Sediment Control BMPs
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Water and Sediment Control Basins
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Constructed earth embankments or a combination ridge and channel. Constructed across the slope and minor watercourses to form a sediment trap and water detention basin.
Benefits
Trap sediment and pesticides adsorbed to soil particles.
Reduce and manage onsite and downstream runoff.
Divert the flow of dissolved substances such as nutrients and pesticides.
Improve the farmability of sloping land, reduce water course and gully erosion.
Improve downstream water quality.
Drawbacks
Basins are not viable for many orchard areas in California, primarily because considerable land acreage would be required to manage the volumes of water typically produced in rainfall events, especially in the Sacramento Valley.
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PAM Applications
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PAM is a polymer compound injected or fed into irrigation water at the head of a field supply ditch or discharge point.
Applications rates range from 5-8 pounds per acre with the material typically metered into the head ditch with a gandy-type applicator.
Benefits
Soil does not move down the row or erode when irrigation water is treated with PAM.
Suspended soil particles drop out of irrigation water containing PAM.
After an irrigation containing PAM, erosion and transport of sediment is greatly reduced in subsequent irrigations.
Erosion reductions of 95% have been documented in numerous field trials and commercial applications in the San Joaquin Valley.
Drawbacks
Additional cost
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Tailwater Return Systems
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Tailwater return systems pump tailwater to the head end of the field for application to other parts of the field.
Benefits
Use of tailwater can offer substantial savings in irrigation power consumption if the water supply is groundwater.
A tailwater recovery system increases yields because of higher irrigation efficiencies.
A tailwater recovery system will not save all the tailwater, but it can increase irrigation efficiency by 25 to 30 percent.
Drawbacks
The loss of the area required for a reuse pit and periodic maintenance of the pump, storage and return facilities.
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Compaction / Wheel Rutting
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Wheel ruts formed by equipment passing through wet fields can create channels for water and sediment to runoff from orchards.
Where possible, minimize creation of wheel ruts with dormant orchard sprayers, brush shredders or other equipment when orchard floor is saturated.
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Drainage System Management
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Filtering runoff water through vegetation allowed to grow in drainage ditches may help mitigate offsite movement of sediment as well as pesticides dissolved in storm runoff.
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Avoiding Channelization of Streams and Creeks
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Allowing streams to naturally flow and meander can increase runoff retention and infiltration.
A modified or channeled stream could also be restored to a more natural state by re-establishment of the riparian vegetation, which also provides stream bank protection.
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Berms at Low Ends of Fields (sandy soils, low slope)
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Raised berms at low ends of fields can trap sediment and adsorbed pesticides reducing runoff of dissolved substances in fields with low slopes and sandy soil types.
Berms hold back water, increasing runoff retention and allowing infiltration.
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Planting 90 degrees to Grade
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Planting orchards and performing tractor work 90 degrees to the grade to reduce erosion and provide for greater water penetration and retention.
Practice is very site-specific and would not be easily adaptable to many existing orchards, particularly those that are flood irrigated.
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Aeration
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Use of specialized tillage equipment to break crusts and aerate orchard soils with the intent of increasing water penetration and retention, thus reducing runoff.
Aeration improves the soil profile with minimal disruption to the orchard floor.
A finishing process may be required, however, for almond orchards where shake-and-sweep harvest methods are used.
Aeration may reduce OP pesticide runoff although no studies have been conducted.
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Ripped Resident Vegetation
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In orchards with permanent or semi-permanent sod, vegetation is ripped at various lengths and/or depths.
Ripping significantly increases soil water due to increased infiltration and porosity.
Heavy rains after fall ripping can leave orchards impassable to heavy equipment such as orchard sprayers.
In recent research, ripped resident vegetation performed the best for infiltration and reduced diazinon transport, followed by non-ripped resident vegetation and bare ground being the least effective.
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Improving Soil Texture (tilth)
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Practices such as tillage, gypsum applications or actions of earthworms have potential to increase water penetration and reduce runoff in compacted soils or where an impermeable soil layer exists. However, no studies have been conducted to show efficacy in reducing OP pesticide runoff with these approaches.
Benefits
Increased water penetration resulting in less runoff and increased recharging of the soil profile.
Less water runoff means less potential for pesticides to be transported off-site.
Drawbacks
Tillage can increase erosion under some conditions and necessitate additional orchard floor finishing work (scraping).
Results vary with soil type and, under some conditions, compaction could increase.
Improved soil permeability may increase movement of nitrate and other chemicals into groundwater.
The balance of benefits versus disadvantages is not clear at this time and more research is needed.
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