SUBCHAPTER 3. DETERMINING THE FLOOD HAZARD AREA AND FLOODWAY

7:13-3.1 General provisions for determining the flood hazard area and floodway along a regulated water
7:13-3.2 Selecting a method for determining the lood hazard area and floodway along a regulated water
7:13-3.3 Flood hazard area and floodway based on a Department delineation (Method 1)
7:13-3.4 Flood hazard area and floodway based on a FEMA flood insurance study (Methods 2 through 4)
7:13-3.5 Flood hazard area determined by approximation (Method 5)
7:13-3.6 Flood hazard area and floodway determined by calculation (Method 6)

7:13-3.1 General provisions for determining the flood hazard area and floodway along a regulated water

(a)        This subchapter provides six methods for determining the flood hazard area and floodway along a regulated water as follows:

1.    Method 1 (Department delineation method) as described at N.J.A.C. 7:13-3.3;

2.    Method 2 (FEMA tidal method) as described at N.J.A.C. 7:13-3.4(d);

3.    Method 3 (FEMA fluvial method) as described at N.J.A.C. 7:13-3.4(e);

4.    Method 4 (FEMA hydraulic method) as described at N.J.A.C. 7:13-3.4(f);

5.    Method 5 (approximation method) as described at N.J.A.C. 7:13-3.5; and

6.    Method 6 (calculation method) as described at N.J.A.C. 7:13-3.6.

(b)        The flood hazard area is the land, and the space above that land, which lies below the flood hazard area design flood elevation, as defined at N.J.A.C. 7:13-1.2. The six methods described in (a) above provide the flood hazard area design flood elevation, from which the flood hazard area limit on a site is determined. In some cases, the limits of the floodway can also be determined using these methods.

(c)        In most cases, the Department shall issue an individual permit under this chapter only if the applicant has determined the flood hazard area and floodway limits on the site, and has received a verification for these limits from the Department pursuant to N.J.A.C. 7:13-6.1. However, under certain conditions as set forth at N.J.A.C. 7:13-9.6, the flood hazard area and/or floodway limits need not be verified in order for the Department to be able to determine whether a regulated activity complies with this chapter. Furthermore, a verification is not required prior to obtaining a general permit authorization under this chapter, except for certain cases as noted under general permits 5, 6 and 7 at N.J.A.C. 7:13-8.7, 8.8 and 8.9, respectively.

(d)        The flood hazard area and floodway described in this subchapter may differ from areas identified as a "flood hazard area," "flood zone," "floodplain" or "floodway" by another public entity such as FEMA or a local government. The methods listed at (a) above are specifically designed and intended for determining compliance with the construction standards and requirements of this chapter.

 

7:13-3.2 Selecting a method for determining the flood hazard area and floodway along a regulated water

(a)        This section establishes the methods by which the flood hazard area and floodway shall be determined along a regulated water. The flowchart at the end of this section illustrates the correct use of this process. The Flood Hazard Area Technical Manual, available from the Department at the address listed at N.J.A.C. 7:13-1.1(g), also provides further guidance on how to perform calculations for those methods that require calculations.

(b)        There are a number of factors that influence the selection of a method for determining the flood hazard area and floodway. These factors include the existence of a Department delineation or FEMA flood insurance study, whether the applicant proposes a regulated activity in the flood hazard area and what type of project is proposed. Furthermore, each method has certain limitations on its usefulness and availability as described in this subchapter. Applicants are encouraged to carefully review the entire subchapter before selecting a method.

(c)        The flood hazard area and floodway limits along a regulated water shall be determined as follows:

1.    If a Department delineation exists for a regulated water, an applicant shall use Method 1 as described at N.J.A.C. 7:13-3.3. Appendix 2 of this chapter lists the Department delineated waters of New Jersey.

2.    If no Department delineation exists for a regulated water, an applicant may:

i.     Determine the flood hazard area and/or floodway from FEMA mapping, if such mapping exists for the section of regulated water in question, using Methods 2, 3 or 4 as described at N.J.A.C. 7:13-3.4(d), (e) and (f), respectively;

ii.     Determine the approximate limit of the flood hazard area using Method 5 as described at N.J.A.C. 7:13-3.5 if no FEMA mapping is exists for the section of regulated water in question; or

iii.    Determine the flood hazard area and/or floodway by calculation using Method 6 as described at N.J.A.C. 7:13-3.6.

(d)        The flood hazard area and floodway shall be determined using only one method for each regulated water on a site, except in the following cases:

1.    If a Department delineation or FEMA flood insurance study terminates within a site, the flood hazard area on the remainder of the site may be delineated using another applicable method described in this subchapter; and

2.    If Method 3 is used to delineate the flood hazard area but no FEMA floodway map exists for the section of regulated water in question, and determining the floodway is necessary to demonstrate compliance with the requirements of this chapter, the applicant shall use Method 4 to calculate the floodway.



 


7:13-3.3 Flood hazard area and floodway based on a Department delineation (Method 1)
(a)   This section sets forth the procedure for determining a flood hazard area design flood elevation and floodway limit from a Department delineation.  Appendix 2 of this chapter lists the Department delineated waters of New Jersey. Requests for copies of a Department delineation, including flood profiles and maps, as well as any questions regarding the use, derivation or modification of these delineations, should be directed to the Department's Office of Floodplain Management at the following address:

       State of New Jersey

       Department of Environmental Protection

       Bureau of Dam Safety and Flood Control

       P.O. Box 419

       Trenton, New Jersey 08625-0419

       Telephone: (609) 984-0859

(b)   The following apply if a Department delineation has been promulgated under this chapter for a regulated water:

1.    The flood hazard area design flood elevation is that which is shown on the flood profile adopted as part of the Department delineation; and

2.    The floodway limit is that which is shown on the flood maps adopted as part of the Department delineation.

(c)   An applicant seeking to modify a Department delineation shall submit an application for a revision as provided at N.J.A.C. 7:13-13.4.

(d)   If an applicant proposes construction in a Department delineated floodway, and must prepare hydraulic calculations to demonstrate that the construction meets the requirements of this chapter, the applicant shall base the calculations on the original data used by the Department to determine the delineation. Such data is available from the Department at the address listed in (a) above.

 

7:13-3.4 Flood hazard area and floodway based on a FEMA flood insurance study (Methods 2 through 4)

(a)   This section sets forth the procedure for determining a flood hazard area design flood elevation and floodway limit from a FEMA flood insurance study where no Department delineation exists. Requests for copies of the available FEMA flood insurance studies or flood profiles, as well as any questions regarding their use, derivation or modification, should be directed to FEMA at (800) 358-9616.

(b)   The methods set forth in this section for determining the flood hazard area and floodway along a regulated water may be used only if the following requirements are satisfied:

1.    No Department delineation exists for the section of regulated water in question; and

2.    A FEMA flood insurance study exists for the section of regulated water in question, which meets the following:

i.     The FEMA flood insurance study includes the information needed for the Method that is being used. For example, Methods 2 and 3 below require that the FEMA study includes the regulated water's 100-year flood elevation, and Method 4 below requires that the FEMA study includes the regulated water's 100-year flow rate;

ii.    The flood insurance study used is dated January 31, 1980, or later; and

iii.   The flood insurance study used is the most recent study published by FEMA for that municipality.

(c)   There are three methods by which a FEMA flood insurance study may be used to determine the flood hazard area and floodway limit along a regulated water as follows:

1.    Method 2 (FEMA tidal method), set forth at (d) below, which applies to a tidal flood hazard area for which a FEMA flood profile exists for the section of regulated water in question. If the FEMA flood insurance study does not provide a 100-year flood elevation, it is not possible to use this method;

2.    Method 3 (FEMA fluvial method), set forth at (e) below, which applies to a fluvial flood hazard area for which a FEMA flood profile exists for the section of regulated water in question. If the FEMA flood insurance study does not provide a 100-year flood elevation, it is not possible to use this method; and

3.    Method 4 (FEMA hydraulic method), set forth at (f) below. This method may be used only if the following requirements are satisfied:

i.     The FEMA flood insurance study provides a 100-year flow rate for the regulated water. In most tidal flood hazard areas a large area is inundated due to flooding from the Atlantic Ocean, and therefore FEMA does not provide a 100-year flow rate for the regulated water itself. In such a case, it is not possible to use this method; and

ii.    The applicant proposes a regulated activity in the flood hazard area and applies for an individual permit under this chapter, for which the Department requires hydraulic calculations comparing pre-construction and post-construction water surface elevations within the regulated water, in order to demonstrate that the regulated activity complies with this chapter. Examples of activities that require such an analysis are detailed at N.J.A.C. 7:13-11.1(f), 11.1(g), 11.7(c) and 11.7(d).

(d)   Under Method 2 (FEMA tidal method):

1.    The flood hazard area design flood elevation shall be equal to the FEMA 100-year flood elevation; and

2.    The floodway limit shall be determined as follows:

i.     If a FEMA floodway map exists for the section of regulated water in question, the floodway limit shall be equal to the floodway limit shown on the FEMA floodway map; or

ii.    If no FEMA floodway map exists for the section of regulated water in question, the floodway limit shall be equal to the limits of the channel. The Atlantic Ocean and other non-linear tidal waters such as bays and inlets do not have a floodway.

(e)   Under Method 3 (FEMA fluvial method):

1.    The flood hazard area design flood elevation shall be equal to one foot above the FEMA 100-year flood elevation; and

2.    The floodway limit shall be determined as follows:

i.     If a FEMA floodway map exists for the section of regulated water in question, the floodway limit shall be equal to the floodway limit shown on the FEMA floodway map; or

ii.    If no FEMA floodway map exists for the section of regulated water in question, the floodway limit cannot be determined using this method. The applicant shall instead calculate the floodway limit using Method 4 as described in (f) below. In such a case, applicants are encouraged to first contact the Department to discuss whether it is necessary to determine the floodway limit on a site for a given project.

(f)   Under Method 4 (FEMA hydraulic method):

1.    The flood hazard area design flood elevation and floodway limit shall be based on a standard step backwater analysis and determined as follows:

i.     For a tidal flood hazard area, a hydraulic analysis shall be performed to determine the flood hazard area design flood elevation using the 100-year flow rate reported by FEMA for the regulated water (see (c)3i above);

ii.    For a fluvial flood hazard area, a hydraulic analysis shall be performed to determine the flood hazard area design flood elevation using 125 percent of the 100-year flow rate reported by FEMA for the regulated water; and

iii.   A hydraulic analysis shall be performed to determine the floodway limit using the 100-year flow rate reported by FEMA for the regulated water, assuming a maximum rise of 0.2 feet in the 100-year flood elevation. The floodway limits shall be calculated assuming equal conveyance reduction, unless the applicant demonstrates (prior to the submission of an application for a verification to the Department) that due to the topography of the area, the proximity of structures to the channel and/or other physical characteristics of the watershed or flood hazard area, use of another method will more optimally calculate the floodway limits at a given location.

 

7:13-3.5 Flood hazard area determined by approximation (Method 5)

(a)   This section sets forth the procedure for approximating a flood hazard area design flood elevation using the method described in chapter Appendix 1. This method does not provide a floodway limit. Therefore, the Department shall issue an individual permit for a regulated activity within an approximated flood hazard area only if the project meets the requirements at N.J.A.C. 7:13-9.7.

(b)   The flood hazard area design flood elevation for a regulated water can be approximated under Method 5, provided the following requirements are satisfied:

1.    Method 1 (Department delineation method) set forth at N.J.A.C. 7:13-3.3 cannot be used because no Department delineation exists for the section of regulated water in question;

2.    Methods 2 through 4 (FEMA fluvial, FEMA tidal and FEMA hydraulic methods) set forth at N.J.A.C. 7:13-3.4 cannot be used because no qualifying FEMA flood insurance study exists for the section of regulated water in question; and

3.    The drainage area of the water at the project site does not exceed 30 square miles.

(c)   An applicant may elect to establish the approximate flood hazard area limit at an elevation higher than that which is provided by Method 5 in order to match an existing topographic feature onsite, such as the top of an embankment, or to run concurrent with a verified freshwater wetland or transition area line.

(d)   Method 5 is intended to be conservative and may in some cases overestimate the actual limits of flooding onsite to ensure that public health, safety and welfare is adequately protected in absence of a Department delineation or FEMA flood insurance study. Note that an applicant may use Method 6 under N.J.A.C. 7:13-3.6 to determine the flood hazard area and floodway along any regulated water for which no Department delineation exists.

(e)   If the Department determines that using Method 5 to approximate a flood hazard area will significantly underestimate the depth of flooding on a particular site due to an unusual hydrologic or hydraulic condition within the drainage area, or due to a unique feature on or near the site, the Department shall not approve a general permit authorization or an individual permit for any regulated activity in the approximated flood hazard area if such approval is determined to constitute a threat to public safety. Should the applicant choose to apply for a permit in such a case, the flood hazard area limit shall first be calculated according to Method 6, as described at N.J.A.C. 7:13-3.6.

 

7:13-3.6 Flood hazard area and floodway determined by calculation (Method 6)

(a)   This section sets forth the procedure for determining a flood hazard area design flood elevation and floodway limit via hydrologic and hydraulic calculations. An applicant may use Method 6 to determine the flood hazard area and floodway along any regulated water for which no Department delineation exists. If a Department delineation does exist on a site, the applicant shall use Method 1 as set forth at N.J.A.C. 7:13-3.3.

(b)   If the following conditions exist, Method 6 is the only method by which an applicant may determine the flood hazard area and floodway along a regulated water:

1.    Method 1 (Department delineation method) set forth at N.J.A.C. 7:13-3.3 cannot be used because no Department delineation exists for the section of regulated water in question;

2.    Methods 2 through 4 (FEMA fluvial, FEMA tidal and FEMA hydraulic methods) set forth at N.J.A.C. 7:13-3.4 cannot be used because no qualifying FEMA flood insurance study exists for the section of regulated water in question; and

3.    Method 5 (approximation method) set forth at N.J.A.C. 7:13-3.5 cannot be used for one of the following reasons:

i.     The requirements for using the approximate method at N.J.A.C. 7:13-3.5(b) are not satisfied;

ii.    The Department determines that the approximate method will significantly underestimate the depth of flooding on the site in question, pursuant to N.J.A.C. 7:13-3.5(e); or

iii.   The applicant is proposing a regulated activity for which the requirements at N.J.A.C. 7:13-9.7 are not satisfied.

(c)   Under Method 6, the flood hazard area design flood elevation and floodway limit shall be based on a standard step backwater analysis and determined as follows:

1.    A hydrologic analysis shall be performed to determine the peak flow rate for the 100-year flood for the regulated water. The hydrologic analysis shall assume existing development conditions in the drainage area, as of the date of the application to the Department;

2.    For a tidal flood hazard area, a hydraulic analysis shall be performed to determine the flood hazard area design flood elevation using the 100-year flow rate determined under (c)1 above;

3.    For a fluvial flood hazard area, a hydraulic analysis shall be performed to determine the flood hazard area design flood elevation using 125 percent of the 100-year flow rate determined under (c)1 above; and

4.    A hydraulic analysis shall be performed to determine the floodway limit using the 100-year flow rate determined under (c)1 above, assuming a maximum rise of 0.2 feet in the 100-year flood elevation. The floodway limits shall be calculated assuming equal conveyance reduction, unless the applicant demonstrates (prior to the submission of an application for a verification to the Department) that due to the topography of the area, the proximity of structures to the channel and/or other physical characteristics of the watershed or flood hazard area, use of another method will more optimally calculate the floodway limits at a given location.