Drainage Design Manual - the City of San Luis Obispo

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Shallow Concentrated Flow occurs where overland flow converges to form small rillsor gullies and swales. Shallow concentrated flow can exist in small, man-made drainageditches (paved and unpaved) and in curb gutters. The recommended maximum length forshallow concentrated flow is 300 m (1000 ft).Determine the velocity of the flow using Equation 3.Then calculate the travel time by following Equation 4.Equation 3: V = K u k S p 0.5Where:V = velocity (m/s)K u = 1.0 (3.28 in Imperial Units)k = interception coefficient (Table 4-2)S p = Slope (percent)Table 4-2Interception Coefficients for Velocity vs. Slope Relationship of Equation 3Flow RegimekGrassed waterway 0.457Unpaved 0.491Paved area; small uplandgullies0.619Equation 4T t (minutes) = L60 VWhere:L = length of shallow concentrated flow (m)V = velocity (m/s, from Equation 3)Note: The calculation of shallow concentrated flow time is frequently not included when using the RationalMethod. However, the procedure is included in this Manual for consistency with other runoff methods.SLO Creek Drainage Design Manual 26 February 2003
Channel or Pipe Flow occurs where flow converges in gullies, ditches, and natural orman-made water conveyances. Channel flow is assumed to exist in streams or wherethere is a well-defined channel cross-section. Use Manning’s Equation for calculatingchannel flow. For the purposes of these calculations, it is acceptable to assume flow isbankfull depth for open channels and pipefull flow for storm drainpipes. If theseassumptions appear to result in over-conservative estimates, the flow rate obtained fromthe initial bankfull Tc estimate can be used to recalculate channel velocity using theManning Equation. A separate computation should be made where channel/pipeconditions change.Equation 5V = 1 2 3RSn12Where:V = average velocity (m/s)R = hydraulic radius (m); r = A/P wA = cross sectional flow area (m 2 )P w = wetted perimeter (m)S = slope of the grade line (channel slope, m/m)n = Manning’s roughness coefficient. See Table *Calculate the velocity (V), and then calculate the travel time using Equation 4:Calculation of Time of ConcentrationTime of concentration equals the summation of the travel time for each flow regime within thedrainage area.Equation 6T c = T c overland + T c shallow conc + T c channel 1 +...+ T c channel nThe minimum time of concentration shall be 10 minutes.Antecedent Moisture RegimeThe Rational Method has been revised for use in the SLO watershed to include consideration ofantecedent moisture conditions. Traditional application of the Rational Method does not accountfor soil saturation or base flow caused by previous storms or rainfall cells. However, especiallyin San Luis Obispo, large wintertime storms often occur in series, so that peak runoff rates aregreatly influenced by rainfall that may have occurred hours or days before the most intenserainfall cell. The antecedent moisture factors shown in Table 4-2 are an attempt to account forchanges in soil infiltration capacity and creek base flow rates that occur during these very wetperiods. They will be considered to apply even within highly impervious areas (such as parkinglots) since baseflow in channels and/or pipes draining these areas would likely be elevated priorto especially large storm events.SLO Creek Drainage Design Manual 27 February 2003
Page 2 and 3: San Luis Obispo CreekWaterway Manag
Page 4 and 5: SECTION 4.0 HYDROLOGIC & HYDRAULIC
Page 6 and 7: SECTION 8.0 DESIGN OF DRAINAGE PUMP
Page 8 and 9: 11.12 Erosion Control Seeding......
Page 10 and 11: DRAINAGE DESIGN MANUALFOR THECITY O
Page 12 and 13: ôó1Ragged PointSan SimeonCambriaM
Page 14 and 15: SECTION 2.0PROJECTS REQUIRING HYDRO
Page 16 and 17: 3. or, is an individual development
Page 18 and 19: • Geomorphic, Geotechnical and St
Page 20 and 21: SECTION 3.0CORE REQUIREMENTS AND RE
Page 22 and 23: elevations, and existing channel st
Page 24 and 25: 1000 0 1000 Meters1 0 1 MilesCity L
Page 26: N300 0 300 MetersLEGEND100-Year Flo
Page 29 and 30: N300 0 300 MetersLEGEND100-Year Flo
Page 31 and 32: N300 0 300 MetersLEGEND100-Year Flo
Page 33 and 34: • All streets to be dedicated to
Page 35 and 36: • A minimum setback of 15 m (50 f
Page 37 and 38: 3.6.4 Preference for Vegetative and
Page 39 and 40: compliance with the measures prescr
Page 41 and 42: 4.1 Hydrologic Analysis4.1.1 Genera
Page 43 and 44: Table 4-1Runoff CoefficientsHydrolo
Page 45: Overland Flow TimeSLO Creek Phase I
Page 49 and 50: 45745766071176260955855860971166050
Page 51 and 52: Table 4-3Rainfall - Intensity Data
Page 53 and 54: 4.1.4 Example ProblemA sample basin
Page 55 and 56: Table 4-7Example Composite Runoff C
Page 57 and 58: Table 4-9Example Rational Method Ru
Page 59 and 60: developed. For minor waterways and
Page 61 and 62: SECTION 5.0OPEN CHANNEL ANALYSIS AN
Page 63 and 64: case, a Natural Channel may be modi
Page 65 and 66: 5.2 Channel Design Flow Requirement
Page 67 and 68: maintenance to maintain the design
Page 69 and 70: The following guidelines should be
Page 71 and 72: Channel PlanformDrainage Design Man
Page 73 and 74: • Native vegetation shall be pres
Page 75 and 76: Manning’s Roughness Values are pr
Page 77 and 78: 6.1 GeneralSECTION 6.0ANALYSIS & DE
Page 79 and 80: 6.3 Design ReferencesThe designer i
Page 81 and 82: stream stabilization needs totaling
Page 83 and 84: causes and modes of failure act tog
Page 85 and 86: (permissive velocity) and/or bounda
Page 87 and 88: Re-run the model after coding in th
Page 89 and 90: Step 2 - Develop and Screen Alterna
Page 91 and 92: Cost. The design must be cost effec
Page 93 and 94: Step 3 - Develop Concept Plan and D
Page 95 and 96: Legally it is up to the applicant t
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e necessary, as well as other work
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(0.6-0.9 m)(0.6-0.9 m)(152-203 mm)L
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(1.2 m)(1.2 m)(12 mm to 51 mm)(1.5
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(0.9 m)(0.6 m x 0.6 m x 914 mm)(457
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(0.6 - 0.9 m)Vegetated GeogridDrain
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Planted Rip RapDrainage Design Manu
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A-JacksDrainage Design ManualCity &
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(1.5 m)(13 to 25 mm)(0.6 to 0.9 m)R
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(13 - 25 mm)(0.6 to 0.9 m)Planted G
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(2.4 m)(2.4 m)Flow DeflectorsDraina
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performance. This technique require
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Boulder ClustersDrainage Design Man
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of a bend, and filled around and on
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horizontal line are SI (metric) nam
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GRADING OF ROCK SLOPE PROTECTION PE
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A layer of Backing No. 1 or No. 2 i
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SECTION 7.0DESIGN OF CONDUITS, CULV
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7.2.3 Storm Drain Location and Alig
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In paved areas, pipe cover shall be
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• Drop inlets shall be spaced suc
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Marine Fisheries Service NMFS South
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For all intermediate channels, eith
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7.4.8 Easements for Closed Conduits
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SECTION 9.0STORMWATER MANAGEMENT FA
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Detention for the 10-year design st
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9.2.1 Provisions For SedimentationT
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9.5 Basin DesignDetention and reten
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mm (24 in). A corrugated metal pipe
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have side panels or other devices t
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SECTION 10.0EROSION CONTROL AND STO
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10.3.1 Gravel Construction Entrance
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Notes:1. PLACE BALES PERPENDICULAR
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• Filter fences (also known as si
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SEED MIX ONE(Application rate = 40
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• Description of soils, geology,
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• The facilities shown on this pl
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The following control measures are
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BMP 3 Dewatering OperationsI. Defin
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BMP 5 Illicit Connection/Illegal Di
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D. All vehicles/equipment that regu
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I. Properly dispose of or recycle u
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BMP 12 Solid Waste ManagementI. Def
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H. Temporary washout facilities sha
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SECTION 11.0RIPARIAN REVEGETATION P
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per second (6 feet per second). Whi
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TABLE 11-2: WOODY SHRUBS FOR SAN LU
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TABLE 11-4: GRASSES AND HERBSFOR SA
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TABLE 11-5: MARSH PLANTS FOR SAN LU
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11.4 Planting Site Considerations11
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Where vandalism is not a problem, t
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Table 11-6Recommended Species Compo
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Larger Crown TreesPlant in clusters
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plant materials (often one growing
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Exotic Treeto be RemovedNative Tree
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Step 4: Select plants suitable for
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• Exotic vegetation on the site s
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• Removal of Exotic VegetationThe
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Placement of weed control fabric or
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11.12 Erosion Control SeedingRevege
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y wind or water runoff; should be e
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Abrasion. Removal of streambank soi
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Confluence. A junction of streams o
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Flood. A general and temporary cond
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Left Bank. The left-hand bank of st
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Shear stress. The force per unit ar
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Velocity (of water in a stream). Th
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Association of Bay Area Governments
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Hoover, Robert F. 1970. The Vascula
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U.S. Army Corps of Engineers, April
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Drainage Design Manual - the City of San Luis Obispo

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