1000 Hydraulics Chapter - Ministry of Transportation

More documents

Recommendations

Info

SUPPLEMENT TO TAC GEOMETRIC DESIGN GUIDE MoT Section 1020 TAC Section Not Applicable BC MoT Table 1020.A Maximum Runoff Coefficient Values For Coastal Type Basins Surface Cover Impermeable Forested Agricultural Rural Urban Physiography mountain (>30%) 1.00 0.90 - - - steep slope (20-30%) 0.95 0.80 - - - moderate slope (10-20%) 0.90 0.65 0.50 0.75 0.85 rolling terrain (5-10%) 0.85 0.50 0.40 0.65 0.80 flat ( 25 years +0.10 +0.05 +0.15 +0.10 +0.10 snowmelt +0.10 +0.10 +0.10 +0.10 +0.10 For small interior drainage basins where the critical runoff events are generally a result of summer rainstorms, the runoff coefficients can be selected from the following: • RTAC Drainage Manual Volume 1 (1982), Table 2.4.1-2.4.3, p. 2.22. For information on runoff coefficients, refer to: ♦ RTAC Drainage Manual Volume 1 (1982), p. 2.22. SCS Soil Groups and Curve Numbers Hydrologic soil groups and soil/land use curve numbers (CN) can be obtained from the following: • Ministry of Environmnet (MoE) Soils Maps • textural classifications provided by geotechnical investigations • CSPI Modern Sewer Design (1996), p. 67 • CSPI Handbook of Steel and Highway Drainage Products (2002), p.109. In areas where flooding is usually the result of winter precipitation (e.g. coastal areas), curve numbers should generally correspond to Antecedent Moisture Condition III (AMC III) to reflect the highest runoff potential. In areas where critical runoff values are the result of summer storms (e.g. interior areas), Antecedent Moisture Condition II should be assumed. For information on SCS soil groups and curve numbers, refer to: ♦ ♦ CSPI Modern Sewer Design (1996), p. 68 &69. CSPI Handbook of Steel Drainage and Highway Construction Products (2002),p. 108. 1020.03 BASIN AND CHANNEL SLOPE For small drainage areas, the slope of the drainage area can be estimated using the following formula: h1 − h2 s = L s is the average slope of drainage area, m/m h 1 is the maximum elevation of drainage basin, m h 2 is the minimum elevation of drainage basin, m L is the maximum length of drainage path, m Vertical drops such as falls and rapids, etc. should be deducted from the calculations. For large or complex drainage areas, the main channel slope should be estimated using the Average Slope Method or the Equivalent Slope Method. Average Slope Method The Average Slope Method is recommended for normal use. It should give reasonable results for streams having short rapids or falls. However, it is not recommended for profiles which are strongly convex or concave for much of their length. For information on the Average Slope Method, refer to: ♦ RTAC Drainage Manual Volume 1 (1982), p. 2.11. Page 1020-2 June, 2007
BC MoT SUPPLEMENT TO TAC GEOMETRIC DESIGN GUIDE MoT Section 1020 TAC Section 2.1.2 Equivalent Slope Method The Equivalent Slope Method is recommended for streams which have intermediate steep sections totaling over 10 percent of the overall length. For information on the Equivalent Slope Method, refer to: ♦ RTAC Drainage Manual Volume 1 (1982), p. 2.13. 1020.04 TIME OF CONCENTRATION For most drainage basins (e.g. those not effected by retention or detention), the “time of concentration” is defined as the time required for the surface runoff from the most remote part of the drainage basin to reach the point of concentration being considered. For very small basins, the following minimum times of concentration are recommended: urban 5 minutes residential 10 minutes natural, undeveloped 15 minutes Water Management Method This method was developed by the Ministry of Environment, Water Management Division, Hydrology Section and is shown in Figure 1020.B. This method is limited to drainage areas up to 10 km 2 when used with the BC Rational Formula and for drainage areas up to 25 km 2 for the SCS Unit Hydrograph Method. The time of concentration is dependent on the basin characteristics. The following parameters should be considered: flat approximately 0% slope rolling approximately 1% slope moderate approximately 2.5% slope steep greater than 10% slope For agricultural and rural basins, the curves labeled flat and rolling should be used. For forested watersheds, the curves labeled rolling, moderate and steep should be used. Figure 1020.B Time of Concentration June, 2007 Page 1020-3
Page 1 and 2: BC MoT SUPPLEMENT TO TAC GEOMETRIC
Page 9: BC MoT SUPPLEMENT TO TAC GEOMETRIC
Page 19: BC MoT SUPPLEMENT TO TAC GEOMETRIC

1000 Hydraulics Chapter - Ministry of Transportation

Create successful ePaper yourself

Delete template?

Save as template?