Abdulla Noman

Rainfall-Runoff Erosion Model for semi-arid catchments using GIS

Abstract in English: 
A mathematical "Sediment Yield" model has been developed and integrated with Rainfall-Runoff Model NAXOS [1] for estimating upland delivery rates of individual storm resulting from rainfall and runoff at the outlet of the catchment area of Wadi Surdud (2370 km2), Tihama, Yemen. The erosion and sedimentation processes of the upland watersheds have to be assessed by means which do not rely on historical storm flow data. Methods that depend on available or measurable representative data were developed for a deterministic approach of the erosion process. Considering the present state of knowledge of the system analysis, GIS techniques offer a unique opportunity for the appraisal of the complex interactions of erosion and sedimentation factors (rainfall, runoff, watershed, physical and land use characteristics) as well as sediment load contributions of the upland watershed. To apply the model, the watershed is divided into 242 subwatersheds using TOPAZ (Topographic Parameterization) [2]. Sediment yield is computed for each of 242 sub-basins using a steady state Sediment Continuity Equation [3] by routing mobilized sediment through a series of linear reservoir [5]. The Model uses a mass balance equation to compute sediment transport, erosion and deposition over the land surface as direct throughfall, leaf drainage and streamflow. Sediment transport is considered as the erosion rate in the plane reduced by the deposition rate within the reach. The erosion occurs due to raindrop impact as well as surface shear. The model may serve as a tool for design of soil conservation measures. The following results were obtained: " Identification of hazard areas for soil erosion, " Assessment of sediment transport at a given point within the basin, " The basis for planning of soil conservation measures. Keywords: erosion modeling; wadi Surdud; sediment yield, GIS
المؤلفون: 

Sediment Problems of Irrigation Canals: Field Studies to Assess the Changes in Canals Profiles and Cross Sections

Title in English: 
Sediment Problems of Irrigation Canals: Field Studies to Assess the Changes in Canals Profiles and Cross Sections
Abstract in English: 
Wadi Zabid is one of the main agricultural Wadis in the Tihama Plain. Wide ranges of crops have been cultivated such as cereals, vegetables, fruits, and some cash crops like cotton, sesame and tobacco. It has provided the country with high valued food basket as well as exporting to the neighboring countries. The government realized the importance of Wadi Zabid and started in 1979 constructing diversion works and canals to maximize the agricultural output of the Wadi. During the past twenty years of operations, sediment deposition in front of the diversion works and along the canal system posed serious threats to the project network. Sediment deposition caused many problems such as blocking the off take pipes and gates, raising canal beds and reducing canals slope, increasing the field levels and reducing canal flow capacity. This study would assess the changes in canal sections and profiles at which the present canal profiles and sections are drawn and compared with the canal profiles and sections of the previous years to provide sound basis for problems assessment. Laboratory experiments and sieve analysis were conducted to analyze canal bed samples in order to draw recent grading curves and compared it with the previous grading curves of the canals. This study exposed the fact that canal sections and profiles are changed greatly due to the accumulation of sediments in the upper reaches of the canals whilst equilibrium sections and profiles existed in the middle parts with section erosion in the lower parts of the canal reaches. It also indicated that greater sediments sizes were deposited in the canal upper reaches, which meant that canal behavior is changed and does not work as it was designed for.
المؤلفون: 
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