«SONOMA COUNTY AGRICULTURAL COMMISSIONER’S OFFICE TABLE OF CONTENTS INTRODUCTION REGULATORY REQUIREMENTS CALIFORNIA TIGER SALAMANDER MAP CHAPTER ONE ...»
4.4.3 Vegetated check dams or straw bale sediment barriers along ditches or swales 4.4.4 Daylight underground outlets to rocked ditches or vegetated swales 4.4.5 Sediment or infiltration basins
4.5.4 Infiltration galleries.
4.6 Use equipment or specialty tires that minimize soil compaction.
4.7 Provide sediment collection features on all drop inlets.
4.8 Provide energy dissipaters for all pipe outfall areas.
4.9 Discharge drainage pipes upslope of riparian areas and stream banks.
4.10 Use trash racks or caps on drop inlets to prevent debris such as branches from entering the system. Maintain capacity of sediment basins by removing sediments when dry and placing sediment in an area where it will not enter a stream. Design the release of water from sediment basins to mimic natural flow patterns while retaining the sediment in the pond.
Perform culvert and drop inlet cleaning on a regular basis, before the wet season begins (October 15) as well as during and after any large storm.
4.11 Check temporary erosion control measures and repair as needed during and after storms:
Remove sediment as needed from silt fences, sandbags, straw wattles, and sediment traps.
Permanent measures, such as seeding, planting, and rocking, are preferred once the source of any runoff problem is corrected.
14 Example4.1-Storm Drain Outfall Modification Drain pipes that outfall in stream channels or on top of stream banks can result in concentrated flow erosion in the channel itself or on the bank. The following photos and drawing is an example of how to modify the pipe outfall so the water will sheet flow through the stream setback area.
Example 4.3- Vineyard Inlet With Sediment Trap All drop inlets should have a sediment collection component.
Surface water should be filtered in some way to allow the fines to settle out before the water enters the pipe. Existing drop inlets that do not have a sediment collection component can be easily modified by adding a corrugated plastic pipe collar around the existing pipe. The collection area (sump) must be a minimum of 6 inches deep.
Example 4.4- Concrete Inlet With Sediment Trap 17 Example 4.
5 - Rock Outlet for Storm Drains All pipe outfalls should have scour protection to minimize sediment delivery downstream. The size of the dissipater is dependent on the size of the pipe. Rock protection can be easily added to existing pipe outfalls. Do not outfall the pipe directly into a creek.
18 Example 4.6- Rock Outlet for Swales All swale outfalls should have scour protection to minimize sediment delivery downstream.
Rock protection can be easily added to existing swales.
19 Example 4.7- Sediment Basin Basins should be designed to drain within 72 hours following storms. The length of the basin should be more than twice the width of the basin determined by measuring the distance between the inlet and the outlet. All slopes should be protected with erosion control blankets.
20 Example 4.8- Ag Road Water Bar Water bars should be installed when the slope of the road or avenue exceeds 15%. Construct water bars not more than 100 feet apart or 50 feet apart for steeper slopes.
21 Example 4.9-Temporary Drainage Swale 22 CHAPTER FIVE- Riparian Zones Riparian zones provide and maintain many of the essential habitat features necessary to complete the salmonid life cycle such as erosion control, shade and temperature regulation, macroinvertebrate food supply, large woody debris supply, and filtration of sediments, nutrients, and pollutants.
Riparian vegetation also increases the water storage capacity of the soil, allowing for increased flow volumes within the streams during the warmer months.
Environmental Concerns Bare stream banks are significantly more likely to erode than forested stream banks. Excessive bank erosion degrades salmonid habitat by filling pools, burying spawning gravels, and decreasing macroinvertebrate production. Removal of riparian vegetation causes elevated stream temperatures which can create thermal migration barriers for migrating salmon, generate stressful rearing conditions, decrease oxygen solubility and encourage disease. Loss of large woody debris alters natural geomorphic functions. Loss of litterfall alters the food source for many aquatic macroinvertebrates which in turn are important salmonid food source.
Evaluate your riparian areas. Measure the smallest and largest portions of the existing riparian zone, as well as vegetation composition, the extent of stream shading, and the distance from the edge of the riparian corridor to the first row of vines/orchard. Note any previous land use practices, infrastructure, roads, or structure within the riparian zone.
Best Management Practices 5.1. !bide by the required stream, pond, and wetland setbacks as defined in the ounty’s rading, Drainage, Vineyard/Orchard Site Development Ordinance.
5.2. Maintain the existing riparian zone. A healthy riparian zone consists of trees, shrubs of different ages growing closest to the channel and a grassy zone closest to the vineyard/orchard operation.
5.3. Maintain existing riparian vegetation to provide at least 65% shading of streams less than 50 feet in wetted width.
5.4. Plant native species in riparian zones that are not presently forested. Irrigate for the first two or three years and protect from browsing. Once established, leave riparian zone in a natural state.
5.5. Replace existing all-weather access roads that are within the county required setback no touch areas with grassy avenues. If the road must be used as an all-weather access road, then move the road out of the setback area and replant the old roadbed with riparian vegetation and/or a filter strip.
5.6. Leave downed trees in the riparian corridor for recruitment as large woody debris, as long as it does not pose an immediate threat to infrastructure or property downstream.
5.7. Maintain grass buffers along natural streams and drainage channels with a defined bed and bank.
5.8. Cooperate in watershed-wide restoration projects that will help to improve riparian habitat.
23 Stream Setbacks Existing riparian corridors should be maintained. The roots of the vegetation provide bank stability.
Shade from trees and bushes keep water temperatures cool, which is important for sustaining aquatic species. Native grasses help filter sediment from surface runoff. However, if the existing vegetative cover is in poor condition the setback area may be improved with a vegetative filter strip for use as an agricultural avenue. The strip must be planted with a filter strip seed mix and maintained for the intended use.
Example 5.1 - Required Stream Setbacks for Level I Projects and All Replants Setbacks apply to all new vineyards/orchards with a slope of 10% or less on highly erodible soils or 15% or less on non-highly erodible soils and all replant projects, unless stricter requirements are established in the general plan, local coastal program, and/or zoning code*
NOTE: Vegetative filter strips may be used as turnarounds or grassy avenues provided the filter strip is maintained for the intended use.
*Excerpted from the Sonoma County Grading, Drainage, Vineyard/Orchard Site Development Ordinance 24 Example 5.2 - Required Stream Setbacks for Level II Projects *Setbacks apply to all new vineyards/orchards with a slope greater than 10% on highly erodible soils and greater than 15% on non-highly erodible soils, unless stricter requirements are established in the general plan, local coastal plan, and/or zoning code*
NOTE: Vegetative filter strips may be used as turnarounds or grassy avenues provided the filter strip is maintained for the intended use.
Example 5.3 -Vineyard Setback/Filter Strip *Excerpted from the Sonoma County Grading, Drainage, Vineyard/Orchard Site Development Ordinance 25 Wetland and Pond Setbacks Existing wetland and pond vegetation should be maintained.
The roots of the vegetation provide bank stability. Shade from trees and bushes keep water temperatures cool, which is important for sustaining aquatic species. Native grasses help filter sediment from surface runoff. However, if the existing vegetative cover is in poor condition, the setback area may be improved with a vegetative filter strip for use as an agricultural road. The strip must be planted with a filter strip seed mix and maintained for the intended use.
Example 5.4 - Required Wetland and Pond Setbacks NOTE: Vegetative filter strips may be used as turnarounds or grassy avenues provided the filter strip is maintained for the intended use.
Setbacks apply to all new vineyards/orchards, unless stricter requirements are established in the general plan, local coastal plan, and/or zoning plan* *Excerpted from the Sonoma County Grading, Drainage, Vineyard/Orchard Site Development Ordinance 26 CHAPTER SIX-Tree Removal and Erosion Control Through the combination of canopy and roots, trees help protect and stabilize the land. Their removal requires proper planning and adherence to land-based best management practices designed to reduce the velocity of run-off, safeguard surface waters from excessive runoff, and maintain the soil’s integrity and its potential to absorb water.
The BMPs in this chapter shall only apply to vineyard and orchard planting projects proposing the removal of more than one-half acre of tree canopy (tree removal).
Removal of trees for vineyard and orchard planting projects shall be prohibited on natural slopes (with identified cohesionless soils) which are steeper than 40 percent.
Removal of trees for vineyard and orchard planting projects shall also be prohibited on identified areas of instability unless the area is repaired in compliance with Chapter 11 of the Sonoma County Code and details of the repair are shown on the project plans.
Tree removal can:
Encourage erosion due to an increase in precipitation runoff and/or soil disturbance. Erosion and sedimentation have the potential to impact aquatic habitat and related resources by affecting turbidity, and altering channel structure.
Alter drainage patterns and may affect sheet flow dispersal and drainage to streams.
Lead to a loss of stabilization of slopes, affecting slope integrity and contributing to substantial increases in erosion and sedimentation in surface waters.
Site Evaluation For blocks in which tree or other vegetation removal has occurred since November 2008, the aerial photos available at www.sonoma-county.org/prmd/activemap (or more recent aerial photo as approved by the Agricultural Commissioner) will be used to determine pre-development cover/canopy levels.
If more than one-half acre of tree canopy has been removed since November 2008, or is proposed for removal, the project shall be subject to the tree removal standards.
A site assessment by an engineering geologist shall be required for all Level II projects proposing tree removal. The engineering geologist shall review each site for areas of instability.
In addition, for sites with natural slopes steeper than 25 percent in mapped areas of potentially cohesionless soils, the engineering geologist shall review the site for cohesionless soils. The preferred approach is to divide the development into blocks with similar landforms and slopes, generally no more than 20 acres in size. This allows for the use of existing drainages, major slope breaks, and topographic divides as natural boundaries.
27 As part of the engineered plan, the civil engineer shall calculate a soil loss or sediment delivery factor to evaluate pre-development and post-development conditions for each block.
Best Management Practices
For Level II projects proposing tree removal:
With natural slopes no steeper than 25 percent, applicants should use the Universal Soil Loss Equation (USLE) to demonstrate no net increase in erosion from pre-development conditions.
With natural slopes steeper than 25 percent,, applicants should use the Revised Universal Soil Loss Equation (RUSLE2) to demonstrate no net increase in erosion from pre-development conditions.
When using USLE, use tabulated USLE slope length/gradient (LS), cover management (C), and conservation practice factors (P), listed in the BMP Handbook Appendix to evaluate the pre- versus post-development soil loss.
Applicants can propose to use another published or peer-reviewed soil loss predictive model consistent with the standard of care to show no net increase in erosion from pre-development conditions.
As an alternative to using a soil loss predictive model, and applicant can prepare a sediment delivery analysis using a published or peer-reviewed method consistent with the standard of care that demonstrates that the project will result in no net increase in sediment delivery to streams, lakes, or wetlands.
Slope Stability 6.1. For all projects proposing tree removal, adhere to the setbacks from identified areas of instability (landslides etc.) called for in Chapter 11 of the Sonoma County Code: 50 feet below or laterally and 100 feet above these landforms, or as recommended by an engineering geologist.
6.2. For all Level II projects proposing tree removal, a report by an engineering geologist shall be
submitted identifying and characterizing areas of instability.
6.3. For Level II projects proposing tree removal with natural slopes steeper than 25 percent in mapped areas of potentially cohesionless soils, a report by an engineering geologist shall be submitted identifying any areas of cohesionless soils. Areas of mapped potentially cohesionless soils are determined from the map titled “!reas of Potentially ohesionless Soils”, which is available at the following web address: http://www.sonoma-county.org/agcomm/vesco.htm 6.4. For Level II projects proposing tree removal with natural slopes between 25 percent and 40 percent having cohesionless soils identified by a geologic report, a slope stability analysis shall be conducted. Tree removal shall be prohibited when the factor of safety will be less than 1.5 under saturated conditions after tree removal.