ANALYSIS OF HISTORICAL INFLOWS AT DARBANDIKHAN DAM IRAQ

Abstract

A Rainfall-Runoff MIKE 11 NAM model was developed to simulate runoff in a transboundary DIYALA-SIRWAN river basin located in Iraq and Iran at Darbandikhan dam. Due to the limited data availability in the basin, many secondary data sources were used to prepare the required data for this study. Data used included daily inflow for Darbandikhan reservoirs from 1962 to 2015, daily rainfall APHRODITE 0.25° resolution gridded data and observed monthly rainfall for seven stations inside Iraq and Iran with bias correction. Daily Temperature grid (0.25° × 0.25°) resolution was extracted from ECMWF website for a Period from 1962 to 2014, monthly PET from 1962 to 2014 were calculated using DrinC Software. MIKE 11 model, used in the study was calibrated during Oct 1963-Sep 1969 and was validated during Oct 1969-Sep 1973 for natural flow regime up to Darbandikhan Hydrometric Station (DHS) located by Darbandikhan Dam. The NSE, R2 and water balance error were found 0.70, 0.71 and 0.67% respectively during calibration and 0.66 , 0.67 and 0.17% respectively during validation of the model. It indicates a good agreement between the observed and simulated runoff in the river. Under the assumption, there is no water withdrawals in the upstream, MIKE 11 NAM model was used to simulate runoff for three scenarios each scenario representing one decade. The reference period for analysing changes in the inflows in Darbandikhan reservoir was from 1962 -1982 a period having no structures in the upstream of the dam. Water departure was found -18.6% less during 1983-1993 and about 43% during 2003-2013. It may be attributed reducing rainfall (negative trends were detected) and/or due to the construction of upstream structures in the river basin. Annual drought index RDI and SDI were calculated for the entire basin during the periods 1962 to 2013 It was found that there are 22 % dry years , 14% wet years and the remaining 64 % are the normal rainfall years. Non-parametric indicators of hydrological alteration (IHA) software was also used for two scenarios i.e. 1983-2001, 2002-2015 to study the inflows variability at the dam site. IHA analysis indicates that there are low to moderate degree of changes in inflows in the first scenario whereas the second scenarios shows a high level changes 46% especially during non-rainy months .