Dukan Dam Reservoir Bed Sediment, Kurdistan Region, Iraq

Rebwar Hassan,Sven Knutsson,Ammar A Ali,Nadhir Al-Ansari,Salahalddin S Ali,Twana Abdullah

doi:10.4236/eng.2016.89054

Abstract

The Dukan Dam Reservoir (DDR) in the Kurdistan Region of Iraq has been studied to determine the characteristics and nature of the reservoir and the deposited sediments on its bottom surface. This study was achieved by doing a field survey and grain size analyses of the collected sediment samples at 32 locations representing the whole reservoir area that had been created when the Lesser Zab River was dammed in 1959. The Dukan Dam, which is a multi-purpose concrete arch dam, was built on the Lesser Zab River for controlling its flood during high rainfall seasons, irrigation and power generation. The catchment area is 11,690 km2. The surface area of the reservoir is 270 square kilometers and the volume is 6.870 × 106 m3 at normal operation level (El. 511.00 m. a.s.l.). The minimum drawdown level is at elevation 469 m above sea level (a.s.l.). The live storage is 6.14 × 106 m3 while the remainder is dead storage. The reservoir has a surface area that reaches 270 square kilometers and is composed of two sub-reservoirs connected by a narrow channel that has a length of 5 kilometers. The relatively bigger reservoir is located in the north and has a triangular shape with a surface area approximately 250 square kilometers. The smaller sub-reservoir is located down south where the dam exists and it has irregular rectangular shape. Thirty-two sediment samples were collected from the bottom of Dukan reservoir. The bed of the reservoir is mainly composed of 15% gravel, 14% sand, 48% silt and 23% clay respectively. Most of the sediments are very fine grained, very poorly sorted, strongly coarse skewed and mesokurtic.

Highlights

In nature, most of the unconstrained rivers by dams are in an equilibrium state, which means that the sediment inflow and outflow are balanced
The relatively bigger reservoir is located in the north and has a triangular shape with a surface area approximately 250 square kilometers
The gravel sediments are deposited at the shore lines of the bigger and smaller sub-reservoirs and this may be due to the wave actions (Figure 9(a))

Summary

Introduction

Most of the unconstrained rivers by dams are in an equilibrium state, which means that the sediment inflow and outflow are balanced. This balance is changed with time in dammed rivers because dams trap both water and sediment which cause increasing flow depth velocity (settling capacity) and decreasing flow velocity (transporting capacity) and lead to the deposition of the carried sediment by rivers in the reservoirs [1]. The dams cause slowing down flow velocity of the dammed rivers which feed the reservoirs and reduce the rivers ability to transport the carried sediments which begin to settle down on the bottom of the reservoirs. The topset, foreset and bottomset deposits at the bottom of dam reservoirs represent roughly (≈95%) the total sediments which enter dam reservoirs and the remained 5% of the entered sediments (fine particles) go out to the front of the dam body as reservoir outflow (Figure 1)

Methods

Results

Conclusion