The Dickinson Bayou watershed encompasses a total area of 105 square miles between Houston and Galveston, lying within Galveston and Brazoria counties and including portions of the cities of Alvin, Dickinson, Friendswood, Kemah, League City, Manvel, San Leon, Santa Fe, and Texas City. The area within the watershed is about 50% developed, but significant natural and agricultural areas remain.
Dickinson Bayou is a 22.7-mile-long, slow-moving coastal stream that drains into Dickinson Bay, a subunit of the Galveston Bay system. Along most of its length the bayou is tidally influenced, while the uppermost reach, from its headwaters to 2.5 miles downstream of FM 517, is not. Dickinson Bayou has ten main tributaries: Oak Creek, Algoa Bayou, and Hickory Bayou in the portion above tidal influence and Gum Bayou, Bensons Bayou, Giesler Bayou, Bordens Gully, Cedar Creek, Hulen Park Bayou, and Arcadia Bayou in the tidal portion. Near its mouth Dickinson Bayou has a significant deep section, where the bottom of the channel dips below the level of the channel at the outlet to Dickinson Bay. This deep section affects the mixing of salt and fresh water in the bayou and the water’s flow to the bay.