DrainageYelm Community Center
Project Precips
[2 yr] 2.20 in
[5 yr] 3.10 in
[10 yr] 3.00 in
[100 yr] 4.10 in
[7-day] 12.00 in
[6mo] 1.58 in
BASLIST2
[Dev-Site] Using [TYPE1A] As [100 yr]
[Dev-Site] Using [TYPEIA] As [7-day]
[Dev-Site-7day] Using [PC7DAY] As [100 yr]
[Dev-Site-7day] Using [PC7DAY] As [7-day]
LSTEND
BasinlD Peak Q Peak T Peak Vol Area Method
----- (cfs) (hrs) (ac-ft) ac /Loss
Dev-Site 0.8757 7.83 0.2835 0.88 SBUH/SCS
Dev-Site 2.5995 7.83 0.8624 0.88 SBUH/SCS
Dev-Site-7day 0.1612 55.00 0.2693 0.88 SBUH/SCS
Dev-Site-7day 0.4884 55.00 0.8470 0.88 SBUH/SCS
Raintype Event
TYPEIA 100 yr
TYPEIA 7-day
PC7DAY 100 yr
PC7DAY 7-day
BASLIST [PC7DAY] AS [100 yr] DETAILED
[Dev-Site] [Dev-Site-7day]
LSTEND
Drainage Area: Dev-Site
Hyd Method: SBUH Hyd
Peak Factor: 484.00
Storm Dur: 24.00 hrs
Area CN
Pervious 0.0000 ac 78.00
Impervious 0.8800 ac 98.00
Total 0.8800 ac
Supporting Data:
Impervious CN Data:
New Impervious 98.00
Impervious TC Data:
Flow type: Description:
Sheet None Entered
Shallow None Entered
Drainage Area: Dev-Site-7day
Hyd Method: SBUH Hyd
Peak Factor: 484.00
Storm Dur: 168.00 hrs
Area CN
Pervious 0.0000 ac 78.00
Impervious 0.8800 ac 96.30
Total 0.8800 ac
Supporting Data:
Impervious CN Data:
New Impervious 96.30
Loss Method: SCS CN Number
SCS Abs: 0.20
Intv: 10.00 min
TC
0.00 hrs
0.05 hrs
0.8800 ac
Length: Slope: Coeff:
115.00 ft 1.00% 0.0110
90.00 ft 1.00% 27.0000
Loss Method: SCS CN Number
SCS Abs: 0.20
Intv: 60.00 min
TC
0.00 hrs
0.05 hrs
0.8800 ac
Travel Time
2.21 min
0.56 min
Impervious TC Data:
Flow type: Description: Length: Slope: Coeff: Travel Time
Sheet None Entered 115.00 ft 1.00% 0.0110 2.21 min
Shallow' None Entered 90.00 ft 1.00% 27.0000 0.56 min
HYDLIST SUMMARY
[1] [2]
LSTEND
HydID PeakQ Peak T Peak Vol Cont Area
--- (cfs) (hrs) (ac-ft) (ac)
1 0.56 2.00 0.3214 0.8800
2 0.56 23.00 1.1937 0.8800
STORLIST
[Trench]
LSTEND
Node ID: Trench
Desc: Infiltration Tre nch
Start EI: 100.0000 ft Max EI: 108.0000 ft
Contrib Basin: Contrib Hyd:
Length Width Void Ratio
200.0000 ft 6.0000 ft 30.00
Bottom area only with infiltration
DISCHLIST
[Infiltration]
LSTEND
Control Structure ID: Infiltration -Infiltration control structure
Descri p: I nfi I tration
Start EI Max EI Increment
100.0000 ft 105.0000 ft 0.10
Infil: 20.00 in/hr Multiplier: 1.00
RLPCOMPUTE [RLP] SUMMARY
100 yr MatchQ=PeakQ= 0.8757 cfs Peak Out Q: 0.5556 cfs -Peak Stg: 101.22 ft -Active Vol: 437.61 cf
7-day MatchQ=PeakQ= 0.4884 cfs Peak Out Q: 0.5556 cfs -Peak Stg: 102.64 ft -Active Vol: 948.71 cf
C.E.S. NWlnc.
Civil Enbineerino & Survepino
~ 308 12th Street East
Suite B
Fife, WA 98424
Business: (253)922-1532
Fax: (253)922-1954
ceservi ces@q west.n et
Y~~~.
USDA Soil Conservation Service Soil Description
ll0- Spanaway bravelly sandy loam, 0 to 3 percent slopes. This very deep, somewhat excessively drained soil is on terraces.
It formed in glacial outwash and volcanic ash. The native vegetation is mainly grasses, ferns, and a few conifers. Elevation ranges
from 100 to 400 feet. The average annual precipitation is 45 to 55 inches, the annual air temperature is about 51 degrees F, and
the average frost-free period is 150 to 200 days.
Typically, the surface layer is black gravelly sandy loam about 1 S inches thick. The subsoil is dark yellowish brown very grav-
ellyloam about 5 inches thick. The substratum to a depth of 60 inches or more is dark yellowish brown extremely gravelly sand.
Included in this unit are small areas of Alderwood soils on till plains; Everett, Indianola, and Nisqually soils on outwash ter-
races; and Spana soils in depressions. Also include are small areas of Spanaway soils that have a stony sandy loam surface layer
and small areas of Spanaway gravelly sandy loam that have slopes of 3 to l 5 percent. Included areas make up about 20 percent
of the total acreage.
Permeability is moderately rapid in the subsoil of the Spanaway soil and very rapid in the substratum. Available water capacity
is low. Effective rooting depth is 60 inches or more. Runoff is slow, and the hazard of water erosion is slight.
This unit is used mainly as hayland, pasture or cropland, as a site for homes, or as a source of grave]. ]t is also used as wood-
land.
The main ]imitation affecting hay and pasture is the low availability of water capacity. Proper gratin' practices, weed control,
and fertilizer are needed to ensure maximum quality of forage. Rotation grazing helps to maintain quality of forage. Periodic
mowing helps to maintain uniform growth, discourages selective grazing, and controls weeds. Animal manure can be applied
periodically during the growing season. Areas.that receive heavy applications should be harrowed at least once a year. In sum-
mer, irrigation is needed for maximum production of most forage crops. Sprinkler irrigation is the best method of applying wa-
ter. The amount of water applied should be sufficient to wet the root zone but small enough to minimize the leaching of plant
nutrients.
This -unit is suited to crops. Wheat, oats, strawberries, raspberries, blackberries, and sweet corn are commonly gown. The
main limitation is the low available water capacity. In summer, irrigation is needed for maximum production of most crops.
Sprinklers can be used, but a slow application rate is needed to minimize runoff: The amount of water applied should be suffi-
cient to wet the root zone but small enough to minimize leaching of plant nutrients. The application rate should be adjusted to the
available water capacity, the water intake rate, and the needs of the crop. Animal manure can be applied periodically during the
growing season. Areas that receive heavy applications should be harrowed at ]east once a year.
This unit is well suited to homesites. Pebbles and cobbles should.be removed, particularly in the areas used for lawns. In sum-
mer, irrigation is needed for lawn grasses, shrubs, vines, shade trees, and ornamental trees. Mulch, fertilizer, and imgation are
needed to establish lawn grasses and other small-seeded plants.
The main limitation affecting septic tank absorption fields is a poor filtering capacity. If the density of housing is moderate or
high, community sewage systems are needed to prevent the contamination of water supplies caused by seepage from onsite sew-
age disposal systems. Cutbanks are not stable and are subject to sloughing.
Douglas fir is the main woodland species on this unit. Among the trees of limited extent are Oregon white oak, ]odgepole pine,
and red alder. Douglas fir and Scotch pine are grown on Christmas tree plantations. On the basis of a 100-year site curve, the
mean site index for Douglas fir is 140. On the basis of a 50-year site curve, it is 108. The highest average growth rate of an un-
managed, even-aged stand of Douglas fir is ] 45 cubic feet per acre per year at 65 years of age.
This soil is suited to year-round logging. Unsurfaced roads and skid trails are slippery when wet. Logging roads require suit-
able surfacing material for year-round use. Rounded pebbles and cobbles for road construction are readily available in this unit.
Disturbance of the protective layer of duff can be minimized by the careful use of wheeled and tracked equipment.
Seedling establishment and seedling mortality are the main concerns in the production of timber. Reforestation can be accom-
plished by planting Douglas fir seedlings. If the stand includes seed trees, natural reforestation by Douglas fir, Oregon white oak,
and ]odgepole pine occurs periodically in cutover areas. Doughtiness in the surface layer reduces the seedling survival rate.
When openings are made in the canopy, invading brushy plants can delay the establishment of planted Douglas fir seedlings.
Common forest understory plants are cascade Oregon grape, salal, western brackenfern, westem swordfern, Indian plum and
scotch broom. This map unit is capability subclass IVs. -
Table 1.3 Runoff curve numbers for selected
agricultural, suburban, and urban areas
(Sources: TR 55, 1986, and Stormwater Management Manual_ 19921
CNs for hydrologic soil group
Cover a and h drol is condition ..................................................................................A B C D
Curve Numbers for Pre-Development Conditions
Pasture, grassland, or range-continuous forage for grazing:
Fair condition (ground cover 50% to 75% and not heavily grazed) ......................................49 69 79 84
Good condition (ground cover >75% and lightly or only occasionally grazed) ...................39 6l 74 80
Woods:
Fair (Woods are grazed but not burned, and some forest litter covers the soil) ....................36 60 73 79
Good (Woods are protected from arazin ,and litter and brush adequately cover the soil)..30 55 70 77
Curve Numbers for Post-Development Conditions
Open space (lawns, parks, golf courses, cemeteries, landscaping, etc.)' ..............
Fair condition (grass cover on 50% - 75% of the area) ....................................................... 77 85 90 92
Good condition (grass cover on >75% of the area) ...............................................................68 80 86 90
Impervious areas:
Open water bodies: lakes, wetlands, ponds etc. 100 100 100 ] 00
Paved parking lots, roofs, driveways, etc. (excluding right-of--way) ................................................. 98 98 98 98
Streets and roads:
Paved ...................................................................................................................................................9 98 98 98
Gravel (including right-of--way) ..................................................................................................:..:.:.. 76 85 89 91
Dirt (including right-of-way) ..............................................................................................................: 72 82 87 89
Pasture, grassland, orrange-continuous forage for grazing:
Poor condition (ground cover <50% or heavily ~ azed with no mulch) .................:....... .68 79
.... 86 89
Fair condition (ground cover 50% to 75% and not heavily grazed)..:. ' .:....... ....... .....49 69 79 84
Good condition (ground cover >75% and lightly or only occasionally grazed) ..................39 61 74 80
Woods:
Poor (Forest litter, small trees, and brush are destroyed by heavy
grazing or regular burning) ...........................................:'..:........:.......:...................................45 66 77 83
Fair (Woods are grazed but not burned, and some forest litter covers the soi]) .....................36 60 73 79
Good (Woods are rotected from °razin ,and litter and brush ade uatel cover the soil)...30 55 70 77
Single family residential : Should only be used for Average Percent
Dwelling Unit/Gross Acre subdivisions > 50 acres impervious areaz,3
1.0 DU/GA....... .._.__..: ....._-:. ....:: :.................................................... 15 Separate curve number
1.5 DU/GA..::......:..'.:::..:.:.......:: :.............................................................. 20 shall be sel ected for
2.0 DU/GA............:........:..: ..................................................................... 25 pervious & impervious
2.5 DU/GA ............::.:............................................................................... 30 portions of the site or
3.0 DU/GA .............................................................................................. 34 basin
3.5 DU/GA .............................................................................................. 38
4.0 DU/GA ..............................................................................................42
4.5 DU/GA .............................................................................................. 46
5.0 DU/GA .............................................................................................. 48
5.5 DU/GA .............................................................................................. 50
6.0 DU/GA .............................................................................................. 52
6.5 DU/GA .............................................................................................. 54
7.0 DU/GA ..............................................................................................56
7.5 DU/GA .............................................................................................. 58
PUD's, condos, apartments, commercial %impervious Separate curve numbers shall
businesses, industrial areas & must be be selected for pervious and
& subdivisions < 50 acres computed impervious ortions of the site
For a more detailed and complete description of land use curve numbers refer to chapter two (2) of the Soil
Conservation Service's Technical Release No. 55 , 210-VI-TR-55, Second Ed., June 1986 .
Composite CN's may be computed for other combinations of open space cover type.
ZAssumes roof and driveway runoffis directed into street/storm system.
'Where roof runoff and drive runoffare infiltrated or dispersed according to the requirements in Chapter 2, the average
percent impervious area may be adjusted in accordance with the procedure described under "Flow Credit for Roof
Downspout Infiltration" and "Flow Credit for Roof Downspout Dispersion" in Chapter 2.
August 2000 Volume III -Hydrologic Analysis and Flow Control Design Page 33
Western Washington Isopluvial 2-year, 24 hour
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Page 78 Volume III -Hydrologic Analysis and Flow Control Design August 2000
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August 2000 Volume III - Hvdrologic Analysis and Flow Control Design Page 79
/~ '- ~l
Western Washington Isopluvial 10-year, 24 hour
Western Washington Isopluvia1100-year, 24 hour
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Page 80 Volume III -Hydrologic Analysis and Flow Control Design August 2000
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