Evaluating sediment yield at King Talal Reservoir from landslides along Irbid-Amman Highway

With a capacity of 86 MCM, King Talal Reservoir is considered a major water supply in Jordan. It was built exclusively to irrigate the land in the Jor dan Valley. Unexpectedly, the design capacity of the reservoir was confront ed by the elevated sediment inflows during and after the construction of th e Irbid-Amman Highway in 1987. Since then the annual sediment inflow measur ed at the mouth of the reservoir was higher than expected in a similar year . Notably, the over-wet season of 1991/2, as a result of six major landslid es along the highway, registered the highest sediment inflow into the reser voir. in the present work the fractional contribution of these landslides t o total sediment yield at the reservoir was evaluated. The evaluation was m ade by applying the well-known erosion model, AGNPS (Young et al., USDA Con servation Research Report 35, 1987). To calibrate the model, it was success ively applied from 1980/1 to 1990/1 on the measured sediment data before th e occurrence of landslides. With a slight tune-up of some of the King Talal watershed erosion variables, fairly good agreement was obtained in some ye ars. However, the disagreement noticed in other years might be attributed t o some conservation measures practised in the watershed. Because the seriou s landslides occurred in the wet season of 1991/2, the model was run for th e two scenarios in this year: with and without landslides. The difference i n results represents the contribution of landslides to sediment yield at th e reservoir. It is concluded, based on these results, that landslides, if c ontinued without control, will definitely jeopardize the design capacity of the reservoir. (C) 2000 Elsevier Science B.V. All rights reserved.