3.17 Manholes and Catch Basins
a. General.
1) All junctions between storm drains shall be made at manholes or catch basins
2) Manholes or junction boxes shall be required at the following locations or as determined by the Director:
a) Maximum joint deflection shall be per manufacturer's recommendation.
b) All connections unless otherwise noted herein.
c) All changes in pipe size.
d) At a spacing no greater than five hundred (500) feet.
3) For new mainline and lateral construction, catch basin laterals of 10 feet or less in length and 10 inches in diameter or less may connect to the main line with a shop fabricated 90 degree "T", provided the connections is located not more than one hundred (100) feet from a manhole or cleanout on the main line and the main line is a minimum of 14-inches or larger in diameter.
4) In lieu of connecting to manholes, catch basins or junction boxes, laterals draining private property may be connected directly to the main line, provided the lateral diameter is 8-inches or less and is no more than half the diameter of the main line. Unless otherwise approved by the Director, the connection to mainlines shall be with an Inserta-Tee connection so as to provide a strong, leak-proof joint. The lateral shall not project inside the main line.
b. Catch Basins.
1) General.
a) Side inlet grated catch basins shall be used at all locations. Exceptions will be considered on a case by case basis.
b) Catch basins may be used for the junction of pipes 15-inches in diameter or less where the depth from rim to invert is less than 4 feet.
c) Catch basins shall be designed to completely intercept the 10 year design storm gutter flow.
2) Materials.
a) Catch basin construction and dimensions shall conform to the Standard Detail Drawings.
b) Catch basin frame and grate shall conform to standard details, and shall be fabricated of structural steel, ASTM A-7, A-36 or A-273.
3) Location.
a) The maximum length of curb and gutter which may be drained by a catch basin is 500 feet or determined by a spread analysis.
b) The maximum impervious area which may be drained by a catch basin is 20,000 square feet.
c) Catch basins shall be installed where the improvement ends on all streets terminating on a descending grade, and piped to an approved point of disposal.
d) Catch basins on comers shall not be located in front of ADA ramps or curb returns.
e) Catch basins in the middle of blocks shall be located within 5 feet of the extension of a common property line.
f) Catch basins shall be installed at all low spots, whether on private or public property, and shall be connected to a storm drainage facility.
4) Drop Across Catch Basin Structure.
a) The vertical drop across flow-through storm drain catch basins shall not be less than 0.1 feet.
c. Manholes
1) Manhole Size
a) Manhole size shall conform to the requirements outlined under Division 4, Sanitary Sewers and the standard details.
2) Manhole Location
a) Manholes shall be installed at all pipe junctions where the depth from rim to invert exceeds four (4) feet or where the pipe is 18-inches in diameter or greater. Exceptions will be reviewed on a case by case basis.
3) Drop Across Manhole Structure.
a) The vertical drop across storm drain manholes shall conform to the requirements outlined under Division 4, Sanitary Sewers.
b) Where pipes of different sizes enter the same manhole, the design shall generally provide that the crowns of the pipes are set at the same elevation. Deviation requires approval by the City Engineer.
c) In cases where two pipes discharge into a manhole from opposite directions and one pipe has a slope more than four percent (4%) steeper than the pipe opposite, the invert of the pipe with the lower slope shall be set a minimum of 0.35 feet or½ the pipe diameter, whichever is greater, above invert of the steeper pipe.
4) Rim Elevation.
a) The rims of all manholes located within paved or other hard surfaced areas shall be set to finished grade.
b) Concrete riser rings shall be used to bring casting to grade. The height from the top of the cone or flattop section to the rim shall not exceed 18 inches.
d. Mainline Storm Cleanouts.
1) Mainline storm cleanouts will not be approved.
e. Junction Boxes.
1) Solid lids on junction boxes shall be minimum 3/4-inch steel plate, and shall be provided with at least one lifting hole. Junction boxes located in a travel lane shall have a manhole frame and cover.
f. Bore and Castings.
1) Carrier pipe used in bore casings shall be Ductile Iron or PVC as specified herein.
2) Bore casing and carrier pipe design and installation shall conform to the requirements outlined under Division 5, Water Distribution.