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Water Management

Water management at the Refuge is undertaken to provide a mosaic of different wetland types, creating a diverse wetland complex. Several strategies are used for water level management on the Refuge. Each water level has its own advantages.

• Recycles nutrients and promotes growth of vegetation for waterfowl food when the impoundment is later flooded.

• Kills rough fish which create turbid water while feeding; this turbidity then reduces the growth of submergent aquatic plants used by waterfowl as food.

• Provides habitat for wading and shorebirds.

• Encourages growth of emergent aquatic plants for waterfowl food.

• Provides resting areas for migrating waterfowl.

• Creates areas where waterfowl can feed on aquatic insects and the seeds of emergent vegetation.

• Provides protection for waterfowl broods from terrestrial predators.

• Provides habitat for muskrats which, in turn, provides nesting and loafing sites for waterfowl and prevents an overgrowth of marsh vegetation.

Sometimes these strategies are combined to enhance habitat conditions and mimic natural wetland processes. These strategies include a dewatering or drawdown of a wetland and subsequent reflooding at various times throughout the year, and are outlined below:

Allow Natural Dewatering After Filled by Spring Runoff and Snowmelt
Objective: Provide seasonal wetlands for spring migration, pre-breeding and breeding activities. Several pools cannot be maintained without continuous supplemental water due to seepage through their dikes. These pools will be filled to within a foot of full pool level as soon as possible in the spring and given no supplemental water. In the absence of rainfall to maintain the pool levels, this will create a situation of a slowly decreasing pool level throughout the season. This mirrors the processes of naturally occurring ephemeral/seasonal wetland types.

Late April Drawdown
Objective: Provide a food source for spring shorebird and waterfowl migrants by exposing and concentrating invertebrates in pools. This is a slow drawdown (6" per two weeks) beginning April 1 until depths in deeper parts of the pool is about one foot. The pool is then reflooded for the remainder of the growing season.

Early June Drawdown
Objective: Produce seeds from moist soil plants which is subsequently re-flooded in the fall to provide a food source for migrating birds, especially waterfowl. Dewatering begins in mid-May to accomplish the drawdown by June 1. Reflooding begins about mid-September. This date may be delayed in an attempt to obtain mature seeds

Early July Drawdown
Objective: Provide an invertebrate food source for fall shorebird migration. Water levels are slowly reduced beginning July 1, until a level of approximately 1 foot is achieved in the deeper potions of the pools.

Early August Drawdown
Objective: Provide a food source consisting of immature moist soil plants (green browse) for Canada geese and sandhill cranes. Exposure of invertebrates for migrating shorebirds also occurs during this time and is an additional benefit. Partial drawdown of the pools is accomplished by August 1 and maintained throughout migration. The pools are reflooded prior to freeze up to prevent freezing of the mudflats.

Early October Drawdown
Objective: Provide a food source for fall migrating waterfowl and shorebirds by exposing and concentrating invertebrates, insect larvae and minnows. this also exposes residual moist soil plant seeds from the previous year. Drawdown begins slowly in late September, early October to achieve a level of about one foot in the deep areas of the pool. All pools managed under this strategy are left at lower levels through the winter, with the exception of usually one pool brought into complete drawdown and not reflooded to create an overwinter fish kill for control of rough fish and provide food for spring migrating bald eagles.