are two supply points on the European side to the city, namely, the old Kağıthane and new Fatih Sultan Mehmet treatment plants. In the new operation system, the minimization of surface water release from the Yildiz dams has been considered as an integral part of the management system in addition to the continuous meeting of the city water demand. Hence, whole new system has 11 dams and two treatment plants.
FULLNESS RATIO
In Istanbul water resources operation, the objective is not the maximization of financial return but the minimization of water shortages. In cities like Istanbul, the more the water is supplied the more will be the revenue. For this purpose, the overspill from any reservoir is desired to attain its minimum. Since there is no flood protection phase in the operation, it is, therefore, necessary to consider possible flood volume existing at all times and for this purpose one of the operation criteria is the use of fullness ratio concept. This ratio, Fi is defined as follows for i-th reservoir in the system
where , , and are the fullness ratio at i-th reservoir, 0 100, the amount of water available in the i-th reservoir, the minimum water volume in the i-th reservoir, and finally, the maximum water volume in the i-th reservoir, respectively, According to this definition, Fi varies between zero and one. If it is close to 1, then almost all the active volume is exploited, otherwise the dam is almost full. Herein, i indicates the number of dam considered. On the other hand, the following relationships are valid between different terms as explained above
and
hence, finally the fullness ratio can be written as,
(1)
If the amount of water withdrawal is equal to from i-th reservoir, then there is a change in the fullness ratio in which case one can write equation (1) as,
(2)
Hence, for each of the reservoir, it is possible to write
...... = ......
...... = ......
Finally, it is possible to obtain,
(3)
The total amount of water that can be withdrawn from all the reservoirs is
Hence, from equation (3) one can obtain
(4)
The definition of fullness ratio with the contribution from all the reservoirs become
(5)
From equation (2) it is possible to obtain
(6)
where is the total amount of water that is drawn from all the reservoirs. In the operation program developed herein equations (4), (5) and (6) are employed.
In this paper, one of the new concepts is the consideration of the fullness ratios according to different percentage levels. These percentages are not dependent on the water excess and in dry years they can be reduced accordingly. The main reason for the consideration of these percentages in the operation program are as follows:
a) Reduction in the amount of possible future flood waters into the Black Sea, and hence their impoundment according to the rules and transportation into the Durusu dam from where the water is pumped to the city.
b) Without consideration any distinction between the reservoirs water levels are reduced according to the predesigned percentages.
c) Instead of hard rules in the operation, these percentages provide a sort of fuzzy rule adjustment which gives flexibility to the overall management program.
d) In cases of pump or pipe restrictions by adjusting these percentages for each reservoir, water can be transported to Durusu dam, before the Yildiz dams overflow.
e) Initially, whole of the fullness ratios in Yıldız mountain creek dams are selected on the same level. In this paper, the fullness ratios are considered in succession ranges as 100 % - 90 %; 90 % - 70 %; and finally, 70 % - 0 %, respectively.
It is important to remember that these fullness ratios are considered only for the active reservoir volumes. If there arises a case for the priority to any dam then it is necassary to modify its upper percentage range, for instance instead of 100 % - 90 % one can consider 100 % - 80 %. This provides the widening of active volume.
OPERATION RULES
The operation program requires first of all the fullness ratios of the dams within the system including 11 dams altogether. In this paper, the dams will be considered as full at the end of each year's March. The configuration of dams, water treatment plants and operation alternatives are given in Figure 2 as a window.
The system configuration with 11 dams is presented in this figure. It is possible to enter any one of the windows under titles of 'Dams', 'Pumps', 'Limits', 'Demands', 'Results', 'Graphs', 'Scheme' or 'Backup' by a single click through the mouse. Each one of these windows provides the limits (restrictions) of dams, pipes and pumps and the monthly rainfalls, runoffs, evaporations and demands. Results window gives a layout of results for each dam whereas 'Graphs' window plots the change of any variable with time during the future operation period. 'Backup' window preserves in the computer memory any operation scenario results for future comparison purposes. It is necessary to provide the name of initial month at the lower left hand side of the window with the operation time at the lower right hand side. Provided that all the necessary inputs are given, the 'computed results' button clicking runs the ISTWATER operation program.
Under the light of the aforementioned information, the operation program will follow the following steps:
1) Determine the fullness ratios of each dam and regulator,
2) The amount of water that will be gathered from the catchment of each dam durıng the following month is calculated by considering water budget equation and the calculated amount is added to the already existing volume in the dam,
3) In order to meet the water demands from Durusu and Büyükçekmece dams the city water budget equation is applied to each dam with proper inputs and outputs. Herein, the only unknown is the amount of water withdrawal. Its calculation by the water budget equation and subtraction from the water volume available in the reservoir gives the final water volume at the end of the month.
4) If the month end volume is greater than the maximum capacity then the excessive water is led to the sea. Otherwise, the new end of month fullness ratio is calculated for subsequent monthly calculations.
5) When all the dams are considered, the priority for water withdrawal is given to the one with the greatest fullness ratio. This withdrawal is continued until the fullness ratio of the dam becomes equal to the fullness ratio of the next dam with the greatest fullness ratio. Subsequently, water is withdrawn from these two dams until their fullness ratios become equal to the third greater fullness ratio. In the preference of the two or more dams with equal fullness ratio the priority is given to the one which is the closest to Durusu dam. This provides reductions in the electric energy revenues. The reductions in the fullness ratios is continued in this systematic manner according to the fullness ratios given in the previous section. This means that first, 90 %, then 70 % and finally 0% levels are considered, respectively.
6) and values are calculated according to previous expalation. Later, substitution of this value into equation (4) leads to the calculation of water withdrawal .
7) By the substitution of this into equation the reduction with amount is made.
8) At this stage, it is checked whether is less than the demand. If it is less than or equal to demand, then the following step is considered, otherwise, step 3 is considered again.
9) This step is applied in the case when as demand is smaller than or equal to . In such a situation the water withdrawal is made as in equation (5). However, equation (6) provides the water withdrawal amounts from each dam.
CONCLUSIONS
In the application of the operation program it is possible to generate two different scanarios and these are:
a) Try and keep all the reservoirs with the same fullness ratios and to start the water withdrawal from the Yildiz mountain dams to Durusu dam in order to reduce the energy costs.
b) The water withdarwals must have priorities in all the scenarios from Sazlıdere and especially Kazandere and Pabuçdere dams.
The following scenarios are considered and the results are obtained during the operation program.
a) Yildiz mountains and Durusu dams joint operation and water supply to the city: Here Sazlıdere and Alibeyköy dams are not considered within the configuration. This means that water should be transported from Yildiz mountains to Durusu dam and then it is supplied to the city through the Kagıthane and İkitelli water treatment plants.
b) Addition of Sazlıdere dam into the previous joint operation: Through a pipe 30 Mm3/year is directed to Sazlıdere from Durusu lake. This water is then transported in the case of need into the İkitelli water treatment plant. This provides an opportunity to impound possible spillage from the Durusu dam to the Black Sea and in this manner about 15 million USA dollars can be saved.