HomeMy WebLinkAbout2004 02 13 - Flow in Blossom DitchLIM t
2301 Maitland Center Parkway, Suite 300
Maitland, Florida 32751
tel: 407 660-2552
fax: 407 875-1161
February 13, 2004
Mr. Ken Jones
City of Sebastian
Stormwater Department
1225 Main Street
Sebastian, Florida 32958
Subject: Flow in Blossom Ditch
Dear Mr. Jones:
Per your request CDM has reviewed the ICPR model utilized in the Sebastian Master
Stormwater Management Plan to obtain representative flows in the Blossom Ditch for the
Mean Annual, 25 Year and 100 Year design storms (all of 24 hour duration). This information
was for comparison with Masteller and Moler, Inc. (M&M) flow estimates documented in a
letter dated September 3, 1998.
As was noted in the City's Stormwater Master Plan, one of the identified capital improvement
projects was to provide a cross drain under Roseland Road to link the Wentworth Ditch to the
Blossom Ditch, as such two sets of flows will be reported. The first will be the flow in
Blossom Ditch solely as a result of runoff within Unit 5; the second will include the additional
flow based upon the modeled improvement. These flows are compared with the flows
reported by M&M in the table below.
Storm Event
M&M Flow (cfs)
CDM Flow — Unit 5 (cfs)
CDM Flow — Unit 5 and Cross Drain (cfs)
Mean Annual
34.6
61
85
25 Year
84.02
88
104
100 Year
113.67
94
110
As M&M's model schematic was not included in the cited letter, the assumption was made
that the locations were comparable. In the case of the CDM ICPR model, the flow was taken
from conduit ID "P-node9" which is the representation of 54" RCP M&M proposed and was
included in the model. The configuration of this conduit was based upon plans obtained
from City staff, dated December 1999 and revised May 2000.
8:@058Z3305AConLlr 04Feo13.doc
consulting - engineering - construction • operations
Mr. Ken Jones
February 13, 2004
Page 2
As noted in M&M letter, it was stated "the diversion system should be designed for the 100 -
Year Storm Event." If one refers to the above table, it is noted that the flows reported by
M&M are approximately consistent with CDM's estimate (113.67 cfs compared with 110 cfs).
The proposed pipe size (54" RCP) appears appropriate to convey the 100 -Year storm event.
If you have any questions please call either myself ((407) 660-6315) or Eric Grotke ((772) 231-
4301).
Ve/ly your
D las?.
P.E.
Project Engineer
Camp Dresser & McKee Inc.
cc: Dave Fisher
Eric Grotke
SA20582V305MCor1U, Web13doc