New Hampshire Code of Administrative Rules
Env - Department of Environmental Services
Subtitle Env-Wt - Wetlands Programs
Chapter Env-Wt 900 - STREAM CROSSINGS; CERTIFIED CULVERT MAINTAINER PROGRAM
Part Env-Wt 904 - DESIGN AND CONSTRUCTION OF STREAM CROSSINGS
Section Env-Wt 904.07 - Design Criteria for Tier 2, Tier 3, and Tier 4 Stream Crossings

Universal Citation: NH Admin Rules Env-Wt 904.07

Current through Register No. 13, March 27, 2025

(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;

(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; and

2. Not affect flows and sediment transport characteristics in a way that could adversely affect channel stability; or

c. 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.

#9714, eff 5-12-10

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