Stormwater_Review Comments.pdfB ORG E N 8 1 IORT P LAT
DRAINAGE CALCULATIONS
Total Area of the Site = 0.475 Acres
As per the Soil Survey of the Snohomish County Area, the entire site is Alderwood
Gravelly Sandy Loam, which corresponds to a Type C soil. For calculation purposes, a
Type "C" soil was used.
EXISTING SITE:
_ln�pervious Area:
Existing House = 1,483 st.
-EX44ing'W, 747-sf,—""
Total 4,709-9f. (0.109 Ae.)
Pervious Area. "t b 3 s 0.
Area = 0.475 (total) 0.366 Ac.
CN = 81 0 a z.; 4c,
Tc = 23.44 minutes
11 = 20 feet, 60 fect
S = 27.5%,2.33%
Developed .-Site.
Onsite Area:
Shared Driveway
= 1,703 sE
Lot I Driveway
1,000 st"
--Lxi,&6ng-hm,sr—
J,493 --s,
Lot 2 Driveway
= 1,150 sf
Lot 2 house — — — —
— — — —= 2800 sf.
Total
S,4-36 sf
Offsite Area:
FrontageImprovements 850 sE
009 4'roff
16 VS 0�rlz
Total Impervious Area =.8,4-3-6 st. --1- 850 sf'.
= 8�969sf- (0-206 Ac.0)
0.x..1'
0�303
Pervious Lima- 0,475 (total) - 0QW
(ins p.) = 0-269 Ac.
os 3;Me"Mov",
*Rainfall I r�) "74,0)
2- Year =,,l-4fJ`m,: 10- Year = 2.00 in.: 100- Year =,k�60 in,
Taken from the NOAA Atlas 2, Vol, JX, Figure 25 k0phivial maps for 2, 10, and 100 year storms
Wl---',S'TERN ENQINEFI8, INC. PROJE"ICT: 06-745-A