WAC 220-110-070 Water Crossing Structures

In fish bearing waters, bridges are preferred as water crossing structures by the department in order to ensure free and unimpeded fish passage for adult and juvenile fishes and preserve spawning and rearing habitat.  Pier placement waterward of the ordinary high water line shall be avoided, where practicable.  Other structures which may be approved, in descending order of preference, include:  Temporary culverts, bottomless arch culverts, arch culverts, and round culverts.  Corrugated metal culverts are generally preferred over smooth surfaced culverts.  Culvert baffles and downstream control weirs are discouraged except to correct fish passage problems at existing structures.

An HPA is required for construction or structural work associated with any bridge structure waterward of or across the ordinary high water line of state waters.  An HPA is also required for bridge painting and other maintenance where there is potential for wastage of paint, sandblasting material, sediments, or bridge parts into the water, or where the work, including equipment operation, occurs waterward of the ordinary high water line.  Exemptions/5-year permits will be considered if an applicant submits a plan to adhere to practices that meet or exceed the provisions otherwise required by the department.

Water crossing structure projects shall incorporate mitigation measures as necessary to achieve no-net-loss of productive capacity of fish and shellfish habitat.  The following technical provisions shall apply to water crossing structures:

(1) Bridge construction.

• (a) Excavation for and placement of the foundation and superstructure shall be outside the ordinary high water line unless the construction site is separated from waters of the state by use of an approved dike, cofferdam, or similar structure.
• (b) The bridge structure or stringers shall be placed in a manner to minimize damage to the bed.
• (c) Alteration or disturbance of bank or bank vegetation shall be limited to that necessary to construct the project.  All disturbed areas shall be protected from erosion, within seven calendar days of completion of the project, using vegetation or other means.  The banks shall be revegetated within one year with native or other approved woody species.  Vegetative cuttings shall be planted at a maximum interval of three feet (on center), and maintained as necessary for three years to ensure eighty percent survival.  Where proposed, planting densities and maintenance requirements for rooted stock will be determined on a site-specific basis.  The requirement to plant woody vegetation may be waived for areas where the potential for natural revegetation is adequate, or where other engineering or safety factors preclude them.
• (d) Removal of existing or temporary structures shall be accomplished so that the structure and associated material does not enter the watercourse.
• (e) The bridge shall be constructed, according to the approved design, to pass the 100-year peak flow with consideration of debris likely to be encountered.  Exception shall be granted if applicant provides hydrologic or other information that supports alternative design criteria.
• (f) Wastewater from project activities and water removed from within the work area shall be routed to an area landward of the ordinary high water line to allow removal of fine sediment and other contaminants prior to being discharged to state waters.
• (g) Structures containing concrete shall be sufficiently cured prior to contact with water to avoid leaching.
• (h) Abutments, piers, piling, sills, approach fills, etc., shall not constrict the flow so as to cause any appreciable increase (not to exceed .2 feet) in backwater elevation (calculated at the 100-year flood) or channel wide scour and shall be aligned to cause the least effect on the hydraulics of the watercourse.
• (i) Riprap materials used for structure protection shall be angular rock and the placement shall be installed according to an approved design to withstand the 100-year peak flow.

(2) Temporary culvert installation.

The allowable placement of temporary culverts and time limitations shall be determined by the department, based on the specific fish resources of concern at the proposed location of the culvert.

• (a) Where fish passage is a concern, temporary culverts shall be installed according to an approved design to provide adequate fish passage.  In these cases, the temporary culvert installation shall meet the fish passage design criteria in Table 1 in subsection (3) of this section.
• (b) Where culverts are left in place during the period of September 30 to June 15, the culvert shall be designed to maintain structural integrity to the 100-year peak flow with consideration of the debris loading likely to be encountered.
• (c) Where culverts are left in place during the period June 16 to September 30, the culvert shall be designed to maintain structural integrity at a peak flow expected to occur once in 100 years during the season of installation.
• (d) Disturbance of the bed and banks shall be limited to that necessary to place the culvert and any required channel modification associated with it.  Affected bed and bank areas outside the culvert shall be restored to preproject condition following installation of the culvert.
• (e) The culvert shall be installed in the dry, or in isolation from stream flow by the installation of a bypass flume or culvert, or by pumping the stream flow around the work area. Exception may be granted if siltation or turbidity is reduced by installing the culvert in the flowing stream.  The bypass reach shall be limited to the minimum distance necessary to complete the project.  Fish stranded in the bypass reach shall be safely removed to the flowing stream.
• (f) Wastewater, from project activities and dewatering, shall be routed to an area outside the ordinary high water line to allow removal of fine sediment and other contaminants prior to being discharged to state waters.
• (g) Imported fill which will remain in the stream after culvert removal shall consist of clean rounded gravel ranging in size from one-quarter to three inches in diameter. The use of angular rock may be approved from June 16 to September 30, where rounded rock is unavailable.  Angular rock shall be removed from the watercourse and the site restored to preproject conditions upon removal of the temporary culvert.
• (h) The culvert and fill shall be removed, and the disturbed bed and bank areas shall be reshaped to preproject configuration.  All disturbed areas shall be protected from erosion, within seven days of completion of the project, using vegetation or other means.  The banks shall be revegetated within one year with native or other approved woody species.  Vegetative cuttings shall be planted at a maximum interval of three feet (on center), and maintained as necessary for three years to ensure eighty percent survival.  Where proposed, planting densities and maintenance requirements for rooted stock will be determined on a site-specific basis.  The requirement to plant woody vegetation may be waived for areas where the potential for natural revegetation is adequate, or where other engineering or safety factors need to be considered.
• (i) The temporary culvert shall be removed and the approaches shall be blocked to vehicular traffic prior to the expiration of the HPA.
• (j) Temporary culverts may not be left in place for more than two years from the date of issuance of the HPA.

(3) Permanent culvert installation.

• (a) In fish bearing waters or waters upstream of a fish passage barrier (which can reasonably be expected to be corrected, and if corrected, fish presence would be reestablished), culverts shall be designed and installed so as not to impede fish passage.  Culverts shall only be approved for installation in spawning areas where full replacement of impacted habitat is provided by the applicant.
• (b) To facilitate fish passage, culverts shall be designed to the following standards:
• (i) Culverts may be approved for placement in small streams if placed on a flat gradient with the bottom of the culvert placed below the level of the streambed a minimum of twenty percent of the culvert diameter for round culverts, or twenty percent of the vertical rise for elliptical culverts (this depth consideration does not apply within bottomless culverts).  Footings of bottomless culverts shall be buried sufficiently deep so they will not become exposed by scour within the culvert.  The twenty percent placement below the streambed shall be measured at the culvert outlet.  The culvert width at the bed, or footing width, shall be equal to or greater than the average width of the bed of the stream.
• (ii) Where culvert placement is not feasible as described in (b)(i) of this subsection, the culvert design shall include the elements in (b)(ii)(A) through (E) of this subsection:
• (A) Water depth at any location within culverts as installed and without a natural bed shall not be less than that identified in Table 1.  The low flow design, to be used to determine the minimum depth of flow in the culvert, is the two-year seven-day low flow discharge for the subject basin or ninety-five percent exceedance flow for migration months of the fish species of concern.  Where flow information is unavailable for the drainage in which the project will be conducted, calibrated flows from comparable gauged drainages may be used, or the depth may be determined using the installed no-flow condition.
• (B) The high flow design discharge, used to determine maximum velocity in the culvert (see Table 1), is the flow that is not exceeded more than ten percent of the time during the months of adult fish migration.  The two-year peak flood flow may be used where stream flow data are unavailable.
• (C) The hydraulic drop is the abrupt drop in water surface measured at any point within or at the outlet of a culvert.  The maximum hydraulic drop criteria must be satisfied at all flows between the low and high flow design criteria.
• (D) The bottom of the culvert shall be placed below the natural channel grade a minimum of twenty percent of the culvert diameter for round culverts, or twenty percent of the vertical rise for elliptical culverts (this depth consideration does not apply within bottomless culverts).  The downstream bed elevation, used for hydraulic calculations and culvert placement in relation to bed elevation, shall be taken at a point downstream at least four times the average width of the stream (this point need not exceed twenty-five feet from the downstream end of the culvert).  The culvert capacity for flood design flow shall be determined by using the remaining capacity of the culvert.

• (E) Appropriate statistical or hydraulic methods must be applied for the determination of flows in (b)(ii)(A) and (B) of this subsection.  These design flow criteria may be modified for specific proposals as necessary to address unusual fish passage requirements, where other approved methods of empirical analysis are provided, or where the fish passage provisions of other special facilities are approved by the department.
• (F) Culvert design shall include consideration of flood capacity for current conditions and future changes likely to be encountered within the stream channel, and debris and bedload passage.
• (c) Culverts shall be installed according to an approved design to maintain structural integrity to the 100-year peak flow with consideration of the debris loading likely to be encountered.  Exception may be granted if the applicant provides justification for a different level or a design that routes that flow past the culvert without jeopardizing the culvert or associated fill.
• (d) Disturbance of the bed and banks shall be limited to that necessary to place the culvert and any required channel modification associated with it.  Affected bed and bank areas outside the culvert and associated fill shall be restored to preproject configuration following installation of the culvert, and the banks shall be revegetated within one year with native or other approved woody species.  Vegetative cuttings shall be planted at a maximum interval of three feet (on center), and maintained as necessary for three years to ensure eighty percent survival.  Where proposed, planting densities and maintenance requirements for rooted stock will be determined on a site-specific basis.  The requirement to plant woody vegetation may be waived for areas where the potential for natural revegetation is adequate, or where other engineering or safety factors preclude them.
• (e) Fill associated with the culvert installation shall be protected from erosion to the 100-year peak flow.
• (f) Culverts shall be designed and installed to avoid inlet scouring and shall be designed in a manner to prevent erosion of streambanks downstream of the project.
• (g) Where fish passage criteria are required, the culvert facility shall be maintained by the owner(s), such that fish passage design criteria in Table 1 are not exceeded.  If the structure becomes a hindrance to fish passage, the owner shall be responsible for obtaining a HPA and providing prompt repair.
• (h) The culvert shall be installed in the dry or in isolation from the stream flow by the installation of a bypass flume or culvert, or by pumping the stream flow around the work area.  Exception may be granted if siltation or turbidity is reduced by installing the culvert in the flowing stream.  The bypass reach shall be limited to the minimum distance necessary to complete the project.  Fish stranded in the bypass reach shall be safely removed to the flowing stream.
• (i)  Wastewater, from project activities and dewatering, shall be routed to an area outside the ordinary high water line to allow removal of fine sediment and other contaminants prior to being discharged to state waters.

Statutory Authority:  RCW 77.12.047 (formerly RCW 75.08.080).  94-23-058 (Order 94-160), 220-110-070, filed 11/14/94, effective 12/15/94.  Statutory Authority:  RCW 77.55.100 (formerly RCW 75.20.100) and 77.12.047 (formerly RCW 75.08.080). 83-09-019 (Order 83-25), 220-110-070, filed 4/13/83.