Estimating the Effect of Urban Growth on Annual Runoff Volume Using GIS in the Erbil Sub-Basin of the Kurdistan Region of Iraq

Hasan Hameed

doi:10.3390/hydrology4010012

Abstract

The growth and spread of impervious surfaces within urbanizing catchment areas pose signiificant threats to the quality of natural and built-up environments. Impervious surfaces prevent water infiltration into the soil, resulting in increased runoff generation. The Erbil Sub-basin was selected because the impervious cover is increasing rapidly and is affecting the hydrological condition of the watershed. The overall aim of this study is to examine the impact of urban growth and other changes in land use on runoff response during the study period of 1984 to 2014. The study describes long-term hydrologic responses within the rapidly developing catchment area of Erbil city, in the Kurdistan Region of Iraq. Data from six rainfall stations in and around the Erbil Sub-basin were used. A Digital Elevation Model (DEM) was also used to extract the distribution of the drainage network. Historical levels of urban growth and the corresponding impervious areas, as well as land use/land cover changes were mapped from 1984 to 2014 using a temporal satellite image (Landsat) to determine land use/land cover changes. Land use/land cover was combined with a hydrological model (SCS-CN) to estimate the volume of runoff from the watershed. The study indicates that the urbanization of the watershed has increased the impervious land cover by 71% for the period from 1984 to 2004 and by 51% from 2004 to 2014. The volume of runoff was 85% higher in 2014 as compared to 1984 due to the increase in the impervious surface area; this is attributed to urban growth. The study also points out that the slope of the watershed in the Erbil sub-basin should be taken into account in surface runoff estimation as the upstream part of the watershed has a high gradient and the land is almost barren with very little vegetation cover; this causes an increase in the velocity of the flow and increases the risk of flooding in Erbil city.

Highlights

The world population has increased rapidly over the last 150 years and continues to do so, which affects hydrologic resources on both a local and a global scale
The study points out that the slope of the watershed in the Erbil sub-basin should be taken into account in surface runoff estimation as the upstream part of the watershed has a high gradient and the land is almost barren with very little vegetation cover; this causes an increase in the velocity of the flow and increases the risk of flooding in Erbil city
The main aim of this study focuses on pattern changes of land use/land cover due to urban growth in the Erbil sub-basin, as well as their impact on rainfall surface runoff

Summary

Introduction

The world population has increased rapidly over the last 150 years and continues to do so, which affects hydrologic resources on both a local and a global scale. An assessment of the impact of land use changes on water resources is one of the recent thrusts in hydrological modelling [1,2,3]. It is expected that approximately 60% of the world’s population will be living in urban areas by 2030. There are 8000 km of land converted to urban growth every year [4]. Mile in the city, the increased rate of surface runoff will be ten times greater than in rural areas [5]. The impact of urban growth is one of the significant land use changes affecting surface runoff within the catchment area [6]. Land use changes could have several influences on the hydrological cycle, water quality and quantity, which will result in flooding and droughts as well as changes in Hydrology 2017, 4, 12; doi:10.3390/hydrology4010012 www.mdpi.com/journal/hydrology

Objectives

Results

Discussion

Conclusion