Equine Best Management Practices Implementation Manual

County of San Diego Watershed Protection Program
2014-07-03
Horse Owners and/or Facilities to Manage Stormwater Runoff

The Equine BMP Implementation Manual has been developed as a useful resource for horse owners and/or facilities to manage stormwater runoff. This manual contains technical information for the following Best Management Practices (BMPs):

  • Composting
  • Manure Spreading
  • Erosion Controls
  • Sediment Controls
  • Infiltration
  • Landscaped Depression
  • Capture and Re-Use

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Professional civil engineers and/or geotechnical engineers should be consulted as necessary in accordance with the Professional Engineers Act, particularly for any BMP with a surface ponding depth of more than 1 foot. Depending on the type and extent of grading and improvements, County permits and/or engineering studies may be required. Examples include (but are not limited to) Grading Permits, Building Permits, Drainage Studies, Water Quality Studies, and Storm Water Pollution Prevention Plans (SWPPPs).

Visit http://www.sdcounty.ca.gov/pds/bldgforms/index.html for information on business and building permits.

This manual focuses on post-construction permanent BMPs. Separate temporary BMPs may also be required during construction. For more information, refer to:

  • County of San Diego Watershed Protection Ordinance

(http://www.sdcounty.ca.gov/dpw/watersheds/watershedpdf/watershed_ordinance_signed_dec2010.pdf)

  • California Stormwater Quality Association (CASQA) website (www.casqa.org)
  • Livestock and Land website (www.livestockandland.org)
  • Natural Resource Conservation Service (www.nrcs.usda.gov)
  • County of San Diego LID Handbook (www.sdcounty.ca.gov/pds/docs/LID-Handbook.pdf)

COMPOSTING

Composting is a highly recommended BMP for manure management. I t is relatively simple and lo w cost, and can be scaled up or down depending on the size of the facility.

Key Considerations

  • Purpose/Benefits
  • Location
  • Type/Size
  • Pile Management
  • Troubleshooting

Purpose/Benefits

  • The purpose of composting is to accelerate the decomposition of manure into humus – an organic matter that is stable and full of nutrients and moisture. Benefits include the following:
  • Reduces the volume of manure by 50% through decomposition.
  • The heat generated during composting kills parasites, weed seeds, and eliminates breeding grounds for flies.
  • Compost generated from manure can be used as a soil conditioner.
  • Reduces odors.

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Photo. Source: farmsandstables.com

Location

It is best to protect compost sites from stormwater runoff and locate them at least 25’ away from receiving waters, wells, property boundaries, and other sensitive areas. Compost piles can be located on compacted soil or on an impervious surface. It is preferred for the ground around the compost area to slope away at 2-4% to stop runoff from coming into contact with the compost material. Ideally, piles are located away from steep or highly erodible slopes. If necessary, diversion structures can be constructed to divert runoff around the compost area. It is recommended to always cover compost sites with a roof, lid, or tarp to prevent direct contact with precipitation.

Type/Size

There are several different composting methods that can be used depending on the size of the equine facility.

Bins

These small-scale operations are ideal f or managing the waste of four (4) or fewer horses. Up to three (3) bins can function together in the system. Utilizing multiple bins allows material to be collected in a separate bin from where the composting is already in process. The bins are recommended to each be at least 5’ wide, 5’ tall, and 5’ long to be effective. This is typically the lowest cost of the different composting options.

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Schematic. Composting bins.

Piles

When working with a large amount of material, long, narrow piles called windrows can be used. It is recommended that the windrows not be higher than 5’ or wider than 12’, but they can be as long as necessary.

Passive Aeration

Passive aeration is typically used for larger composting operations (i.e., 5 or more horses). Several perforated PVC pipes are placed on the ground before starting the compost pile. The pipes typically extend beyond the limits of the pile to allow air to flow freely. Pipes can also be installed in the middle of larger piles. The pipes increase air flow through the system and limit the need to turn the pile.

Forced Aeration

Forced aeration is more complicated than passive aeration and is typically only used for larger municipal or commercial facilities. It uses thermostatic triggers and a blower to force air through the system. These systems do not require turning. This is typically the highest cost of the different composting options.

Vermicomposting

Vermicomposting is another option for composting horse manure with worms. Worm composting is not done thermostatically, but is an effective method of composting. Vermicomposting is conducted in small windrows,

How to Compost

Step 1. Choose Site Location

  • A proper composting location is ideally designated on a flat compacted/impermeable surface.
  • Take care not to place the pile in the path of runoff. If this is infeasible, a berm can be constructed to divert runoff around the pile.
  • The best location is at least 25 feet from a watercourse and 50 feet from animal pens.

Step 2. Choose a Composting Method

Select one of the composting methods described above, based on the size of the facility and the amount of manure generated.

Step 3. Obtain the Necessary Ingredients

  • carbon materials (brown: straw, hay, bedding, etc.)
  • nitrogen materials (green: manure, grass clipping, etc.)
  • water

Step 4. Blend Ingredients

Be sure to blend the ingredients evenly to achieve maximum results. The ratio of the ingredients will impact the effectiveness and speed of the composting. The ideal carbon to nitrogen ratio for composting is between 25:1 and 30:1. The ideal water content is 50-60%.

Step 5. Cook Compost

Allow the compost to reach a temperature between 120˚F and 145˚F. This temperature will kill most weed seeds and parasites. It is best to monitor and document daily the temperature of the middle of the pile. This can be done using a long-probed compost thermometer (available online and in some gardening stores). If the temperature is too high, the necessary microbes can be killed, reducing the effectiveness of the process. To reduce the temperature, increase the frequency of turning.

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Photo. Source: Florida Department of Environmental Protection

Turning the pile will generally speed up the composting process, and can be done as frequently as three (3) times per week. Turning also helps mix the ingredients, rebuild porosity in the pile, and ensure even exposure of the material to the air.

Water content can be tested by squeezing a handful of compost. The ideal compost is as damp as a wrung out can be turned more frequently if it is found to be too wet.

Step 6. Cool Compost

Over time, the compost will cool and will not increase with turning. This is a sign that the compost is finished. The finished material should have an even texture and an earthy smell. Compost will typically take 3-8 weeks to complete.

Step 7. Use Compost

The finished compost material can be used for gardens or crops.

Troubleshooting

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Table. Troubleshooting symptoms/problems/solutions.

Additional Resources

  • County of San Diego Watershed Protection Ordinance (http://www.sdcounty.ca.gov/dpw/watersheds/watershedpdf/watershed_ordinance_signed_dec2010.pdf)
  • California Stormwater Quality Association (CASQA) website (www.casqa.org)
  • Livestock and Land website (www.livestockandland.org)
  • Natural Resource Conservation Service (www.nrcs.usda.gov)
  • County of San Diego LID Handbook (www.sdcounty.ca.gov/pds/docs/LID-Handbook.pdf)

MANURE SPREADING

The spreading of manure is an alternative manure management practice to composting. It involves the collection and spreading of manure over a large vegetated area or an area to be planted. If not done correctly, the manure can be a significant source of bacteria and nutrient pollution for receiving waters.

Key Considerations

  • Manure Generation
  • Available Area
  • Vegetative Cover

Manure Generation

Knowing the amount of manure produced is critical in order to determine the number of acres over which it can be spread. One single horse will typically produce about 50 pounds of manure per day, with a density of about 63 pounds per cubic foot. This means that each horse will generate about 290 cubic feet of manure each year.

Available Area

Manure should be spread and blended with the existing soil. Do not spread non-composted manure in areas where animals graze or walk; pathogens from this un-composted manure can be easily transferred to other animals.

Based on the manure generation rates discussed previously, each horse would require an area approximately 60 feet by 60 feet to spread manure for the year.

If the intent is to use the manure to provide needed nutrients to crops, it is best to first laboratory test the manure to determine the standard nitrogen-phosphorus-potassium value. This information can then be used to determine a more exact spread rate based on the crop needs.

Vegetative Cover

Manure can be spread ½-1” thick over a vegetated area and worked into the ground. It is not recommended to spread manure over areas without vegetation. It is advisable to provide a 20’ wide vegetated buffer strip around the perimeter of the area of spreading.

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Photo. Source: shutterstock.com

Additional Resources

 

  • County of San Diego Watershed Protection Ordinanc http://www.sdcounty.ca.gov/dpw/watersheds/watershedpdf/watershed_ordinance_signed_dec2010.pdf)
  • California Stormwater Quality Association (CASQA) website (www.casqa.org)
  • Livestock and Land website (www.livestockandland.org)
  • Natural Resource Conservation Service (www.nrcs.usda.gov)
  • County of San Diego LID Handbook (www.sdcounty.ca.gov/pds/docs/LID-Handbook.pdf)

 

EROSION CONTROLS

Erosion control measures protect the surface of the soil and prevent the soil particles from becoming detached as a result of rainfall, runoff, or wind. These measures can be used for any disturbed area, although certain measures may be more appropriate than others depending on the level of activity in that area.

Primary Recommended Controls

 

  • Slope vegetation/stabilization
  • Mulching and compost amendments
  • Dikes, berms, and swales
  • Velocity dissipation
  • Wind erosion control

 

Slope Vegetation/Stabilization

Slopes are a critical source of erosion since they are far more prone to erosion than flat areas. Slopes can also pose difficulties with establishing and maintaining vegetation. Hydroseeding, compost blankets, soil binders, and geotextiles and mats can be used.

Hydroseeding

Hydroseeding is an effective method of slope stabilization. Hydroseeding consists of a mixture of wood fiber, seed, fertilizer, and stabilizer. The mixture is then applied evenly across the slope and irrigated until vegetation establishes.

Step 1:

Select the appropriate hydraulic seed mixture based on site conditions (soil, site topography and exposure, season and climate, vegetation types, maintenance requirements, sensitive adjacent areas, water availability, and plans for permanent vegetation).

Step 2:

Prepare the soil on the slope by disking or otherwise scarifying the surface.

Step 3:

Apply the hydroseed in either a single or multi-step process.

In the multi-step process, the hydraulic seed is applied first. Next it is covered with either mulch or a Rolled Erosion Control Product (RECP).

In the single-step process, a hydraulic matrix that contains seed and mulch is applied. When the single-step process is used, the seed rate is increased to compensate for all seeds not having direct contact with the soil.

Compost Blankets

Compost blankets (4” thick) are also among the most effective slope stabilization methods. Compost blankets can help with vegetation establishment, weed suppression, and erosion control.

Step 1:

Prepare the slope by removing roots, stumps, loose rocks, and other debris larger than 2” in diameter. Prepare the soil surface on the slope by scarifying it or track walking/roughening it.

Step 2:

Apply the compost uniformly between 1/2 and 4 inches thick using a bulldozer, skid steer, manure spreader, pneumatic blower, or hand shovel.

Extend the compost blanket 3 to 6 feet over the top of the shoulder of the slope or use a compost sock or compost berm at the top of the slope.

Soil Binders

Several types of soil binders are available, but they are more temporary than hydroseed and need to be reapplied after each storm event. One benefit to these soil binders is that they cure within 24 hours of application, making them effective even when applied shortly in advance of a forecast rain event.

Step 1:

Select the soil binder for application based on soil texture, expected pedestrian or vehicular traffic, and humidity. The soil binder must be environmentally benign. Get the Material Safety Data Sheet (MSDS) from the manufacturer to ensure non-toxicity.

Note that runoff from poly-acrylamide (PAM) treated soils should pass through a sediment basin or other sediment control BMPs before discharging to surface waters.

Step 2:

Prepare the slope by roughening embankment and fill areas. Follow the manufacturer’s recommendation for prewetting of the application area.

Step 3:

Follow the manufacturer’s directions for application rates. Often, more than one treatment is necessary.

Rolled Erosion Control Products (RECPs)

RECPs (geotextiles and mats) can also be effective measures for slopes, but are typically used on smaller slopes due to high cost and difficulty of installation.

Step 1:

Select the appropriate RECP. They may have limitations based on soil type or slope gradient; it is best to consult the manufacturer for proper selection.

Step 2:

Prepare the slope by removing roots, stumps, loose rocks, and other large debris. Loosen the top 2 to 3 inches of topsoil and ensure the RECP will have complete, direct contact with the soil.

Step 3:

Seed the slope prior to blanket installation for erosion control and re-vegetation. (For turf reinforcement application, seeding is often specified after mat installation.)

Step 4:

Install check slots as required by the manufacturer.

Step 5:

Install the RECP following the manufacturer’s directions. These will typically be as follows:

  • Start at the top of the slope and anchor the blanket in a 6 inch deep by 6 inch wide trench. Backfill the trench and tamp the earth firmly.
  • Unroll the blanket downslope.
  • Overlap the edges of adjacent parallel rolls by 2 to 3 inches and staple every 3 feet.
  • When blankets have to be spliced, place them end over end with 6 inches of overlap. Staple through the overlapped area about 12 inches apart.
  • Lay blankets loosely and keep direct contact with the soil. Do not stretch the blanket.
  • Staple blankets enough to anchor the blanket and keep contact with the soil. Place staples down the center and staggered with the staples along the edges. Follow manufacturer’s directions on the recommended staple pattern.

Mulching and Compost Amendments

Application of shredded wood or compost to disturbed soils will reduce erosion by protecting exposed soils from rainfall. If properly blended, the mulch can amend the existing soil to increase infiltration and promote plant growth.

Step 1: Select the Compost

Compost can be manure-based or plant-based, although plant-based is preferred.

Step 2: Amend Soil

Amend compost into soil at a rate of 12%-15% by volume.

Step 3: Apply the Amended Soil

It is best to evenly distribute the mulch across the soil surface. Shredded wood/bark can be applied at a depth of 2 to 3 inches. Green material can be applied at a depth of no more than 2 inches.

Step 4: Apply Mulch

A 3” mulch layer can be applied over the top of the amended soil layer.

Dikes, Berms, and Swales

Berms, dikes and swales can be used to divert runoff from sensitive areas (slopes, paddocks, or arenas) or convey it to a BMP. Berms, dikes, and swales greater than 1 foot in height/depth require consultation with a licensed engineer. The berms and dikes discussed in this manual are intended to be used at the tops of slopes to prevent small amounts of runoff from flow uncontrolled down the slope. Consultation with a licensed engineer is required for other types/locations of berms or dikes, or if a berm or dikes is observed to be overtopping.

Gravel Bag Berms and Dikes

Chart Graph Placeholder 

Schematic. Gravel Bag Berm/Dike.

Step 1:

Build the berm or dike with gravel bags with a maximum height of 12 inches.

Step 2:

Make sure the berm or dike is draining to an outlet. It is recommended that the outlet be monitored for erosion. If necessary, velocity dissipation can be added to the outlet area.

Step 3:

Gravel bag check dams are recommended at 25’ intervals along the length of the berm or dike.

Swales

Swales work best when no more than 5 acres drains to a swale. Typically swales are at least 2 feet wide at the bottom and 12 inches deep with side slopes of 2H:1V or flatter. For best results, swales are laid at a grade between 1 and 5 percent.

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Schematic. Swale.

Step 1:

Remove all obstructions (trees, stumps, etc.) and other objectionable material from the swale area.

Step 2:

Dig the swale and compact any fill material along its path.

Step 3:

Make sure the swale is draining to an outlet, not ponding along the way. It is recommended that the outlet be monitored for erosion. If necessary, velocity dissipation can be added to the outlet area.

Step 4:

Stabilize the swale using seed and mulching. Geotextiles and mats can also be used. For further protection, velocity dissipation can be installed.

Velocity Dissipation

Runoff through channels or at pipe and swale discharge points can be slowed using velocity dissipation devices. For locations with significant erosion or velocities in excess of 5 ft/s, velocity dissipation measures should be designed by a licensed engineer. A licensed engineer should also be consulted for velocity dissipation at outlets to pipe larger than 36” in diameter.

Channels or Runoff Courses

Installing gravel bags (check dams) perpendicularly across existing earthen drainage channels or runoff courses serves to reduce the velocity of the flowing water thereby reducing erosion to the channel.

Step 1:

Woven polypropylene or burlap bags are recommended with a burst strength of at least 300 pounds per square inch. Typical bags are 18” in length, 12” in width, and 3” thick, with a weight of approximately 33 pounds. The recommended fill material is 0.5” to 1” Class 2 aggregate base.

Step 2:

Place the first check dam about 10 ft from the outfall of the channel. Construct the check dam by stacking bags across the channel, shaped as shown in the drawing below. Do not stack bags higher than three feet.

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Schematic. Gravel Bag Check Dam Elevation. 

Step 3:

Place the next check dam upstream of the first such that the toe of the upstream dam is at the same elevation as the top of the downstream dam. See the drawing below. Place other check dams as necessary.

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Schematic. Check Dam Upstream/Downstream Dam.

Pipe and Swale Discharge Points

Rip rap can be used at discharge locations for pipes and swales.

Step 1:

The recommended minimum size for the rip rap apron is 10’ wide and 10’ long. Rip rap is most effective when installed on a flat area and should never be installed on a steep slope. A concrete sill can be installed if necessary to prevent the rip rap from migrating downstream.

Step 2:

The recommended size of rip rap is “No. 2 backing” installed at least 1.1’ thick. Installing a filter blanket longevity of the facility.

Dust Control

Applying water to dry exposed soil areas such as fields, arenas, pens, or dirt roads will prevent or alleviate nuisance dust created by wind or riding activities. Reducing dust in the air can improve animal health.

Organic products such as lignosulfonate and synthetic products such as Durasoil can also be used. These products can be installed either by direct application to the ground or by mixing the product into the top layer of the soil.

Lignosulfonate can effectively be applied at a rate of 0.5 gallons per square yard. Durasoil can be applied as a rate of 0.025 gallons per square yard. Products will need to be re-applied over time, particularly in areas with high vehicular, pedestrian, or equestrian traffic.

Additional Resources

 

  • County of San Diego Watershed Protection Ordinance (http://www.sdcounty.ca.gov/dpw/watersheds/watershedpdf/watershed_ordinance_signed_dec2010.pdf)
  • California Stormwater Quality Association (CASQA) website (www.casqa.org)
  • Livestock and Land website (www.livestockandland.org)
  • Natural Resource Conservation Service (www.nrcs.usda.gov)
  • County of San Diego LID Handbook (www.sdcounty.ca.gov/pds/docs/LID-Handbook.pdf)

 

SEDIMENT CONTROLS

Sediment control measures trap soil particles that have been detached by rainfall, runoff, or wind. These measures should not be used as the primary method of limiting sediment discharge from the site, but rather should be used in combination with appropriate erosion control measures. Sediment control measures function by filtering or settling particles out of the water.

Primary Recommended Controls

  • Gravel bag check dams
  • Berms

Gravel Bag Check Dams

Gravel bags can be installed perpendicularly across channels or drainage course to slow the flow of water and allow time for sediment to settle out. The check dam will also reduce the velocity of the flow which will reduce erosion.

Step 1:

Woven polypropylene or burlap bags are recommended with a burst strength of at least 300 pounds per square inch. Typical bags are 18” in length, 12” in width, and 3” thick, with a weight of approximately 33 pounds. The recommended fill material is 0.5” to 1” Class 2 aggregate base.

Step 2:

Place the first check dam about 10 ft from the outfall of the channel. Construct the check dam by stacking bags across the channel, shaped as shown in the drawing below. Do not stack bags higher than three feet. Include a spillway for the check dam to allow for controlled release and prevent water from undercutting or bypassing the dam. This is done by removing several bags from the top layer of the check dam.

Chart Graph Placeholder 

Schematic. Gravel Bag Check Dam Elevation.

Step 3:

Place the next check dam upstream of the first such that the toe of the upstream dam is at the same elevation as the top of the downstream dam. See the drawing below. Repeat installation as necessary to cover the channel or drainage course.

Chart Graph Placeholder 

Schematic. Check Dam Upstream/Downstream Dam.

Additional Resources

 

  • County of San Diego Watershed Protection Ordinance (http://www.sdcounty.ca.gov/dpw/watersheds/watershedpdf/watershed_ordinance_signed_dec2010.pdf)
  • California Stormwater Quality Association (CASQA) website (www.casqa.org)
  • Livestock and Land website (www.livestockandland.org)
  • Natural Resource Conservation Service (www.nrcs.usda.gov)
  • County of San Diego LID Handbook (www.sdcounty.ca.gov/pds/docs/LID-Handbook.pdf)

INFILTRATION

Infiltration is an effective way to reduce the volume and pollutant load of stormwater runoff. Although it can be very effective, its feasibility is limited by the soil characteristics and available space (compared to the tributary drainage area). The recommendations in this manual are for informal gravel infiltration depressions. Design of formal infiltration trenches and basins should only be performed by licensed engineers.

Key Considerations

  • Location
  • Sizing
  • Inspection

Location

The best locations for infiltration depressions are at least 50 feet away from wells, slopes and building foundations. Infiltration facilities are not suitable for areas with high clay content soil or high ground water. Facilities need to be located and designed to allow water to be safely conveyed if the facility becomes clogged or overwhelmed.

Sizing

In order to be effective, the size of the infiltration facility is based largely on the tributary drainage area. Although this manual provides some general guidance, it is intended only for use with small drainage areas. A licensed engineer should be consulted if the area draining to the facility is larger than 1 acre.

The following steps describe how to size a gravel infiltration depression.

Step 1. Identify the Area

Identify the area (A, in acres) that drains to the proposed infiltration facility. This includes all areas that will contribute runoff to the proposed facility, including pervious areas (pastures, pens, arenas or dirt/gravel roads), impervious areas (such as roofs, roads, parking lots, etc), and could even include off-site areas beyond the limits of the property.

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Schematic. Infiltration Depression Detail.

Step 2. Determine Appropriate Storage Volume

The most effective facility is sized to capture and infiltrate the runoff from a typical rain event (approximately 0.6”). This storage volume must be contained within the void space of the infiltration facility. This is typically 40% of the total facility volume.

Based on 0.6” of precipitation and a 40% void ratio, for tributary areas that are completely impervious (roofs, concrete, asphalt, etc.) the facility size would be 5,500 cubic feet per acre. For pervious tributary areas (pens, arenas, dirt roads/trails, pastures, etc.) which generate less runoff, the facility volume would be 2,000 cubic feet per acre. For areas with a mixture of pervious and impervious, the facility would be sized by prorating between the two values based on percent impervious.

Step 3. Determine the Depth and Surface Area

Since infiltration facilities rely on the ability to infiltrate runoff into the native ground, the effectiveness is based largely on the surface area. Even if adequate storage volume is provided, inadequate surface area will result in ponded water within the facility of an extended period of time. This can lead to vector and safety issues. In order to ensure adequate surface areas, a maximum depth of 1 foot is recommended for infiltration facilities. For depths greater than 1 foot, a licensed engineer should be consulted.

Inspection

If the facility takes longer than 72 hours to drain, it requires repair or replacement under the direction of a licensed engineer.

Additional Resources

  • County of San Diego Watershed Protection Ordinance (http://www.sdcounty.ca.gov/dpw/watersheds/watershedpdf/watershed_ordinance_signed_dec2010.pdf)
  • California Stormwater Quality Association (CASQA) website (www.casqa.org)
  • Livestock and Land website (www.livestockandland.org)
  • Natural Resource Conservation Service (www.nrcs.usda.gov)
  • County of San Diego LID Handbook (www.sdcounty.ca.gov/pds/docs/LID-Handbook.pdf)

LANDSCAPED DEPRESSION

Landscaped depressions filter and remove pollutants from stormwater runoff by collecting flow and allowing it to pass through a soil matrix. They will also improve water quality and add aesthetic appeal to your property.

Key Considerations

  • Location
  • Design
  • Sizing
  • Maintenance

Picture Placeholder 

Photo. Source: Euclid Creek Watershed Program, cuyahogaswcd.org

Location

The ideal facility location is at least 50 feet away from wells, slopes and building foundations. The landscaped depression needs to be located and designed to safely convey flow that exceeds the capacity of the facility. It is also recommended that landscaped depressions be constructed in locations that are accessible for long-term maintenance purposes.

Design

The key design features of landscaped depressions are the:

  • surface storage area,
  • soil matrix, and
  • subdrain system.

The optimum depth of the surface storage reservoir is 6”- 12.” The surface storage reservoir is best vegetated with species that can survive without irrigation and are also capable of surviving when periodically inundated with ponded water. It is also recommended that the surface storage area include a controlled overflow in case the landscaped depression fails or is overwhelmed in a large storm event.

The ideal soil matrix consists of an 18” layer of sandy loam on top of 9” of crushed rock/gravel.

The perforated PVC subdrain is typically 3” or 4” in diameter. The perforated pipes extend across the entire bottom of the landscaped depression and connect to a cleanout prior to discharge from the facility. It is best when the discharge pipe leaving the cleanout is a solid pipe that discharges overland somewhere within the property. Rip rap energy dissipation can be provided at the discharge location.

Sizing

Sizing of the facility is dependent on drainage area. A licensed engineer should be consulted if there is an area larger than 1 acre draining to the facility. The surface area of the landscaped depression is usually approximately 4% of the total area draining to the BMP.

 Picture Placeholder

Photo: Landscaped Depression Detail.

Installation

Step 1:

Excavate to the desired depth and remove native soil.

Step 2:

Install 3” perforated PVC underdrain throughout the bottom of the facility and connect to a cleanout structure that will allow for inspection and maintenance.

Step 3:

Place the crushed rock/gravel to a depth of 9 inches. Cover with filter fabric.

Step 4:

Place 18” of planting soil lightly compacted. Overcompaction during construction can cause significant damage.

Step 5:

Plant vegetation and water it at the end of each day for fourteen days following the planting.

Step 6:

Apply two to three inches of fine shredded hardwood mulch or shredded hardwood chips.

Maintenance

The landscaped surface storage area will need regular care including trimming, weeding, and removal of dead vegetation. Inadequate maintenance can lead to clogging of the soil matrix, which can reduce the effectiveness of the BMP. This can also lead to standing water in the surface storage area, which can become breeding grounds for mosquitos. If standing water is observed more than 72 hours after a rain event, the soil matrix may need to be replaced and a licensed engineer should be consulted.

Additional Resources

  • County of San Diego Watershed Protection Ordinance (http://www.sdcounty.ca.gov/dpw/watersheds/watershedpdf/watershed_ordinance_signed_dec2010.pdf)
  • California Stormwater Quality Association (CASQA) website (www.casqa.org)
  • Livestock and Land website (www.livestockandland.org)
  • Natural Resource Conservation Service (www.nrcs.usda.gov)
  • County of San Diego LID Handbook (www.sdcounty.ca.gov/pds/docs/LID-Handbook.pdf)

CAPTURE AND RE-USE

Capture and re-use of stormwater can reduce pollution to receiving waters by reducing annual runoff volume. Rain water can be collected and stored in containers and used for irrigation.

Key Considerations

  • Capture Potential
  • Re-use Potential
  • Storage Sizing

Capture Potential

Cisterns and rain barrels can be connected to roof downspout drains to capture rain water for reuse. The capture potential is the volume of rain water that the system can capture. This region typically receives 12”-15” of rainfall annually. The potential annual capture volume is determined by multiplying the annual rainfall depth by the area over which the system will capture runoff.

Re-Use Potential

The primary use for captured rain water is irrigation of existing on-site vegetation. Irrigation rates vary based on the type of vegetation. Turf grass used for lawns typically need 0.5” of irrigation per week. The irrigation rate multiplied by the area of vegetation will determine the volume of the potential for re-use.

Detailed methodology for calculating irrigation needs is published in the Water Use Classifications of Landscape Species (WUCOLS) guide created by the University of California in cooperation with the California Department of Water Resources.

Storage Sizing

The required storage is based on the relationship between the capture potential and the re-use potential. The optimal storage volume is an amount that can be captured from a typical rain event (approximately 0.6”) and then used for irrigation within a 1-2 week period.

System Components

A capture and re-use system includes six basic parts:

  • Catchment Surface: the collection surface from which precipitation runs off
  • Gutters and Downspouts: structures to channel water from the roof to the tank
  • Leaf Screens, First-Flush Diverters, and Roof Washers: devices that remove debris and dust from the captured rain before it enters the tank
  • Cistern(s): storage areas
  • Delivery System: system to get collected water to the end use by either gravity feed or pump
  • Treatment/purification: devices to filter or otherwise treat the water if re-purposed for drinking

Installation

Step 1: Determine Catchment Surface

Runoff can be captured from any roof surface. Figure out which roof surface(s) to use for rain water capture.

Step 2: Calculate Number of Downspouts

Having an inadequate number and size of downspouts can cause spillage or over-running. In general, every 1 inch of downspout diameter can drain 1,200 square feet of roof area.

Step 3: Determine Cistern Location

Locate the cistern on level ground. It is recommended for the cistern to sit on a tank pad or foundation capable of supporting the cistern when full.1 Ideally, the pad consists of a compacted soil layer, covered by a level layer of sand such that the tank load will be distributed evenly.

Depending on the cistern location, 4-inch PVC or polyethylene piping can be used to convey water around the building to the cistern.2

1 A gallon of water weighs 8.34 pounds.

2 http://www.motherearthnews.com/homesteading-and-livestock/rainwaterharvesting-system-zmaz03aszgoe.aspx?PageId=4#ArticleContent

Step 4: Install Gutters and Downspouts

Gutters are to be installed with slope towards the downspout and the outside face of the gutter lower than the inside face to encourage drainage away from the building wall.

Step 5: Connect to the Cistern

There are several options for devices to connect the downspout(s) to the cistern. Some include leaf screens and first flush diverters. Follow the installation instructions for the selected connector.

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Photo. Source: shutterstock.com.

Additional Resources

  • County of San Diego Watershed Protection Ordinance (http://www.sdcounty.ca.gov/dpw/watersheds/watershedpdf/watershed_ordinance_signed_dec2010.pdf)
  • California Stormwater Quality Association (CASQA) website (www.casqa.org)
  • Livestock and Land website (www.livestockandland.org)
  • Natural Resource Conservation Service (www.nrcs.usda.gov)
  • County of San Diego LID Handbook (www.sdcounty.ca.gov/pds/docs/LID-Handbook.pdf)
  • Texas Rainwater Harvesting Manual
  • • How to Estimate Roof Rain Downspouts, eHow.com
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