Drainage facilities shall be provided and constructed by the subdivider or developer in accordance with current design criteria adopted by the city and the city standard specifications for street and drainage construction and the following basic requirements, subject to the provisions of article IV hereof:
(1) 
When conditions upstream from a proposed channel or storm drain outside the limits of the ownership of the subdivider or developer do not permit maximum design flow, the drainage facilities shall be designed based on potential and fully developed conditions.
(2) 
When conditions downstream from a proposed channel or storm drain outside the limits of the ownership of the subdivider or developer do not permit maximum design flow, water surface elevations for a 100-year design frequency shall be indicated considering the downstream condition in order to define the potential flood hazards. Solutions to protect the property shall be developed.
(3) 
All drainage improvements shall be designed to an acceptable outfall.
(4) 
Where there is a question as to the justification or size of drainage facilities, doubt will be resolved in favor of additional drainage capacity.
(5) 
The combined capacity of storm drain pipe, street and surface drainage shall contain the 100-year design flow at the right-of-way lines. The finish floor elevation shall be at least one foot above the 100-year flood base flood elevation (BFE).
(6) 
The developer shall install an underground storm drain beginning at the point where the calculated stormwater runoff is of such a quantity that it will overflow the street at curb height. The storm drain shall be constructed from this point to an approved outlet where the stormwater can be discharged safely without damage or flooding of adjacent property.
(7) 
The developer may install a concrete lined channel in lieu of installing pipe larger than 60 inches. When the pipe required to meet these subdivision regulations is less than 60 inches, the flow from this rain event must be carried in such a pipe. When an open channel is necessary, it shall be at the rear of residential lots and meet the requirements of North Central Texas Council of Government Standard Specifications for Public Works Construction. In the event it is necessary to locate the drainage facility adjacent to and parallel to a street, it shall be a closed conduit even though pipe sizes larger than 60 inches are required.
(8) 
A permanent six-foot chainlink fence or other fence meeting the requirements of the city shall be constructed to enclose the channel area where it is adjacent to residential lots and also in other cases where it is deemed necessary to restrict access to the channel.
(9) 
All drainage facilities shall be constructed on public rights-of-way or easements dedicated for the purpose. Drainage easements shall be of a sufficient size to permit access for maintenance of the drainage facility.
(10) 
When a drainage ditch or storm drain pipe, culvert or bridge is proposed, calculations shall be submitted showing basis for design.
(11) 
When a drainage channel, storm drain pipe, culvert or bridge is proposed, completed plans, profiles and specifications shall be submitted, showing complete construction details and a detailed cost estimate.
(12) 
The subdivider or developer shall indicate present DA's I 25, I 100, Q 25 and Q 100.
(13) 
The subdivider or developer shall indicate proposed DA's I 25, I 100, Q 25 and Q 100.
(14) 
The subdivider or developer shall indicate both present and proposed contours and direction of drainage.
(15) 
Any present adverse drainage problems shall not be made worse.
(16) 
Proposed drainage shall flow to drainage easements, storm drain facilities and/or publicly dedicated streets only.
(17) 
Existing capacities of drainage easements, storm drain facilities and/or publicly dedicated streets shall be indicated.
(18) 
Existing capacities of drainage easements, storm drain facilities and/or publicly dedicated streets shall not be exceeded.
(19) 
Directing or allowing drainage onto private property will not be allowed.
[Ord. No. 819-97, § 11(K), 6-10-1997; Ord. No. 1063-06, § 19, 8-22-2006]
(a) 
Drainage requirements shall be based on the Rational Method of Design (Q = CIA).
Q
=
Discharge or surface runoff in cubic feet per second.
C
=
Coefficient of runoff:
 
 
0.35 for parks and undeveloped areas.
 
 
0.50 for single-family or duplex residential areas.
 
 
0.80 for multifamily residential areas.
 
 
1.00 for paved, commercial, and industrial areas.
I
=
Intensity of runoff in inches per hour.
A
=
Drainage areas in acres.
(b) 
A minimum time of concentration of ten minutes shall be used, with detailed computation made to determine the exact time of concentration to each inlet facility.
Design Storm Frequency
Type of Facility
Description of Area to be Drained
Maximum Allowable Time of Concentration
(Minutes)
Recommended Design Frequency
(Years)
*Storm sewers
Residential, commercial and manufacturing
20
25
*Culverts, bridges, channels and creeks
Any type of area less than 100 acres
30
100
*Culverts, bridges, channels and creeks
Any type of area greater than 100 acres but less than 1,000 acres
45
100
*Culverts, bridges, channels and creeks
Any type of area greater than 1,000 acres
60
100
*In all cases, the discharge from a 100-year rain event for fully developed conditions shall be completely carried within a drainage easement and/or right-of-way.
[Ord. No. 819-97, § 11(K), 6-10-1997]