Flood Analysis and Mitigation Strategies in the Santa Catarina Watershed

The increasingly recurrent extraordinary flood events in the city of Monterrey, Mexico have led to stakeholder interest in understanding the hydrologic response of the Santa Catarina River watershed to these high intensity events. This study analyzes two flood mitigation strategies proposed by stakeholders through a participatory engagement process and assessed using two hydrological models: The Hydrological Modeling System (HEC-HMS) from the US Army Corps of Engineers and the TIN-Based Real-time Integrated Simulator (tRIBS). The first strategy consists on strategically placing small dams in the upper part of the watershed. The topography in the upper basin is complex and therefore requires some planning to select the locations in which to place these flood control structures. To analyze the impacts of this strategy, we utilize the official HEC-HMS model application of the National Water Commission of Mexico (CONAGUA) to simulate the flood event caused by Hurricane Alex in July 2010, calibrated with streamflow data from CONAGUA and forced with a meteorological scenario based on local rain gauge observations. To further analyze the subset of locations selected for the inclusion of a reservoir we moved to a higher resolution model (tRIBS) that allows to capture the spatial variability of rainfall using a satellite-based product from the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) data. We adjusted this data with rain gauge observations using a mean-field bias correction and created a new meteorological forcing scenario. Additionally, we implemented a new reservoir algorithm in the higher resolution model to mimic conditions in the official CONAGUA simulations. The second strategy consists of reforestation activities within priority conservation areas in the upstream part of the watershed where the majority of the discharges that go into the Santa Catarina River are generated. For this mitigation strategy, we utilize both models to simulate the flood event under the aforementioned forcing scenarios. We take into account the topography, soil types, geology, land use and current vegetation cover in the basin. The CONAGUA model uses a CN number to determine the infiltration of each subbasin while tRIBS uses the hydraulic conductivity for each type of soil found within the basin. To compare the infiltration capacity of the models, a study that determined their saturated hydraulic conductivities was done and the results yielded consistent values between the models.  Finally, we consider some hybrid settings combining reservoirs and reforestation in these management areas. Comparison of the two modeling approaches is intended to complement the analysis of available observations for the flood event and provide a framework within which to derive a multimodel approach for stakeholder driven solutions.