Hydrologic Modeling and Flood Frequency Analysis of the Sonora River Watershed in Sonora, Northwest Mexico

The state of Sonora is located in northwest Mexico and shares its border with the states of Arizona and New Mexico. Approximately 95% of Sonora is described as arid or semiarid. Precipitation across the state averages 437 mm per year; however, the most arid areas average less than 100 mm of rainfall annually. Sonora's climate is recognized as having a bi-seasonal rainfall pattern, characterized by frequent periods of little or no rainfall followed by periods of heavy rainfall, especially in the summer months of July and September. These periods of drought develop land cover and soil conditions that are conducive to heavy flash flooding during the rainy months, followed by quick recession of flood waters and a return to dry conditions and low streamflows. The high degree of climatic variability has presented serious challenges to water resource planning and management in Sonora. Further, recent drought conditions have led to an almost complete reliance on groundwater sources to meet the needs of the growing population. The goals of this study are to develop an understanding of how different meteorological events impact streamflow in the study area, how changes in land use and development in the Sonora River basin might impact streamflow, and to better characterize streamflow behavior through various statistical approaches on flood flow data dating from 1942 to 2002. More specifically, a hydrologic model of the area of interest was developed and calibrated using the U.S. Army Corps of Engineers' HEC/HMS version 3.1.0 watershed modeling software, and an array of future development scenarios was simulated in order to predict the impacts to streamflow in the basin as a result of these changes. The work of this study also involved the collection and analysis of an extensive set of geographic data of the region, as well as a detailed flood frequency analysis of 58 years of peak annual flow data in order to select an extreme value distribution to model the river's behavior and predict flood quantiles.