§ 33-7.4.4. Assessment of adequacy.

(a)

For all proposed developments, other than single-family residential, totaling ten thousand (10,000) square feet or more (all phases), and all single family residential developments totaling five (5) acres or more (all phases), the ten (10) year storm event post-development rate of run-off shall not exceed the ten (10) year storm event pre-development rate of run-off. To insure that the post-development rate of run-off does not exceed the pre-development rate of run-off, on-site detention will be required in a manner approved by the Jefferson Parish Public Works Department. The detention system cannot release water from the site at a rate greater than the pre-development rate of run-off.

(b)

The design concepts for detention facilities and determination of storm run-off shall be consistent with sound hydrological and hydraulic engineering principles and practices, and the provisions of the Jefferson Parish Subdivision Public Improvements Standards Manual. The public works director shall approve any and all modifications to the drainage manuals.

(c)

The developer shall submit drainage design calculations including a drainage map along with engineering plans to the public works department for approval by the engineering director. The drainage map shall include a line diagram reflecting the existing drainage system from the outfall end of the proposed development to the receiving outfall canal, reflected in the applicable current master drainage plan. The developer shall also submit calculations showing the impacts to the detention facility from a one hundred (100) year storm event.

(d)

Drainage calculations shall consider all relevant information that would affect the hydraulics of the drainage system including, but not limited to, the following:

(1)

Drainage basin characteristics;

(2)

System hydraulics; and

(3)

Other external influences upstream and downstream from the drainage system that may impact or be impacted by the proposed system.

(e)

Drainage calculations shall consist of:

(1)

Ten (10) year pre-development flow;

(2)

Ten (10) year post-development flow;

(3)

Description of release facility and volume of release versus depth of storage in detention facility for ten (10) year and one hundred (100) year storm events;

(4)

Maximum depth of water in the detention facility for design storms;

(5)

Description of impact to the proposed facility resulting from increased depth of storage; and

(6)

The description of how the system will be maintained.

(f)

Unless unstable or highly erosive soil conditions indicate a lower design velocity is desirable, or unless ditch paving at the outlet is provided, the maximum velocity for culvert design shall adhere to the criteria in the Jefferson Parish Subdivision Public Improvements Standards Manual.

(g)

The public works director shall review for approval each proposed development covered by this section prior to the issuance of permits to proceed with said development. Any decision in which the public works director denies a request or which requires a waiver shall be submitted to the Citizens' Drainage Advisory Board for review and recommendation. Decisions of the Citizens' Drainage Advisory Board recommending approval of a waiver shall be submitted for final approval by the parish council.

(h)

Any denial of a waiver request by the Citizens' Drainage Advisory Board may be appealed to the parish council for final resolution.

(Ord. No. 24989 , § VII, 8-12-15)