GRAIP_Lite uses DEMs, already existing road GIS layers with surfacing type information, and a small field calibration dataset to determine 6th code subwatershed scale road sediment production and delivery. Road layers are broken into GRAIP-style segments. Production is calculated in the usual GRAIP way, and delivery is based on the flow distance from the road to the stream and the calibrated probability of delivery at that distance. GRAIP_Lite is good at narrowing a large potential project area to the smaller watersheds with the most sediment problems.
Though GRAIP and GRAIP_Lite share some elements, the two models are not equivalent. GRAIP is used to inventory and analyze forest roads at a fine road-segment scale, and utilizes an intensive field inventory to accomplish this. GRAIP results are spatially explicit within a few meters and can be used to locate, prioritize, analyze, and monitor specific road treatments. Because GRAIP is so comprehensive, the time investment often prohibits its application it on a scale wider than a 5th code watershed at a time.
GRAIP_Lite uses the same principles as GRAIP to determine broad-scale road surface sediment risks over a much wider area very quickly, and is used as a tool to determine where the largest problems likely occur on a 6th code subwatershed scale. Further work such as a full GRAIP inventory can then be applied in order to find the specific locations within the subwatershed that have problems that should be addressed. There is a minimal field component (to gather a calibration dataset), but most of the modeling uses existing datasets and can be completed in the office.
We suggest that you start in your areas of critical concern. In Oregon, Washington, and Idaho we are focused on roads impacting aquatic habitat for endangered fish species. We have worked on watersheds that are on the 303(d) list due to elevated fine sediment input. Other regions have concerns about road related landslides and gullies, post-fire effects and restoration, or decommissioning un-needed roads. GRAIP_Lite can help determine which watersheds in a larger area are likely to be most impacted by road surface fine sediment.
GRAIP_Lite is a GIS tool for predicting the sediment delivery from forest roads to streams using minimal field data. The required inputs are a road line and a DEM. The model is a component of ArcHydro and runs in ArcGIS 10.3 and higher.
GRAIP_lite was developed by Charlie Luce, Nathan Nelson and Tom Black at the US Forest Service Rocky Mountain Research Station and Christine Dartiguenave and Dean Djokic at ESRI. The development of the software was made possible by support from the Environmental Protection Agency.
GRAIP_Lite is a streamlined and efficient way to predict road sediment impacts across watersheds and larger areas when field data are limited. If you need to model site specific road impacts on smaller project areas where field data can be applied, then the GRAIP tool set may be more appropriate.
Below are useful resources to help assist in gathering information about past, present, or planned GRAIP_Lite projects: