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Department of Agriculture and Aquaculture
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1.0 |
DEFINITION |
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A natural or constructed channel shaped
or graded to required dimensions, and established in suitable vegetation
for the safe disposal of runoff water. Grassed waterways may be used alone
or in combination with diversion terraces and other structures to
discharge surface runoff as part of an erosion control
system
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2.0 |
GENERAL |
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2.1 |
All grassed
waterway design and construction shall be in accordance with Chapter
7 "Grassed Waterways and Outlets" of the USDA-SCS Engineering Field
Manual for Conservation Practices and as specified in the
following: |
2.2 |
The NB
Department of Environment Watercourse Alteration Regulations and
Guidelines will apply to all projects including Regulation 90-80 and
90-120 under the Clean Water Act as revised in
1993. |
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3.0 |
PLANNING AND DESIGN |
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3.1 |
The minimum
capacity shall safely convey the peak runoff expected from a 10 year
frequency - 24 hour duration storm. If the waterway is used as an
outlet for a companion conservation structure or within an urban /
residential area the capacity will be increased to accommodate a
higher design frequency (25 yr. - 24 hr. duration
storm). |
3.2 |
The design
discharge used to determine the grassed waterway capacity shall be
calculated using the USDA-SCS EFM2 method or the TR55
method. |
3.3 |
Generally, the
grassed waterway cross-section shall be parabolic to reduce
meandering risk. Trapezoidal grassed waterway cross-sections are
recommended for steeper slopes and for larger runoff discharge. See
figure 1 - Typical waterway cross sections. |
3.4 |
The minimum
grassed waterway depth shall be 0.3 m (1.0 ft). The depth shall be
increased as required to properly outlet diversion terraces and/or
other structures that are designed to outlet into the waterway and
to assure better row drainage. The recommended side slopes shall be
6:1 to 8:1 to improve waterway crossing and
farmability. |
3.5 |
The maximum
grassed waterway width shall be less than 20 m (66 ft.) except where
other suitable outlet locations or methods cannot be found. The
minimum width shall be greater than 6 meters (20 ft) where crossing
with farm equipment is required. |
3.6 |
Where the design peak discharge of the grassed waterway is greater than 2.8 m3/s (100 cfs) and/or the design velocity
is greater than the permissible velocity, the waterway shall be
designed with a stone centre, non-degradable erosion control matting
or in combination with other special conservation structures as
required to safely discharge peak flow. |
3.7 |
Subsurface
drainage shall be installed as required to eliminate continuous or
base flow in the waterway and provide proper conditions for
vegetative growth. Drains shall be located on each side of the
waterway and not installed within the centre two-third width of the
waterway and shall. |
3.8 |
Maximum
permissible velocities shall be selected in accordance to values
specified in table below, recommended in S.C.S., E.F.M.H. (Exhibit
7.3). |
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Cover |
Slope Range (%) |
Permissible Velocity |
Erosion Resistant Soils m/s
(ft/s) |
Easily Eroded Soils m/s (ft/s) |
Tall Fescue Mixture (70%) |
<5 5-10 over 10 |
2.13 (7) 1.82 (6) 1.52 (5) |
1.52 (5) 1.22 (4) 0.91 (3) |
Grass Mixture Reed Canary grass |
<5 5-10 |
1.52 (5) 1.22 (4) |
1.22 (4) 0.91 (3) |
Redtop Alfalfa Red Fescue |
<5 |
1.06 (3.5) |
0.76 (2.5) |
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3.9 |
For waterways
with stone-lined centers, maximum permissible velocity in the above
table may be increased by 2 ft/s or the maximum permissible velocity
for erosion resistant soils maybe
used. |
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4.0 |
Construction and Maintenance: |
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4.1 |
All trees,
brushes, stumps, obstructions and other objectionable material shall
be removed from the side and disposed of in a manner consistent with
environmental concerns and proper functioning of the
waterway. |
4.2 |
The waterway
shall be excavated or shaped to the lines and grades as required to
meet this standard and be free of bank projections or other
irregularities which will impede normal flow. |
4.3 |
Topsoil shall be
removed from excavation areas and replaced during final grading as
required to promote good vegetative growth. |
4.4 |
Fill shall be
compacted or field rocks used as required to prevent
excessive/unequal settlement that would result in damage to the
completed waterway. |
4.5 |
Excessive
subsoil removed during waterway construction shall be used for land
forming, access road construction and/or stockpiled in an unused
area outside of the waterway. |
4.6 |
Grassed
waterways designed and constructed as part of a system that diverts
water runoff from its natural outlet shall require the written
permission of affected downstream or adjacent landowners, or the
Department of Transportation if road ditches are used. |
4.7 |
A New Brunswick
Watercourse Alteration Permit may be required for waterways
constructed that outlets directly into a natural watercourse, such
as a lake, river, or stream. |
4.8 |
All construction
operations shall be performed as required to reduce soil erosion,
and shall be built in a period where seeding can take place prior to
August 31 so adequate vegetative cover can be established to protect
against fall and spring runoff. If constructed after August 31,
waterway must be protected with appropriate erosion control matting
to limit damage from runoff events until vegetative cover can be
established in the following summer season. |
4.9 |
Erosion control
mats will be used in place of temporary ditches to encourage the
proper establishment of vegetative cover in the waterway. The width
of the mat installed shall be equal to the width of the waterway
required to safely discharge a 5 year - 24 hour storm. |
4.10 |
The owner of the
grassed waterway shall be advised of other complementary soil
conservation practices and of grassed waterway maintenance
procedures. |
4.11 |
Grassed
waterways shall be properly limed, fertilized and seeded to
recommended conservation grass mixture and maintained with a
permanent weed-free sod cover. |
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![](/web/20061104025919im_/http://www.gnb.ca/0173/images/il2005001.GIF) |
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Fig. 1. Typical waterway cross sections.
The New Brunswick Department of
Agriculture, Fisheries and Aquaculture reserves the right to revise the above
standard at any time.
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