Introducing Relationships to Determine the Critical Hydraulic Gradient and Non-cohesive Sediment Transport Discharge in Rock-fill dams

Rockfill dams are a type of hydraulic control structures used to protect river bed in cases where a considerable reservoir volume is available behind these structures; it could mitigate the floods and provide a gradual depletion of incoming volume of water so that the discharge passing downstream is decreased. One of the main issues on utilizing rockfill dams is to keep its permeability enough so that it could be able to pass the flow as well as the sediment load through its body during flooding, avoiding sediments resettlement inside the pores. In this regard, the design of rockfill dams should be carried out so that the available hydraulic gradient is always kept greater than the critical hydraulic gradient, which consequently results in transporting the sediment through the dam body. In this research, a relationship to estimate the critical hydraulic gradient to transport noncohesive sediment through rockfill dam body is introduced. We tested the new equation using a set of published data. Also, using laboratory data obtained from tests on a rectangular rockfill dam, performing dimensional analysis, and using linear regression, an exponential relationship between the required discharge to transport the sediments through the body of rockfill dam, the physical characteristics of rockfill dam, size of the sediments, and the hydraulic characteristics of the flow passing the dam, is prevented. When we investigated the validity of exponential relationship, we found a good accuracy for the equation indicating that the introduced relation predicts the nondimensional sediment transport capacity well.