Water Resources Research Act Program

Details for Project ID 2008CO199S

Development of a Correction Function for the 3-Inch, Thin-Walled, Helley-Smith Sampler Deployed on Coarse Gravel Beds

Institute: Colorado
USGS Grant Number: 08HQGR0142
Year Established: 2008 Start Date: 2008-07-01 End Date: 2009-07-31
Total Federal Funds: $0 Total Non-Federal Funds: Not available

Principal Investigators: Steven Abt, Kristin Bunte

Project Summary: Kristin Bunte in collaboration with Steve Abt, both at Colorado State University, will review existing data sets of bedload transport rates for coarse gravel bedded mountain streams where samples were collected at approximately the same time with both a thin-walled Helley- Smith bedload sampler and a bedload trap developed by Bunte. The purpose of the review is to develop a numerical correction function for data collected with the Helley-Smith bedload sampler. A Helley-Smith type bedload sampler is often used for measuring transport in coarse gravel-bed streams. However, transport rates and bedload particle sizes obtained from Helley-Smith samplers can be biased. Although bias of transport rates measured with Helley-Smith type samples is generally known, Helley-Smith type samplers are currently used for a wide range of applications (e.g., river restoration; monitoring changes in sediment supply) as well as basic research (e.g., bedload dynamics, relationships between transport and flow, incipient motion studies). Alternative samplers that are equally inexpensive and easy to use and do not require wadeable flows are not available. The uncorrected use of biased transport rates measured with a Helley-Smith thin-walled sampler has a variety of detrimental consequences, such as endangering the outcome of river restoration projects and causing misleading conclusions to be drawn about bedload transport dynamics and incipient motion conditions. The correction function derived from this study could serve to reappraise existing data sets as well as improve the accuracy of current Helley-Smith measurements undertaken in river restoration projects. Implementation of a correction function that renders transport rates and bedload particle size measured with Helley-Smith samplers less biased would greatly improve the credibility of historical bedload data sets in which thin-walled Helley-Smith samplers were used to collect samples in coarse gravel-bed streams. The need and proposed work has been endorsed by the Federal Interagency Sedimentation Project (FISP) Technical Committee which is composed of representatives from the U.S. Geological Survey, U.S.D.A. Forest Service, U.S.D.A. Agricultural Research Service, U.S. Bureau of Land Management, U.S. Army Crop of Engineers, U.S. Bureau of Reclamation, and the U.S. Environmental Protection Agency. The work will be divided in three phases. Phase I will result in the data gathering from existing data sets, collected by the researchers during the past 10 years. Phase II will include data analysis, including sorting, stratification, evaluation, transformation, and the development of a correction function. Phase II work will also clarify whether the correction comprises a single function for gravel bedload or separate functions for each bedload size class and whether correction functions vary with streambed characteristics. Phase III results in the completion of a FISP final report that includes the data sets used in the study and the correction function or functions for relating thin walled Helley-Smith data to bedload-trap data. Criteria for acceptance of the report is that the report meets the format as supplied by FISP and that it is completed by established delivery date.