OAR 141-093-0141: Transportation-Related Structures - Eligibility Requirements

(1) Definitions. For the purposes of this rule: (a) “Entrenchment ratio” is the ratio between the flood prone width and the width at the elevation at which a stream first reaches the top of its natural banks and overflows. (b) “Floodplain” means that portion of a river valley, adjacent to the channel, which is built of sediments deposited during the present regimen of the stream and which is covered with water when the waterway overflows its banks at flood stage. (c) “Flood Prone Area” means the area adjacent to the stream that is inundated or saturated when the elevation of the water is at twice the maximum depth at bankfull stage or three times the average bankfull depth. (d) “Functional floodplain” means the flood prone area up to 2.2 times the width at OHWL for streams with an entrenchment ratio of 2.2 or greater, and the entire width of the flood prone area for streams with an entrenchment ratio less than 2.2. This area may be reduced by the presence of natural constrictions, flow regulation, or encroachment of built infrastructure. (2) Thresholds. To be eligible a project must be limited to no more than: (a) In waters of this state, other than wetlands, a total of five thousand (5,000) cubic yards of material filled, removed or altered, for the entire project. Up to one thousand (1,000) cubic yards of the allowable 5,000 cubic yards of material may be used for streambank stabilization; and (b) One-half (0.5) acre of permanent impact to wetlands is allowed for the entire project. (3) No impacts to Aquatic Resources of Special Concern. The project must not involve impacts to Aquatic Resources of Special Concern. Aquatic Resources of Special Concern include alkali wetlands and lakes, bogs, cold water habitat, fens, hot springs, interdunal wetlands, kelp beds, mature forested wetlands, native eelgrass beds, off-channel habitats (alcoves and side channels), ultramafic soil wetlands, vernal pools, wet prairies, wooded tidal wetlands, and others, as determined by the Department. (4) Notwithstanding the requirements of OAR 141-093-0105 through OAR 141-093-0135, the following projects will not require compensatory mitigation, and the applicant may use best professional judgment to assess functions and values if the proposed design meets all of the following requirements: (a) Widening, replacing, or maintaining an existing culvert or bridge (A) A clear, unobstructed opening above the expected depth or scour of the streambed within the functional floodplain must be maintained; (B) A single span bridge or culvert must span 1.5 times the width of the stream at the ordinary high water line (OHWL), or wider; (C) A multiple span structure must span 2.2 times the width of the stream at the OHWL, or wider, without including the width of interior supports; (D) Conduits must be installed within road fill, if necessary, to allow water to flow across the floodplain; (E) All artificial constrictions within the functional floodplain must be removed that are not otherwise a component of the culvert or bridge, unless otherwise approved by the Department; (F) Streambanks and newly exposed floodplains must be reshaped to either match or be flatter than upstream and downstream contours; (G) Streambank stabilization methods are limited to techniques in ORS 141-089-0730 through 141-089-0735, plus the minimum amount of rock necessary to protect the integrity of the culvert or bridge. Rock on streambanks above OHWL must incorporate soil and woody vegetation; (H) Streambanks and newly exposed floodplains must provide or be planted to achieve a density of at least 1 live native shrub or tree per 6 linear feet, except under a bridge or within areas needed for site distance and safety, unless otherwise approved by the Department; and (I) ODFW fish passage requirements for adult and juvenile fish must be met. (b) Restoring natural fluvial processes if the proposed design meets all the following requirements: (A) The activity is integrally related to widening, replacing, maintaining, or removing an existing structure; (B) Limited to use of materials sized appropriately for the system and that mimic natural substrate found within the system, unless otherwise required for fish passage; (c) Reestablishing bank slopes adjacent to an existing structure to the previous extent of the toe of the slope. (A) Reestablishment may expand the toe of pre-existing structure fill for no more than 50 feet of channel when necessary to maintain a 2:1 fill slope or steeper. At least 80% of the previous channel width at OHWL must be retained. (B) Streambank stabilization methods are limited to techniques in ORS 141-089-0730 through 141-089-0735, plus the minimum amount of rock necessary to protect the integrity of the road and stabilize the toe of the slope. Rock on streambanks above OHWL must incorporate soil and woody vegetation, unless otherwise approved by the Department. (C) A reestablished streambank must be planted to achieve a density of at least 1 live native shrub or tree per 6 linear feet, unless otherwise approved by the Department.