*4.6. Flow Data*

Waterbody monitoring data are used to portray historical data that would represent most conditions of the study area. Flow data encompassed the volumetric flow rate for each waterway recorded from each station available. HWMD waterway flow data reflect high flow values in 2019 with a mean value of 12 CMS, and in 2018 the mean value was below 10 CMS. These levels reflect a high correlation with flooding patterns with respect to sudden storm events from those years. Moreover, the RVD flow data showed high flow values in 2018 of almost 10 CMS (Figure A1 in Appendix A). Both HWMD and RVD flow data correspond to past abnormal flooding events in the LRGV region. The region has experienced high storm events since 2018 with over 38.1 cm to 50.8 cm of rainfall causing severe flooding damage [65]. Such flooding's caused a halt to everyday functions for weeks and months because of minor to destructive varying degrees of flood damage in city roads, frontage roads, residences and businesses, and infrastructure in the LRGV region. Hidalgo, Cameron, and Willacy counties have received the Presidential Disaster Declaration in which have been determined to be the most impacted areas [66]. There are limited data for this watershed since they are only available for three years with limited monitoring campaigns. Therefore, among the three watersheds, it has been determined that the HWMD waterway has the highest flow values that affect the loadings even if the water quality concentrations are low.

The IBWCNF watershed has two stations: Mercedes and Sebastian. However, only the flow values utilized for further analysis were the ones from Sebastian since the water quality samples were obtained near that station. This finding would represent a better overview of the IBWCNF watershed behavior with respect to load concentrations. In 2017 and 2018, flow data measured were more than 10 CMS. The flow values throughout 2012 to 2020 seem to have mean values below 5 CMS, which suggests a constant uniform flow for this watershed.
