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The Galveston Bay Watershed

Galveston Bay and the land around it fit the concept of a watershed. A watershed is the area of land that drains into a water body. In the case of Galveston Bay, the watershed comprises all of the watersheds of the tributaries—the Trinity River, the San Jacinto River and all of the creeks and bayous that feed into the rivers or directly into the bay, plus a small area of adjacent land that drains directly into the bay.

All of the changes that humans make to the land surface and the stormwater drainage system alter the dynamics of water flow through the Galveston Bay watershed. So much land is covered by buildings and roads that it is much less likely for a raindrop to soak into the ground now than 100 years ago. It is likely that the water moving to the bay will carry dissolved or suspended pollutants or debris. Small tributaries to the bay now tend to have more highly variable flows because there are fewer acres of wetlands to hold and slowly release stormwater. Many areas have drainage ditches or channelized bayous that are designed to move water quickly to the bay.

In contrast, the major river tributaries have been dammed as water supplies and have more uniform flows than in the past. The San Jacinto River has 2 major reservoirs: Lake Houston resulted from a dam across the East San Jacinto River in 1953; Lake Conroe, on the West San Jacinto River, was completed in 1973. The Trinity River has several reservoirs along its length, but the most important for the dynamics of Galveston Bay is Lake Livingston- the one farthest downstream, completed in 1969. These reservoirs change the dynamics of runoff and inflow in the Galveston Bay watershed.

The network of smaller water bodies has also been altered in the Galveston Bay watershed over the last century. Travel across the prairie was very difficult in the 19th century. Agriculture was also challenging due to the periodic wetland nature of much of the land. The solution of developers and agriculturists was to dig drainage channels, which still exist, and produce much more rapid runoff than the natural landscape. The Harris County Flood Control District estimates that about 800 miles of natural drainage channels existed in the county before human modification (HCFCD 2009). At the present time there are more than 2,500 miles of channel in Harris County’s drainage system.

Watersheds in the Galveston Bay system take many shapes and sizes, with smaller watersheds nested within larger ones. Residential, industrial and agricultural lands all reside within these watersheds. Land-based activities often diminish the quality of water within the watershed. Fertilizers and pesticides from lawns, herbicides from fields, and oil and grease from roads and parking lots can progress from the land into the water when transported via surface runoff. In recent years, water management strategies have begun to follow a watershed approach to address these nonpoint sources of water pollution.


Literature Cited

HCFCD. Harris County's drainage network. Harris County Flood Control District 2009 [cited 28 May 2009]. Available from

NOAA. 2006. "Gulf Coast Land Cover." Web PageNational Oceanic and Atmospheric Administration (NOAA), Coastal Services Center, Coastal Change Analysis Program (C-CAP), from




Related Pages:

Water and Sediment Quality
Water Quantity
Oil Spills


Watershed Map Map depicting the entire Galveston Bay Watershed extending from the Gulf of Mexico to the Dallas–Fort Worth metroplex. The Lower Galveston Bay Watershed is in dark orange. Image source: Houston Advanced Research Center. Map depicting the entire Galveston Bay Watershed extending from the Gulf of Mexico to the Dallas–Fort Worth metroplex. Image source: Houston Advanced Research Center.



Developed Land in Lower Galveston Bay Watershed Map of developed land in the Lower Galveston Bay watershed. Data source Coastal Change Analysis Program (NOAA 2006).

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