Computer Design of Lateral Weirs System for Irrigation on Vegetative Strips

Abstract

Jobos Bay National Estuarine Research Reserve (JBNERR) is located at the south eastern coast of Puerto Rico. The reserve includes subtropical forests, mangrove forests, coral reefs, seagrass beds, salt and mud flats, lagoons and freshwater wetlands. Mar Negro wetland is the biggest mangrove forest in the area, located at the south boundary of JBNERR. The north side of the Reserve has been used for agricultural activities since the Spanish Colonial times. Since 1993 the mangrove population started to diminish. Its mortality was promoted by antropogenic activities such as deforestation, domestic sewage discharging into the mangrove lagoon, change of hydrologic patterns caused by urban developments and agricultural practices. During the decade of 1990 intensive agricultural activities north of the reserve caused a negative impact on mangroves. Pesticides, fertilizers and chicken manure applied in agricultural fields were being discharged directly into de mangrove forest, mainly through two drainage earth channels. The objectives of this project were: 1) To model the hydrologic conditions existing north of JBNERR, 2) Hydraulic design of side-weirs along channels to promote uniform distribution of irrigation water from agricultural activities and runoff. Water discharges into a vegetative strip before discharging into Mar Negro. The hydraulic analysis was performed using ArcGIS, in-house computer models and, EPA’s Storm Water Management Model (SWMM). The hydraulic design resulted in an innovative system of lateral weirs which distribute water uniformly along the vegetative strip. This water distribution system controls surface runoff from irrigation and rainfall, reduces surface erosion and improves the quality of overland flows discharging into Jobos Bay.