HAR §13-190.1-4
HAR §13-190.1-4. Minimum design requirements
Cite as Haw. Code R. § 13-190.1-4
(a) Regulated dams and reservoirs shall incorporate the following minimum design requirements:
(1) Embankment slopes that are not steeper than 2.5 horizontal to 1 vertical unless a specific design for a steeper slope shows that the embankment is stable and capable of being safely maintained;
(2) An embankment crest that has a minimum width of ten feet;
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(3) Earthen spillways that are constructed in natural ground; and
(4) A low level outlet shall be designed to drain the reservoir by gravity flow.
(b) Significant and high hazard dams shall also have a stability analysis of the structure demonstrating the stability of the embankment slopes for various loading conditions and minimum factors of safety generated by a methodology accepted by the department.
(c) Regulated dam spillways shall safely pass the appropriate inflow design flood, as shown in the following table:
| Hazard Classification | Size Classification | Inflow design flood |
| --- | --- | --- |
| Low | Small | 100 year |
| | Intermediate | 100 year |
| | Large | ½ PMF |
| Significant | Small | ½ PMF |
| | Intermediate | ½ PMF |
| | Large | PMF |
| High | All Sizes | PMF |
| Category | Impoundment | |
| --- | --- | --- |
| | Storage (Acre-feet) | Height (feet) |
| Small | <1000 and ≥50 | <40 and ≥25 |
| Intermediate | ≥1,000 and <50,000 | ≥40 and <100 |
| Large | ≥50,000 | ≥100 |
Note: "PMF" or "Probable Maximum Flood", is defined as the flood that may be expected from the most severe combination of critical meteorologic and hydrologic conditions that are reasonably possible in the region. The PMF is derived from the 24-hour probable maximum precipitation (PMP), which information is available from the National Weather Service, NOAA, Publication HMR-39, "Hydrometeorological Report No. 39 - Probable Maximum
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Precipitation in the Hawaiian Islands", or current standard. ½ PMF = PMF divided by two. "100 year" is defined as the flood associated with the 1 per cent probability storm event that is derived from the 24-hour 100-year precipitation rate, which is identified in the US Weather Bureau Technical Paper No. 43 Rainfall-Frequency Atlas of the Hawaiian Islands and as updated by NOAA Atlas 14, Volume 4 Precipitation-Frequency Atlas of the United States, Hawaiian Islands, or current standard.
(d) Freeboard shall be the greater of the following:
(1) Two feet above the water level during the peak spillway flow associated with the inflow design flood;
(2) Sum of the wave run-up and reservoir setup resulting from a 100 miles per hour wind speed during the peak spillway flow associated with the inflow design flood.
[Eff. FEB 20 2012 ] (Auth: HRS §179D-6)
(Imp: HRS §179D-6)