To facilitate review, the grading plan should have the drainage areas delineated on it. The grading plan should also show the location and size of each channel and structure and the applicable flow rates (Qs) to each. This data does not need to be repeated on the street and channel construction plans, but arrows denoting the direction of flow do need to be shown for all street gutter flows.
A. Engineering Report: An engineer's report shall be submitted for all drainage. The report shall include:
1. Drainage area (DA) at each structure.
2. Flow rate (Q) at each structure and the computations leading to the flow rate determination.
3. Physical dimensions and hydraulic computations, nomographs cross sections, etc., for each drainage structure and storm sewer.
4. Physical dimensions and hydraulic computations, nomographs cross sections, etc., for each drainage channel and for the gutter flows.
5. Where culverts and reinforced concrete boxes are designated, they shall be in accordance with the bureau of public road circulars.
B. Grading Plan: The grading plan shall be to a minimum scale of one inch equals one hundred feet (1" = 100') showing existing and proposed finished two foot (2') contours.
C. Drainage On Lots: Lots shall not be graded such that one lot does not drain across more than two (2) adjacent lots, before it reaches an improved channel or street. A drainageway shall be constructed to intercept stormwaters, unless the drainage from all lots is sloped to the abutting streets.
D. Flow: On local and collector streets Q100 shall be less than, or equal to, eighteen inches (18") above the gutter, but in no case shall the flow be within twelve inches (12") of the finished building pad. The Q10 flow shall be less than, or equal to, the depth of the curb. Q100 shall be less than curb height and shall not be allowed to back up in the street. Maximum length of gutter flow shall be one thousand feet (1,000').
E. Flumes: Concrete flumes leading from streets where runoff is removed from the streets:
1. Shall be extended to the back of the lot or to intersect a main drainage channel.
2. Shall not run street flow across lots to deposit flow into another street.
3. Minimum flow shall be three and five-tenths (3.5) feet per second (fps).
4. Shall have a sufficient opening to preclude ponding in the street, and the water surface elevation in the channel shall be less than, or equal to, the water surface elevation in the street for the same rated storm.
F. Storm Sewers: Storm sewers:
1. Shall carry as a minimum the Q10 flow from the streets.
2. Shall have a velocity greater than, or equal to, three (3) fps.
3. Shall have inlet computations and nomographs submitted in the engineer's report.
G. Open Channels (OC):
1. Typical sections.
2. Slope of channel.
3. Profile and stationing of channel along centerline or cross sections.
4. Erosion control (excelsior mat, enkamat, riprap, and slab, etc.).
5. Three (3) fps Velocity six (6) fps for Bermuda grass lined channel.
6. Maximum side slope on grass lines slopes shall be 3:1.
7. The existing flowline elevations shall be shown for a distance of one hundred feet (100') beyond the beginning and end of storm drainage.
8. Tempered steel (9 x 9 @ 10 feet OC minimum) shall be specified for concrete liners.
H. Valley Gutters:
1. Shall be constructed of Portland cement concrete.
2. Shall be seventy two inches wide by nine inches thick (72" x 9").
3. Shall have a rounded valley of a minimum of three-fourths inch (3/4") deep.
4. Shall always be used in conjunction with concrete fillets to carry flow across asphaltic concrete pavement.
5. Valley gutters specified between intersections shall be twice the width of the flume it drains to, or ten feet (10') wide, whichever is greater, and seven inches (7") thick.
I. Manning's "n":
1. Grass lined channel, n = 0.030.
2. Concrete lined channel, n = 0.015.
3. Reinforced concrete pipe (RCP), n = 0.013.
4. Corrugated galvanized metal pipe (CGMP), n = 0.024 to 0.027 (see handbook of street drainage and highway construction products).
J. Rational Formula "C":
1. C residential = 0.6 to 0.90.
2. C commercial = 0.75 to 0.90.
3. C industrial = 0.75 to 0.90.
4. See city standard graph for "C" values. (Ord. 98-25, 9-1-1998)