Wetland Conservation and Management for the Texas Central Coast

Water Level Management

Adding or removing a single board from
a water control structure can manipulate
water levels by 4-6 inches.

Each species of plant and wildlife adapted for living in wetlands respond differently to changes in water levels. With the aid of a water control structure, water levels in a managed wetland can be manipulated efficiently to promote specific conditions beneficial for waterfowl and other wildlife. The following sections provide recommendations for managing water levels to benefit different groups of waterfowl and wetland birds.

Migratory Waterfowl: Shallow freshwater impoundments and fallow rice fields can be managed to promote plants that produce abundant seeds desired as food by waterfowl. Annual plant communities that produce abundant crops of seed respond positively to the gradual lowering of water levels during the growing season. Generally, drawdowns should commence after the beginning of the spring migration period for waterfowl (mid-March). Water should be released slowly, over a period of 1 to 2 months. Water control structures equipped with a riser and boards can achieve a slow release by removing a single board every 1 to 2 weeks. When the unit is completely dry, treatments to disturb the soil or remove rank vegetation may be necessary (see Vegetation Management). Water control structures should be closed in late summer and early fall to begin flooding wetland units prior to the arrival of migrating waterfowl.

Mottled Ducks, Whistling Ducks and Other Wetland Birds: Mottled ducks are present year-round on the Texas Coast. They depend on freshwater and intermediate wetlands for foraging, breeding, raising young and molting feathers. Wetland impoundments and fallow rice fields can be managed for mottled ducks by maintaining shallow water (6-24 inches) from late winter through summer. Managing water levels during the growing season also provide benefits for black-bellied and fulvous whistling ducks, wading birds (egrets, herons and ibis) and waterbirds (moorhens, gallinules and rails) that reside and breed in the Central Coast region. Maintaining water levels through most of the growing season promotes emergent vegetation, such as duck potato, large spikerush and bulrush, which produce tubers and rhizomes. These underground parts are high in carbohydrates and are commonly eaten by geese and large ducks in the fall and winter.

Shorebirds: The Texas Coast is an important migration corridor and wintering area for many shorebirds. These birds feed on small aquatic invertebrates in mudflats and in water less than 6 inches deep with little or no vegetation. Wetland impoundments and fallow rice fields are ideal sites to manage for such habitat. Managing for shorebird foraging habitat on the Central Coast requires a slow drawdown (1-2 months) or allowing water to evaporate naturally during the fall through spring migration period (mid-July through May). The fall migration period is considered the most crucial for shorebirds; thus, water level management providing the most benefits for shorebirds should occur from mid-July through early November.