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Runoff Water Management for Animal Production and Environmental Protection
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Introduction •
Runoff Volumes •
Runoff Management •
Key Concepts of Runoff Management •
Keeping the Clean Water Clean •
Diverting Roof Runoff Water •
Diverting Ground Surface Runoff Water •
Managing Heavy Use Areas •
Treating the Heavy Use Area Runoff •
Recommended Filter Strip Widths •
Summary • References
Introduction
With livestock operations,
one of the first considerations when addressing production and environmental
practices is the collection, storage and utilization of manure. One aspect that
is often overlooked is the impact of runoff water on manure management. During a
rain, the water will do one of several things. It may evaporate back into the
air. It may infiltrate into the soil. Or, it may move as surface runoff.
Vegetation and surface depressions may provide temporary storage or retention of
the water, but eventually it will evaporate, infiltrate or run off.
Runoff concerns start when
the water comes in contact with animal holding and traffic areas. Typically, due
to heavy use, these areas are not vegetated and have manure on top of or mixed
into the surface. Under these conditions, the runoff water can carry nutrients,
sediment and microorganisms from the heavy use area into streams and lakes. This
extra loading of nutrients, sediment and microorganisms raises environmental as
well as human and animal health concerns.
Runoff water also increases
the amount of mud located in cattle and equipment traffic areas. Excessive mud
not only causes traffic problems for cattle and equipment, it also increases the
potential for cattle health problems. In addition, on farms with manure holding
ponds and lagoons, runoff water has the potential to greatly increase the volume
of liquid manure that needs to be stored and land applied. This will increase
the cost of application and shorten the effective storage time.
Runoff Volumes
To understand the factors
that affect runoff volume the equation below is helpful.
Runoff Volume = (Inches of
Rain - Infiltration - Evaporation) x Area of Concern
This equation shows that
less rain and a smaller area of concern will reduce the runoff volume.
Increasing infiltration and evaporation will also reduce the amount of runoff.
Unfortunately, it is usually
difficult or impossible to control these factors. Rain and evaporation are
weather conditions that cannot be influenced. Usually, infiltration is also
beyond control. No infiltration occurs when rain falls on roofs and concrete
surfaces. In vegetated areas, the vegetation serves to slow surface water
movement, which increases the time for infiltration and evaporation to occur.
Because of the factors that
influence runoff, it is difficult to predict volumes. However, looking at a
couple of example situations can help to provide a feel for potential runoff
volumes. The maximum runoff will be generated when infiltration and evaporation
are zero. Assuming they are zero can be a reasonable assumption for such areas
as roofs and concrete surfaces. Under these conditions, a 1-inch rain generates
0.62 gallons of runoff water for each horizontal square foot of surface. This
means that in a 1-inch rain, a 25- by 100-foot (2,500 square feet) roof area can
generate 1,550 gallons of runoff water.
If you assumed that half the
rainwater falling on grass either evaporated or infiltrated, the same 1-inch
rain would generate over 13,000 gallons of runoff water per acre or 0.31 gallons
per square foot.
Runoff Management
Since very little can be done
to reduce runoff volumes, the existing runoff must be managed. The three basic
concepts of runoff management are to keep the clean water clean, manage the
heavy use areas and treat the runoff water from heavy use areas.
Key Concepts of Runoff
Management
• Keep the clean water
clean.
• Manage heavy use areas.
• Treat the runoff water
from heavy use areas.
Keeping the Clean Water Clean
The idea is to prevent clean
runoff water from entering heavy use areas or manure storage units. The clean
water that enters these areas can pick up nutrients, sediments and
microorganisms. Avoiding this is accomplished by redirecting the flow of runoff
water. The runoff water that needs to be redirected comes from roofed areas or
ground surfaces up-slope from heavy use areas or manure storage units. Where
water does not enter heavy use areas or manure storage units, it is usually not
necessary to redirect runoff.
Diverting Roof Runoff Water
If the runoff is from a roof,
there are two options. The first is to use gutters to direct the runoff water to
downspouts. At each downspout the water can be either released to flow away from
the heavy use area or enter a pipe or drainage channel to flow to an acceptable
release point. Normally, a gutter system is designed for the heaviest 5-minute
rain event that is expected to occur about every 10 years. In Arkansas, this
means the northern counties should design for a 0.6-inch rain. The southern
counties should design for a 0.65-inch rain. When the gutter system is used to
prevent roof water from entering manure storage units, a 25-year 5-minute rain
event should be used. In Arkansas this means the northern counties should design
for a 0.65-inch rain. The southern counties should design for a 0.75-inch rain.
The second option is to use
drainage channels under the roof eaves to catch runoff water and direct it
around the heavy use area to an acceptable release point. Drainage channels
under the roof eaves should not be used if they will be located within a heavy
use area or there is less than a 12-inch roof overhang. In addition, if blowing
rain is a concern, such as with a free stall barn or feed barn, unguttered roof
runoff water may contribute to problems inside the buildings. Drainage channels
may be open surface channels or gravel-filled trenches with perforated pipe in
the bottom. All surfaces beneath roof eaves, including drainage channels, should
be designed to move the water away from the building and to avoid standing of
water. In general, they should be sloped at a 1 to 5 percent grade away from the
building. All drainage channels should also be protected from erosion by
vegetation, gravel or concrete.
Roof runoff control systems
will often contain a combination of gutters and drainage channels as well as
areas of unmodified drainage where the runoff water does not need to be
redirected. The decision of where to use gutters and drainage channels is
affected by owner preferences and site conditions. Larger roof areas require
larger gutters and larger and/or more downspouts. Also, there are often concerns
about snow and ice damage to gutters. However, the reduction in the amount of
water entering premilk holding areas and free stall barns under windy conditions
may justify the additional expense. With proper placement, the potential for
snow and ice damage is reduced. Situations where a heavy use area is under a
roof’s drip line will typically require either the use of gutters or the
moving of the heavy use area.
Diverting Ground Surface
Runoff Water
Surface diversions are
usually used to redirect the runoff water from up-slope areas. These diversions
catch the runoff water and divert the flow to an acceptable release point. They
should be vegetated to prevent erosion. In certain situations, gravel-filled
trenches with a perforated pipe may be appropriate. They are sometimes used in
situations where it is desirable to redirect the flow of water that occurs
beneath the ground surface.
As indicated previously,
steps should be taken to prevent erosion and standing water in the diversions.
When designing surface diversions, care should be used to consider not only the
flow of water but also vehicle and animal traffic. Since large volumes of water
and significant flow rates are possible, care should be used where the roof and
ground runoff water is released to prevent erosion.
Assistance in the design of
both roof and surface water diversions is available through local county
Cooperative Extension Service and Natural Resources Conservation Service
offices.
Managing Heavy Use Areas
Proper management of a heavy
use area starts with the design of the area itself. Ideally, it should be no
larger than necessary to handle the flow of cattle and equipment. Excessively
large areas take land out of other potentially productive uses and increase the
volume of rainwater being exposed to the soil/manure mixture of the heavy use
area. However, areas that are too small or poorly laid out will not meet animal
traffic and confinement needs. In addition, the flow of animal and equipment
traffic in the area should be considered when the placement of fences and gates
is determined.
One of the biggest problems
of heavy use areas is getting them to support cattle and equipment traffic
during the wet periods of the year. Reducing the volume of water and the time of
exposure to the water helps the heavy use areas stand up to the traffic. The
clean water diversions discussed earlier reduce the amount of water entering the
heavy use area. Proper surface grading of the heavy use area helps to move the
water off the area and prevent standing water. A cross slope of 1/4 inch per
foot should be enough slope to ensure drainage without causing excessive
erosion. Avoid steep slopes as they will cause the runoff to form gullies and
washes. In addition, the distance water flows should be kept to a minimum.
In soils where clean water
diversions and proper grading will not be sufficient to avoid excessively muddy
conditions, practices such as gravel (with or without geotextile underlayment),
coal ash products or concrete are options. Remember that the best approach is to
address drainage and clean water diversion problems first. Then, if necessary,
consider constructing surfaces to support cattle and equipment traffic.
After a heavy use area is
installed, routine management determines the time cattle are in the area and the
frequency of manure removal. With the exception of total confinement areas, the
amount of time cattle are on the heavy use area should be kept to a minimum.
This reduces both manure accumulation and the traffic the area is exposed to.
The frequency of scraping
depends on many factors. Heavy use areas with minimal manure accumulations and
earthen surfaces may not need much, if any, scraping. It may be desirable to
scrape some concrete surfaces, such as premilk holding areas, more than once a
day. When scraping earthen and graveled areas, care should be taken not to
remove soil or gravel, which will affect surface drainage. Any low spots should
be filled to reestablish a uniform grade. In earthen areas, a 3- to 4-inch layer
of soil/manure mix will help to seal the surface and prevent infiltration, which
helps to protect groundwater. In addition, this soil/manure layer tends to help
reduce the amount of soil erosion. However, the retention of moisture increases
the importance of good surface drainage.
Assistance in the design and
maintenance of heavy use areas is available through local county Cooperative
Extension Service and Natural Resources Conservation Service offices.
Treating the Heavy Use Area
Runoff
Since there will always be
some runoff water leaving heavy use areas, it should be treated to reduce its
sediment and nutrient loading. One option is to catch and store the runoff water
for later treatment by land application. However, the Arkansas Department of
Environmental Quality regulates this approach since it is considered a liquid
waste system.
The more commonly used
approach is to use vegetative filter strips to treat runoff water. Filter strips
are bands of vegetation down-slope of heavy use areas designed to remove
sediment and nutrients from runoff water. Filter strips operate by causing
solids to settle out of the runoff water, allowing water to infiltrate into the
soil and providing opportunities for the plants and soil to process and use
nutrients. For filter strips to be effective, the water needs to move as a
uniform sheet across the filter strip. Filter strips lose effectiveness when
channelized flows occur.
Filter strips are normally
vegetated with grasses that are suitable to the site and that will adequately
filter runoff. A filter strip may require some earthwork before seeding. Often,
however, existing pasture areas with well-established forage can serve as the
filter strip. The width, or length of flow, of a filter strip is based primarily
on the slope of the land in the strip. Steeper slopes require wider filter
strips.
Filter strips require some
management for successful and continued operation. The objective is to maintain
a uniform stand of vegetation and have the runoff flow as a uniform sheet of
water across the surface. Overgrazing and traffic damage to the vegetation needs
to be avoided. Excessive vegetative growth and sediment deposits may also cause
channelized flows to occur. Fertilizer requirements for filter strips may also
be different from surrounding areas. Therefore, it may be necessary to
occasionally mow and remove plant material and sediment that has been deposited
in the filter strip.
| Recommended
Filter Strip Widths |
| 0 - 3% |
30 ft |
| 3 - 8% |
50 ft |
| Greater than 8% |
100 ft |
| Up-slope from such landscape features as springs, seeps,
sinkholes, wells and rock outcops |
100 ft |
|
Adapted from NRCS Conservation Standard
Filter Strip 393-(1) |
Assistance in the design and
maintenance of vegetative filter strips is available through local county
Cooperative Extension Service and Natural Resources Conservation Service
offices.
Summary
The design and routine
management of livestock operations should address rainfall runoff as part of
their manure management practices. With proper design and management, the
adverse effects of excessively muddy conditions on production can be minimized.
In addition, the water quality impacts are also minimized. The key concepts to
runoff management are to keep the clean water clean, manage the heavy use areas
and treat the runoff water from heavy use areas. Assistance for all three of
these concepts is available through local county Cooperative Extension Service
and Natural Resources Conservation Service offices.
References
Agricultural Waste Management Field Handbook. USDA Natural
Resources Conservation Service, Washington D.C.
How to Build an All-Weather
Travel Lane or Feeding/ Watering Pad. Handout. Eldridge R. Collins, Jr., Dept. of Biological Systems
Eng., Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
MWPS-18, Livestock Waste
Facilities Handbook. 3rd ed. 1993. Midwest Plan Service, Iowa State
University, Ames, Iowa.
NRAES-1, Post-Frame
Building Handbook: Materials, Design Considerations, Construction Procedures.
1984 revision. Northeast Regional Agricultural Engineering Service, Ithaca, New
York.
NRCS-AR, Conservation
Practice Standard Filter Strip 393-(1). USDA Natural Resource Conservation
Service-Arkansas, Little Rock, Arkansas.
WQ322, Roof Gutters for
Dairy Barns. C. D. Fulhage and D. L. Pfost. 1994. Department of Agricultural
Engineering, University of Missouri-Columbia.
This publication was written
as part of an EPA 319(h) project. For the entire project, $83,263 was provided
by the Environmental Protection Agency and $56,382 was provided as matching
funds. The Arkansas Soil and Water Conservation Commission received $71,263 in
federal funds and provided $48,382 in matching funds. The Cooperative Extension
Service, University of Arkansas, received $12,000 in federal funds and provided
$8,000 in matching funds.
Author:Karl VanDevender, Extension
Agricultural Engineer
John Langston, Extension Agricultural Engineer, Section Leader -
Agricultural Engineering, Farm Safety
Dr. Karl VanDevender is an Extension agricultural engineer and
John Langston is an Extension agricultural
engineer, section leader - agricultural engineering, farm safety, Cooperative
Extension Service, University of Arkansas, Little Rock.
FSA1036-6M-12-00N
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