PONDS For Work or Play
Ponds are one of the most popular and visible soil and water conservation practices. Over 28,000 ponds now dot the Ohio landscape. They vary in size from one-tenth of an acre to many acres.
Many ponds built in
the early years of conservation were put in to do a particular job on the farm. Now, ponds
are built for many uses. They store water in orchards and for fire protection. Ponds also
catch sediment that would otherwise pollute our streams.
Recreation is now a
primary use for many new ponds. The popular water areas are usually stocked with fish and
many provide excellent fishing. More and more Ohio landowners and their families attest to
the many enjoyable hours spent fishing, swimming, boating or ice skating on their pond.
Ponds also make ideal areas for family picnics and, if managed properly, are great
wildlife areas.
Building a pond is a
practical way to supply water for work or play.
So
You Want To Build A Pond
Answering
these questions honestly and comparing them to the following information will help you
decide on how to build, or not to build, a pond.
1.
If you want a crystal clear swimming area, you will be much better off if you build a
swimming pool. The price of this may be
comparable to building a pond.
2.
If you are worried about the safety of the people in your household or your neighbors
while they are in or around the water, we recommend that you teach them about water safety
before
3. The cost of a properly constructed
pond in this area is approximately $7000 and up. (1/4 acre)
4.
To build the minimum sized pond that we recommend (1/4 acre) you will need a minimum of
1/2 acre (21,780 square feet) of area.
5.
Ohio has a dam law pertaining to embankment ponds. Does your community also have one?
6.
Check the laws regarding your liability in case of injury or death resulting from the use
of your pond. You may find that you will need to protect yourself with insurance.
There
are two general types of manmade ponds, excavated and embankment.
Excavated
ponds or
pit ponds are mostly used where the existing ground is relatively flat. Normally built
where the demand for water is small, and constructed simply by digging a pit below the
surrounding ground level and placing a fill around them. Surface runoff or groundwater
(water table) maintains the water supply.
Embankment
ponds
are the most commonly built ponds in this area. They are suited to areas where the
surrounding topography is moderately steep and the bottom is relatively flat. They consist
of constructing a fill (dam) across a small watercourse so that water is impounded behind
it. In general, the cost of constructing an embankment pond is less than an excavated pond
due to the amount of soil moved.
The
State of Ohio has a dam safety law governing the impounding of water. The Ohio Department
of Natural Resources, Division of Water (614-265-7617), has a booklet explaining the law.
Many communities also have laws pertaining to ponds, so be sure that you and your engineer
comply with them.
Check
the laws regarding your liability in case of injury or death resulting from the use of
your pond. You may find that you will need to protect yourself with insurance.
Designing
a pond requires making engineering surveys; computing the expected flow of water into the
pond; setting elevations for earth spillways, pipe spillways and the top of dam;
determining the dimensions of the dam and spillways; establishing the degree of slope of
the sides of the dam to be sure it is stable; calculating how much earth fill and other
materials are required; preparing drawings; and prescribing construction methods and
procedures.
At
this time, ponds are not a high priority item; however, if the schedule permits, you can
obtain technical assistance from the Butler County Soil and Water Conservation District,
along with t he USDA (NRCS). A private engineer would also be able to assist you for a
fee.
Become
familiar with the plans and specifications before construction begins. You will then be
able to determine whether the work is going as planned when the engineer or technician is
not there to inspect it. Be sure your pond is built according to the plans and
specifications. Failures have occurred as the
result of cutting corners in an attempt to save a little money.
Suitability
of most pond sites depends on the ability of the soil in the reservoir area to hold water.
With an embankment pond, the soils must also be suitable for the dam site and the dam.
Site
SelectionSelecting
a suitable site for your pond is important. Preliminary studies of any site are needed
before making a final decision on a specific site. If you are considering more than one
location, study each one in order to select the most practical and economical site on
which to build.
For ponds where surface runoff is the main source of water, an ideal site would be one where an earthen dam could be constructed between two moderately steep slopes and where the reservoir is wide and flat. Avoid sites where the pond area would have large shallow areas. Such areas pose problems resulting in plant growth and evaporation losses.
The
extent of active erosion in the watershed also must be considered. If there is excessive
erosion taking place within the watershed, your pond will probably be filled with sediment
in a short period of time. If erosion is severe, it is advisable to delay building the
pond until the needed soil and water conservation measures to control the upstream erosion
have been installed.
Pollution
of pond water is always a possibility. Pollution of pond water may be minimized by
selecting a site where drainage of septic systems, farmsteads, corrals, dumps and similar
areas do not reach the pond area.
Do not
locate your pond where failure of the dam could cause loss of life and injury to persons,
property, livestock, railroads, highways, or
interrupted use of service
of public utilities. If the only suitable pond site presents one or more of these hazards,
employ a registered engineer to reduce the possibility of failure from improper design,
const ruction or maintenance.
Be
sure that no buried pipelines, cables or other utilities cross a proposed pond site. If it
is necessary to use a site crossed by pipelines or cables, notify the utility company
before seriously considering construction. The company’s permission must be obtained.
This is the landowner’s responsibility.
Avoid
sites under power lines. These wires may cause a hazard to all uses of a pond. If live
wires were to fall into the pond or if fishing poles, ropes, etc., were to contact the
power lines, severe electrical shock could result.
Avoid
building a pond in a site that is too small. A minimum surface area should be ¼ acre
(10,890 square feet) with 50 percent of the pond bottom six feet deep or 25 percent eight
feet deep. A pond that is too small will probably be an eyesore filled with a growth of
unwanted aquatic plants. The area must be large enough t o allow proper construction
equipment room to work and, in the case of an excavated pond, disposal of excavated
material. The soil removed from a small pond can easily exceed the size in volume of a
small three bedroom house. Just imagine a mound of soil as large as your planned pond and
about eight to ten feet high.
Very
few ponds are crystal clear. Under ideal constructions, a pond is a uniform greenish color
with visibility about a foot or two. This color is caused by tiny free-floating plants
which indirectly serve as food for fish. Remember, you can swim in a fish pond but you
can’t expect fish to live in a swimming pool. Anyone who wants a crystal clear pond
should strongly consider a swimming pool.
Watershed AreaThe size of the watershed, the area that drains into a pond, is very important in selecting a pond site. If the watershed is too large, you may have difficulty in preventing erosion at the pond site and an expensive overflow structure will be needed to bypass excess runoff during storms. If the watershed is too small, runoff may not be adequate to fill the pond and then keep it full. In Southwestern Ohio, in order to maintain the water level in a pond of recommended depth with one surface acre of water, you will need approximately a minimum drainage area of six acres and maximum drainage of 20 acres. Sometimes drainage areas can be made larger or smaller using construction equipment; however, state laws do exist making the practice of diverting or changing natural drainage areas illegal.
Spillway Requirements
For
most ponds, both a principal and emergency spillway are needed.
The principal
spillway generally is a type of drop inlet or hooded inlet. Drop inlets consist of a
pipe located under the dam and a riser connected to the upstream end of the pipe. The size
of the pipe depends on the required discharge capacity. The size of the riser must be
somewhat larger if the pipe is to flow full.
A
hooded inlet consists of a pipe layed through the fill from the downstream toe to the
waterline on the upstream slope. Once again, the size of the pipe depends on the required
discharge.
On
both of these principal spillways, antiseep collars should extend into the fill a minimum
of 24 inches perpendicular to the pipe. These antiseep collars decrease the flow of water
along the outside of the pipe through the fill, preventing seeps, dam wetness and possible
failure.
Proper
construction and design of principal spillways cannot be over emphasized. Two-thirds of
pond failures involve principal spillways.
On
both types of ponds built, an earthen emergency spillway should be constructed to
pass excess storm runoff around the dam. Any excess water that cannot pass through the
principal spillway would outlet by this method. The emergency spillway is lower in
elevation than the top of the dam. Usually located at the end of fill, the emergency
spillway allows water to flow freely through this bypass and not over the top of the dam.
Soil
surveys can
give you a general idea of what type of material you might encounter. You can pick one up
at the Butler SWCD. They are free of charge and consultation on the survey's contents is
available. The best way to determine if the soil is suitable for a successful pond would
be to bore or dig test holes over the proposed site. When doing these test holes, make
sure you dig deeper than the depth of the proposed pond. In most cases, a backhoe should
be used to dig test holes which will allow you to see and determine the depths of
different geologic materials you encounter and their suitability for pond construction.
Constructing
the pond correctly is as important as the initial investigation itself. Careless and
shoddy construction can make an entirely safe and adequate design worthless and cause
failure of the dam. Good const ruction is important regardless of the size, or cost, of
the pond and will generally cost less in the long run then trying to repair dams built
carelessly.
The
foundation of the dam could be the most important part of the pond construction. If the
dam's foundation is underlain by sands and gravels, a pond failure may occur due to
seepage or piping. On most embankment ponds, a core trench or cutoff will be needed to
join the foundation with the base of the dam. The trench is cut along the centerline of
the dam deep enough to extend into a layer that eliminates seepage. The trench should have
a width of eight feet and side slopes no steeper than 1:1. The trench is then backfilled
and compacted in thin layers, 6 inches at a time, with good, clean clay material. The fill
above the core trench should also be compacted in these thin layers.
When
placing the principal (pipe) spillway through the fill, the material around the pipe must
be hand or mechanically tamped until it has two feet of cover. The importance of the soil
material and soil compaction on the dam and around the pipe cannot be overlooked. The
pond's life expectancy depends largely on this part of construction. During excavation of
the pool area, if poor materials are encountered, some type of sealing may be needed.
Soon
after construction, vegetative cover should be established on bare areas to prevent
erosion from occurring. Grasses like fescue are quick growers and easily established.
Trees or other woody plants should not be planted or allowed to grow on the dam. They
eventually die and water can flow through the channels left by their roots, resulting in a
leaky pond.
Complete
fencing of areas on which embankment ponds are built is usually recommended if livestock
are grazed or fed in adjacent fields. Fencing
ensures clean drinking water and eliminates drainage damage or pollution by livestock. If
the pond is to be used for watering, you will need to install a gravity-fed watering
trough just below the dam and outside the fenced area.
DesignFollowing
the initial investigation, and after soil tests have determined a probable location for
the pond, an engineering survey or design should be made to determine the dam spillway and
other features.
Pond
surveys usually consist of a profile of the dam, location and size of the spillways and
measurements that give an accurate estimate of the pond capacity. The plan should show all
elevations, dimensions, and kinds of building materials required. Consulting engineers can
provide you with these types of plans.
Depth:
In order to ensure a permanent water supply, the water must be deep enough to meet
intended use requirements and to offset probable seepage and evaporation losses. Ideal
pond depth in this area would have at least one-fourth of the pond with a depth of eight
foot or more. Deeper ponds are needed where seepage losses exceed three inches per month.
Top
Width: For dams less than 10 feet in height, recommended top width should be a minimum
of 6 feet. When the height exceeds 10 feet, the top width should increase also. The
recommended minimum top width with comparison to height is:
Height
of dam (ft.) Minimum top width (ft.)
Under
15..…………...………………..……...
........................8
15 to
19.9............…………………………………................10
20 to
24.9..........…..…………..……………..
………............12
25 to
34.9...............………………………………….............14
35 to
40................……...……………………………............15
Side
Slopes: Slopes must be sufficiently flat to ensure a stable embankment, however, in
all cases the combined upstream and downstream side slopes of the settled embankment shall
not be less than five horizontal to one vertical with neither slope steeper than 2:1.
Excessive
seepage in a pond is usually due to a poor pond site or improper construction techniques.
Sites where inadequate soils are encountered during construction should be sealed by
"clay blankets" which consist of well graded material containing at least 20
percent clay. Thickness of the blanket depends on the depth of the water to be impounded.
The minimum thickness is 12 inches for all depths of water up to 10 feet. Increase this
thickness by two inches for each foot of water over 10 feet. Compact the clay material in
layers of 6-8". Existing ponds that have excessive leaks may also need clay blankets.
Other
materials to be used for sealing leaky ponds are Bentonite, chemical additives, and
waterproof linings. Bentonite is a fine textured colloidal clay. When saturated, it grows
to many times its original volume. If mixed with well-graded, coarse grained material,
thoroughly compacted, then saturated, the material tends to fill pores and blanket the
leaking areas. Some chemical treatments can be added to fine-grained clay soils to help in
sealing seepage areas. This method can be quite complicated and a laboratory analysis of
the soil is essential to determine which type of chemical additives will be most effective
and at what rate it will be applied. Many types of materials are being used as waterproof
linings. Polyethylene, vinyl, and butyl-rubber membranes are just a few. They could
virtually eliminate seepage if properly installed. A cover of earth may be needed for some
linings to protect against punctures.
It is
very likely that your pond will be used for swimming or boating regardless of the intended
main use. Be sure to remove all trees, stumps and brush from the ponded area that is
likely to be used for swimming. Also, remove all rubbish, wire, discarded machinery, and
old fences and eliminate drop-offs and holes in the swimming area.
Mark
the swimming area with a float line and place warning signs at all danger points. It is
also a good idea to place lifesaving equipment such as ring buoys, ropes, planks and long
poles on the shore near the swimming area. If ice skating is likely, place a long plank or
ladder near skating area for rescue operations.
The
information contained in this publication was obtained from the United States
Department of