K. A. T. Schreuders

Extraction of hydrological proximity measures from DEMs using parallel processing

Land surface topography is one of the most important terrain properties which impact hydrological, geomorphological, and ecological processes active on a landscape. In our previous efforts to develop a soil depth model based upon topographic and land cover variables, we derived a set of hydrological proximity measures (HPMs) from a Digital Elevation Model (DEM) as potential explanatory variables for soil depth. These HPMs are variations of the distance up to ridge points (cells with no incoming flow) and variations of the distance down to stream points (cells with a contributing area greater than a threshold), following the flow path. The HPMs were computed using the D-infinity flow model that apportions flow between adjacent neighbors based on the direction of steepest downward slope on the eight triangular facets constructed in a 3 x 3 grid cell window using the center cell and each pair of adjacent neighboring grid cells in turn. The D-infinity model typically results in multiple flow paths between 2 points on the topography, with the result that distances may be computed as the minimum, maximum or average of the individual flow paths. In addition, each of the HPMs, are calculated vertically, horizontally, and along the land surface. Previously, these HPMs were calculated using recursive serial algorithms which suffered from stack overflow problems when used to process large datasets, limiting the size of DEMs that could be analyzed. To overcome this limitation, we developed a message passing interface (MPI) parallel approach designed to both increase the size and speed with which these HPMs are computed. The parallel HPM algorithms spatially partition the input grid into stripes which are each assigned to separate processes for computation. Each of those processes then uses a queue data structure to order the processing of cells so that each cell is visited only once and the cross-process communications that are a standard part of MPI are handled in an efficient manner. This parallel approach allows efficient analysis of much larger DEMs than were possible using the serial recursive algorithms. The HPMs given here may also have other, more general modeling applicability in hydrology, geomorphology and ecology, and so are described here from a general perspective. In this paper, we present the definitions of the HPMs, the serial and parallel algorithms used in their computation and their potential applications.

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.