Section Env-Wt 904.07 - Design Criteria for Tier 2, Tier 3, and Tier 4 Stream Crossings(a) Unless otherwise specified, all design criteria in this section shall apply to new and replacement tier 2, tier 3, and tier 4 stream crossings.(b) Tier 2 and tier 3 stream crossings shall be designed in accordance with the NH stream crossing guidelines, available as noted in Appendix B;(c) Tier 2, tier 3, and tier 4 stream crossings shall be designed: (1) To meet the general design considerations specified in Env-Wt 904.01;(2) Of sufficient size to accommodate the greater of: a. The 100-year 24-hour design storm;b. Flows sufficient to: 1. Prevent an increase in flooding on upstream and downstream properties; and2. Not affect flows and sediment transport characteristics in a way that could adversely affect channel stability; orc. Applicable federal, state, or local requirements;(3) With the bed forms and streambed characteristics necessary to cause water depths and velocities within the crossing structure at a variety of flows to be comparable to those found in the natural channel upstream and downstream of the stream crossing;(4) To provide a vegetated bank on both sides of the watercourse or to provide a wildlife shelf of suitable substrate and access to allow for wildlife passage;(5) To preserve the natural alignment and gradient of the stream channel, so as to accommodate natural flow regimes and the functioning of the natural floodplain;(6) To simulate a natural stream channel;(7) So as not to alter sediment transport competence; and(8) To avoid and minimize impacts to the stream in accordance with Env-Wt 313.03.(d) In addition to meeting the criteria specified in (c), above, new, repaired, rehabilitated, or replaced tier 4 stream crossing shall be designed: (1) Based on a hydraulic analysis that accounts for daily fluctuating tides, bidirectional flows, tidal inundation, and coastal storm surge;(2) To prevent creating a restriction on tidal flows; and(3) To account for tidal channel morphology and potential impacts due to sea level rise.N.H. Code Admin. R. Env-Wt 904.07
Amended by Volume XXXVIII Number 32, Filed August 9, 2018, Proposed by #12578, Effective 7/21/2018, Expires 7/21/2028.Amended by Volume XXXIX Number 28, Filed July 11, 2019, Proposed by #12809, Effective 12/15/2019, Expires 12/15/2029.