lifeENVIRONMENTAL ISSUES
IN LIVESTOCK PRODUCTION
HOME STUDY COURSE

The Environmental Issues in Livestock Production home study series was developed for livestock producers, educators, students, and others seeking to better understand potential air and water quality impacts of animal agriculture, and to learn more about management practices that can minimize these impacts.

Modules in this series include:

    Open Feedlot Runoff;
    Odor Assessment and Control;
    Manure Application;
    Livestock Environmental Regulations;     and
    Manure Treatment

For information concerning home study course completion certificates, and supplemental teaching materials (Power Point presentations) for use in the classroom, contact Agricultural & Biosystems Engineering Extension, 207 Davidson Hall, Iowa State University, Ames, IA 50011-3080 (phone 515-294-6360), email tglanvil@iastate.edu, or visit our World Wide Web site at http://www.abe.iastate.edu.

Environmental Issues in Livestock Production was developed through an Iowa State University Extension grant, and is part of the Livestock Industry Facilities & Environment (LIFE) project of the Department of Agricultural & Biosystems Engineering. Project team members included the module authors: Dr. Mark Hanna, Dr. Jay Harmon, Dr. Jeffery Lorimor; and project coordinator Dr. Tom Glanville.

Iowa State University
University Extension
Ames, Iowa

 

lifeOpen Feedlot Runoff

Home Study Lesson 1

 This lesson discusses runoff from open feedlots for all species, and how to manage it to minimize environmental damage. This module was developed by Jeffery Lorimor, Extension Ag Engineer and Assistant Professor, Agricultural and Biosystems Engineering, Iowa State University, Ames, IA.

Objectives:

Upon successful completion of this unit, agricultural producers or support personnel will:

  • Be able to control runoff from open feedlots to protect the environment.
  • Know how rainfall amounts affect the size of runoff control structures.
  • Design different components of a runoff control system.
  • Know the legal environmental regulations for open feedlots.

Open feedlots and surface runoff

Livestock production in open feedlots has long been a part of agricultural life in Iowa. Recently we, as a society, have become more aware of the pollution hazards associated with livestock production. Because of increased societal pressure, and because it's the "right thing to do," livestock producers must be diligent in the collection, containment, and use of manure and runoff produced by livestock feedlots. Preservation of environmental quality makes it imperative that wastes be handled appropriately to prevent surface and groundwater contamination. Regulations, such as the Clean Water Act, provide enforceable criteria for environmental protection from contamination by livestock wastes. Therefore, it is imperative that livestock producers understand the implications of environmental contamination and work to ensure it does not happen.

Open animal feedlots are defined by the Department of Natural Resources (DNR) as "unroofed or partially roofed animal feeding operations in which no crop, vegetation, or forage growth is maintained during the period that animals are confined in the operation." In Iowa, these feedlots often have runoff caused by excessive rainfall or snow melt, and possibly from leaking pipes and waterers. Runoff from feedlots is of concern because it transports soil and/or animal manure. These animal manures contain nutrients that are of value for crop production. If runoff is not contained, the nutrients will not be available for crop production, but more importantly, the runoff may end up in lakes, streams or rivers where it is a pollutant. Organic matter in the runoff can deplete the oxygen supply in streams, causing fish kills. Ammonia can be toxic to fish. Excess nutrients accelerate plant and algae growth. The impact of uncontrolled runoff can be visible and detrimental, and is generally undesirable.

Rainfall and runoff

The amount and composition of runoff from a feedlot are affected by many factors, including precipitation, drainage area, feedlot size and slope, animal density, and whether the feedlot is paved or not. Precipitation is one of the primary variables that determines runoff amounts. The runoff caused by individual storms is used for designing settling basins. The total annual runoff is used for designing retention basins.

Individual storms

Precipitation events (storms) are classified by their intensity and duration. The combination of the two defines a "return period." For example the 10-year, 1-hour storm is defined as the greatest amount of rainfall (the most intense storm) to occur in an hour on the average of once every 10 years. The 10-year, 1-hour storm varies from 2.1 to 2.5 inches across the state (Figure 1), and is the storm used to design feedlot settling basins in Iowa.

Figure 1. 10-year, 1-hour rainfall intensity, inches/hour (adapted from Livestock Waste Facilities Handbook, MWPS-18, Midwest Plan Service, Ames, Iowa).

The 25-year, 24-hour storm designates the maximum rainfall that occurs over a 24-hour period on the average of once every 25 years. Figure 2 shows the 25-year, 24-hour precipitation amounts for Iowa. It is used in the design of feedlot retention basins. (Settling basins and retention basins will be discussed in detail in the design section that follows.)

Problem 1:

From Figure 1, determine the 10-year, 1-hour rainfall intensity for your location.

From Figure 2, find your own 25-year, 24-hour rainfall amount.

10-year, 1-hour intensity: ________________________inches/hour

25-year, 24-hour amount: ________________________inches

Runoff rates and runoff accumulation amounts for a feedlot can be determined by multiplying values from Figures 1 and 2 times the feedlot size, using appropriate conversion factors as in the following example:

Figure 2. 25-year, 24-hour rainfall, inches (adapted from Livestock Waste Facilities Handbook, MWPS-18, Midwest Plan Service, Ames, Iowa).

Example 1:

Determine the maximum runoff rate from an individual storm for a paved feedlot in Northwest Iowa that is 70 feet by 200 feet.

The feedlot surface area drained is 14,000 square feet (70 feet x 200 feet). The 10-year, 1-hour storm (Figure 1) is 2.4 inches for Northwest Iowa.

To determine the runoff flowrate in cubic feet per second (cfs) use the following formulas:

Determine the runoff volume (rainfall x area):

2.4 in/hr x 14,000 sq ft divided by 12 in/ft = 2,800 cu ft/hr

Divide by the seconds in an hour:

2,800 cu ft/hr ÷ 3,600 sec/hr = 0.78 cfs

(Notice we assumed all the rainfall ran off.)

Problem 2:

Determine the maximum runoff rate (in cfs) to expect from a paved feedlot in Northeast Iowa that is 100 feet x 200 feet.

Feedlot area = _______ x ________ = _________sq ft

Runoff(rainfall) intensity = ________ in/hr divided by 12 in/ft = _________ft/hr

___________ ft/hr x (feedlot area) __________ sq ft = _________cu ft/hr

___________ cu ft/hr ÷ by 3,600 sec/hour = _________cfs

Once the runoff rate has been determined, you are ready to go ahead and design a settling basin below the lot. The design of the settling basin will be discussed later in this lesson.

Cumulative runoff

The total amount of runoff between periods of land application is important for designing effective runoff facilities. A retention basin is an earthen impoundment constructed below a feedlot to capture and hold runoff until it can be spread on the land. For retention basin design, you need to know the amount of runoff that will accumulate through the year, or the cumulative runoff rather than the flow rate for an individual storm. This is long term storage, typically several months. The length of storage depends on how often the basin is emptied. The total volume of runoff expected over the selected time span is used for retention basin design. Since most retention basins are emptied once a year, annual precipitation is most frequently used. The percentage of annual rainfall, which becomes runoff over the course of a year, varies by area within the state, and by the type of feedlot surface—earth or concrete. Earthen feedlots normally have less runoff than paved lots because more of the precipitation soaks into the soil-manure mixture on the surface of the earthen lots. Small storms may not result in any runoff. Figure 3 shows estimated annual runoff from paved lots as determined by the Natural Resources Conservation Service (NRCS).

Figure 3. Annual runoff from paved feedlot as percent of mean precipitation (from NRCS Animal Waste Management Field Handbook, 210-V-AWMFM), Amend. IA4, June, 1986).

Figure 4 shows annual runoff from earthen feedlots as a percentage of the precipitation that falls throughout the year. The annual depth of runoff is calculated by multiplying the percentage that runs off (from Figure 3 or 4) times normal annual precipitation, as shown in Figure 5. To determine total runoff from a feedlot, combine the runoff depth, as just discussed with the physical size of the feedlot and a conversion factor to change inches to feet.

Figure 4. Annual runoff from unpaved lots as percent of mean precipitation(from NRCS Animal Waste Management Field Handbook, RCN 90, 210-V-AWMFM), Amend. IA4, June, 1986).

Figure 5. Normal annual precipitation, 1951-1980(from NRCS Animal Waste Management Field Handbook, 210-V-AWMFM), Amend. IA4, June, 1986).

Example 2:

Find the normal annual runoff depth and total cubic feet of runoff volume from a 300 foot x 600 foot unpaved feedlot in far Southwest Iowa.

From Figure 4, we find that about 24 percent of annual rainfall will runoff.

From Figure 5, we can expect 34 inches of rainfall per year

so, multiply 0.24 x 34 = 8.16 inches of runoff depth/year

volume = (8.16in/12 in per ft) x 300 ft x 600 ft = 122,400 cubic feet runoff/year

Feedlot design

The design of an open feedlot can have a major impact on the runoff facilities needed. Diverting unpolluted water from building roofs and non-feedlot surfaces around the feedlot and runoff area, reduces the size of facilities needed to collect and treat the feedlot runoff. Surface slope of the feedlot influences the speed of runoff, but not the amount. Some feedlots are designed to have a solid settling area within the feedlot itself. This is largely dependent on the available space within the feedlot and the physical layout.

An open feedlot runoff control system is shown in Figure 6. Diversions around the top and sides of the feedlot would prevent clean runoff from above from reaching the lot. The runoff from the feedlot is all channeled toward the settling basin, where it is contained and held long enough for the solids to settle. From the settling basin, the liquids are released to the retention basin, where liquids are stored until spread on land. In some cases, infiltration areas rather than retention basins are used below settling basins. Lot size determines if a retention basin in needed.

Figure 6. Runoff control system (NRCS sketch).

Settling basin design

Settling basins remove solids from feedlot runoff to prevent them from reducing storage capacity of a retention basin, from building up in an infiltration area, or from reaching nearby water bodies. Settling basins are usually located adjacent to the edge of the lot, Figure 6. After the liquid passes through the settling basin, the solids can be scraped up and either stockpiled or spread on fields.

Settling basin designs are based on individual storm runoff. DNR has designated the 10-year, 1-hour storm (Figure 1) for sizing a settling basin. Settling basins should be sized to slow the runoff just long enough for the solids to settle. The liquid then flows to a retention basin or infiltration area. Because of the flow-through characteristic of settling basins, designs are based on individual storms, not cumulative runoff.

DNR rules state that slowing the flow to 1/2 foot per second for 5 minutes is adequate for solids separation to occur. For concrete lots, 100 percent of the rainfall amount is used for design. For earthen lots, 50 percent is used, as some liquid would be absorbed into the soil-manure surface of the lot.

Settling basins should be designed with a large surface area. They are usually less than three feet deep and should have a concrete bottom. An access ramp should not slope more than 1 inch per foot of horizontal run so manure removal equipment can remove the settled solids easily. If the settled solids are not hauled to fields after each storm, a separate manure storage area should be used. Failure to remove solids will reduce the performance of the settling basin. Cleaning the feedlot frequently helps avoid overloading the settling basin. If the lot will be cleaned infrequently, increasing the size of the settling basin by 25 to 50 percent will help compensate for the increased solids in the runoff.

Example 3:

Now we can determine the appropriate size for the settling basin of the Northwest Iowa feedlot in Example 1. That example showed the flow rate to be 0.78 cfs. To determine surface area of the basin, multiply the flowrate by a conversion factor of 900:

(The 900 assumes a liquid depth of 1 foot, and a detention time of 15 minutes x 60 sec/min) 0.78 x 900 = 702 sq ft

The width of the settling basin can be determined by multiplying the flowrate by another conversion factor of 32.7 (from Midwest Plan Service): 0.78 x 32.7 = 25.5 ft

The dimensions of the basin can then be determined. Using a basin width of 26 feet, the basin length can be determined by dividing the area of the basin by the width: 702 sq ft ÷ 26 ft = 27 ft

So the settling basin could be built to be 26 ft x 27 ft x 1 ft deep, plus any freeboard. (Typically, 1 foot of freeboard is used for settling basins.) Freeboard is the difference in height between the lowest point along the top of the basin wall and the highest level of liquid in the structure.

Settling basin outlet design

Settling basin outlets should be designed to carry the flow, but to hold back solids that reach it. Typically outlets are made of planks with spaces between them, or perforated pipe risers similar to terrace tile line inlets. The plank outlet (Figure 7) was designed with 1.5 inch gaps between the planks. Other widths can be used; typically one-half inch should be a minimum. The objective is to slow the flow, but keep the openings wide enough to avoid plugging.

Figure 7. Settling basin plank outlet (graphic from MWPS-18 Livestock Waste Facilities Handbook)

When the water depth is 12 inches the outlet should carry 0.5 cfs for each foot of width to meet the velocity criteria from IDNR of 0.5 feet/second. To calculate the width needed, divide the flow in cfs by 0.5. For our Northwest Iowa example with 0.78 cfs flow, the width of the outlet would be 0.78/0.5 = 1.6 feet.

Retention basin design

Retention basins should be sized to hold the runoff for the total length of time between removals of liquid (calculated from Figure 3, 4, and 5), plus the 25-year, 24-hour storm runoff (Figure 2), plus 2 feet of freeboard. For example, if the basin is to be emptied spring and fall, at least 180 days of storage is needed, plus the 25-year, 24-hour storm runoff, plus freeboard. It is best to size the basin 10 to 15 percent larger, as some sludge will accumulate on the bottom, which reduces storage volume. It is best to not pump the basin completely dry, so the bottom does not have a chance to dry out and uncompact. Another management factor that affects the basin size is whether outside water from roofs, non-feedlot surfaces, etc., is diverted around the feedlot and runoff area.

Problem 3:

Using the information from Example 1 (the 70' x 200' Northwest Iowa feedlot) determine the required retention basin volume (cu ft) if liquid is pumped out once a year, and all water from roofs and areas around the feedlot are diverted away from the feedlot and runoff control structures?

Mean annual precipitation ______inches x % runoff (Figure 3) ________ ÷ 100

equals annual runoff = ________ inches

plus 25-year, 24-hour storm runoff = ________ inches

equals the total annual runoff depth = ________ inches

Volume = ______ft x ______ ft x depth _______ in ÷ 12 = ________ cu ft

Infiltration areas-grass filters

An alternative to a retention basin for small feedlots is a grass filter strip, or infiltration area. These are simply vegetated areas, usually long and narrow, that the runoff must flow through before reaching a lake or stream (Figure 8). The vegetation does provide additional filtration and physical treatment as the runoff flows slowly across it. To achieve treatment, shallow flow depths and slow velocities are necessary. Serpentine designs are sometimes used for long, narrow channels. Design is fairly complex, so it will not be described here. The NRCS has design standards for different flows, slopes, channel widths, etc., so the best course to obtain a system design is to contact your local NRCS office.

Figure 8. Vegetative filter strip/infiltration area below settling basin.

Legal requirements

To protect the environment, there are a number of legal requirements associated with runoff from open feedlots. The minimum requirements for waste control include:

  • Removal of all settleable solids from runoff before the liquid waste enters a stream or other water of the state.
  • Feedlots required to have operation permits must contain all runoff up to, and including, the 25-year, 24-hour storm. Larger storms can legally cause some runoff.
  • Restriction of wastes so none is discharged directly into a publicly owned lake, a sinkhole, or an agricultural drainage well.
  • Runoff must be applied to land in a manner that does not cause surface or ground water pollution.
  • Any open feedlot that discontinues operation must remove all runoff and land-apply it as soon as practical (but not more than six months) after closure of the feedlot.

In addition, the DNR may require a greater degree of waste control if it is determined, after an on-site inspection, that the minimum level of waste control is inadequate.

Open feedlots with 1,000 animal units (AUs) or more are required to obtain an operation permit from the DNR. Since different animal species produce different quantities of waste, each species is assigned a different animal unit equivalency factor so all can be compared on equal terms. The animal unit equivalency factors are listed below:

Animal species Factor

Slaughter and feeder cattle 1.0

Mature dairy cattle 1.4

Swine (over 55 pounds) 0.4

Sheep or lambs 0.1

Horses 2.0

Turkeys 0.018

Chickens, broiler or layer 0.0

Any number of head of a single species or combination of various species that totals 1,000 AUs or more would require an operation permit. For example, if an operation had 150 mature dairy cattle, 400 feeder cattle and 1,000 head of swine over 55 pounds, a permit would be required because they total 1,010 AUs.
150 mature dairy cattle x 1.4 = 210
400 feeder cattle x 1.0 = 400
1000 head of swine x 0.4 = 400

Total 1010

Even though none of the individual species enterprises is greater than 1,000 AUs, since the total exceeds 1,000 AUs, (if they're all at one location), an operation permit is required. An additional requirement is that any open feedlot with 300 AUs or more must obtain an operation permit if the wastes are discharged into a stream or other water of the state through a human-made drainage system.

Problem 4:

What is the total number of animal units at each location of your livestock operation?

Summary

Elaborate and expensive structures are not required to meet legal requirements. The law requires small lots to settle solids prior to releasing liquids. Large lots (over 1,000 AUs) must capture and retain their runoff between pumpouts, plus the 25-year, 24-hour storm. In this course you have learned that small lots also contribute to surface water quality degradation. By controlling open feedlot runoff, surface water quality can be protected and preserved.

Producers need to know how much runoff occurs from their feedlots, and what can be done to keep it from adversely affecting nearby water resources. With the completion of this home study lesson, you should be able to calculate how much runoff your lot produces, and design a settling basin and outlet, and/or a retention basin, to control the runoff and reduce its contamination potential. For further information, or to obtain additional help, contact your local Iowa State University Extension or NRCS office.

Answers to problems:

Problem 2: 200' x 100' x 2.1" ÷ 12 in/ft / 3,600 sec/hr = 0.97 cu ft/sec (cfs)

Problem 3: [(26" x 53% ÷ 100 + 5") ÷ 12 in/ft] x 200' = 21,910 cu ft

Problem 4: = your own answer

Conversion factors

There are a number of conversion factors which are useful for making the calculations necessary for properly sizing runoff control structures. Those conversion factors are listed below: