Watersheds
The San Antonio–Nueces Coastal Basin, shown in the map below, consists mainly of flatland. The soil in the area is mostly sandy and porous. Rainfall that collects in this area drains into the Gulf of Mexico by a series of waterways.
The San Antonio–Nueces Coastal Basin is one of more than 20 major watersheds in Texas. A watershed is a geographic area that drains water collected on its surface. Watersheds provide a way for water to move from areas of higher elevation to areas of lower elevation. Sediment and dissolved materials are also moved to lower elevations.
Rivers and streams form a general pattern within a watershed. The map shows this general pattern within the San Antonio–Nueces Coastal Basin. This type of pattern is called a dendritic pattern and can be observed in many natural structures, including the network of nerves in the human nervous system and branching patterns in trees.
Watersheds can change as the geography and other features of an area change. Some of the causes of change are more obvious than others. For example, the clearing of wooded areas for the construction of buildings may change the way rainfall collects and drains from an area.