drainage system design and layout. design process flowchart background information (soils, topo,...
Post on 17-Dec-2015
222 Views
Preview:
TRANSCRIPT
Design Process FlowchartDesign Process Flowchart
Background Information
(Soils, Topo, Crops)
Confirm Outlet
Drainage Needed
Select DC, Spacing & Depth
Determine Grades & Depth
Develop System Layout
Determine DrainSizes
Installation
NO
NO
Design Process FlowchartDesign Process Flowchart
Background Information
(Soils, Topo, Crops)
Confirm Outlet
Drainage Needed
Select DC, Spacing & Depth
Determine Grades & Depth
Develop System Layout
Determine DrainSizes
Installation
NO
NO
Outlet channels designed according to Curve B will provide excellent agricultural drainage in Illinois. Use this curve for drainage of truck crops, nursery crops, and other specialty crops. Designs based on curve B will provide the best drainage that can normally be justified in agricultural areas.
Design Design CurvesCurves
Channels that are designed according to curve C will provide good agricultural drainage in Illinois. This curve is the one most often recommended for drainage of Illinois cropland
Design Design CurvesCurves
Drainage OutletsDrainage OutletsDesigns based on curve D provide satisfactory agricultural drainage as long as frequent overflow does not cause excessive damage. This curve is generally recommended for pasture or woodland. It may also be adequate for drainage of general cropland in northern Illinois, provided that the landowner carries out an excellent maintenance program. Designs based on curve D provide the minimum amount of drainage recommended in Illinois.
Drainage CFS/ Acre In/Day Curve 100 Acres (Drainage Coefficient)
B 20 4.8
C 8 2.0
D 5 1.2For comparison: For a 100 acre watershed, RCN = 75, Avg. Slope = 1% in Central Illinois
A 2 Yr., 24 Hr. Rainfall yields 1” of Runoff and would result in a Peak
Flow of 30 CFS.
A 10 Yr., 24 Hr. Rainfall yields 2” of Runoff and would result in a Peak
Flow of 70 CFS.
Design Design CurvesCurves
Ditch ConfigurationDitch Configuration
Once you know what the capacity of the outlet channel must be, you need to determine the size that will enable it to convey the desired amount of flow without letting the water surface rise above a predetermined elevation. The following sections describe some basic hydraulic concepts that will help you design a channel of the proper size
.
Outlet Outlet DitchesDitches
Velocity The velocity of water flow must be high enough to prevent siltation in the channel but low enough to avoid erosion. Listed on the next page are the maximum velocities for drainage areas of 640 acres or less. The velocity should be no lower than 1.5 feet per second. A lower velocity will cause siltation, which encourages moss and weed growth and reduces the cross section of the channel.
Soil TextureMaximum Velocity
(ft/sec)
Sand or sandy loam 2.5
Silt loam 3.0
Sandy clay loam 3.5
Clay loam 4.0
Clay or silty clay 5.0
Fine gravel, cobbles, or
graded loam to cobbles5.0
Graded mixture silt to cobbles 5.5
Coarse gravel, shales,
or hardpans6.0
Channel Channel VelocityVelocity
The most widely used equation for designing outlet channels was developed by Robert Manning in 1890 and is known as Manning's equation:
whereV = average velocity of flow (ft/sec),
n = coefficient of roughness,R = hydraulic radius (ft),
s = slope of hydraulic gradient (ft/ft).
2
1
3
249.1sR
nv
Design Process FlowchartDesign Process Flowchart
Background Information
(Soils, Topo, Crops)
Confirm Outlet
Drainage Needed
Determine Grades & Depth
Develop System Layout
Determine DrainSizes
Installation
NO
NO
Select DC, Spacing & Depth
•Design for uniform depth throughout system(depends on layout)
•Depth will of course vary on flat and rolling topography
Drain Spacing & DepthDrain Spacing & Depth
Depth-Spacing Relationships
0
20
40
60
80
100
120
2.5 3 3.5 4 4.5 5
Drain Depth (ft)
Dra
in S
pa
cin
g (
ft)
3/8" Drainage Coeff icient 1/2" Drainage Coeff icient
3/4" Drainage Coeff icient
10 358820 182530 125640 97250 80260 68870 57480 51790 460
100 452
Spacing (ft) Costs ($/acre)
Drainage Costs
Corn Soybean10 24.2 52.720 24.2 52.730 24.2 52.740 24.2 52.750 24.2 43.3560 22 33.1570 22 23.880 17.6 14.4590 15.4 5.95100 13.2 3.4
Spacing (ft)Increase Yield (bu/acre)
10 4.8720 9.5530 13.3740 16.8150 17.1660 15.8270 14.6380 10.8590 6.66100 4.42
Spacing (ft) Rate of Return (%)
100
Tile Density
Pro
fita
bili
ty
Cost/Acre Crop Yield Rate of Return
Co
st o
r Y
ield
Rat
io (
%)
Spacing
Design Process FlowchartDesign Process Flowchart
Background Information
(Soils, Topo, Crops)
Confirm Outlet
Drainage Needed
Select DC, Spacing & Depth
Determine Grades & Depth
Determine DrainSizes
Installation
NO
NO
Develop System Layout
90.0 ft
91.5 ft
93.0 ft
94.5 ft
96.0 ft.
90.0 ft
91.5 ft
93.0 ft
94.5 ft
96.0 ft.
Optimized for Drainage Water ManagementOptimized for Cost of Installation
90.0 ft
91.5 ft
93.0 ft
94.5 ft
96.0 ft.
90.0 ft
91.5 ft
93.0 ft
94.5 ft
96.0 ft.
Optimized for Drainage Water ManagementOptimized for Cost of Installation
System LayoutSystem Layout
Cost Differential: $50/acreCost Differential: $50/acre
Design Process FlowchartDesign Process Flowchart
Background Information
(Soils, Topo, Crops)
Confirm Outlet
Drainage Needed
Select DC, Spacing & Depth
Develop System Layout
Determine DrainSizes
Installation
NO
NO
Determine Grades & Depth
top related