CENTRAL KITSAP COUNTY WASTEWATER FACILITY PLAN ...

3: Wastewater Characteristics Central Kitsap County Wastewater Facility Plan
data are necessary to estimate peak hour flows, which are required for designing wastewater infrastructure.
However, the available hourly data were used for this document. Even though peak day and peak hour flow
rates are not available, average annual flows (AAFs) and PMFs (ADF) can be calculated and are useful.
3.2.2.2 Hydraulic Peaking Factor Overview
Reliable hydraulic peaking factors are required to effectively design wastewater facilities. There are two
acceptable methods for determining hydraulic peaking factors: examining historical flow records and
developing estimates based on generally accepted engineering sources.
The first method includes examining actual flow records to determine the ratio of a peak flow parameter to
an average flow rate parameter. The peak hourly flow to ADWF ratio, or peak hour hydraulic peaking factor,
is one such ratio. However, with the exception of Poulsbo (Poulsbo Sewer Plan), sufficient historical data
were not available from any of the metering stations to develop a peak hour hydraulic peaking factor. While 1
year’s worth of per-minute flow data are now available for Northern and Southern Service Area flows (LS-24
and AS-1), the recorded data did not capture a storm event that would be considered appropriate to use as a
design basis. The event selected to support peak hour design flows should have a minimum of a 5-year
recurrence interval, and preferably be a 10- to 20-year event. Because peak hour flows were not available, the
peak hour hydraulic peaking factor could not be determined based on historical flow records.
The second method to determine hydraulic peaking factors is to estimate them from information found in
generally accepted engineering sources. The American Society of Civil Engineers (ASCE) publishes curves
that express PDWF to ADWF ratios as a function of ADWF. A copy of these curves is located in Appendix
3B.
Discussions of specific peaking factors developed for the Facility Plan are included throughout the
subsequent sections.
3.2.2.3 Historical Wastewater Flows
Table 3-3 summarizes existing Central Kitsap wastewater flows for 2002–2006. The flows are developed from
the flow measurement data as discussed in Section 3.2.2.1.
Flow parameter
Table 3-3. Summary of Central Kitsap Wastewater Flows from 2002 to 2006
for the CKWWTP Service Area
Southern Service Area Northern Service Area Total system
Central Kitsap and
Silverdale
(mgd)
Poulsbo
(mgd)
Bangor
(mgd)
Keyport
(base)
(mgd)
CKWWTP
(mgd)
AAF 2.36 0.66 0.48 0.13 3.63
ADWF 2.09 0.59 0.44 0.10 3.22
AWWF 2.70 0.79 0.52 0.19 4.21
ADF 2.88 0.91 0.58 0.22 4.58
PDF N/A a 2.70 b N/A a N/A a N/A a
a. Existing flow data are insufficient to estimate peak hour flow.
b. From Poulsbo Comprehensive Sanitary Sewer Plan 2007 Update (Parametrix, 2007).
3-6
DRAFT for review purposes only.
Use of contents on this sheet is subject to the limitations specified at the end of this document.
P:\132857 Kitsap WW Facility Plan Ph II\600 Facility Plan\Revision 3 Draft Final Facility Plan\Chapter 3\Chapter 3_draft(BP).doc