The following minimum standards apply to drainage construction within new subdivisions:
(a) 
Storm sewers and culverts.
(1) 
Minimum diameter: twenty-four inches (24"); eighteen inches (18") for pipe serving one inlet.
(2) 
Minimum slope: Storm sewers: 0.1 percent. Culverts shorter than one hundred feet (100'): 0.1 foot.
(3) 
Material: Class III reinforced concrete pipe, and Texas Highway Department standard box culverts and headwalls.
(4) 
Joints: Ram-Nek asphaltic sealer.
(5) 
Location: See Figure I.[1]
[1]
Editor's note—Figure I is on file in the city offices.
(b) 
Open channels.
(1) 
Unlined ditches.
a. 
Side slopes: Three horizontal, one vertical.
b. 
Bottom slope: 0.05 percent minimum.
c. 
Easement width: Top width plus sixteen feet (16') on one side plus six feet (6') on other side.
(2) 
Lined channels.
a. 
Bottom slope: 0.05 percent minimum.
b. 
Lining material: Five-inch-thick (5") concrete with 43 bars at 18 inches (18").
c. 
Concrete characteristics:
Same as for street paving.
d. 
Easement width:
Top width plus twelve feet (12') on one side and four feet (4') on other side.
(3) 
Junction boxes and manholes.
a. 
Size: Nominal pipe size plus twelve inches (12").
b. 
Material: Reinforced concrete, designed for load. (Brick walls are permissible.)
c. 
Location: At changes in pipe size or direction, and at 400 foot (400') intervals.
d. 
Access: twenty two inch (22") diameter cast iron cover.
(4) 
Inlets.
a. 
Minimum thread size: Six inches (6") high by five feet (5') long.
b. 
Material: Reinforced concrete, designed for load. (Brick walls are permissible.)
c. 
Wall thickness: Six inches (6").
d. 
Access: twenty-two inch (22") diameter cast iron cover.
(5) 
Runoff criteria.
a. 
Storm period: twenty-five (25) years.
b. 
Runoff coefficient: Single-family area, fifty (50) percent.
c. 
Multi-family or commercial: eighty (80) percent.
(c) 
Storm water detention pond.
For all subdivisions, the developer or property owner must obtain a letter from the Brookshire-Katy Drainage District stating the proposed development meets or is exempt from the district's storm water detention requirement. Such a letter is not required if the proposed development meets all of the following criteria:
(1) 
Each lot contains twenty thousand (20,000) square feet or more and is for a single-family residence;
(2) 
The area of the roof and paved surfaces, minus the area of landscape beds containing at least six inches' (6") thickness of mulch, is less than ten percent of the total area of the lot;
(3) 
The lot grading and arrangement is such that all drainage from the roof and paved surfaces leaves the lot as sheet flow (not in a pipe or ditch);
(4) 
The above criteria in subsections (3)a, b and c of this section are included as deed restrictions and also on the subdivision plat; and
(5) 
Each lot fronts on an existing paved public street.
(Ordinance 26-747-16 adopted 4/2/2026)