The Effect of Crosss Tructureon Flooding Augmentation in Manshad Basin

Non-normative construction and occupation of the land along the river bed of Manshad basin in Yazd Province has significant effects on distress and exacerbation of flood risk. In many cases، the width of main channel is less than the allowable width of the bed and the floods with return period less than 25 years were limited. Under existing regulations، the bed widths based 25-years floods as river limits is necessary. As results، average bed width range in main channel is 8. 07 meters. The bed of Manshad River is 1. 2 meters is higher than the natural or initial condition. For passing a 25-yr flood، the width of Manshad River should be broader to 12. 8 meters. It''s suggested for offloading flood quickly from Manshad basin، cross structure and retaining walls should be destroyed. Also، to reducing the risk of damage and natural disasters، with acceptance of only 5% risk، should not allow any construction at a distance of 25 meters from the river Tallweg.