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DEÜ FMD 22(66), 793-800, 2020 Hydrological Droughts and Runoff Trends of the Demirköprü Dam Reservoir Basin on Gediz River, Turkey Gediz Nehri Demirköprü Baraj Havzasının Hidrolojik Kuraklıkları ve Eğilimleri Ahmet Ali Kumanlıoğlu* *Manisa Celal Bayar Üniversitesi Mühendislik Fakültesi , Manisa, Sorumlu Yazar / Corresponding Author *: İnşaat Mühendisliği Bölümü TÜRKİYE [email protected] Geliş Tarihi / Received: 01.10.2019 Araştırma Makalesi/Research Article Kabul Tarihi / Accepted: 10.12.2019 DOI:10.21205/deufmd.2020226614 Atıf şekli/ How to cite: KUMANLIOGLU, A.A.,(2020). Hydrological Droughts and Runoff Trends of the Demirköprü Dam Reservoir Basin on Gediz River, Turkey. DEUFMD 22(66), 793-800. Abstract In recent years, the impacts of climate change on water resources are much more noticeable. In terms of sustainable management of water resources, it is important to identify drought occurrences in river basins and to identify drought trends. For this purpose, many drought indices have been developed in orders to define the droughts quantitatively and- Streamflow Drought Index (SDI) method is frequently used to determine the hydrological droughts among them. In- this study, hydrological- droughTht of on Acısu, Selendi, Deliiniş, Demirci sub basins and incoming total runoff to Demirköprü Dam reservoir on the Gediz River were analyzed in monthly,- quarterly, six month and annual time scales. e total inflows of Demirköprü Dam reseroir trends were investigated at same time trendsscales. As a result of the study, it was determined that the all sub basins runoff and incoming total runoff to Keywords:Demirköprü SDI; Dam hydrological reservoir drought;were trend affected analysis; from Demirköprü hydrological Dam; Gediz drought basin s for long periods and of incoming runoff to Demirköprü Dam reservoir were towards the dry periods. Öz Son yıllarda, iklim değişikliğinin su kaynakları üzerindeki etkileri çok daha belirgin bir biçimde ortaya çıkmaktadır. Su kaynaklarının sürdürülebilir yönetimi açısından, nehir havzalarındaki kuraklık olaylarını ve kuraklık eğilimlerini tanımlamak büyük önem taşımaktadır. Bu amaçla, kuraklıkları niceliksel olarak tanımlamak için birçok kuraklık endeksi geliştirilmiştir ve bilhassa hidrolojik kuraklıkları belirlemek amacıyla Streamflow Drought Index (SDI) yöntemi sıkça kullanılmaktadır. Bu çalışmada Gediz Nehri'ndeki Acısu, Selendi, Deliiniş, Demirci havzaları ve Demirköprü Baraj rezervuarındaki hidrolojik kuraklık ve eğilimleri aylık, üç aylık, altı aylık ve yıllık zaman ölçeklerinde Keywords:incelenmiştir. SDI; Hidrolojik Çalışma kuraklık sonucunda,; eğilim anal Demirköprüizi; Demirköprü Barajı barajı ; havzasıGediz havzası girişlerinin uzun süre hidrolojik kuraklıklardan etkilendiği ve kuraklık analizlerinin kurak dönemleri işaret ettği tespit edilmiştir. 793 DEÜ FMD 22(66), 793-800, 2020 1. Introduction irrigation area is covered by the Demirköprü , Dam reservoir located on the Gediz River, Droughts, often caused by deforestation, Turkey. Therefore, the hydrological droughts urbanization and similar factors related to s occurring in the basin streams feeding the changing climate conditions and population Demirköprü dam reservoir significantly affect growth [1, 2]. The meteorological drought, which - supply of Gediz Basin irrigation water is defined as the lack of the precipitation over the requirements. This study covers the long term averages, will lead to decreases in the determination of the hydrological drought and stream runoff as a result of the continuation of a -2007 trend analyses incoming total runoff to certain period of time, and hydrological drought s and trends Demirköprü Dam reservoir between 1970 will occur. In other words, hydrological drought water years. Hydrological drought of can be defined as decreases in runoff in surface - incoming runoff to Demirköprü Dam reservoir and -groundwater forms [3]. Hydrological were examined on monthly, quarterly, semi droughts have a significant negative impact on - annual and annual timescales using the SDI enesocio economic life as given rise to restrictions 2.method Materials and Mann and MethodsKendall test, respectively. especially on agricultural irrigation, decreasing 2.1. Study area and data rgy production and water supply [4]. Characterization of hydrological droughts occurring in the basin is important for reducing 004’–390 these impacts and sustainable water resources 26The042’ Gediz–29 0Basin lies between northern latitudes management [5]. Hydrological drought indices of 38 13’ and southern longitudes of have been developed in order to determine 45’ in Aegean Region, western duration and magnitude intensity of droughts in Turkey (Figure 1). The basin covers an area of basin runoff such as, Streamflow Drought Index 17500 km², which is equal to 2.2% of- the total (SDI), Surface Water Supply Index (SWSI), area of Turkey and the total irrigation area is Reclamation Drought Index (RCDI) and 110000 ha. The Gediz River, is 275kilometer Nonlinear Multivariate Drought Index (NMDI) long. The Demirköprü Dam was built on the [6, 7, 8, 9]. The SDI method examines droughts Gediz River in Manisa Province of Turkey based on different time scales and requires only between 1954 and 1960, in an effort to enhance monthly runoff data; therefore, reduces irrigation, power generation, and flood control computational- difficulties and data activities. The height of this embankment dam requirements and gives powerful assessing at from the streambed is 75.00 m. The basin drought [6, 10, 13]. hydroelectric powerL plant built in the –dam generates 193 GWh electric power annually– with Many studies have been carried out worldwide a capacity of 69 MW. ying between 28° 18' 28° due to the fact that the SDI methodnths) can be 28' eastern longitudes and 38° 36' 38° 45' applied to hydrological droughts at different northern latitudes, thethe Demirköprü Dam time -periods (1, 3, 6, 9, 12 and 24 mo [10, reservoir also provides water 2for, that the irrigation 11]. The hydrologic droughts occuring in the - of 99.220 hectares. With reservoir catchment Sefid Rud basin have been determined by SDI that covers an area of 5520 km constitutes during the seasonal, 6 months and annual - 32% of all Gediz basin. Demirköprü Dam periods between 1984 and 2013 watera yearsn reservoir is fed by Acısu, Selendi, Deliiniş and [12]. The hydrological -droughts of Seyhan Demirci tributaries of the Gediz River (Figure 1) Ceyhan rivers have been investig ted o and the number of runoff gauge stations on these between the years 1970 2005 in 3, 6 and 12 tributaries are 523, 514, 515, 522,2 respectively. months periodss using with SDI. As a result of the Among these, Acısu Tributary has the biggest study, severe hydrological droughts occurred in s catchment area with 32722 km . The smallest the basin in 2001 [13]. catchment area, however, belongs to Selendi The water scarcity ignificantly will occur in Tributary with 689.6 km hectares [18]. Gediz River Basin on supplying of irrigation water. Approximately 90% of the Gediz basin 794 DEÜ FMD 22(66), 793-800, 2020 Fig. 1. Gediz River Basin and the Demirköprü Dam Reservoir 2.2. Streamflow Drought Index (SDI) Table 1. The claasification of droughts for SDI Periodical drought indices of the streams in Drought Classes SDI question were measured using the SDI developed by Nalbantis [6]. The SDI indices are Extreme wet (EW) SDI > 2 calculated by Eq.1 in consideration of total Severe wet (SW) 1.5 < SDI ≤ 2 monthly streamflow, values. , = Moderate wet (MoW) 1.0 < SDI ≤ 1.5 − (1) i k Mild wet (MW) -0 < SDI ≤ 1 Mild drought (MD) - 1 < SDI ≤ 0- where, " " isV iequal,k to the water year, " " refers to the3 period (monthly, quarterly, semiannual and Sk is the - - annual), total monthly flow volume Moderate drought (MoD) 1.5 < SDI ≤ 1 k(mth /month), is the mean and Severe drought (SD) 2 <- SDI ≤ 1.5 standard deviation of the total streamflow of the period. 2.3Extreme Mann -droughtKendall (ED) Test 2 ≤ SDI - If cumulative streamflow data corresponds to a - distribution such as log normal distribution, the SDI values are calculated by taking the natural In the study, The Mann KendallThe test Mann was -usedKendall for logarithms of the cumulative streamflow data- - defining the trends- for total incoming runoff to [6]. Suitable probability functions for the runoff Demirköprüi Dam reservoir. data are investigated using several goodness of test has a non parametric nature. This test is - j i fit test and thereby the Normal distribution is applied to x and x data sets, ordered as i=1,2,…, chosen as the best- onen samong the successful N 1 and j=i+1,…,N, respectively. Each ordered x distributions in this study. The hydrological figure is taken as a point of reference and figures j droughts of all sub basi runoff and incoming are compared with 1the x; data> set using Eq.2. total runoff- to Demirköprü Dam reservoir were 0 ; = = (2) invetigated at month monthly (SDI1), quarterly 1 ; < (SDI3), 6 month (SDI6) and annual (SDI12) time � − � � scales in the study. The Mann-Kendall− test (S) statistics are calculated using Eq.3., with the help of the results to be obtained through Eq.3. 795 DEÜ FMD 22(66), 793-800, 2020 = (3) −1 For N≥8, S shows normalE distribution with an average (E[S]) and variance (Var(S)) same as � � � − � =1 =+1 those calculated with q.4 and Eq.5. However, if N≥30, z test value will be closer to t test [15]. [ ] = (4) ( )( + ) ( )( + ) ( )= − − ∑= − (5) t - he Considering the SDI1, SDI3, SDI6 and SDI12 of where, the number of relative groups in P data he sub basins runoff and incoming total runoff set refers to an observation in t i series. The to Demirköprü Dam reservoir, the drought- term "total" in Eq.5- is only used if a relative events occurred more frequently in period of observation exists6 within the data set. The 1985 and thereafter especially between 1985 standardized Mann Kendall statistics (z) are strate that the 1995 water years. The variation of SDI values for calculated by 1Eq. ; > 0 all examined timescales demon -2007 ( ) − extreme wet event is happened, but the extreme = ⎧ 0 ; = 0 (6) drought event is not seen between 1970 ⎪�+ 1 water years.