ENFORCE35980 - Laserfiche WebLink

Home Browse Search

Mr. Rick Siebel, Regional Director -6- May 16, 1995 Office of Surface Mining Western Region Coordinating Center (a) Establish or restore meandering pattern with approved by the Division; the channel to approximate its natural a geomorphically acceptable gradient as (b) Allow the drainage channel to remain in dynamic equilibrium with the drainage basin system without the use of artificial structural controls unless approved by the Division; (c) Establish or restore the stream to include a diversity of aquatic habitats (generally a series of riffles and pools) where appropriate, that approximates the premising characteristics; and (d) Restore, enhance where practicable, or maintain natural riparian vegetation on the banks of the stream in accordance with the require- ments of 4.15. The Starkville Gulch, an ephemeral dry drainage with little vegetation, was diverted in 1980. The Division believes the 2275-foot-long permanent diversion, including the 675-foot section comprised of the eight-foot-diameter culvert, meets both hydraulic and regulatory requirements for permanent retention, for the following reasons: (a) The culvert does not contribute to a diminution of downstream water rights. The culvert is designed to pass 465 cubic feet per second, the flow associated with the 100-year, 24-hour precipitation event and, as such, does not serve as an impediment to any appropriated or non-appropriated flow. (b) The average stream gradient has been maintained with a stable longitudinal profile. The upstream end of the permanent diversion is installed at the level of original channel. The outlet of the permanent diversion discharges into the original bedrock-lined stream channel at the west end of the permit boundary. The original overall gradient through this section of the stream bed is estimated to be no steeper than 4.35 %, based on the current 100-foot difference in elevation between the culvert inlet and the permanent diversion discharge point, and the 2300-foot horizontal distance measured between the two points on Map 12 from the permit. The overall gradient of the 2275-foot permanent diversion is 3.4%, with one 675-foot section lined by the culvert, and one 750-foot section lined by riprap designed to maintain the channel bottom stable up to the 100-year, 24-hour precipitation event. The third section, the center one, has no armoring, as it has been designed flat enough that armoring is not required. The reconstructed channel gradient of 3.4%, as compared to the estimated premising gradient of 4.35%, is a difference of less than 1%. We believe this difference falls within the regulatory criteria of "approximate premising configuration." (c) The channel has been established to approximate the natural meandering pattern with a Division-approved, geomorphically acceptable gradient. The natural steep channel gradient