Basit Akarsu Modeli(sismod) Kullanılarak Akarsularda Ekolojik İhtiyaç Debisi Belirlenmesi

Abstract

Akarsular, ekosistemlerin önemli bir parçasını meydana getiren, birçok bitki ve hayvan türü için yaşam alanı oluşturan, tarım, içme suyu, sulama, turizm, ulaşım, balıkçılık ve enerji alanlarındaki ihtiyaçları karşılayan tatlı su kaynaklarıdır. Ülkemizdeki akarsuların fiziksel yapılarının farklı olduğu ve akıttığı su miktarlarının mevsimlere göre değişiklik gösterdiği bilinmektedir. Bu nedenle her akarsuyun hizmet açısından potansiyel kullanım yapısı, bulunduğu bölgeye, su kalitesine, su miktarına bağlı olarak seçilmeli ve ekosistemle birlikte değerlendirilmelidir. Bu şekilde, akarsu üzerinde minimum akım debisi olan ekolojik debi belirlenerek akarsu ve havza ekosisteminin sürdürebilirliği sağlanmış olacaktır. İşlevsel olarak çok yönlü bir hizmet sunan akarsular üzerinde insan eliyle yapılan çalışmaların ve projelerin uzun periyotlarda planlanması gerekirken kısa vadede çabuk sonuç almayı hedeflemesi, mevcut çalışmaların ekosistemle entegre bir biçimde ele alınmaması, çevresel ve sosyal açılardan olumsuz sonuçlar ortaya çıkaracaktır. Akarsuyun enerji veya başka bir alanda kullanımı sırasında ortaya çıkacak en önemli problemlerden biri de suyun alındığı akarsuda ekosistemin tamamen veya kısmen tahrip olmasıdır. Bu nedenle suyun kullanımı nedeniyle ortaya çıkabilecek bu tahribatın önlenebilmesi amacıyla çevresel faktörlerin dikkate alınarak geliştirilmesine ihtiyaç vardır. Bu çalışmada, akarsularda, ekosistemin tahribatının önlenmesi ve devamlılığı için bırakılması gereken su miktarı ile ilgili dünya ölçeğinde kullanılan başlıca yöntem ve yaklaşımlar özetlenmiş, akarsular için ekolojik ihtiyaç debisinin hesaplanmasında SİSMOD modeli kullanılarak hipotetik bir akarsu yapısına uygulanmıştır. Modelin, daha önceden yapılan çalışmalarda su kalitesi açısından güvenilir sonuçlar vermesi, hızlı bir değerlendirme imkanı sunması, karmaşık olmayan basit bir yaklaşım içermesi, ekolojik ihtiyaç debisi belirlenmesinde alternatif bir değerlendirme metodu olarak ele alınmasını sağlamıştır. Her akarsu havzası için akarsuda bulunması gereken minimum debi miktarı farklı olacaktır. SİSMOD modeli kullanılarak, akarsuda bulunması gereken debi miktarı, ilk aşamada hidrolik veriler ele alınarak, suda yaşayan balık türlerinin fiziksel aktivitelerini sağlıklı bir şekilde sürdürdüğü su hızı ve su derinliğine göre hesaplanmıştır. İkinci aşamada, hidrolik açıdan uygun bulunan ekolojik ihtiyaç debisinin su kalitesi açısından birçok parametreye göre uygunluğu kontrol edilmiş ve hipotetik akarsuyun ekolojik ihtiyaç debisi su kalitesi açısından belirlenmiştir.

Water is an indispensable natural resource for all alives. Despite big percentage of earth covered by water, only %3 of this percentage can be used as available-fresh water. Streams are only %0,6 of percent of the world total freshwater reserves. Use of streams has been changing dramatically by the increase of population and water demand in the world. As well as increase of population in the world in the last decades, climate change also affected the streams. Thus identification, protection and sustainable management of stream have become crucial. As is the case in all over the world, the fact that both the quality and the quantity of stream water have been increasingly degrading in Turkey has leveraged concerns and led to more efforts in the area. Within this scope, the water management understanding in Turkey has been oriented towards two areas of concern; namely, the increased usable water potential on one hand and on the other hand, river basin-based organization and prevention of water pollution. Streams are fresh water resources which are a crucial part of ecosystem provide habitats to many animals, plants and meeting the needs in agriculture, drinking water, tourism, transportation, fishing, irrigation and energy. Streams in Turkey differ in their structure and the amount of water circulated changes according to the seasons. Thus, each resource should be evaluated based on the region, quality and quantity of water within the ecosystem. In this way, the ecological flow rate, the minimum flow rate, will be determined and the sustainability of the river basin ecosystem will be realized. Streams tend to adjust and reconstruct themselves with their self healing capacity and if necessary, a healthy stream ecosystem must mimic the most natural condition as much as possible. Overdesigning or enlarging the channel cross section can create a conflict in the large woody debris balance and may give rise to the thrash accumulation and eventually a slow death of a functioning river. For a sustainable river ecosytems, selection of river cross-section is vital since it has a great influence on determining the magnitude of flood for a given discharge; defining fishes characteristics and transport process mechanism and thoroughly understanding the stream ecosystem. Within the last years due to the demand for more energy many new projects have been developed. Projects are on rivers, have effects on water amount, water quality and consequently on water ecosystem. In this reason, determination of required environmental flow to protect water ecosystem in river mouth constitutes a significant problem. Maintenance of river ecosystems’ health depends on environmental flow (required ecological flow rate) calculations. An analysis of the required ecological flow rate of a stream, a tributary of the original to maintain the ecological status of the current regime downstream of a particular water structure itself, could be expressed as what proportion of the flood protection will be to reveal. EFR analysis, typically present the development of water resources organized or planned streaming systems with flow of activities linked with the streams restoration carried out to support the decision-making process. As a result of this type of work with the recommended EFR flow rate for a single-year or for different seasons with different flow rate of streams for targeted protection of ecological status could be accomplished. Especially in our country while determining the policy and practice of the project guidelines for hydroelectric plants people and the views of non-governmental organizations and the people living in the region are not taken into consideration. Without clarifying the needs of flora and fauna properly and targeting results in a shorter period of time instead of handling all projects in a longer period of time and not integrating into the existing ecosystem, brings up a set of serious environmental and social issues. Besides, significant economic loss occurs because of various planning mistakes. The last ten years average stream flow rates required for many projects which are related to ecological flow needs to be allocated in rivers and ensuring the continuity of the ecosystem are defined as at least 10% of the work. It is impossible to have the same rate for each river basin. For each basin a rate should be determined to sustain the natural balance of the rivers and guaranteeing other water rights. On the other hand a series of legislation include provisions that virtually make protection of natural ecosystems impossible. Streams ecosystems are among the areas containing many species. Therefore, while assessing the required flow rate for the ecosystem water quality and biodiversity should be taken into consideration. In case of absence of biodiversity and inadequate water quality parameters, this data should be handled carefully and evaluated clearly. Stream perform a variety of biogeochemical functions, including sediment deposition, nitrogen and phosphorus removal, and transformation of inorganic nutrients to organic forms. Because of this important functions and values streams play very important roles in water quality. Previous watershed studies prove that SISMOD model could give reliable results in simulating water quality, has quick evaluation capability, and utilizes an uncomplicated simple approach. thus, it can be accepted as an alternative method for the determination of required ecological flow rate. In this study, the main methods and approaches used worldwide on the amount of water should be allocated for the prevention and sustainability of the ecosystem have been summarized. On the basis of mathematical equations involving fluid is capable and accountable in terms of water quality, SİSMOD model was introduced and applied to a hypothetical stream structure for the determination of required ecological flow rate in terms of hydraulic characteristics and water quality. The minimum amount that must be present in stream flow for each river basin will be different. In the model the hypothetical structure of a river is discussed, it is assumed that there are different types of fish in this river continuing their vital activities. By using SİSMOD model, river flow rates were evaluated by using hydraulic data in the first stage. The most critical cross-section of the set is the slope of the river stream, length, by taking the bed width, the minimum flow rate required has been determined by the healthy physical activities of the fish species that live in the water according to the velocity of the water and water depth. In the second stage, water quality parameters were checked whether they comply with the standards for the designated water quality when the ecological flow rate calculated in the first stage flows through the hypothetical stream system... When water quality is not suitable for the designated water quality class the flow rate was increased, and the minimum stream flow rate that ensures the designated water quality was identified as the ecological flow rate. Ecological flow rates determined with the model results were evaluated according to current regulations and limits. Ecological flow requirement for the hypothetical river structure was also determined by considering different methods used forrivers in literature, and were compared with the ecological flow rates calculated with SİSMOD model. According to the model results it can be concluded that only hydraulic data could not give ultimate results for the determination of ecological flow rate of rivers. The needs of aquatic species living in the ecosystem and and water quality had to be assessed in the study. The model used in the study determines the ecological flow rate, and offers solutions on different scenarios that may occur in streams. It can propose alternative solutions for effective and efficient decision making. The method proposed in this study could be used for the determination of ecological flow rate in rivers; thus, it can be accepted as an alternative method for calculating the minimum amount of water that should be released into river in Hydroelectric Power Plant Projects.