Integration of hydrological process models with watershed network models: Darlik creek case study

Population growth, agriculture and livestock farming industries development and climate change create excessive pressure on water and land resources day by day. Effects of these pressures range from ecological and hydrological consequences of over-allocation of river basins and groundwater aquifers, to public health issues and ecological damage arising from water quality problems. Thus, necessity of management and development of water bodies has emerged in order to keep environment clean for next generations. Water is essential for life and also an important social factor in terms of national economy and human – nature relationship. Efficient management of water resources focuses on the problem of enhancing and managing number of sources and use sectors while sustaining or improving water quality. Engineering optimization approach have been carried out for large number of issues involving water resources management problems. Watershed network models have been developed to find optimal water allocation strategies when there is a challenge for water among various users and solve water resources management problems. Modeling is one way that planners, engineers and economists utilize to estimate the impacts of possible design management and operation decions or policies. Models are tools, not alternatives for human decision-making. Application of models to real systems have enhanced our understanding of such systems. In addition, models also help engineers in operation, management and also design. Water resource modeling has been important in the last decades for sustainaible management of water bodies and evaluating future scenerios for these water bodies. Models produce information, not decisions. Water resource planners and managers have to admit the fact that decisions may not be influenced by their planning and management model results. There is a widespread literature on water resource modeling and several computer programs are available both commercially and in the public domain. Some of those computer programs are free to college students to use such as the WEAP model. In this study, information about models that can be used as water resource models, which are important in terms of integrated watershed management and opportunities that models can offer, are given briefly. WEAP, SWAT, HEC – HMS, MIKE SHE, HSPF, AGNPS are models that use as hydrological process models and MODSIM, RIBASIM, GOLDSIM and STELLA are models that can be used as watershed network models. These models commonly used by engineers, plannners, managers and decision-makers all around the world. Istanbul is the most crowded city of Turkey and its population is increasing gradually. Therefore, water resources of this metropolitan are under extreme pressure. Today more than 14 million people living in Istanbul and this mega city needs more than 2 million cubic meter water per day. Most of this demand is supplied from dams around the city and by interbasin water transfer. İstanbul has 7 watersheds in total. Watersheds in Eurpoean side of İstanbul are Alibeyköy, Büyükçekmece, Sazlıdere and Terkos. Watersheds in Asian side of İstanbul are Elmalı, Ömerli and Darlık. Darlık Reservoir, located north-east of İstanbul, supplies the 11% of İstanbul's water demand, which has a 209 km2 catchment area, is one of the vital reservoirs of this metropolitan and has not been severely affected by urbanization and industrialization yet. Studies conducted in this area have been concentrated on Darlık Dam and its water quality rather then Darlık River and its tributaries. In this study, field study has been conducted. In the field study, cross-section and average velocity measurements were carried out at 7 stations, which are selected based on climate and land conditions. From this data average flow rate has been calculated and used in model to estimate coefficients. Flow routing is an analytic method to determine the time and magnitude of flow at a point on a hydrological system from known or assumed hydrographs at one or more points upstream. That hydrological system could be a river, gulf, channel or sewer system. Flow routing is used to determine the change in shape of a hydrograph of a flow as it travels through system and different flow routing simulation techniques can be used. Flow routing can be classifed as 2 seperate procedures: lumped and distributed that are well known as hydrologic and hydraulic. However, semi-distributed models has been started to use recently. In this study, MODSIM model, which uses Muskingum Method as hydrologic flow routing method was selected. Model can calculate its routing coefficients by using the Muskingum formula. Alternatively, the user may directly input any desired routing coefficients and lagging factors. MODSIM, is a river basin management decision support system, designed as a computer program for satisfying the need emerging from watershed and water resources management. In this case, MODSIM can help engineers and planners to develop improved basin strategies for short-term water management, long-term operational planning, drought planning, water rights analysis and resolving conflicts between urban, agricultural and environmental concerns. MODSIM provides the integrated evaluation of hydrologic, economic, environmental and legal impacts as related to alternative development and management scenerios including combined use of surface water and groundwater resources. This study aims to integrate a hydrological model, WEAP, and a watershed network model, MODSIM. Subwatersheds used in MODSIM were delineated using ArcSWAT, which is compatible with Geographic Information System program ArcGIS 10.2. Setup of MODSIM is described step by step and data from the study prepared by Cüceloğlu (2013) with WEAP were integrated to MODSIM model with hydrological flow routing. Importance of sustainable watershed management is increasing everyday by growing population and climate change with pressure on surface waters in Istanbul. In this context, optimum operation of dams that supply water to Istanbul becomes a significant issue. MODSIM is one of the models that can be used for this purpose. In this study, MODSIM and WEAP models were integrated successfully in a critical area which supplies drinking water to Istanbul. MODSIM wais used in an area in Turkey; thus, this study will be used as a guide for future studies in this area.