Storm Sewers 0 Inlets capture stormwater 0 Junctions connect laterals to trunk lines. 0 Conduits (pipes) convey water to outfall
Design Flow 0 A design flow is the anticipated discharge for a specified AEP. 0 Typically 2-yr – 5yr AEP for subdivision type of drainage. 0 50-yr for major highways 0 Storm sewers may have extra capacity (ability to convey more than the design flow) – but are not expected to completely drain during flows in excess of design flow.
Conduit Sizing 0 Determine design flow required for a conduit (hydrology and continunity) 0 ASSUME pipe will be full (but not pressurized) – apply Manning’s equation to solve for diameter
Inlet Sizing 0 Determine allowable depth at inlet 0 Consider ponded width at the inlet 0 Hydrology to determine discharge that the inlet(s) must capture 0 Apply appropriate equation(s) to size inlet to achieve complete or partial capture. 0 Partial, then need to route carryover to next downstream inlet.
Inlet Sizing 0 Alternative is to determine capacity of inlets of known sizes (10-foot, 15-foot, …) 0 Then apply hydrology to determine the area that the inlet can serve 0 Assumes you will grade that entire area to drain to the inlet.
Junctions 0 Junctions are to connect pipes 0 Use drops to control velocity 0 Use to change pipe sizes – pipes get bigger moving downstream.
Example 0 3 drainage areas -> 3 inlets 0 4 conduits to outfall 0.5 Acres S=0.006 Parking 0.5 Acres S=0.006 Parking 1.2 acres S=0.006 Grass 1.2 acres S=0.006 Grass 1.73 acres S= 0.005 Residential 1.73 acres S= 0.005 Residential 200 ft 300 ft 400 ft 600 ft
Inlets 0 Suppose all will be curb-on-grade 0 Cross slope in streets is 2% (typical). 0 Longitudinal slope is 0.5%. 0 Allowable depth is 6-inches. 0 Design AEP is 2-yr 0 Calculate capacity for 5 foot, 10 foot, and 15 foot inlets.