Minimum Requirements
A. Storm Sewers (Type B & C Conduits)
1. Design Frequency (Just Full) 10 Year.
2. Hydraulic Gradient Shall Not Exceed:
a. 12 inches below grade of pavement for 25 year frequency storm.
b. Catch basin grate or lip of inlet for 25 year frequency storm.
3. Method used to estimate peak or design discharge, AQ@ RATIONAL OR OTHER APPLICABLE METHODS.
4. Determine time to first catch basin or pavement inlet BY OVERLAND FLOW TIME PLUS PAVEMENT FLOW TIME
5. Minimum Time To:
a. First ditch catch basin 15 minutes.
b. First pavement inlet or catch basin 10 minutes.
6. Minimum Cover Over Sewers:
a. Reinforced or extra strength pipe
I. Type B conduit (under pavement and paved shoulders) 9"
II. Type C conduit (beyond pavement and paved shoulders) 18"
B. Roadway Ditches
1. Method used to estimate peak or design discharge:
a. Rational method or other applicable methods.
2. Design frequency to determine:
a. Depth of flow and protection (where required) 10 year.
b. Velocity determination 5 year
3. How estimate time of flow to ditch: OVERLAND FLOW PLUS DITCH FLOW TIME
4. Allowable velocities for:
a. Seeded line 2 F.P.S.
b. Sod, jute or other temporary lining 4 F.P.S.
5. Ditch Configuration:
a. Roadway min. depth 12"
b. Toe of embankment min. depth 12"
6. Type of ditch catch basin:
a. Shall conform to Standard Construction Drawings.
7. Minimum longitudinal slope of ditches in cut sections:
a. 0.40% desirable minimum
b. 0.24% absolute minimum
8. Minimum width of ditch lining:
a. Sod 6'
b. Temporary 7.5'
C. Drainage for curbed pavements
1. Controls for determination of inlet or catch basin spacing:
a. Design frequency using rational method 2 year
b. How to determine time to first inlet or catch basin:
1. 10 minutes minimum
2. Overland flow plus pavement flow times
c. Maximum spread of flow into traveled lane 8' feet
d. Maximum depth of flow at curb 5 inches.
2. Type of inlet or catch basin proposed for:
a. Continuous grades: CB-3A or I-2A-6 preferred.
b. Sags: CB-3, preferred.
3. Inlet lip of curb opening inlet will be depressed .2 inches below normal gutter
A local depression of 0.5 inches will be used to determine spacing of combination grate and curb opening catch basins.
See Drawings Attached to Ordinance 2001-13