20160105084657.pdfu� S
Civil Engineering Design and Consulting
1037 NE 65"' Street #153
Seattle, WA 98115
RE: BLD20150609 Plan Review Comments 2"d Review Dated 10-14-15
City of Edmonds
1215' Ave North
Edmonds, WA 98020
Provided below are responses to the above referenced plan review corrections:
1) — No response required.
2) — No response required.
3) — No response required.
4) — impervious surfaces have been identified on the architectural plans as requested.
5) — No response required.
6c) —The Site Plan has been revised as requested.
email Ocspengi neering.com
www.cspeng1neering.com
206406 9965
December4, 2015
7a) —The raingarden size has been revised to mitigate the proposed roof area of 1,439 sf and 72 sf of the 333 sf
impervious surface created in the right of way. The 261 sf balance of the regulated impervious surface created
in the right of way has been mitigated by conversion of existing onsite driveway impervious surface to
permeable concrete pavement.
8) —The requested document has been prepared and is attached for review by the City priorto recording.
9) —The plans have been revised as requested.
10) —The driveway approach has been reduced to be a maximum 30' wide in the right of way.
11) — A permeable pavement section has been added to the plan sheet as requested.
12) — Please see attached December 3, 2015 letter from South Fork Geosciences.
13) — Per our email correspondence a sizing factor of 5.7% is acceptable.
14) - The upwell configuration of the raingarden is modeled as an outlet control culvert with equivalent
pipe lengths utilized for the anticipated fittings. The tail water is set at 0.75' above the raingarden
bottom elevation to incorporate the 0.5' design storage depth and an additional 0.25' to account for
additional depth which might be created during overflow conditions through the spillway. With a pond
bottom elevation set at 104.4 the tailwater is 105.15. The "Roadway Elevation" for the culvert analysis
program is set to 105.9 which is the top of the downspout riser pipe at 0.5' above the finish floor
elevation.
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r 01 00AS DROP -W CRATE
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The plan length of pipe conveying downspout runoff to the raingarden is —115' with an additional —114'
added for the anticipated head loss due to fittings up to the 8"x4" upwell tee for a total length of 229'.
To account for the 8"x4" upwell tee and beehive grate an additional 21' of equivalent pipe length is
estimated for a design length of 250'.
Friction Loss Equivalent Length - feet of Straight Pipe (ft)
900 Elbow, standard sharp inside radius 13.1' x 5 = 65.5'
45° Elbow
Tee Flow — Run
5.1'x3=15.3'
8.3'x4=33.2'
Total 114'
Roof runoff is estimated utilizing the Rational Method and a 100 -year design storm intensity of
3.5"/hour. Q=CIA with C=0.9, 1=3.5, A=(1,436 sf/43,560 sf) results in a flow of 0.10 cfs.
Conveyance pipe slope in the culvert calculator program is set to 0% since the pipe flow is controlled by
the headwater and tailwater elevations and not affected by pipe slope.
Culvert Calculator Output
Entered Data:
Shape ...........................
Circular
Number of Barrels ............... 1
Solving for .....,........--....
Headwater
Chart Number ....................
1
Scale Number .................... 1
Chart Description ...............
CONCRETE PIPE CULVERT; NO BEVELED RING ENTRANCE
Scale Description ............... SQUARE EDGE ENTRANCE WITH HEADWALL
Overtopping .....................
Off
Flowrate ........................
0.1000 cfs
Manning's n .....................
0.0090
Roadway Elevation ............... 105.9000 ft
Inlet Elevation .................
0.0000 ft
Outlet Elevation ................
0.0000 ft
Diameter ........................ 4.0000 in
Length .......................... 250.0000 ft
Entrance Loss ................... 0.0000
Tailwater ....................... 105.1500 ft
Computed Results:
Headwater ....................... 105.4996 ft Outlet Control
Slope ... .....„..,..... --- ... 0.0092 ft/ft
Velocity ........................ 1.1459 fps
Messages:
Outlet head > Inlet head.
Computing Outlet Control headwater.
Outlet submerged.
Full flow.
Headwater depth computed using FHWA equation.
Headwater: 105.4996 ft
The resulting headwater required to convey a flow of 0.10 cfs is 105.5 leaving 0.4' of freeboard during the 100 -
year storm event to the downspout inlet riser elevation of 105.9.
15) — A note has been added to the plan to ensure replaced impervious asphalt in the right of way will
be sloped to the west.
Respectfully Submitted
Jeff Haynes P.E.
CSP Engineering Inc. P.S.