Morphology of Tigris River inside Baghdad City

Detta är en avhandling från Luleå : Luleå tekniska universitet

Sammanfattning: Tigris and Euphrates rivers represent the artery of life in Iraq. Tigris River rises from Turkey and flows toward the southeast to enter Iraq. It drains a catchment area of 473 100 km² of which about 58% lies in Iraq. In this study the reach, about 50 km long, of the river inside Baghdad was been studied. It starts at Al-Muthana Bridge and ends at Tigris-Diyala River confluence. Generally, the river reach is part of an alluvial plain, single channel and meandering. The bed material of the river is composed mainly of fine sand and small portion of silt and clay. Other significant features of the reach are the growing islands and bank depositions. Recently water resources of Iraq are negatively affected by climatic changes and the huge water projects in the riparian countries. As a result, the flow of Tigris River at Baghdad city has significantly decreased where the average monthly flow is 520 m³/s for the period 2000-2012 which represents about 50% reduction compared to previous periods. The estimated trend for the average monthly discharges is a reduction of 5.4 % during the last 23 years. Low flow and low water levels have enhanced the water to erode the banks below its protected part. This might affect the future stability of the banks. The drop of the river discharge together with debris from the last wars in 1991 and 2003 enhanced the growing of islands in the river. In this research, changes in the morphology of Tigris River within Baghdad are to be investigated and the causes will be highlighted in order to take the right measures to restore the river system. This is a first step toward studying the hydrological characteristics of the reach. One-dimensional gradually varied flow model, using HEC-RAS, was applied to examine the flood capacity and the possibilities of inundation of the banks. The geometry of the river was represented by the findings from the river survey of 2008. Additional data about the locations and dimensions of the bridges were supplied to the model. The average monthly discharge at Sarai Baghdad for the years 2000-2012 was assumed as the base flow. A range of different scenarios were examined by increasing the discharges in order to determine the critical discharge that may cause inundation. Model calibration was achieved by adjusting the Manning’s roughness coefficient for an observed water surface profile along the lowest part of the reach. The associated error with the computed water surface profiles was in order 0.026m. Additional water level observations at Sarai Baghdad were used for verification purposes. It was found that the discharges higher than 2700 m3/s could cause partial inundation in some areas in the northern part of the reach and these areas extend to approximately 9 km for discharges greater than 3500 m3/s. The southern part of the reach is still safe from inundation for discharges below 3500 m3/s. The slope of water surface profile varies from 6.03 to 10 cm/km for discharges between 400 and 4000 m3/s respectively. In this study, a field survey was conducted between May, 2012 and January, 2013. It involved the installation of 25 bench marks, surveying the upper river banks (from the crest of the stony protection to the water surface) and 250 cross sections. Three kinds of samples were collected at this stage work: (i) river bed material, (ii) suspended load samples and (iii) bed loads samples. Hydraulic measurements were conducted and included water surface elevations, water depths at sampling points, water discharges and transversal velocities. Water temperature and other environmental measurements were also conducted. Particle size distribution, specific gravity and concentration of suspended sediment were executed in the laboratory for the collected samples.