Modeling the water quality of rivers and assessing the effects of changing conditions is often hindered by a lack of in situ measurements for calibration. Here, we use a combination of satellite measurements, statistical models, and numerical modeling with CE-QUAL-W2 to overcome in situ data limitations and evaluate the effect of changing hydrologic and climate conditions on water temperature (Tw) in the Tigris River, one of the largest rivers in the Middle East. Because few in situ estimates of Tw were available, remotely-sensed estimates of Tw were obtained from Landsat satellite images at roughly 2 week intervals for the year 2009 at the upstream model boundary (Mosul Dam) and two locations further downstream, Baeji and Baghdad. A regression was then developed between air temperature and Landsat Tw in order to estimate daily Tw. These daily Tw were then used for the upstream model boundary condition and for model calibration downstream. Modeled Tw at downstream locations agreed well with Landsat-based statistical estimates with an absolute mean error of <1 °C. A model sensitivity analysis suggested that altering upstream river discharge had little impact on downstream Tw. By contrast, a climate change scenario in which air temperatures were increased by 2 °C resulted in a 0.9 °C and 1.5 °C increase in Tw at Baeji and Baghdad, respectively. Since Tw is a fundamental state variable in water quality models, our approach can be used to improve water quality models when in situ data are scarce.

ACKNOWLEDGMENTSThis study benefited from several people and organizations.  Dr. Scott Wells provided guidance and advice  The Higher Committee for Education Development in Iraq (HCED)  My Mom  Water Resources Ministry in Iraq  National Center for water resources Management  The Civil and Environmental Engineering department at Portland State University has supported my work  My Wife iii ABSTRACT The Tigris River is the eastern member of the two great rivers in Iraq. Two big rivers pass through Iraq, Mesopotamia. Tigris and Euphrates Rivers with their tributaries form a major river system in the Middle East. Four riparian countries, Turkey, Syria, Iran, and Iraq, share the Tigris River basin area and Iraq has the majority of this basin area. The total length of the Tigris is 1850 km from which 1418 km is within Iraq. A study area of 880 km from Mosul dam to Kut barrage is modeled using a water quality CE-QUAL-W2 model. CE-QUAL-W2 is a two-dimensional (longitudinal and vertical) water quality model developed by the U.S. Army Corps of Engineers and Portland State University. W2 simulates river circulation, stage, vertical and horizontal velocities, water temperature, and a host of water quality constituents. Total dissolved solids(TDS) is the main concern in Iraq because Iraq heavily depends on its water for irrigation purposes. Therefore, this project discusses the implementation of CE-QUAL-W2 model on Tigris River to simulate flow, temperature, and TDS.

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The headwaters of the Tigris River basin in Iraq is controlled by Turkey due to a series of dams constructed over the last few decades. Since Total Dissolved Solids (TDS) in the Tigris River within Baghdad and downstream cities can reach 1000 mg/L exceeding both drinking water and irrigation guidelines, a hydrodynamic and water quality model, CE-QUAL-W2, of the river was developed to understand how changes in flow affect TDS downstream. A model of 880 km of the Tigris River from Mosul Dam to Kut Barrage including Tharthar Lake was constructed for 2009. Model development was challenging due to a lack of in-situ measurements for calibration. Comparison of flow measurements and model predictions at downstream locations agreed well with field measurements, with model flow errors generally less than 2%. We evaluated the effect of changing upstream flow cond itions on total dissolved solids concentrations in the Tigris River in order to see how headwater flow control affects TDS. A sensitivity study suggested that increasing upstream river flow by 15% results in about a 5% decrease in TDS concentration. It was recommended to maintain an average annual flow in the Tigris River within Baghdad above 420 m 3 /s to keep total dissolved solids concentration below 500 mg/L and to strictly control flows through Tharthar Lake and irrigation return flows into the mainstem of the Tigris River.