Measuring Water and Sediment Discharge From a Road Plot With a Settling Basin and Tipping Bucket Thomas A. Black and Charles H. Luce United States Department of Agriculture / Forest Service Rocky Mountain Research Station General Technical Report RMRS-GTR-287 June 2013 Black, Thomas A. and Luce, Charles H. 2013. Measuring water and sediment dis- charge from a road plot with a settling basin and tipping bucket. Gen. Tech. Rep. RMRS-GTR-287. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 38 p. Abstract A simple empirical method quantifies water and sediment production from a forest road surface, and is well suited for calibration and validation of road sediment models. To apply this quantitative method, the hydrologic technician installs bordered plots on existing typical road segments and measures coarse sediment production in a settling tank. When a tipping bucket gauge and a flow splitting device are added to the installation, both coarse and fine sediment can be collected along with a continuous discharge record. Included in this report is the design of a simple and inexpensive tipping bucket system and the procedures for measuring plot discharge up to 60 gal (227 L) per minute. Keywords: fine sediment monitoring, sediment budget, road sediment, road runoff, road discharge, non-point source sediment, effectiveness monitoring, sediment trap, tipping bucket The Authors Thomas A. Black is a Hydrologist with the USDA Forest Service, Rocky Mountain Research Station in Boise, Idaho. He completed a B.A. degree in Geography from the University of California and an M.A. degree in Geography from the University of Colorado. Charles H. Luce is a Research Hydrologist with the USDA Forest Service, Rocky Mountain Research Station in Boise, Idaho. He completed a B.S. degree in Forest Management at the University of Washington, an M.S. degree in Forest Hydrology at the University of Washington, and a Ph.D. in Civil Engineering at Utah State University. Acknowledgments We appreciate those who have helped us further the understanding of road sediment over the years including our partners at the Bureau of Land Management and the Environmental Protection Agency. Barry Williams, Cliff Fanning, Rosy Mazaika, Mike Turaski, Lee Woodruff and Eric Monschein. Debora Hennessy, Richard Cissel, Nathan Nelson, Aaron Prussian, and Robert Hassmiller provided helpful input and reviews of this document. A special thanks to David Watts, Mike Dewey, Amy Lichter, Bernie Reilly, Dennis Fletcher, and Mike Green and all of the others who have helped carry the load to move this effort forward. You may order additional copies of this publication by sending your mailing information in label form through one of the following media. Please specify the publication title and number. Publishing Services Telephone (970) 498-1392 FAX (970) 498-1122 E-mail [email protected] Web site http://www.fs.fed.us/rmrs Mailing Address Publications Distribution Rocky Mountain Research Station 240 West Prospect Road Fort Collins, CO 80526 Contents Introduction .............................................................................................................. 1 Previously Used Data Collection Methods............................................................ 5 Sediment Production .................................................................................... 5 Measurements of Discharge ......................................................................... 6 Road Plot System with Settling Basin and Tipping Bucket ................................ 7 Site Selection ................................................................................................ 7 How Many Plots? .......................................................................................... 7 Sediment Plot Construction Details ............................................................ 10 Plot Maintenance ........................................................................................ 14 Methods of Sediment Measurement .................................................................... 14 Tripod Method............................................................................................. 14 Crane Method ............................................................................................. 17 Tipping Bucket System for Flow and Fine Sediment Measurement ................. 23 Design Overview.................................................................................................... 24 Designs and Costs ..................................................................................... 26 Installation .................................................................................................. 29 Calibration .................................................................................................. 30 Maintenance and Data Collection ............................................................... 30 Fine Sediment Collection ............................................................................ 32 Summary ................................................................................................................ 32 References ............................................................................................................. 33 Appendix A: Road Sediment Plot Field Sheet .................................................... 37 Appendix B: Density of Pure Water ..................................................................... 38 The use of trade or firm names in this publication is for reader information and does not imply endorsement of any product or service by any of the organizations represented here. Measuring Water and Sediment Discharge From a Road Plot With A Settling Basin and Tipping Bucket Thomas A. Black and Charles H. Luce Introduction ______________________________________________________ Forest road runoff and fine sediment delivery are widely acknowledged to have seri- ous impacts on aquatic ecosystems (Cederholm and other 1981; Platts and other 1989; Thurow and Burns 1992; Lee and others 1997; Luce and Wemple 2001). Roads influ- ence a variety of watershed processes, including sediment production (Megahan and Kidd 1972; Reid and Dunne 1984; Bilby and others 1989; Luce and Black 1999, 2001a; MacDonald and others 2001), hydrologic event timing (Wemple and others 1996; Jones and Grant 1996), and slope stability (Sessions and others 1987; Montgomery 1994). As a consequence, water quality regulations and cumulative effects modeling of forest management have frequently focused on forest roads. Land managers and watershed specialists use models to predict sediment delivery from forest roads. Several empirical models are used to evaluate road sediment risks, but are limited by a lack of calibration data. For example, the R1-R4 model (Cline and others 1984) predicts sediment production in western cordilleran watersheds; however, its derivatives rely on a data set measured in the 1960s and 1970s in the Idaho Batholith. Developments since then have used results from other studies to parameterize the effects of various road treatments (Washington Forest Practices Board 1993; NCASI 2003), but interpolating the data results to new and unique geology, precipitation, and design standards still often relies on professional judgment. Physically based erosion models predict the amount of water discharge and road sedi- ment transport using physical equations and a particular configuration of input variables. WEPP (Elliot and others 1999) and DHSVM (Wigmosta and others 2001, 2002; Doten and others 2006) are two examples of the physically based erosion models. One of the theoretical promises of physically based models in contrast to empirical models is being able to define significant variables or parameters that can work across many different precipitation regimes and soils. There are many parameters in physically based models such as hydraulic conductivity and soil erodibility, many of which cannot be measured directly but are derived from observations of outputs under varying inputs. While tools like rainfall simulation may be helpful for smaller scales or components of a road system (e.g. Luce and Cundy 1994), finding the effective parameters for a whole road segment with all of its spatial variability and multiple water pathways (Luce 2002) requires observations of erosion under real precipitation and snowmelt events. Put succinctly, these parameters need calibration at the scale of the typical road segment (sidebar 1). USDA Forest Service Gen. Tech. Rep. RMRS-GTR-287. 2013 1 Outside of the context of modeling road impacts, land managers, engineers, and regu- lators want better information about how new designs, materials, or methods might help prevent erosion or delivery of sediment. While a general understanding of erosion and transport process can guide the design and estimated effectiveness of new approaches, observations of how treatments affect erosion (e.g. with a before-after control-impact design) are the most objective ways to assess treatment effectiveness. While adaptive management is an expressed ideal for both managers and regulators, high quality obser- vations are required, and costs for acquiring data can be a barrier to rigorous learning. While the value of data on road erosion and runoff is clear for model calibration and adaptive design, relatively inexpensive yet reliable methods for systematically collecting road erosion data have not been described with much