No land area in the Township shall be developed so that:
A. The rate of stormwater runoff occurring at that area is increased
over what occurs there under existing conditions.
B. The drainage of adjacent areas is adversely affected.
C. Soil erosion during and after development is increased over what
naturally occurs there.
D. Soil absorption and groundwater recharge capacity of the area is
decreased below what occurs under existing conditions.
E. The natural drainage pattern of the area is significantly altered.
In order to duplicate as nearly as possible natural drainage
conditions, the regulation and control of stormwater runoff and erosion
for any land area to be developed shall be through on-site water detention
and/or ground absorption systems, which include but are not limited
to the following:
A. Detention areas, which may be depressions in parking areas, excavated
basins, basins created through use of curbs, stabilized earth berms
or dikes or any other form of grading which serves to temporarily
impound and store water.
B. Rooftop storage through temporary impoundment and storage of stormwater
on flat or slightly pitched building rooftops by use of drain outlets
which restrict the stormwater runoff from the roof surface.
C. Dry wells or leaching basins which control stormwater runoff, ground
absorption and temporary storage.
D. Porous asphalt pavement, which preserves the natural ground absorption
capacity of a site and provides a subsurface reservoir temporary storage
of stormwater.
E. Any system of porous media, such as gravel trenches drained or porous
wall or perforated pipe, which temporarily stores and dissipates stormwater
through ground absorption.
F. Any combination of the above-mentioned techniques which serves to
limit stormwater runoff from a given site to what presently occurs.
G. Preservation of natural vegetation.
The following list of general structural criteria shall be used
when reviewing a proposed stormwater detention basin:
A. Principal outlets and structures.
(1)
To minimize the chance of clogging and to facilitate cleaning,
outlet pipes should be at least 18 inches in diameter. All pipes are
to be reinforced concrete pipe conforming to ASTM C 76 with rubber
gaskets pursuant to ASTM C 443.
(2)
Eight-inch-thick anti-seep collars are to be installed along
outlet pipes. Reinforcement steel shall be No. 5 at 12 inches both
ways with two inches of cover on both faces.
(3)
All principal outlet structures shall be steel reinforced concrete
cast in place. All construction joints are to be watertight. All pipes,
stubs, and/or fittings are to be cast ethically in the walls.
(4)
Trash racks and anti-vortex devices will be required where necessary
and should be designed to facilitate cleaning. A rise-type outlet
structure which conveys flow over its top should have an anti-vortex
cover constructed of reinforced concrete.
(5)
Suitable lining is to be placed upstream and downstream of principal
outlets as necessary to prevent scour and erosion. Such lining shall
conform to the criteria contained in "Hydraulic Engineering Circular
No. 15 - Design of Stable Channels with Flexible Linings," or "Standards
for Soil Erosion and Sediment Control in New Jersey," published by
the State Soil Conservation Committee.
(6)
All concrete shall have a minimum twenty-eight-day compressive
strength of 3000 PSI. Allowable extreme fiber stress in compression
shall be 1200 PSI.
(7)
All reinforcing steel shall be intermediate grade, new deformed
billet-steel conforming to ASTM A615 (latest edition). Grade 40 minimum.
Allowable stress in tension shall be 20,000 PSI.
B. Emergency spillways.
(1)
Vegetated emergency spillways shall have side slopes not exceeding
four horizontal to one vertical.
(2)
Emergency spillways not excavated from undisturbed soil shall
be suitably lined and shall comply with criteria contained in "Hydraulic
Engineering Circular No. 15" or "Standards for Soil Erosion and Sediment
Control" mentioned above.
(3)
Maximum velocities in vegetated emergency spillways excavated
from undisturbed soil shall be checked based on the velocity of the
peak flow in the spillway resulting from the routed emergency spillway
hydrograph.
C. Dams and embankments.
(1)
The minimum top widths of all dams and embankments are listed
below. These values have been adopted from the "Standards for Soil
Erosion and Sediment Control in New Jersey."
|
Table II
Minimum Top Widths
|
---|
|
Height
(feet)
|
Top Width
(feet)
|
---|
|
0 to 15
|
10
|
|
15 to 20
|
12
|
|
20 to 25
|
14
|
(2)
Maximum side slopes for all dams and embankments are four horizontal
to one vertical.
(3)
All earth fill shall be free from brush, roots and other organic
material subject to decomposition.
(4)
Cutoff trenches are to be excavated along the dam or embankment
center line to impervious subsoil or bedrock.
(5)
An impervious central core is to be constructed in the dam/embankment
consisting of compacted clay material.
(6)
Safety ledges shall be constructed on the side slopes of all
detention basins having a permanent pool of water. The ledges shall
be four feet to six feet in width and located approximately 2 1/2
feet to three feet below and one foot to 1 1/2 feet above the
permanent water surface.
(7)
The upstream face of the dam and/or embankment of a permanent
pool detention basin shall be stabilized to protect it against wave
erosion.
(8)
The fill material in all earth dams and embankments shall be
compacted to at least 95% of the maximum density obtained from compaction
tests performed by the appropriate method in ASTM D698.
(9)
A detention basin with a permanent pool shall have a gravity
drain to permit complete emptying of the basin when necessary.