An environmental flow method analysis at the scale of Cemisgezek Cevizlidere Dam

Water is an essential and indispensible substance for continuation of human life and existence with no other equivalent or alternative. Throughout the known history, due to their dependance on water, human beings have always felt a need for planning use of water for such purposes as determining location of settlement areas, sustainability of agricultural activities and satisfaction of energy requirements. Ever-increasing population all over the world, unfavorable changes in people's consumption habits and changing climate conditions resulted in existing rivers becoming insufficient and inadequate in their natural cycles of flow within their aquatic habitats. Especially, the fact that water needed for agricultural activities could not possibly be met from agricultural lands has given rise to the need of storing water for irrigation purposes. Irrigation activities gaining a momentum in Eastern Anatolia Region of Turkey as part of Southeastern Anatolia Project continue under the leadership and guidance of the competent public authority, General Directorate of State Hydraulic Works. However, number of water holding and storage structures built for purposes of meeting energy needs, supply of drinking water and flood control are increasing with each passing day. Dams built on our rivers and streams are not only known for the benefits they provide us with, but also the damages they do to and harmful effects they have on the rivers and their surrounding areas. Such effects as changes in natural courses of rivers and disruption of natural cycles in riparian zones which occur together with dam construction bring about, in the long run, the threat of death and loss of rivers along with their living inhabitants. Therefore, in dam construction projects, sustainability of natural cycle in riparian zones should have priority over their expected benefits. In dam projects both in Turkey and abroad, the efforts aimed at determining environmental flows - which can be summarized as release of sufficient amount of water into the river mouth required for ensuring continuation of ecological life in river bed - has come to be one of the most important concerns of the 20th century. Within the process starting from the Tennant Method which is the oldest known environmental flow determination method, changing needs and advancing technology brought along tens of modifications made to the Tennant Method which was recognised and regarded as the fundamental method as well as development of many other methods relying on different approaches. Whereas some countries determine environmental flows by using only one method, in many others there has arisen a need for utilization of integrated and combined methods. In Turkey, use of Tennant Method in determining environmental flows was set down as appropriate by the regulation issued in 2003. As stipulated by the said regulation, amount of environmental flow to be released into downstream area in dam projects is limited to 10% of the average monthly flow of the last ten years. It is known that in studies conducted using climatic variables, for any data to provide any information about climate of a region, at least thirty years' data is required to be analysed. However only if a data set has existed for the required period of time is it possible to determine statistical significance thereof. Given all these arguments, it is highly suspicious that average ten-year flows have a climatic and statistical significance for dam projects with an expected lifetime of at least 50 years. Furthermore, this approach overlooks and does not take into account variability of natural flows prior to dam construction, which constitutes a basis for and plays an essential role in dam projects. In this study, what has been addressed and discussed is that single method approaches should not be employed in determination of environmental flows and that different methods can be used in rivers with different flow regimes. Pre-dam environmental flows recorded in 1985-2012 and meteorological parameters recorded in the same period were used in this study to determine the amount of environmental flow of Cevizlidere Dam located in Çemişgezek town of Tunceli Province. In this study, only pre-dam flow data were used, for in Turkey there is a lack of necessary human power for developing hydraulic models and an absence of an adequate measurement and observation network for supply of data type needed to implement and use current models available in the world literature. Using pre-dam flow data, different amounts of environmental flows were calculated through methods of Wetted Perimeter, Aquatic Base Flow, Flow Duration Curve and Low-Flow Indices. Based on the results obtained, it has been observed that in October, November, July, August and September environmental flow amounts to be released into downstream of Cevizlidere Dam are required to be calculated by using Q75 statistics of Flow Duration Curve Method whereas in December, January, February, March, April, May and June they are required to be calculated by using averages of the last ten years. In this study, it is intended to demonstrate that use of alternative methods and approaches is needed as the current environmental flow method used in Turkey is not sufficient and satisfying even at the scale of Cevizlidere Dam.