HomeMy WebLinkAbout6-1 Revised Sewer Narrative 12-31-2019 1
Sewer
This section is a response to the requirements of the City of Bozeman Unified Development
Ordinance Section 38.220.060 relative to Water and Sewer. The original Sanitary Sewer Design
Report provides analysis for the entire PUD including Phase 4. Flows from Phase 4 are designed
to flow west to the existing sewer main in Fowler Avenue (see updated sewer main exhibit).
Since the report was written, the City of Bozeman Design Standards and Specifications have
been revised to reflect a lower required flow rate for B-2 zoning, decreasing from 3495
gal/ac/day to 2000 gal/ac/day. Previous calculations combined with the reduction in B-2 flow
rates indicate that the existing system will meet the required sewer design criteria for Phase 4 of
the Bozeman Gateway.
The manhole located at the intersection of Fowler and Technology Blvd was dipped on
12/30/2019 and was found to have a sewage depth of 0.2’. Due to the timing of this measurement
during the holiday season, it is conservatively assumed that the average existing flow depth is
0.5’. The outlet pipe has a diameter of 21”. Assuming a minimum slope of 0.1% has a capacity
flowing full of 6.3cfs (2,827.6gpm). At a depth of 0.5’ the pipe is approximately 29% full and
flowing at a rate of 1.06cfs (475.8gpm). Based on the Sewer Facility Plan’s 2000 gal/ac/day for
15.8 acres, the wastewater produced by Phase 4 is 31,600gpd or 0.05cfs (21.9gpm). The
contribution of Phase 4 increases the flow to 1.11cfs (498gpm) which equates to a pipe depth of
0.51 or 29%. The 21” pipe has more than enough capacity to accommodate the development.
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Sunday, Dec 29 2019
21in PVC Flowing Full
Circular
Diameter (ft) = 1.75
Invert Elev (ft) = 100.00
Slope (%) = 0.10
N-Value = 0.011
Calculations
Compute by: Q vs Depth
No. Increments = 10
Highlighted
Depth (ft) = 1.58
Q (cfs) = 6.312
Area (sqft) = 2.28
Velocity (ft/s) = 2.77
Wetted Perim (ft) = 4.38
Crit Depth, Yc (ft) = 0.93
Top Width (ft) = 1.05
EGL (ft) = 1.69
0 1 2 3
Elev (ft)Section
99.50
100.00
100.50
101.00
101.50
102.00
Reach (ft)
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Dec 31 2019
Existing Pipe Flow
Circular
Diameter (ft) = 1.75
Invert Elev (ft) = 100.00
Slope (%) = 0.10
N-Value = 0.011
Calculations
Compute by: Known Depth
Known Depth (ft) = 0.50
Highlighted
Depth (ft) = 0.50
Q (cfs) = 1.061
Area (sqft) = 0.57
Velocity (ft/s) = 1.86
Wetted Perim (ft) = 1.98
Crit Depth, Yc (ft) = 0.37
Top Width (ft) = 1.58
EGL (ft) = 0.55
0 1 2 3
Elev (ft)Section
99.50
100.00
100.50
101.00
101.50
102.00
Reach (ft)
Channel ReportHydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Tuesday, Dec 31 2019Proposed Pipe FlowCircularDiameter (ft) = 1.75Invert Elev (ft) = 100.00Slope (%) = 0.10N-Value = 0.011CalculationsCompute by: Known QKnown Q (cfs) = 1.11HighlightedDepth (ft) = 0.51Q (cfs) = 1.110Area (sqft) = 0.59Velocity (ft/s) = 1.89Wetted Perim (ft) = 2.00Crit Depth, Yc (ft) = 0.38Top Width (ft) = 1.59EGL (ft) = 0.570123Elev (ft)Section99.50100.00100.50101.00101.50102.00Reach (ft)