§ 30. Drainage and drainage structures.

30-1

Plans. The required plans shall show the following information:

A.

Construction details of all drainage structures including dimensions, reinforcing, and components such as grates and manhole covers.

B.

Alignment of drainage easements showing beginning and ending stations; each deflection angle of the centerline, and the station at the point of intersection; the station of the point of curvature and the point of tangency of each curve; the station and angle of intersection of each intersection with another drainage easement; the location of each drainage structure, and the location and size of all storm sewers.

C.

The centerline grade at each end and at each fifty-foot station of drainage ditches, the direction of storm drainage flow at each intersection, the flow line elevations of each drainage structure, the flow line elevation of each storm sewer, at each point of change, each end, and at the intervening gradients.

30-2

Drainage computations.

A.

Runoff rates shall be computed as determined by the city engineer. In all cases, runoff rates shall be computed on the basis of ultimate development of the entire watershed contributing runoff water to the proposed subdivision, on the basis of concrete lined channels and streets carrying stormwater in the contributing area.

B.

Streets may be used to carry stormwater if the calculated flow does not exceed that required by the engineer, or the velocity does not exceed ten (10) feet per second. Minor streets shall be designed on a five-year frequency and all other streets on a ten-year frequency. Where streets are not capable of meeting the above requirements, drainage structures shall be provided. Street widths shall not be widened beyond width determined by street classification.

C.

Concrete and earth lined channels and storm sewers shall be designed on the basis of twenty-five-year frequency.

D.

Alleys shall be designed on the basis of a five-year frequency to carry stormwater from only the lots within the blocks abutting the alleys.

30-3

Construction standards.

A.

All drainage structures shall be constructed in accordance with the plans and specifications and to the lines and grades established or approved by the city engineer.

B.

All concrete used in drainage structures shall develop a comprehensive strength of three thousand (3,000) p.s.i. in twenty-eight (28) days. All castings shall conform to the Standard Specifications for Gray Iron Castings A.S.T.M. Designation A-48 for Class 2 Gray Cast Iron.

C.

Drainage ditches: In concrete lined ditches, the lining shall extend one (1) foot beyond the height of the design flow line. Between the top of the lining and the top of the ditch and earth sodded side slopes, not steeper than two (2) horizontal to one (1) vertical may be used. Vertical concrete walls shall not exceed two (2) feet in height unless properly fenced or enclosed. Earth sodded channels shall be mulch sodded over the entire surface area of the channel, and the side slope shall not be steeper than [three] (3) horizontal to [one] (1) vertical.