السلام عليكم
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Evaluation of Rainfall-Runoff Realationship for Durbndikahn basin with aid of remote sensing and GIS techniqe
ABSTRACT
Knowledge of total runoff due to rainfall is most important for protecting any existing hydraulic structure and designing any new one.
Direct measurement of runoff is the accurate way of measurement but in most it is not possible at desired time and dcilocation, thus use of hydrological model for estimating runoff depth has become increasingly popular.
Ungaged basins pose a challenge to hydrological studies as they lack both calibration and validation data for the use of land surface models. Therefore, satellite data are recommended to be used to describe the aspects/attributes of the basin for a hydrological perspective.
A large ungaged catchment area (Durbendekhan Basin) of (3800) with elevation range from 300 to 2000 masl, which is located in the north-eastern part of Iraq within AL-Sulymaniah governorate (Kurdistan region), extends between (35°-00´ to 35°-45´ Northern Latitude) and(46°-00´ to °45-00´ Eastern Longitude) ,have been selected to obtain a relation between rainfall and runoff, since the basin have a major effect on Dyiala River system.
An empirical model suggested by the US department of agriculture, soil conservation service (USDA-SCS), was used in this study for determining the runoff depth depending on curve number value. The runoff curve number (CN) value is determined based on several factors that are related directly by the geomorphologic variations of catchment area such as hydrologic soil group (HSG) ,land use , land treatment and antecedent moisture content condition.
GIS and remote sensing are used in this study to provide quantitative measurements of drainage basin morphology for the runoff models so as to estimate the curve number value. Many maps and measurements are implement by using this technique such as, surface soil map, (land use / land cover) map and hydraulic soil group map.
Field work in this study involves reconnaissance of the study area, identifying the discharges in some tributaries feeding Durbendekhan Lake and providing laboratory with soil sample.
Laboratory work on other hand involves many experiments that are executed in the (University of Technology lab. & National Center for Laboratories and Research), such as (moisture content, specific gravity, sieve analysis, liquid limit, plastic limit and permeability test), the laboratory experiments have shown that there were four main types of surface soil in Durbendekhan basin (silty sand ,gravelly sand, poorly graded sand &sandy clay soil) in addition to the limestone rocks.
The permeability test shown there are three levels of permeability rate ,low rate range from (0.00001-0.000025cm/sec),medium rate range from (0.00038-0.0001cm/sec) and high permeability rate range from (0.00075-0.00095cm/sec).
General target from these experiments is surface soil classification according to USCS system. The classification results have been used to provide the GIS and remote sensing with ground truth that is used in supervised classification process.
Practically the Durbendekhan basin is divided into five sub-basins according to water divide courses (Tanjero,Zelum,Zemnako,Berke &Seroan) Tanjero is the largest occupying (65%) of the total area of the basin followed by Zelum with (18%),Zemnako is the smallest occupying (1.2%),Berke occupying (12%) and finally Seroan occupying (2.8%) of the total area of the basin , the rainfall-runoff relationship were found for each sub-basin.
Results obtained from this research were related directly to the varying topography and land cover for each sub- basin. High runoff depth obtain in (Berke & Tanjero) sub-basins that have governed hydraulic soil group ,Type "C" with pasture land cover which is specified by a low infiltration rate and high retention ability. Low runoff depth obtain in (Zemnako & Zelum) sub-basins that have a governed hydrologic soil group, Type "A" and shrub land cover with exposed rock that specify by low retention with a high infiltration rate.
The model was verificated by using data of two previous studies prepared by Parsons & Polservice, the results showed an acceptable coincidence between observed and calculated runoff depth.
