Introduction

The hydraulic geometry of channels has conventionally been measured in the field by wading with survey equipment. Obviously, this method requires legal access to a stream. Such surveys are also labor-intensive, time-consuming, expensive and dangerous in some flow conditions. As a result, field surveys are usually infrequent, done in low-flow conditions, and limited to reach-scale channel lengths; normally less than 500 m long. Often the argument is made, also often with limited supporting evidence, that these occasional measurements of local topographic sample sites well represent some larger channel domain.

New remote sensing techniques, such as airborne water-penetrating Light Detection and Ranging (LiDAR) and passive optical sensors, or boat-mounted multi-beam acoustic instruments, are frequently capable of producing very accurate Digital Elevation Models (DEMs). These remote surveys also can have spatial extents much greater than the reach-scale accessible by field methods and now routinely map tens- to hundreds-of-kilometers of channel length. It is difficult to completely exploit these extensive DEMs by manually measuring channel characteristics at a few locations.

The US Forest Service, Rocky Mountain Research Station, Boise, Idaho, has contracted ESSA Technologies Ltd. to develop the River Bathymetry Toolkit (RBT), a suite of GIS tools designed to interpret high-resolution DEMs of channels with a minimum of manual data manipulation. Users will ultimately be able to employ the RBT to characterize both in-stream channel geometry and aquatic habitat and floodplain geomorphology.

Currently the RBT has tools for calculating the bankfull polygon and centerline, and for cutting cross sections through the channel to extract hydraulic parameters such as wetted area, bankfull width and hydraulic radius. Cross sections can be explored as profiles or using a longitudinal viewer. Cross section properties can also be saved as a ShapeFile and then added to a map. Calculations for stream gradient and sinuosity have also been automated.

An automated detrending algorithm removes the overall valley slope from the DEM, allowing for rapid assessment of flooding as flow moves out of the channel and into the floodplain. Tools still under development will use the detrended DEM to investigate "off-channel" aquatic habitat conditions during any given discharge or water stage in the main channel.

For more information about the River Bathymetry Toolkit, including a list of related publications, please visit the ESSA Technologies Ltd. web site (http://www.essa.com/tools/RBT/highlight.html).