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Flooding services

King County, Washington

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Flooding services and information in King County, WA

Farm Pad Program

King County is working in the Snoqualmie Valley Agricultural Production District to help mitigate flood damages to farming operations. The Farm Pad Program provides:

  • technical assistance for flood modeling;
  • engineering and design assistance;
  • logistical support for construction of farm pads, such as facilitating the movement of material from King County capital project sites in the vicinity to the farm pad site; and
  • assessment of alternative means of mitigating flood risks without placing fill material in the floodplain.

To qualify for assistance, applicants must have a Farm Management Plan (external link) to construct a farm pad in the flood plain.

Determination of Non-Significance, Three Farm Pads in the Snoqualmie Agricultural Production District

King County has issued a Determination of Non-Significance and Environmental Checklist (1.7 Mb Acrobat pdf) for the construction of three farm pads on farms in the Snoqualmie Valley, which will involve placing fill within the floodplain of the Snoqualmie River. Farm Pad 1 is an existing farm pad that will be expanded by 38,900 square feet in top surface area, and will be 17 feet high. The expansion will require approximately 34,000 cubic yards of fill. Farm Pad 2 is an existing farm pad that will be expanded by 42,500 square feet in top surface area and will be 17 feet high. The expansion will require approximately 34,000 cubic yards of fill. Farm Pad 3 will be a new farm pad, 20,000 square feet in top surface area, and 14 feet high. Construction of the pad will require ¬¬15,000 cubic yards of fill.

Because the farms on which pads will be constructed are all located in the Snoqualmie Valley Agricultural Production District and have similar geographical characteristics, and because the possible impacts of the proposals are similar, King County Water and Land Resources Division is analyzing them as a multi-project SEPA in a single checklist, as allowed in WAC 197-11-060, and is addressing them together in its determination. King County will conduct an analysis of potential upstream and downstream flood impacts on each proposed farm pad. The County will not permit any pad that would result in a detectable flood level rise. 

Comments on this project must be received no later than July 22, 2014. For additional information, please contact Ms. Richelle Rose, Program Manager, at 206-477-4815, or write to the address below:

Attn: Richelle Rose
King County River and Floodplain Management Section
201 South Jackson, Suite 600
Seattle, WA  98104
Phone 206-477-4815
FAX: 206-296-0912

A farm pad being constructed in the Duvall area of the Snoqualmie Valley, 2012.

Technical assistance

With funding from the King County Flood Control District (external link), King County will provide technical assistance to help applicants locate and construct an elevated farm pad to store livestock, farm machinery and other agricultural equipment and supplies. King County cannot be held liable for the stability of the pad during a flood.

King County can provide:

  • ideas for possible structures;
  • offer general engineering advice as to the types of soil and methods of compaction to construct a farm pad;
  • assistance with the permitting process; and
  • preparation of a site plan and farm pad drawings.
Applicants are responsible for:
  • getting a grading permit;
  • providing any supporting engineering calculations required for building permits;
  • hiring a private engineering firm to provide construction documentation if a plan includes placing a building or structure on the farm pad; and
  • oversight of all construction.

A farm pad in use on a Snoqualmie Valley dairy farm during a major flood in the 1990s.

Things to consider when building a farm pad

Location

The location of the farm pad needs to be selected after considering and weighing the options of several agricultural, engineering and ecological variables. King County staff will assist applicants with the technical assessments necessary to determine if a farm pad can be constructed based on these variables:

  1. Is it easy to access?
  2. Is it out of high-velocity flood waters?
  3. Is it on existing high ground to minimize the amount of fill?
  4. Will it increase negative flood impacts on neighboring structures or roads?
  5. Is it out of wetlands and away from wetlands and streams to the extent possible?

Size

The smaller the farm pad the less likely it is to exceed regulatory standards for conveyance or compensatory storage (KC 21.A.24, PDF). There is a very limited capacity for fill in the valley if we are to preserve conveyance capacity of floodwaters over time. Other landowners, and other floodplain uses need to have capacity also. If the conveyance standard is exceeded, the pad will not be allowed.

If a pad larger than 2,000 square feet is proposed, staff from the King County Agriculture Program or the King Conservation District (external link) will provide consultation about efficient use of the space, and propose as small a pad as possible to meet individual needs.

Drawing for permit submittal

Design

  • Side slopes should be no steeper than two horizontal slopes to one vertical slope.
  • Ramp(s) - Slopes of the approach and departure ramps are dependent on the climbing capability of equipment and/or livestock. A slope steeper than four to one is not recommended.
  • Height/elevation - Farm pads should be built at a minimum of one foot above base-flood elevation level (provided by King County). Since pads are built on top of organic soils, settlement should be expected.

Construction

Materials: The type of dirt used to make the farm pad can make the difference between a solid pad your livestock can stand on and one that they sink in. Granular “pit run” type soils compact well, whereas rich, high-organic soils do not. Organic soils can be used on the surface of the side slopes of the completed pad to encourage plant growth that will help hold the soil in place during a flood. If granular material is not readily available, it is possible to use other soil as long as a filter-fabric material is placed over the base material and at least two feet of granular soil is used to cap the other soils.  

Compaction: Compaction is the second most important component in construction of a farm pad. Thin six inch lifts during construction add time but result in a farm pad that provides firm footing and easy loading of machinery. Lifts should not exceed a thickness of one foot. While bulldozers are good for placing dirt in lifts during construction, they do not compact the material well. Using a vibratory drum roller or a heavily loaded truck or wheeled tractor to track soil back and forth is recommended. If tracking is used, track back and forth in one direction and then repeat 90 degrees to the original direction.

Building/structure: King County provides advice and guidelines for farm pads only. A private engineer should be hired if farm pad plans include building a shelter or structure. An engineer can anticipate drainage needs, proper soil placement to support a structure and other considerations.

Drainage: The top of the pad needs to be domed so rainfall will runoff the pad rather than saturating it.

Permit conditions

Construction: Once permitted, there will be conditions for constructing the farm pad. Examples include: ensuring road safety (e.g., loose dirt on a road is slippery if it rains); protecting nearby streams or wetlands (e.g., building a silt fence between the construction site and a nearby wetland or stream may be necessary); ensuring trucks dump fill within the perimeter of the pad.

Use: A signed covenant indicating that there will be no residential use of the pad in the future is required. The pad is to support farm viability. While it may provide flood free space for some personal belongings, it is not intended to be sized or used for secondary activities on the farm that are not agriculturally related.

Thumbnail image of a map of the Snoqualmie Valley Agriculture Production District

Click to enlarge thumbnail of Snoqualmie Valley Agriculture Production District (PDF, 514KB)

For more information about the Farm Pad Program, please contact Richelle Rose, King County River and Floodplain Management Section.