DEÜ FMD 22(66), 793-800, 2020

Hydrological Droughts and Runoff Trends of the Demirköprü Dam Reservoir Basin on , Gediz Nehri Demirköprü Baraj Havzasının Hidrolojik Kuraklıkları ve Eğilimleri Ahmet Ali Kumanlıoğlu* * 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, 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.

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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 , 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 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

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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 𝑉𝑉𝑖𝑖 𝑘𝑘 − 𝑉𝑉𝑘𝑘 𝑆𝑆𝑆𝑆𝑆𝑆𝑖𝑖 𝑘𝑘 (1) i 𝑆𝑆𝑘𝑘 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 𝑘𝑘 (mkth /month), 𝑉𝑉 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 s among 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 ; = = 𝑗𝑗 𝑖𝑖 (2) invetigated at month monthly (SDI1), quarterly 1 ; 𝑥𝑥 < 𝑥𝑥 (SDI3), 6 month (SDI6) and annual (SDI12) time 𝑗𝑗 𝑖𝑖 𝑥𝑥𝑗𝑗 𝑥𝑥𝑖𝑖 𝑠𝑠𝑠𝑠𝑠𝑠�𝑥𝑥 − 𝑥𝑥 � � scales in the study. 𝑗𝑗 𝑖𝑖 The Mann-Kendall− test 𝑥𝑥 𝑥𝑥

(S) statistics are calculated using Eq.3., with the help of the results to be obtained through Eq.3.

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= (3) 𝑁𝑁−1 𝑁𝑁 For N≥8, S shows normalE distribution with an average (E[S]) and variance (Var(S)) same as 𝑆𝑆 � � 𝑠𝑠𝑠𝑠𝑠𝑠�𝑥𝑥𝑗𝑗 − 𝑥𝑥𝑖𝑖� 𝑖𝑖=1 𝑗𝑗=𝑖𝑖+1 those calculated with q.4 and Eq.5. However, if

N≥30, z test value will be closer to t test [15]. [ ] = (4) ( )( + ) ( )( + ) 𝑬𝑬 𝑺𝑺 ( )𝟎𝟎= 𝑷𝑷 𝑵𝑵 𝑵𝑵 − 𝟏𝟏 𝟐𝟐𝑵𝑵 𝟓𝟓 − ∑𝒊𝒊=𝟏𝟏 𝒕𝒕𝒊𝒊 𝒕𝒕𝒊𝒊 − 𝟏𝟏 𝟐𝟐𝒕𝒕𝒊𝒊 𝟓𝟓 𝑽𝑽𝑽𝑽𝑽𝑽 𝑺𝑺 𝟏𝟏𝟏𝟏 (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 ( ) 𝑆𝑆 − extreme wet event is happened, but the extreme = ⎧ 0 ; 𝑆𝑆 = 0 (6) drought event is not seen between 1970 ⎪�𝑉𝑉𝑉𝑉𝑉𝑉+ 1𝑆𝑆 water years. The highest severe drought events ; < 0 𝑧𝑧 𝑆𝑆 for incoming- total runoff of dam reservoir- were ⎨ ( ) 𝑆𝑆 occurred May 1989 and June 2001 for SDI1, in ⎪ 𝑆𝑆 ⎩�𝑉𝑉𝑉𝑉𝑉𝑉 𝑆𝑆 April June 1984 for SDI3, in April September and1984 for SDI6 and in 1989 water year for SDI12 A significanceis level α is used for testing either an (Fig.2 ,Fig. 3). The durations of drought2 period upward or downward trend. An absolute value of significant trends of incoming total runoff to α/2 z higher than z at α significant level also dam reservoir are- shown in Table . The longest indicates a trend. A negative z value means that drought- duration is observed in- November the trend is downward, while a positive (+) one between 1985 2009 water- years for SDI1, in- refers to an upward trend. Significant trends of October December - between 1985 1997 water- total incoming runoff at different timescales years for SDI3, in October March between- 1988 wer3. Resultse determined and Discussion at 0.05 level of α. 1997 and in April September between 1985 1994 for SDI6 and between 1988 1997 water - years for SDI12. The trends of the incoming total In the study, hydrological droughts for all sub runoff to dam reservoir have downward trends basins runoff and incoming total runoff to in October, November, January, June, July, August and September and the other months of SDI1 Demirköprü Dam reservoir and the trends of have shown no trend. When trends in SDI3 total incoming runoff rswere discovered at the - different time scales in the period between the periods total runoff -are examined, it is seen that re are downward trends in October 1970 to 2007 water yea . The distributions of SDI for only monthly timescale for investigated December and July September periods and no trend in other periods. The incoming total runoff period are given in Figure 2. Quarterly,r - semiannual and annual SDI time series between trends are identified in SDI6 as a downward trend for both semi annual periods, in SDI12 has 1970 and 2007 water years are shown in Figu e 3. a downward trend

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October November

December January

February March

May

April

June July

August September

Fig.2. Monthly SDIs time series between 1970 and 2007 water years for 514, 515, 522, 523 and total

runoff of Demirköprü Dam Reservoir

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- - - -Mar

Oct Nov Dec Jan Feb

- - -May- Jul Aug Sep Apr Jun

O- -D- -F-M -M- - - -

N J A J J A S

O- -D- -F-M- -M- - - -

N J A J J A S

Fig.3. Quarterly, semiannual and annual SDI time series between 1970 and 2007 water years for the 2 - stations 514, 515, 522, 523 and total runoff of Demirköprü Dam Reservoir

Table .Monthly, quarterly, semi annual and annual timescales drought periods and trends of the incoming total runoff to Demirköprü Dam Reservoir

SDI1 –SDI3 – SDI6- SDI12- Mar Months Mar Mar r Oct. Jan. Oct.. Oct. Oct. Nov. Dec. Jan. Feb. . - - Dec. . . Sep. ------1971 1989 2007 997 - - 1999 1985 1992 1977 1987 1992 1985 1988 1988 1988 Drought 2004 2005 1 1988 1995 2001 1997 1997 1997 1997 9 6 19947 9 4 years years years years years years years years years years Max 19 13 10 10 10 Length 798

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Trend

( ↓ ↓ α=0.05) ↓ ↓ ↓ → ↓ → ↓ - → - - May e

Apr. July Apr. Months Apr. Jun July Aug. Sep. ------June- Sep.- Sep.-

2007 1985 1985 1987 1993 1998 1987 1985 1992 1985 Drought 1994 19928 1997 19986 19959 19928 19987 1994 years years years years years years years years years Max 10 11 10 10 TrendLength

( ↓ α=0.05) → → ↓ ↓ ↓ ↓ → ↓

- 4 O - November, SDI3 October December, SDI6 Figure shows that the wet and drought events-2007 ctober March and SDI12, respectively. The frequencies of incoming total runoff to drought events are much more happened than Demirköprü Dam reservoir between 1970 - the wet events according to the all examined water years. The highest drought frequency level timescales. is observed to be 68%, 66%, 58%, 58% for SDI1Wet Drought

80 70 60 50 40 30 20 Frequency (%) Frequency 10 0

4

Fig. . The frequency of wet and drought events of incoming total runoff to Demirköprü Dam Reservoir for SDI1, SDI3, SDI6 and SDI12 timescales When the results obtained in the SDI1, SDI3, operating plans of the dam to restricted6, SDI6 and SDI12 timescales are evaluated- irrigation7 of the 99000 ha area that supplied together, it is seen that there are significant water from the Demirköprü dam reservoir [1 drought periods especially at between 1988 14. Conclusion]. 1997 water years and downward trends in the , the incoming total runoff to the Demirköprü dam reservoir basin. Hydrologic drought, which In this study, hydrological droughts for all runoffare thestarted 3- in 1985, 6- on a monthly timescale in with by SDI method, and the trends of incomings in Demirköprü dam basin runoff, were occured in total runoff to Demirköprü Dam reservoir month month and annual timescale found out at 1, 3, 6 and 12 month time scale droughts in 1988 and continued until 1997. The period between 1970 to 2013 water years for the impact of this drought caused the changes in the799 Demirköprü Dam reservoir basin runoff, Turkey.

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