§ 34-111. Technical standards and specifications.

(a)

Hydrologic and hydraulic computations.

(1)

Models. All computations of runoff volumes and peak flow rates used in the development of erosion control and storm water management plans in accordance with this division shall be based on United States Department of Agriculture - Natural Resources Conservation Service (NRCS) methodology. Models such as SLAMM, P8 or other village engineer approved models may be used to evaluate the efficiency of the design in reducing total suspended solids to meet this division. Models such as SLAMM, RECARGA or other village engineer approved models may be used to evaluate the efficiency of the design in meeting the infiltration requirements of this division. Models distributed and supported by the Wisconsin Department of Natural Resources may be used to determine compliance with calculating soil loss on construction sites.

(2)

Rainfall depths. To determine compliance with this division, the following design storm rainfall depths shall be used, which are derived from NRCS publications and extrapolated for the Village of Mukwonago:

Design Storm	1-year 24-hour	2-year 24-hour	10-year 24-hour	100-year 24-hour
Rainfall Depth	2.4 inches	2.7 inches	3.81 inches	6.18 inches

 

(3)

Runoff curve numbers. All computations of pre-development conditions as specified in this division shall use those NRCS runoff curve numbers assigned for a "good" hydrologic condition for each land cover type. For lands where the pre-development land use was woodland, grassland, meadow or cropland, the following NRCS curve number values shall be used as maximums:

Predevelopment Land Use	Hydrologic Soil Group (Letter)/ Maximum Runoff Curve Number (#)
	A	B	C	D
Woodland	30	55	70	77
Grassland/Meadow	39	61	71	78
Cropland	55	69	78	83

 

(4)

Average annual rainfalls. All modeling involving average annual rainfall or runoff volumes shall use rainfall data from the Milwaukee area between March 28 and December 6, 1969 as the typical annual rainfall pattern for Village of Mukwonago, unless otherwise prescribed in BMP design standards.

(5)

Rainfall distribution. All peak flow calculations shall use MSE3 rainfall distribution patterns, as defined in NRCS methodologies.

(6)

Other methods. All velocity and peak flow computations for open channels and storm sewer pipe flows shall be based on Manning's Formula. Flow routing, culvert design, weir and orifice flow and other related hydraulic computations used to design storm water management facilities shall be based on standard applicable engineering formulas. Any design data or methodology proposed to be used for hydrologic or hydraulic computations other than those prescribed in this division shall be approved by the village engineer. Revisions or updates to the rainfall depths and distribution prescribed above may be allowed upon approval by the applicable regulatory agencies and the village engineer.

(b)

Best management practice (BMP) design standards.

(1)

The design, installation and maintenance of all BMPs used to meet the requirements of this division shall comply with the technical standards identified, developed or disseminated by the Wisconsin Department of Natural Resources under Subchapter V of Ch. NR151, Wis. Adm. Code.

(2)

Where BMP standards have not been identified or developed under subsection (1) above, the village may approve the use of other available standards, such as those from other states or the USDA-Natural Resources Conservation Service.

(c)

Technical guidelines. The village may adopt technical guidelines to facilitate the consistent administration of certain provisions of this division.

(d)

Construction specifications. The construction or installation of all BMPs and BMP components shall comply with all applicable manufacturers and industry standards and specifications, including but not limited to those published by ASTM and the USDA—Natural Resources Conservation Service (NRCS).

(e)

Soil evaluations. All soil profile evaluations and forms submitted for review by the village engineer under the provisions of this division shall be completed in accordance with Chapter SPS 385 Wis. Admin. Code and any applicable state or village standards. Where there are no specific standards for the number, location or depth of soil profile evaluations for a proposed BMP, the village engineer shall determine the minimum requirements based on the design of the BMP and the likely variability of the on-site soils.

(f)

Availability. Copies of all technical references made in this section shall be available for review and distribution through the village engineer office during normal business hours, or over the Internet. Fees may be charged for hard copies of these items.

(g)

Future revisions or updates. The technical references in this section are made a part of this division and shall be updated periodically in order to keep current with field experiences, research, technological advances and the development of related technical standards by other agencies and units of government. Any future revisions of the documents incorporated herein are also made part of this section unless otherwise acted upon by the village.

(Ord. No. 816, § IV, 1-6-09; Ord. No. 914, § VII, 5-17-16; Ord. No. 928, § VII, 4-18-17)