Project Overview

This project builds upon the efforts and studies performed for the development of the Update to the Arroyo Colorado Watershed Protection Plan. The update identifies the restoration of the Llano Grande Lake as a key implementation measure to achieve water quality standards. Originally, the lake was 8-10 feet deep with an upwelling natural spring. It acted as a silt trap as flow slowed. When the International Boundary Water Commission (IBWC) stopped dredging in the 1960s, the lake began to silt in, causing an associated decline in water quality. The Arroyo Colorado Habitat Work Group concluded that dredging the lake to its original depth and restoring groundwater flow will improve water quality. A hydraulic analysis by IBWC for a vulnerable portion of the Arroyo Colorado in Harlingen made recommendations on ways to slow flooding and siltation, including upstream detention. Modeling shows that the Llano Grande Lake Restoration will provide more capacity and restore native deep-water habitat to accomplish stakeholder goals.