4.1 |
Open ditches shall
normally be dug during the period of June 1 to September 15 when
there will normally be low flows of water thus limiting the amount
of sediment that can be transported. |
4.2 |
The design ditch
bottom grade shall be no less than 0.05 percent. The maximum grade
shall not result in the design/permissible velocity being
exceeded. |
4.3 |
The ditch bottom
width shall be a minimum of 0.45m (1.5 ft.) and excavated to the
lines and grades as required to meet this standard. Banks should be
free from projections or other irregularities which will impede
normal flow. Banks should be seeded with a recommended grass mixture
within three days of construction. |
4.4 |
Open ditch side
slopes shall not exceed the following: |
|
|
|
Soil |
Shallow Channels < 1.2m (4')
in depth |
Deep Channels > 1.2m (4') in
depth |
Peat and Muck |
Vertical |
0.25 : 1 |
Heavy Clay |
0.5 : 1 |
1
: 1 |
Clay or Silt Loam |
1
: 1 |
1.5 : 1 |
Sandy Loam |
1.5 : 1 |
2
: 1 |
Loose Sand |
2
: 1 |
3
: 1 |
|
|
|
4.5 |
The spoil from the
ditch excavation should be placed a minimum of 3.0m (10 ft) from the
edge of the ditch and shall be leveled to a maximum grade of less
than 0.3m above original ground. |
4.6 |
Open ditches shall
be designed to safely discharge the peak flow resulting from a 10
year - 24 hour rainfall. The design peak flow shall be increased in
critical areas (municipal/housing areas, etc.). |
4.7 |
The design
discharge used to determine the open ditch capacity shall be
calculated using the USDA-SCS EFM2 method or the TR55
method. |
4.8 |
On steep grades, or
highly erodible soils, or also where the design peak discharge
and/or design velocity is greater than the permissible, the ditch
shall be designed with a stone center, appropriate erosion control
matting or other systems to safely discharge peak flow. |
4.9 |
Settling basins
should be installed to allow the water to slow down and any silt to
settle out. The dimensions of the settling basin shall be a minimum
of 0.6m (2 ft) deeper than the ditch bottom, a length equivalent to
ten ditch bottom widths, and a width of two times the ditch bottom
width. The side slopes of the settling basin should be the same as
the ditch. |
4.10 |
Any culvert to be
installed in an open ditch shall meet the following
criteria: |
|
4.10.1 |
Minimum
diameter of culvert to be 150mm (6"). |
4.10.2 |
Culverts
shall be manufactured of galvanized steel, concrete or high
density polyethylene and meet the following
standard: |
|
4.10.2.1 |
Galvanized steel CSA G
401-M 81 |
4.10.2.2 |
Concrete CSA A 257.3 M 1982 - for 150 mm <O.D.> 300 mm CSA 257.2 M 1982 - for 300 mm
<O.D.> 3700 mm |
4.10.2.3 |
High density polyethylene ASTM F 667 - 87 A - for 150 mm <O.D.> 400 mm AASHTO M 294 - 851 - for 400 mm
<O.D.> 750 mm |
|
4.10.3 |
The culvert
diameter shall be designed to safely discharge the peak flow
resulting from a 10 year - 24 hour rainfall. The design peak
flow shall be increased in critical areas (municipal/housing
areas, etc.). |
4.10.4 |
Culverts
shall be backfilled in a manner to prevent erosion, settling,
culvert damage and to permit safe
crossing. |
|
4.11 |
A buffer strip of
2.0m (6.5 ft) should be maintained parallel to the ditch banks.
Tillage operations should not be carried out within this zone.
Livestock access should also be denied within this zone to prevent
the breakdown of the ditch banks. |