Bureau of Reclamation Automated Modified Einstein Procedure (BORAMEP)
The objective of this Science and Technology (S&T) Program research project is to create a personal computer application that automates the process of computing multiple total sediment discharges using the modified Einstein procedure (MEP) for computing total sediment load as presented by Colby and Hembree in 1955 and revised by Reclamation in 1966.
Examples of studies where computation of total sediment load is important include: assessments of channel stability and migration, channel aggradation, degradation or scour, reservoir lifespan, levee failure risk, dam decommissioning studies, and canal dredging volumes. BORAMEP would improve and extend the capabilities of the existing single-sample tool PSANDS by standardizing and increasing the efficiency of the MEP computations as currently used by Reclamation. The new tool would be applicable to a wide range of flow and sediment conditions and provide information to identify areas where additional research might be needed.
Need and Benefit
Developing a reliable and consistent method of computing total sediment discharge in open channels is an important practical objective of research in fluvial processes. The movement of sediment in an alluvial stream is complex and the ability to calculate the amount of sediment being transported by a given flow can be very complicated. The quantity of sediment discharge is fundamental to analyses of channel bank stability and migration, channel aggradation, degradation or scour, reservoir lifespan, levee failure risk, dam decommissioning, etc.
An improved tool to compute total sediment discharge by the modified Einstein procedure (MEP) with expanded capabilities can help conserve existing water supplies or avoid water conflicts by:
* Potentially reducing the risk of levee, bridge, or road failure from migrating channels, canal or siphon failures, the loss of habitat from channel incision or planform conversion
* Providing improved estimates of reservoir life and capacities through more detailed analyses at lower costs
Current techniques for suspended sediment collection do not allow sampling throughout the entire depth of flow and so the concentration and particle size distribution in only part of the flow can be determined from the suspended-sediment samples. The unsampled flow near the streambed usually contains higher concentrations and coarser particle-size distributions than the flow in the sampled zone. The sediment discharge computed from suspended sediment samples is called measured load, and the difference between the total load and the measured load is called the unmeasured load. Ratios of unmeasured load and the measured load are highly variable from stream to stream, cross section to cross section, and from time to time at a given cross section. They can vary with depth, velocity, sediment concentrations, particle size of the suspended and bed sediments, and other factors. The unmeasured load is composed mostly of sand or coarser sediments, and knowledge of the rate of discharge of sediment of these larger sizes is often more helpful in design and other problems than knowledge of the rate of discharge of the fine sediment. As a result, a method of computing sediment discharge in the unmeasured zone is of great importance.
The MEP is widely used by engineers and water resource managers. It requires a great deal of experience and judgment to obtain reliable results and often the results are not easily replicated by multiple users. Computations are made for several ranges of particle sizes and involve many variables resulting in a very complex process of computing total sediment load. Time to calculate one sample by hand averaged three hours.
In 1966, Reclamation revised the method for computation of Z values used in the MEP and automated it for single sampled reducing time to four samples per hour. This modification requires user input to select the sediment size classes to be used in the calculation. More representative total load calculations are the result for the experienced user, but repeatability by multiple users is reduced.
The MEP uses data collected during routine U.S. Geological Survey (USGS) field observations that may occur bimonthly at a gauged site with periods of record extending back to the 1960s. This volume of data explains the need for a tool to process multiple samples on a personal computer. BORAMEP meets that need, standardizes results, and reduces calculation time to about 2,000 samples per hour. The tool allows engineering judgment by calculating results for all possible samples but calls attention to those that may be questionable. This cost effective automated method of computing total sediment discharge for a given reach that can be reproduced by numerous users could be distributed as an electronic S&T bulletin.
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