Section Env-Wr 502.06 - Specific Requirements and Breach Parameters(a) The dam breach analysis shall be performed under the direction of and stamped by a professional engineer licensed in New Hampshire and experienced in hydrology and hydraulics.(b) The breach parameters shall be in accordance with Table 5.1 and Figure 5.1 below, unless the department approves the use of other parameters pursuant to (c), below: Table 5.1 Dam Breach Parameters
| PARAMETER | TYPE OF DAM | VALUE |
| Average Width of Breach (BR) | Arch | BR = Crest Length |
| Masonry, Gravity | BR = Width of one or more monoliths, usually BR <=0.5 W |
| Earth, Rockfill, Timber Crib | HD <= BR <= 5HD (usually between 2HD and 4HD) |
| Horizontal Component of Side Slope of Breach (Z) | Arch | 0 <= Z <= slope of valley walls |
| Masonry, Gravity | Z = 0 |
| Earth, Rockfill, Timber Crib | 1/4 <= Z <= 1 |
| Time to Failure (TFH) in hours | Arch | TFH <= 0.1 |
| Masonry, Gravity | 0.1 <= TFH <= 0.3 |
| Earthen (Engineered, Compacted) Timber Crib | 0.1 <= TFH <= 1.0 |
| Earthen (Non-Engineered, Poor Construction) | 0.1 <= TFH <= 0.5 |
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(c) The department shall allow use of different parameters due to specific dam or site conditions, if the applicant requests to use different parameters and demonstrates by clear and convincing evidence that the use of the alternative parameters would result in an accurate model and would not underestimate the effects of a dam failure.(d) A dam breach flow shall be routed together with each of the following base flows: (1) The sunny day flow as defined in Env-Wr 101; and(2) The 100-year flood flow.(e) The breach flow together with the base flows in (d), above, shall: (1) Be routed downstream of the dam; and(2) Include provisions to identify the number of hours or minutes from the start of a failure to the time when the river initially starts to rise and the time to reach peak stage.(f) Peak flow velocities also shall be determined and shown on the inundation map for critical stations such as road crossings and populated areas below the dam.(g) The routing shall continue downstream until:(1) The point at which the water surface elevation due to dam failure is no more than 2 feet above the non-failure conditions in areas of potential threat to life and major property damage; or(2) A point upstream of the point determined pursuant to (1), above, if the owner shows that there is no longer a threat to public safety beyond that point.N.H. Admin. Code § Env-Wr 502.06
#8414, eff 8-20-05; ss by #10510, eff 1-22-14