Feature Results The HAR method described here produced maps that were smoother, easier to interpret, and required less time to produce than ones created using comparable one-dimensional methods. All calculations were performed using ArcGIS and the Spatial Analyst extension and did not require fieldwork. The kernel size can be adjusted to vary the extent and smoothness of the height-above-river map. Larger kernel sizes incorporate longer stretches of the river into the calculation allowing greater mapping extent and a smoother surface. A smaller kernel size results in a smaller extent but more detailed and more precise estimates. Estimates appear to be most accurate along low-gradient stretches of the river with few tributaries. These are precisely the same areas where a typical low-resolution DEM would have the most difficulty detecting subtle changes in elevation. Stretches of river with a nonlinear gradient and tributaries with strongly differing gradients are likely to produce less accurate results. HAR and flood height were incorporated into statistical models to predict the distribution of vegetation communities within the Walker River Basin. When predicting the 10 major vegetation communities in the basin, HAR and flood height were the first and second most important predictor variables. Wetland vegetation and communities The figure on the left shows cross sections that have been generated perpendicular to the river crossing the river channel every 10 meters. The figure on the right shows horizontal cross sections that are generated every 10 meters. Both figures illustrate the problems with automated methods of generating cross sections. On the left, large gaps are left in areas where coverage of cross sections is poor. Where cross sections come close to one another, values can differ greatly because they refer to different parts of the river. On the right, the cross sections can intersect the river in more than one location. dependent on frequent flooding exhibited the lowest HAR values, while communities that tended to be located farther from the river but were still dependent on groundwater exhibited higher HAR values. Upland communities able to tolerate low water tables had the highest HAR values. Future Directions As restoration efforts move forward for the Walker River Basin, HAR and flood height maps will be incorporated into a decision support system that helps land managers identify low-lying areas that can be reconnected to the river channel. Using HAR and flood height maps Continued on page 20 www.esri.com ArcUser Winter 2010 19