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Techniques for Wetland Construction and Management

Shawn L. Locke, Ph.D., Texas Cooperative Extension, Department of Wildlife and
Fisheries Sciences, Texas A&M University, College Station, Texas, USA

Carl Frentress, Advanced Ecology Ltd., Athens, Texas, USA

James C. Cathey, Ph.D., CWB, Texas Cooperative Extension, Department of Wildlife and Fisheries Sciences,
Texas A&M University, College Station, Texas, USA

Corey D. Mason, CWB, Texas Parks and Wildlife Department, Austin, Texas, USA

Rick Hirsch, Texas Cooperative Extension, Athens, Texas, USA

Matthew W. Wagner, Ph.D., CWB, Texas Parks and Wildlife Department, Austin, Texas, USA

ACKNOWLEDGEMENTS
This document represents the second in a series of publications involving a partnership between Texas A&M
University, Texas Cooperative Extension, Department of Wildlife and Fisheries Sciences, Institute of Renew-
able Natural Resources, and Texas Parks and Wildlife Department. We thank the Texas Parks and Wildlife
Department for funding for this work. Additional funding was provided from the Renewable Resources Exten-
sion Act. We thank James and Jim Reed, owners of the Reed Family Ranch, for sharing their ideas of wildlife
management and access to their property. The Trinity Basin Conservation Foundation was a catalyst for this
work, and we appreciate the collaboration with its members. Photos were provided by James C. Cathey, Wes
Littrell, Corey Mason, Michael Masser and Wesley Newman. We appreciate the efforts of Billy Higginbotham,
Michael Masser, Cody W. White, and R. Montague Whiting Jr. for providing editorial review of this manu-
script.

TABLE OF CONTENTS

Page
INTRODUCTION.....................................................................................................................................1
What are Wetland Ecosystems? ....................................................................................................2
Examples of the Economic Benefi ts of Wetlands .........................................................................2
Richland Creek WMA ......................................................................................................2
Reed Family Ranch ..........................................................................................................2
The Value of Wetlands ..................................................................................................................3
WETLAND CONSTRUCTION AND MANAGEMENT......................................................................3
Site Selection ................................................................................................................................4
Wetland Placement and Land Surveys ..........................................................................................4
Levee Construction Planning ........................................................................................................5
Benefi ts of Levee Side Slopes and Spillways ...............................................................................5
Borrow Areas and Deep Water Zones ...........................................................................................5
Levee Management Considerations ..............................................................................................6
Water Sources and Control Devices .............................................................................................7
WETLAND MANAGEMENT TECHNIQUES ...................................................................................10
Water Manipulation and Wetland Vegetation .............................................................................10
Annual Plant Communities ............................................................................................10
Perennial Emergent Plant Communities .......................................................................11
Submergent Plant Communities ....................................................................................11
Farm Practices and Wetland Management ..................................................................................13
Nuisance Vegetation....................................................................................................................14
Nuisance Wildlife .......................................................................................................................15
SUMMARY .......................................................................................................................................16
RESOURCES .......................................................................................................................................18
GLOSSARY .......................................................................................................................................18
APPENDIX A .......................................................................................................................................19

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Top of Levee

Water Level

Discharge Pipe

Drop Pipe

Figure 6. Drop pipes can be used in wetland management. However, a disadvantage is that they typically maintain
water at a constant level, preventing the drawndown needed to stimulate seed germination for many wetland plants.
Side slopes in the diagram are depicted at 3:1; however, levees may have higher side slope ratios (e.g., 10:1).

The most versatile and desirable type is the
fl ashboard riser system. Flashboard ris-
ers function through the use of a series of
“boards” fi tted in slots in such a way as to
form one side of the riser box (Figure 3).
Aluminum and PVC fl ashboards are practi-
cal replacements for wooden fl ashboards.
Boards are removed or added to regulate
water levels in the wetland compartments.
The capability to regulate water levels is
necessary because several zones of desired
vegetation can be produced by water level
drawdowns. The rate of discharge can be
slowed by the use of wedges placed between
the top and second fl ashboard or by substi-
tuting top fl ashboards that are half the height
of normal fl ashboards. More discussion on
drawdowns is given in the section on veg-
etation management.

A fl ashboard riser box is coupled to a culvert
pipe that passes through the levee. An anti-
seep collar that is fi tted to the culvert pipe
midway along its length may be placed in
the center of the levee. However, with thor-
ough soil compaction during installation, the
anti-seep collar is sometimes omitted from
the pipe assembly.

Installation of fl ashboard riser systems
requires attention to several details. Systems
must be placed in such a way that the top of

the riser box has adequate freeboard to im-
pound water at the desired level. Make sure
that the elevation of the desired water level
(the water’s edge when the compartment is
fi lled at normal operating level) is the same
as the top board in the riser box. Use of a
survey level is recommended for determin-
ing these elevations. Flashboard riser sys-
tems are placed in levees at locations that
allow for maximum drainage of water stored
in the unit (e.g., lowest elevation point).

Large riser boxes must be anchored into the
ground. All boxes have displacement when
the boards are in place and the unit is fi lled
with water. Displacement of water causes
buoyancy that exerts force on the structure.
If not anchored, the box would be forced
to fl oat in a fashion similar to a boat. On
small systems, the weight of the materials
and the secure fastening of the box to the
culvert pipe overcome the buoyancy factor.
However, on larger systems, the buoyancy
force can be strong enough to bend or break
the box-to-pipe attachment. In these situa-
tions, additional anchors are recommended.
Anchors similar to those used for securing
mobile homes can be used. Also, chains or
cables attached to the boxes and encased in
concrete footings provide suffi cient anchors.
Design personnel and/or vendors for water
control systems can assess buoyancy factors.

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WETLAND MANAGEMENT
TECHNIQUES
Wetland management techniques are de-
signed to enhance the natural processes
of a wetland ecosystem. This is often ac-
complished through mimicking the natural
hydrology of the area via the construction
of impoundments and water control struc-
tures, and by manipulating water levels. The
timing and rate of water release has a signifi -
cant impact on the plant communities that
become established. Wetlands have a tre-
mendous impact on improving water qual-
ity, and they are also benefi cial to wildlife,
particularly waterfowl. Therefore, wetland
management techniques often focus on the
manipulation of wetland plant communities
and the associated wildlife.

Water Manipulation and Wetland
Vegetation
Annual Plant Communities — Moist soil
management refers to the growing condi-
tions needed to encourage desirable, annual
seed-producing plants. These plants produce
heavy crops of seed because they germinate,
grow to maturity, and die in one growing
season. Seeds lie dormant through the winter
and germinate to produce new plants dur-
ing the following growing season. Seeds
of these annual plants are used as food by
many wildlife species, especially waterfowl
such as dabbling ducks.

In wetlands, annual plants respond positive-
ly to the gradual lowering of water levels.
Drawdown occurs naturally because 1) rain-
fall gradually ceases through the summer
months, 2) evaporation increases in propor-
tion to spring and summer weather, and 3)
live vegetation takes up and disperses water.
Management techniques simply attempt to
simulate the annual dynamics of water levels
in natural wetlands. Timing of the onset and
duration of the drawdown period strongly

infl uences the kinds of plants that grow in
wetlands.

Drawdowns are generally conducted in
stages (early, mid, and late), and rates (slow,
moderate, and rapid). This situation in natu-
ral wetlands has two characteristics that are
important for managers. First, the process is
variable and dynamic. Second, the process is
continuous. Even when wetlands are com-
pletely dry or completely fl ooded, wetland
vegetation is subject to the infl uences of
temperature, oxygen availability and other
factors. These situations must be kept in
mind, although management is normally
conducted in terms of stages and rates.

Water manipulation and soil disturbance are
the practices that cause major changes in
wetland plant communities. In East Texas,
the most benefi cial drawdowns begin in
early to mid-season with gradual to mod-
erate water discharge rates. Early season
periods are regarded as beginning in late
winter to early spring. This timing is as-
sociated with the onset of soil warming. As
soil temperatures reach about 60º F, many
early season seeds begin to germinate. An-
nual smartweeds, such as pink smartweed,
are examples of plants that respond to early
drawdowns. Midseason periods may be
considered to be from mid-spring to early
summer. By this time, soils usually warm
considerably, thus stimulating germination
of plants adapted to midseason conditions.
Barnyardgrass is an example of a desirable
moist soil plant that prospers with midsea-
son drawdowns. Whether an early or mid-
season drawdown is preferred, drawdowns
should be made slowly, often taking 1–2
months to completely drain the wetland.

Once dry, mowing and burning are tech-
niques used to enhance the dynamics of
wetland plant communities. Midseason to

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softstem bulrush Scirpus tabernaemontani (S. validus) P

spikerush Eleocharis spp. A, P

yellow nutgrass (chufa) Cyperus esculentus P

Shrubs

common buttonbush Cephalanthus occidentalis P

indigobush (false indigo) Amorpha fruticosa P

swamp privet Forestiera acuminata P

American snowbell Styrax americana P

downy viburnum (rusty blackhaw) Viburnum rufidulum P

possum-haw viburnum Viburnum nudum P

water honey locust Gleditsia aquatica P

Trees

baldcypress Taxodium distichum P

blackgum (black tupelo) Nyssa sylvatica P

bur oak Quercus macrocarpa P

cedar elm Ulmus crassifolia P

flowering dogwood Cornus florida P

laurel oak Quercus laurifolia P

live oak Quercus virginia P

pecan Carya illinoensis P

Shumard oak Quercus shumardii P

southern red oak Quercus falcata P

water elm (planer tree) Planera aquatica P

water hickory Carya aquatica P

water oak Quercus Nigra P

white ash Fraxinus americana P

white oak Quercus alba P

willow oak Quercus phellos P

Vines

Alabama supplejack (rattan vine) Berchemia scandens P

common greenbriar Smilax rotundifolia P

riverbank grape Vitis riparia P

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1 Additional information on each plant can be found on Texas Parks and Wildlife
Department’s Texas Plant Information Database (http://tpid.tpwd.state.tx.us/index.asp).
2 Life cycle of the plant is annual (A), biennial (B) or perennial (P).

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The information given herein is for educational purposes only. Reference to commercial products or trade names is made with
the understanding that no discrimination is intended and no endorsement by the Texas AgriLife Extension Service is implied.

WETLAND

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