Numerical models are used to check the stability of earth dams and to simulate the effects of all the parameters, which affect its safety. The physical properties of the materials used in the construction of an earth dam are one of these important parameters. The finite element analysis software used for numerical modeling in this study is GeoStudio 2007(SEEP/W and SLOPE/W). The total number of finite elements used to simulate the standard model is 13508 (triangular elements with global size = 2m), while the total number of nodes is 6939. The selected case study is Al-Adhaim dam, which is an earth dam, located in Diyala governorate at the eastern part of Iraq, crossing Al-Adhaim River with a total length of (3.1 km). The major objective of this study is to derive an empirical equation to calculate the factor of safety for earth dams of similar geometries and materials without the need for sophisticated analysis, by assuming different soil conditions. In addition to the soil parameters (the total weight density ɣ, the angle of internal friction ϕ, the cohesive strength C) for the shell, core and filter within the dam, more parameters have been taken into consideration in predicting the critical factor of safety against slope failure to derive the empirical equation, which are: water depth H (m), coefficient of permeability k (m/s) and Seepage rate Qs (m 3 /s/m). The values of the computed factor of safety (Fs) using nine installed slope stability methods: Ordinary, Bishop, Morgenstern-Price, Janbu Generalized, Lowe-Karafiath, Corps of Engineers #1 and #2, Spencer and General Limit Equilibrium (GLE) are close to the safety factors values calculated using the general empirical equation which is a function of the soil and hydraulic parameters of the shell, core and filter within the dam.
An applied hydrological models were performed to model the rainfall-runoff relationship for Upper Adhaim River Basin. Three lumped integral models (hydrologic models) based upon the concept of the unit hydrograph were applied to analyze the rainfall-runoff relationship on a daily basis. These models are: the Simple Linear Model (SLM), the Linear Variable Gain Factor Model (LVGFM), and the Non-Linear Model (NLM). Five performance evaluation criteria have been used in this study. The application results of the (SLM) model showed a weak rainfall-runoff relationship. It was demonstrated that the linear assumption is valid only for the first four antecedent days. A considerable non-linear rainfall-runoff relationship was clearly observed from the results of (LVGFM) and the (NLM) models. Both models were satisfactorily identified at system memory of (17) antecedent days. However, the (LVGFM) was slightly superior to the (NLM). The (LVGFM) identified at system memory of seventeen antecedent days was used to simulate runoff flows. The simulation results show an acceptable applicability for the (LVGFM) in terms of simulating runoff events in time of its occurrence and volumetric fitness. The water budget for Upper Adhaim River Basin showed that an average of 73.4% from annual rainfall was evapotranspired, 8.0% was infiltrated and 18.6% was observed as direct runoff.
Due to the lack of surface runoff data in that area, the Mosul dam reservoir watershed was modeled by using the Soil and Water Assessment Tool, which has an interface with the geographical information system (ArcGIS). This model was calibrated for the period extended from 1979–1991 with a monthly intervals and validated for the period from 1992–1999. A SUFI – 2 algorithm procedure within the SWAT- CUP program was applied in the calibration and validation process and sensitivity analysis. The accuracy of this model for the studied area was classified as very good for the calibration period and good for validation according to the statistical parameters. The results of the sensitivity analysis showed that there are eight parameters that have the greatest impact on the hydrological processes in the study area. Results illustrated that the area of the Mosul Dam watershed was 11108 km2. Results showed that the average annual net runoff that entered the Mosul dam reservoir was 2565 MCM. This represents 13.5% of the average annual total runoff volume. Due to the shortage of water during the dry seasons, this amount is more relevant. As a result, it is necessary to improve the groundwater reservoirs during the rainy seasons and reuse water, as well as increase the effectiveness of water distribution for all uses. Furthermore, the sub-basins in the Iraq region contribute 57.8% of that percentage, 38% of those in Turkey, and 4.2% from sub-basins in Syria.
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