Haw. Code R. § 13-190.1-21 - Additional requirements for removal of dam or reservoir

(a) No person shall remove any dam, reservoir, or appurtenant works until written approval is obtained from the board. The application for removal shall include, but not be limited to, the following information:

(1) The current height and storage of the dam;

(2) The current hazard classification;

(3) The proposed flow through channel width and side slopes;

(4) A description of and quantitative analyses of the flow through conditions during the 100-year, 24-hour storm event including provision for erosion protection;

(5) Evaluation of all potential effects on life, property, and environment downstream; and

(6) For a partial removal of a dam that will still store water, the relevant deficiencies X identified in the initial investigation or inspection reports shall be addressed.

(b) Plans for removal of a dam or reservoir, shall meet the following requirements:

(1) The dam shall be excavated down to the level of the natural ground or to sufficient cut depth to prevent silt previously deposited in the reservoir or material excavated for the channel from washing downstream. The plan shall address sediment that has been previously deposited in the reservoir;

(2) The channel shall be of sufficient width to pass the 100-year, 24-hour flood with maximum depth of five feet of water anywhere in the channel at any time during the flood. Results of analyses demonstrating the 100-year, 24-hour flood can be safely passed within the breached section while maintaining five feet or less of water in the remaining reservoir shall be submitted for review;

(3) Regardless of the hydraulic requirements, the bottom width of the channel shall be a minimum of fifteen feet;

(4) The side slopes of the channel shall be excavated to a slope that is stable, but not steeper than 2:1 (horizontal:vertical). Slope stability analysis that provides an adequate factor of safety for steeper slopes may be accepted by the department but in no case steeper than 1:1;

(5) A detailed flood study for the 100-year storm frequency events shall be performed for the existing conditions and proposed removed or partially removed dam;

(6) If the partially removed dam will store more than 2 million gallons (6 acre-feet) of water, the plan shall provide a dam break inundation map of the downstream community at risk from the altered dam structure, assuming full water level at the time of failure;

(7) Transitions to downstream channels shall be investigated and appropriate provisions made to mitigate against possible damage or flooding;

(8) The exposed slopes within the 100-year, 24-hour storm depth shall be protected with riprap, vegetation, or other suitable means to prevent headcutting, downcutting, and lateral slope erosion; and

(9) The reservoir shall be emptied before removal of the dam.

Notes

Haw. Code R. § 13-190.1-21

[Eff. FEB 20 2012] (Auth: HRS § 179D-6) (Imp: HRS § 179D-6)