Thomas A. Black

Sediment production from forest roads in western Oregon

Prevention and estimation of soil erosion from forest roads requires an understanding of how road design and maintenance affect sediment production. Seventy- four plots were installed on forest roads in the Oregon Coast Range to examine the relationship between sediment production and road attributes such as distance between culverts, road slope, soil texture, and cutslope height. An additional comparison was made between road segments with cutslopes and ditches freshly cleared of vegetation and segments with established vegetation on cutslopes and in ditches. All road segments were 5 m wide and insloped with aggregate surfacing, light traffic, and no overhanging forest cover. Sediment production was correlated to the product of segment length times road slope squared. Sediment production from aggregate covered roads on a silty clay loam was about 9 times greater than that from roads constructed on a gravelly loam. Sediment production was not correlated to the cutslope height. Road segments where vegetation was cleared from the cutslope and ditch produced about 7 times as much sediment as road segments where vegetation was retained, showing the potential reduction in erosion by revegetation following construction and the potential impact of ditch cleaning during maintenance. Relationships and estimates from this study provide a basis for improved erosion estimates by commonly used empirical procedures.

MODELING EROSION FROM INSLOPING LOW-VOLUME ROADS WITH WEPP WATERSHED MODEL

Low-volume roads can be a major source of sediment to streams in forest watersheds. For soil erosion from roads to be economically mitigated, the processes that cause erosion need to be understood. The Water Erosion Prediction Project (WEPP), a physically based erosion and sedimentation model, was used for predicting erosion from forest roads that can be described as hillslopes. Watershed applications of WEPP predicted erosion and sedimentation values for insloping roads that can be described as microwatersheds. How well WEPP models insloping roads through a sensitivity analysis and validation process using two studies in the Oregon Coast Range is discussed.

Measuring water and sediment discharge from a road plot with a settling basin and tipping bucket

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.

The Geomorphic Road Analysis and Inventory Package (GRAIP) Volume 1: Data Collection Method

An important first step in managing forest roads for improved water quality and aquatic habitat is the performance of an inventory. The Geomorphic Roads Analysis and Inventory Package (GRAIP) was developed as a tool for making a comprehensive inventory and analysis of the effects of forest roads on watersheds. This manual describes the data collection and process of a GRAIP road inventory study using GRAIP v. 1.0.8 and the field data dictionary INVENT 5.0. The GRAIP model uses field data collected with a GPS and a specific data dictionary using drop-down menus that is designed to be imported into an ArcGIS model. The inventory data are used to describe the road-stream sediment delivery and hydrologic connectivity; gully, landslide, and stream crossing failure locations and risk; and the condition of the existing road drainage network. Point data are collected for each point where the road water leaves the road surface describing the stream connection, condition, and discharge location of the drainage feature. Detailed information is collected at stream crossings to allow for risk assessment of blockage by woody debris and sediment, as well as the potential for flow diversion. For the road, data are collected as a line describing the locations of flowing water, flow path vegetation, surface type, and the condition of the flow paths and road surface. Point data are also collected for each gully and landslide, as well as for photos, gates, and other features. This document describes the field process as well as each feature in the data dictionary. It also addresses frequently asked questions and specialized field processes used during data collection. The GRAIP road inventory and model work together to provide a flexible tool box to quantify the impacts of roads on watersheds and aquatic systems.Related website: http://www.fs.fed.us/GRAIP/index.shtml

The Geomorphic Road Analysis and Inventory Package (GRAIP) Volume 2: Office Procedures

An important first step in managing forest roads for improved water quality and aquatic habitat is the performance of an inventory. The Geomorphic Roads Analysis and Inventory Package (GRAIP) was developed as a tool for making a comprehensive inventory and analysis of the effects of forest roads on watersheds. This manual describes the data analysis and process of a GRAIP road inventory study using GRAIP v. 1.0.8 and the field data dictionary INVENT 5.0. GRAIP uses field data collected with a GPS and a specific data dictionary that is imported into ArcGIS as shapefiles. The data are corrected and then run through the GRAIP toolbar, which also uses inputs from TauDEM (for stream network delineation) and SINMAP (for landslide risk). GRAIP estimates the quantity of sediment generated for each road segment by modifying a base erosion rate with road slope, segment length, flow path vegetation, and road surface type. The sediment at each drain point is routed to the stream network based on field observations of delivery, and output as accumulated sediment in the entire network, direct sediment for each stream segment, and specific sediment per unit contributing area. Observations of delivery at each drainage feature can also be used to calculate road-stream hydrologic connectivity. GRAIP calculates landslide risk associated with additional water from road network drainage, and gully risk using the locations of mapped gullies with the road length draining to each gully and the slope of the hillslope below each gully. Stream blocking risk is calculated using the width and entrance angle of each channel compared to the crossing culvert width and angle. This document describes each of these steps in sufficient detail that an ArcGIS user with basic skills will be able to perform the analysis. The GRAIP road inventory and model work together to provide a flexible tool box to quantify the impacts of roads on watersheds and aquatic systems.Related website: http://www.fs.fed.us/GRAIP/index.shtmlGRAIP Manual - Volume 2 - Office Procedures - 1.0.9 ADDENDUM (2014): This update to the office manual is necessary for use with the latest version of the GRAIP software, 1.0.9. Use it alongside the full office manual. If you are a new user, it is a good idea to skim the office manual and then the addendum so that you know which parts of the office manual are replaced by the addendum. Some procedures are different in 1.0.9.