At-A-Station Temporal Variations in Flow under Drought and Flood Conditions and Associated Sediment Problems

by Muhammad Ashiq, (M.ASCE),

Document Type: Proceeding Paper

Part of: North American Water and Environment Congress & Destructive Water


The way flow variations take place with time under drought and flood conditions, in comparison with normal flow condition, has been investigated along with the related sediment transport problems caused by these variations. The river system under study was the Snake River System. It has been observed, based on mean daily flow, that for all the flow conditions (generally) the months of May and June are the highest flow months. While mean monthly flow based analysis (i.e. both for yearly based and flow condition based) proved that for the drought and flood flow conditions flow hydrographs did not follow a typical pattern, contrary to the normal and average flow conditions. Similarly, large variations in flow were also proved by the mean annual flow based analysis in which flow passed during the flood flow period was 47% compared with 36% of flow passed during the normal flow period and 17% during the drought flow period. Three models defining the relationship between flow rates under drought, flood and normal flow conditions have been developed, which can be used for determining flow rate under different flow conditions. The variations in flow conditions also affected the associated transport of total load (bed load + suspended load) that was 3% for the drought flow period and 65% for the flood period in comparison with 32% for the normal flow period. Drastic variations also took place in the bed load and suspended load proportions individually and in their proportions to the total sediment load. The ratio of suspended load to bed load increased for flows above the normal flow condition and decreased below the normal flow condition toward minimal flow rate. These large variations in sediment loads may cause problems of aggradation and degradation within the river channel and can expedite sediment deposition (problem) in an immediate downstream reservoir?that reduces the water storage capacity of a reservoir.

Subject Headings: Suspended loads | Bed loads | Sediment loads | Floods | Droughts | Flow patterns | Sediment

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