§ 155.035  DESIGN BASIS.
   Storm water drainage systems, roadways and other drainage systems shall be designed to handle stormwater runoff as outlined herein.
 
(A)   Frequency of rain event.
 
(1)   Storm sewers, open ditches, driveway, culverts
25-year frequency
(2)   Road culverts
25-year frequency or meet INDOT requirements if necessary
(3)   Protection for buildings
50-year frequency
(B)   Runoff.
 
(1)   25 acres or less
Rational method Q=CIA
(2)   25 acres or more
S.C.S.-TR-55 or other method approved by the City Engineer
(C)   Overland flow time.
Use chart A
(1)   First pavement inlet
Minimum   - 10 minutes
(2)   First ditch catch basin
Minimum   - 10 minutes
(D)   Rainfall intensity.
Use chart B
 
   (E)   Run-off coefficients.
      Weighted averages shall be used to define run-off coefficient.
 
Type of area
Run-off coefficient
Business
0.60   -   0.75
Residential - Single family
0.40   -   0.50
Residential - Multi-Family
0.60   -   0.75
Industrial - Light
0.60   -   0.80
Industrial - Heavy
0.70   -   0.90
Parks, Cemeteries
0.25    -    0.40
Playgrounds
0.30   -   0.45
Railroad Yard
0.30   -   0.40
Woodland
0.20   -   0.40
Grassland
0.25   -   0.45
Cropland
0.50   -   0.70
Pavement
0.90
Roofs
0.90
Lawns, Dense soil, Flat, 0-2%
0.20   -   0.25
Lawns, Dense Soil, Avg. 6% or less
0.25   -   0.35
Lawns, Dense Soil, Steep, Over 6%
0.35   -   0.40
 
(Ord. - -, passed - -03; Am. Ord. 16-2020, passed 12-7-20)
Editor’s note:
   Charts A and B can be found in Exhibit “A” attached to Ordinance 16-2020.