Yazoo National Wildlife Refuge - Topography

Topography

Yazoo National Wildlife Refuge's 12,941 acres (52.4 km²) of undulating Delta soils range from heavy clay to silt loam and limited sand ridges (hot spots). Most farm area is classed as prime agricultural land. Elevations range from 90 feet (27 m) in the main drainage to 113 feet (34.4 m) in agricultural areas.

Yazoo NWR's primary feature is a 4,000+ acre (16 km²) oxbow lake named Swan Lake which formed thousands of years ago when the Mississippi River abandoned a segment of riverbed. In years past, Silver Lake Bayou flowed into the oxbow lake, accelerating the deposit of silt and sediment on the lake bottom, making the lake more shallow. Recently, the Corps of Engineers constructed a new channel to divert silt-laden waters around Swan Lake. Weirs and water control structures maintain water levels in the oxbow lake while the new channel diverts silt-laden flows around the north side of Swan Lake and into Steele Bayou. The Corps project successfully prevents the accelerated build-up of sediment that has reduced water depths in Swan Lake.

The past meanderings of the Mississippi River have created a "ridge-and-swale" topography on the refuge that varies by 23 feet (7.0 m) in elevation. From 90 feet (27 m) above sea level in the swamp to 113 feet (34 m) on sandy ridges, this mixture of elevations translates into a diversity of habitats for wildlife. Refuge staff have utilized this rolling landscape and through the years have installed 96 water control structures creating over 70 impoundments which have provided a myriad of habitats for migratory waterfowl, colonial wading birds, alligators, and other wildlife.

Since 1968, approximately 2,000 acres (8 km²) of marginal agricultural lands have been reforested on Yazoo National Wildlife Refuge. Reforestation has been accomplished by direct-seeding with acorns and with seedling plantings. At least 20 tree species have been planted on refuge lands. These plantations, some of which are among the oldest on record, now provide unique opportunities for researchers to study the development process for the restoration of bottomland hardwoods over time. Reforestation on Yazoo National Wildlife Refuge catalyzed similar habitat restoration on other refuges and private lands throughout the southeast region.

Habitats vary from bottomland hardwoods to cypress swamps and agricultural fields. Emphasis is placed on providing food for wintering waterfowl, which utilize the refuge in large numbers, at times exceeding 250,000 birds. These foods consist of corn, milo, rice, wheat, etc. and moist-soil plants. The refuge has over 70 water management units and has restored over 2,000 acres (8 km²) of marginal agricultural land to bottomland hardwoods.