New Jersey Administrative Code › Title 7 - ENVIRONMENTAL PROTECTION › Chapter 13 - FLOOD HAZARD AREA CONTROL ACT RULES › Appendix 1

Current through Register Vol. 56, No. 14, July 15, 2024
APPROXIMATING THE FLOOD HAZARD AREA DESIGN FLOOD
				ELEVATION
As described in detail at
				N.J.A.C.
				7:13-3, the Department and FEMA have adopted
				flood mapping along many of the State's waters. In absence of a Department
				delineation1, or FEMA flood mapping that meets the
				requirements at
				N.J.A.C.
				7:13-3.4(b), an applicant
				may use the approximation method described at
				N.J.A.C.
				7:13-3.5 in conjunction with this
				appendix.
Note that this method approximates only the flood hazard area
				design flood elevation. This method does not approximate the floodway limit.
				Many activities are restricted within floodways and some calculations cannot be
				performed if the floodway limit is unknown. Therefore, the Department shall
				issue an individual permit for a regulated activity within an approximated
				flood hazard area only if the regulated activity meets the requirements at
				N.J.A.C.
				7:13-3.5(f).
HOW TO USE METHOD 5 (APPROXIMATION METHOD)
1. Determine which Watershed Management Area (WMA) the project
				is located within based on Figure 5 below. The Department can help in this
				determination at the applicant's request.2
2. Determine the contributory drainage area (CDA) of the water
				in question. USGS provides topographical mapping that can be used to make this
				determination. The Department can also help in this determination at the
				applicant's request.
3. Find the approximate depth of flooding from Table 1 below
				based on the WMA and CDA.
4. Find the low point elevation of each roadway crossing or
				other water control structure within one mile downstream of the
				site.3 Figure 1 illustrates a typical roadway
				profile with a low point.
5. The approximate flood hazard area design flood elevation
				will be the higher of the following (see Figures 1 through 4):
The depth from Table 1, measured above the average
				streambed.4
The depth from Table 2, measured above the highest roadway low
				point described in 4 above.
NOTES
1. See Appendix 2 for a complete list of delineations and
				N.J.A.C.
				7:13-3.3 for more detail.
2. If a project spans more than one WMA, the approximate flood
				hazard area shall be determined separately within each WMA.
3. Some roadway or railroad crossings over very large bridges
				need not be included if the Department determines that such crossings will not
				affect flooding on the site. Contact the Department for further
				information.
4. The average streambed is the general "smooth" grade of the
				bottom of the channel, and does not include small pockets of erosion,
				individual boulders, or other minor irregularities. The average streambed
				always has a positive slope toward downstream.
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EXAMPLE: Going from left to right in any row, each number
				represents the upper drainage area limit for the flood depth shown at the
				bottom of the column. For example, in the row for WMA 10, a water with a
				drainage area of 70 acres or less has a flood depth of six feet. Similarly, any
				water draining between 70 and 110 acres has a flood depth of seven feet. In the
				example illustrated with arrows above, any water with a drainage area of
				between 19.4 and 30.0 square miles in WMA 10 has a flood depth of 19
				feet.
NOTES
1. The numbers in this column denote the Watershed Management
				Areas shown in Figure 5.
2. Flood depths shall be measured above the average streambed
				elevation as described elsewhere in this Appendix and as shown in Figure 3
				below.
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