Wetland Construction and Management (Part 2)

Wetland management techniques focus on manipulating water levels to have desired effects on wetland plant communities. Wetlands are dynamic systems. Therefore, wetland management must also be dynamic and often requires professionals to identify the individual and changing management needs of a wetland. Management is a continuous, variable, and dynamic process. However, the basic techniques of wetland management are relatively straight forward. The goal of wetlands designed the way I’ve described in this post is to grow annual plants which will produce large amounts of seeds that provide a valuable food source to many wildlife species, especially dabbling ducks such as mallards, wigeon, gadwall, and teal. Annual plants respond favorably to wetlands which gradually dry out during the spring and summer months and to soils that are periodically disturbed. Therefore, water level manipulation and disking are the 2 most common and useful wetland management tools.

In our part of the state, the most beneficial time to begin releasing water from a wetland is late winter to early spring when soil temperatures reach about 60 degrees F. Valuable plants such as pink smartweed respond favorably to this early drawdown. However, if drawdown is delayed until mid-spring to early summer, desirable plants such as barnyard grass will grow rapidly. Regardless of the timing of drawdown, drawdown should be made slowly, often taking up to 1-2 months to completely drain.

Once the wetland is dry, mowing and burning can control undesirable plants such as cocklebur, sumpweed, or sesbania and encourage more beneficial food plants. Mowing and burning can also reduce heavy stands of rushes, sedges, and other species that can take over an area and crowd out other plants. Once monocultures and undesirable plants become established, mowing and burning will become only temporary fixes and require follow up treatments at least once a year. Disking can also be used to reduce perennial species and increase seed producing annuals. Disking is usually only recommended every 3-4 years.

With proper water level manipulation and soil disturbance, an abundance of native plants and seeds can be produced to attract migratory waterfowl. This method is recommended over planting crops such as corn, milo, soybeans, and rice. However, if a crop is desired, choose Japanese millet. The first step in growing Japanese millet is to obtain a soil analysis for the area to be planted. Contact NRCS or the Texas AgriLife Extension county offices for assistance submitting and interpreting results. Disk and harrow to prepare a good seedbed. Blend the seed with the fertilizer and broadcast over the field at a rate of 20lbs/ac. Because Japanese millet can produce mature seed in 60 days, it is recommended to plant from July 1 to August 15 so that the seeds are mature as late as possible prior to the first frost. An alternative seeding method for Japanese millet is to delay drawdown until mid- or late summer and then quickly reduce the water level to expose wet mudflats. Then broadcast the seed and fertilizer at the same rate as above. If you plan to hunt near of over this wetland, be sure to check with a local game warden to be sure you are not illegally baiting ducks through this practice.

At some point, your wetland will be invaded by nuisance plants and animals that should be reduced or eliminated. Cocklebur, sumpweed, and sesbania respond favorably to rapid drawdown in the summer. While a slow drawdown in the late winter and early spring can help to minimize these nuisance plants, mowing or herbicide treatment may be necessary to reduce or eliminate them. Once detected, these plants should be treated quickly to avoid seed production which will increase problems in subsequent years. Because willow or cattail cannot withstand competition, these pest plants are best avoided by producing desirable plants on bare moist soil in late spring or early summer. Since there is often an abundance of bare moist in the first year of a new wetland unit, it may be necessary to plant Japanese millet or other beneficial plant to keep willow and cattail from establishing.

Beavers can be expected to occupy your wetland project. Beavers often plug water control structure and/or burrow into levees. To keep beavers from plugging your structure, place a pen constructed of cattle panel or similar material around the control structure. Although beavers may still stack material along the fence, it is much easier to remove debris along a fence than it is in a control structure. Nutria are fast reproducing herbivores that can become quickly overpopulated and destroy vegetation within a wetland. They will also clog control structures and burrow into levees. Every attempt should be made to remove nutria from your wetland unit. Feral hogs will also do extensive damage to levees and wetland areas. Hogs should be trapped and shot whenever possible to protect the investment you’ve made in your wetland project.

Remember, wetlands are more than just a place to duck hunt. The collective efforts of creating, restoring, and enhancing wetlands on your properties will have a tremendous impact on water quality and quantity and wildlife habitats.

Wetland Construction and Management (Part 1)

Those of you who have spent a little time in the field with me know that wetlands and waterfowl are my favorite habitats and wildlife species to talk about. That’s why I was excited to see the comments about wetlands made by Richard and Dan Dawson on the Harvey WMA blog last week. Since other Harvey members could probably benefit from information on wetland construction and management, I’ve dedicated to post discussing the basics. All of the following information can be found in a Texas AgriLife Extension publication titled “Techniques for Wetland Construction and Management”. As always, if you would like additional information or a copy of the publication, please contact me.

Many people see wetlands as “wastelands” or as areas suitable only for snakes, alligators, and mosquitoes. Wetlands, however, provide many important ecological functions as well as recreational and aesthetic functions to those who learn to recognize them. Wetlands help regulate the climate, provide flood and erosion control, store and recycle nutrients, protect water quality, provide wildlife habitat, and provide recreational hunting and wildlife viewing opportunities. Many of these functions are enhanced on wetlands that are closely tied to a river system and waterfowl travel corridor like those of the Harvey WMA. Many of you have the opportunity to create, restore, or enhance wetlands on your property, and I hope the remainder of this post will provide you with the basic tools needed to begin.

The first step to a wetland development project is to assess the soil characteristics, seasonal availability of water, abundance of wetland adapted plants in the soil, and existing plant communities. Impermeable soils, adequate surface water during the fall and winter, and a community of annual seed producing plants indicate an area suitable for wetland development. After a suitable site has been identified, contact a private land surveyor or engineering personal with NRCS to supply an elevation survey accurate to one-foot contours. This level of accuracy is necessary for best placement of levees and control structures. Waterfowl and other wetland wildlife are attracted to plants that grow in shallow (<3ft).

Before beginning levee construction, contact a qualified contractor or NRCS personnel to provide soil sampling and engineering design to ensure that levees (1) will not leak, (2) will impound the desired amount of water, and (3) will withstand extreme flood events. Levees should not be more than 4-5 feet tall. The distance from the water level to the top of the levee should be between 18 and 30 inches. Levee side slopes should be no steeper than 3:1, but may be as gradual at 10:1. Levee elevations should be uniform throughout to prevent erosion at lower areas where floodwaters would overtop the levee. The levee should, however, be at its highest point near the control structure and discharge pipe to prevent washouts at this important location. A large and well-designed spillway should be set about 1-6 inches above the normal water level so that flood waters will immediately pass through the wetland and avoid placing unwanted stress on the levee system. Levee material should be borrowed from inside the constructed wetland area. This will create a narrow barrow ditch which may occasionally be more than 3 feet deep along the inside of the levee. If a levee will completely surround the wetland, remember to leave an area without a borrow ditch to allow access by hunters and/or equipment. After levee construction, immediately re-vegetate exposed soil on levees and borrow areas. Common or coastal Bermuda grass offers the best option for sod-forming grasses to hold soil and reduce erosion on these areas. Roots from woody plants and trees can penetrate the levee embankment and cause a washout. Shredding or herbicide treatments should be used to remove trees from levees.

Water control structures provide the ability to control water levels in the wetland. The most common types of structures are flashboard risers, screw gates, flap gates, and drop pipes. The flashboard riser is the most versatile and desirable. A flashboard riser functions by using a series of wooden, aluminum, or PVC “boards” fitted in slots to form one side of the riser box. Boards are added or removed to regulate water levels in the impoundment. The riser box is coupled to a culvert pipe that passes through the levee to discharge water. Install flashboard riser(s) near the lowest point(s) of the wetland to provide for maximum drainage capability. When placing risers in the levee, be sure that the top board in the riser box is the same elevation as the normal operating water level will be.

Check back next week for Part 2 on how to manage your wetland once it is built.

Native Prairies of Texas - June Link of the Month

Many of you have heard me recommend planting native grasses or making other efforts toward restoring native prairies on the properties you manage. What are native grasses? What is a native prairie? I didn't plant these grasses, so aren't they native? These are some of the responses I get when I suggest restoring native grassland areas. Your properties lie in the Post Oak Savannah ecosystem. This means that historically the landscape was a savannah with a prairie understory and an open canopy of post oaks and other trees above. A prairie is a diverse ecosystem of mainly native grasses and flowering plants with wildlife, soil, geology, and fire playing important roles. Cotton and grain farming, cattle ranching, and urban development have eliminated or severely altered more than 99% of the nearly 20 million acres of prairie that once existed in Texas.

This month's link of the month is to the Native Prairies Association of Texas. Click on the title of this post or the similarly named link on the right panel of this blog to learn:

• What is a prairie?
• How is a prairie different from fields of grass?
• Where you can visit native prairies in Texas
• How to recognize and protect prairie remnants
• How to plan and install small prairie areas
• What to plant in your native prairie area

You will also be able to follow links to pictures and slide shows of native prairies and beautiful wildflowers, NPAT newsletters, suggested reading materials, and additional links concerning native plants and prairie restoration. If you are interested in restoring natural beauty and wildlife value to the open areas of your property, this website (especially the 'photo album' and 'learn' tabs) deserves at least 20-30 minutes of your time!

For details on restoring native prairie plants on your property or cost share programs offered by state and federal agencies, contact me or comment to this post.