Redlined_DrainageCalc_Comments.pdfW 00 k S � 10 RT PLAT
7, RRAINAGE CALCULATIONS
11.1
.1 otal Area of the Site 0.694 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:
Impervious Area:
Existing House = 2,334 sf.
4 07-
Existing Shop = -
.Existing Shed =
Gravel Driveway >7111 Nd7 df.7W)i
Concrete Patio 836 sf / "?/ 00(o
-4 0
AMI-talt Driveway —2
406,if
Total = 8,611 sf. (0.198 Ac.)
Pervious Area:
Area = 0.694 (total) - 0. 1 98(imp.) 0.496 Ac.
CN = 81
Te = 16.99 minutes
L = 85 feet
M
Develoned Site
1mvervious area:
Onsite Area:
Shared Driveway = 2,031 sf.
Lot I house = 2,400 sf.
Lot I driveway = 850 sf. lv4"W
. ........... -,3-34-s+
6"0
Lot 2 Driveway 900 sf.
Lot 3 house = 2,400 sf.
.1
ISig,:,
-lot 3 Driveway = 1,000 .
Total =1 1,915 sf. (0.274 Ac,)
Pervious area: 0,694 (total) - 0.274 (imp.) = 0,420 Ac.
*Rainfall .00
Yiif� W -
2- Year = 1.50 in.: 10- Year = 2.4,0 in.: 100- Year = 3.3d in. t Do
Taken from the NOAA Atlas 2, Vol. IX, Figure 25 isopluvial maps for 2, 10, and 100 year stojj-ns
WL-'S'1'1",'RN ENGINEERS, INC. PROD F'C'I': 06-774-A
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