Ecohydraulics in applied river restoration: a case study in the San Marcos River, Texas, USA

The Upper San Marcos River is home to Texas wild rice (Zizania texana), an endangered aquatic macrophyte. Introduced aquatic plants Hydrilla verticillata and Hygrophila polysperma now occupy over 45% of the areal distribution. A two-dimensional hydraulic model was integrated with biological response functions for Zizania, Hydrilla, and Hygrophila to predict optimal locations for Zizania currently occupied by Hygrophila or Hydrilla. At these locations, non-native plants were manually removed and Zizania planted over approximately 20-50% of the exposed areas. Fixed grid locations were monitored bi-weekly over the next year to document plant responses. Monitoring showed a high success rate of expanding Zizania areal coverage and reductions in the non-native species distributions in restoration areas. Utilization of hydraulic modeling to direct spatially explicit aquatic plant restoration activities was shown to be an effective approach with a high success rate at identified restoration sites in the San Marcos River.