A Natural Channel Vs. Natural Channel Design: A Case Study in the San Antonio River, Bexar County, Texas

In 1998, the San Antonio River Authority began the San Antonio River Improvements Project (SARIP), a $384.1 million investment in flood control, recreational improvements and ecosystem restoration; in total, 20.9 km of the river were restored.  The uppermost section of the river not directly impacted by the SARIP is a 0.72 km stretch of the original channel referred to as the San Juan Remnant Channel (SJRC).  This natural stretch of river runs parallel to the modified main stem, providing a unique point of comparison for the ecological restoration.  Mussel surveys in the SJRC have resulted in three species observed, including golden orb (Quadrula aurea), a candidate species for listing under the Endangered Species Act; surveys on the main stem have resulted in no live individuals.  Average nekton Index of Biotic Integrity (IBI) scores from the SJRC from 2010-2015 were 41.3 compared to 32.4 in the main stem.  Benthic macroinvertebrate communities in the main stem have been frequently disturbed over the past six years but consistently achieved higher Rapid Bioassessment IBI scores.  Due to the stream restoration efforts on the main stem, Habitat Quality Index (HQI) scores have consistently been greater than those in the SJRC despite frequent instream cover removal.