干旱区生态环境知识资源中心

Delineation of Ordinary High Water (OHW) under the Clean Water Act (CWA) is based on the use of physical features that represent "ordinary" levels of ponding or flowing waters. On and western United States playas, where the climate is an unevenly distributed series of precipitation events that are spread over many years, the use of surface water monitoring can be limiting due to occasional years with almost no hydrological information. To substitute for a general lack of monitored surface water conditions, we used processed satellite images and precise topographic modeling to determine ponded water areas. To test the reliability of select field indicators for delineation purposes, we used a two-phase field test on a hard playa in the Mojave Desert, California. First, we verified that ponded water was associated with these playa surface features. Then, to test the statistical reliability of these surface features, we developed a decile ponding zone map by stacking processed satellite imagery, collected detailed laser altimetry (LiDAR) elevation data, sampled surface features occurring in the various decile zones, and developed reliability statements for these OHW delineation features. These field indicators represent surface features that have developed over a series of years representing the wetter portion of the El Nino climatic cycle.