There are about 310 miles of open streams within the watershed, including the primary streams and tributary channels. Based on the 2010 U.S. Census, the estimated population of the Harris County portion of the San Jacinto River watershed is 197,570.
The San Jacinto River flows from its headwaters near Huntsville, through Lake Conroe and Lake Houston. Lake Houston was developed as a water supply reservoir and therefore does not provide significant storage during flood events. The Port of Houston Authority operates the Houston Ship Channel, which originates at the Turning Basin and follows the original alignment of Buffalo Bayou to the San Jacinto River. The Ship Channel continues through the San Jacinto River and San Jacinto Bay to Galveston Bay, which is the ultimate outfall for all drainage in Harris County.
Structural flooding has occurred in low-lying areas adjacent to the water bodies. However, water surface elevations in the Houston Ship Channel, the San Jacinto River and Galveston Bay are not affected by the flow from any single watershed. These waterways are tidally influenced and can be affected by storm surge.