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HomeMy WebLinkAboutStorm Drainage StandardDEPARTMENT OF PUBLIC WORKS COUNTY OF HAWAII Storm Drainage Standard OCTOBER 1970 A P P R O V E D i PIEFENGINEER, COUN OF HAWAII BUREAU HEAD, DEPARTMENT OF PUBLIC WORKS I N T R 0 D U C T I 0 N: These standards have been prepared to guide County engineers and personnel, engineers for subdivision de- velopers, consultants employed by the Department of Pub- lic Works and other interested parties in the general features required for the design -of storm drainage facil- ities in the County of Hawaii. These standards are not intended to limit the init- iative and resourcefulness of the engineer in develop- ing drainage plans, or be viewed as maximum limits in de- sign criteria. Higher criteria should be used where such is indicated. Lower criteria for specific basins may be permitted where substantiated by detailed studies. The Storm Drainage Standards of the City and County of Honolulu dated March, 1969 has been used as the basis for these standards. iv Part I Hydrologic Criteria 1. RECURRENCE INTERVAL OFor drainage areas of 100 acres orless, Tm (recurrence interval) = 10 years, unless otherwise specified. OFor drainage areas of 100 acres or less with sump, or tailwater effect and for the design of roadway culverts and bridgesuti — Ilzing static head at entrance, Tim (recurrence interval) = 50 years. OFor' drainage areas greater than 100 acres and all streams, design curves based upon maximum recorded flood peaks. IF 2. RUNOFF QUANTITY OFor drainage areas of 100 acres or less, the rational method shall be used. 0 For drainage areas greater than 100 acres and all streams, refer to Plate 6 on page 19 titled "Design Curves for Peak Discharge vs. Drainage Area ". The rational method and flood frequency analysis may be used as a check. 3. RATIONAL METHOD The formula Q = CIA shall be used to determine quantities of flow rate, in which Q = flow rate in cubic feet per second; C = runoff coefficient; I = rainfall intensity in inches per hour for a duration equal to the. time of concentration; and A = drainage area in acres. ORUNOFF COEFFICIENT The runoff coefficient shall be determined from Table 1 (page 141 It shall be based on the ultimate use of the drainage area. For dis= tinctive composite drainage areas, a weighted value of runoff coeffi- cient shall be used. OTIME OF CONCENTRATION 1. Determine overland flow time from Plate 3 (page 17) generally for paved, bare soil and grassed areas. 2. Determine flow time over small agricultural areas with well - defined divides and drainage channels from Plate 5 (page 18) a. Use upper curve for well- forested areas, representing Tc = 0.0136 Ko' b. Use lower curve for areas with little or no cover, repre- senting Tc = 0.0078 K017 3. In case of uncertainty, check the time of concentration by dividing the estimated longest route of runoff by the appro- priate runoff velocity from Table 2 (page 14). ORAINFALL INTENSITY The design rainfall intensity of a drainage area shall be determined by the following procedure: 1. Select the appropriate I -hour rainfall value from Plate I and 2 (pages 15 & 16) for the design recurrence interval. 2. Enter Plate 4 (page 17) with the one hour rainfall value ond the required time of concentration. Obtain the design rainfall intensity in inches per hour. 3 4. FURTHER HYDROLOGIC STUDIES Although hydrologic data in Hawaii have greatly increased since 1959, they are still insufficient for advanced hydrologic analysis to develop better criteria for the design of drainage facilities. For example, only scanty coordinated rainfall and runoff data are available that are useful for deriving unit hydrographs. In most cases, rainfall and runoff data are collected separately by different agencies. Thus, the rain gauge and stream flow gauge networks are designed and maintained often for uncoordi- nated purposes. The data so obtained are usually unsuitable for use in the analysis of rainfall runoff relationships because they do not adequately match geographically and are unsynchronized on many occasions. The hydrologic condition on the Island of Hawaii is extremely hetero- geneous because of irregular orographic characteristics and soil types. Each drainage basin often has its own unique hydrologic condition, even within one basin, the hydrologic condition varies radically. On the wind- ward side of the island, for example, there is a radical change in rainfall amounts from sea level to the peak of Mauna Kea. The upper slopes have little or no runoff because of light rainfalls and extremely permeable soils and the lower slopes are subject to high intensity storms and runoff. Thus, a unit hydrograph developed from runoff data measured at a downstream gauging station cannot be reliably applied to the upstream areas. In view of the lack of hydrological homogeneity, a regional analysis of rainfall and runoff can only be considered approximate. Since the hydrologic condition is heterogeneous, dense hydrologic net- works should be developed and more hydrologic data must be collected. As the drainage basins show individual characteristics, further analyses of the accumulated data must be made for all individual basins and at various places inside the basins. The results of such analyses would be most use- ful and reliable for the design of drainage facilities at a given place in a given drainage basin. Extensive hydrologic analysis of individual drainage basins would be too costly and time consuming, therefore, an approximate regional analysis such as the type of envelope curve shown in Plate 6, must be further im- proved and refined. When more peak discharges of record are measured, a frequency analysis will be incorporated in it to determine envelope curves for various recurrence intervals. Also, synthetic peak discharges may be computed from available unit hydrograph information and may be used to develop peak discharge frequency envelope curves separately for a number of regions on the Island of Hawaii. 4 Part II Design Standards I. GENERAL CONDITIONS The design and capacity of a drainage system shall be predicated on the following conditions: QOn the basis of the runoff resulting from the selected design storm, the system shall dispose of surface runoff and subsurface water without damage to street facilities, structures or ground and cause no serious interruption of normal vehicular traffic. ORunoff exceeding the design storm must be disposed of with the least amount of interruption to normal traffic and minimum amount of damage to surrounding property. OSystem must have maximum reliability of operation with minimum maintenance and upkeep requirements. QSystem must be adaptable to future expansion, if necessary, with minimum additional cost. © Where sump conditions exist; a safety measure such as an over- - - low swale shall be provided to prevent flooding of adjacent lots in the event the design capacity of the closed conduit is exceeded. Floor levels of homes adjoining sumps shall be a minimum of 3 feet above low point on roadway. OFloor levels of homes abutting streams and open channels shall be a minimum of 3 feet above freeboard elevation computed at design flow. 0 In general, natural gullies, waterways, streams and tributaries shall not be replaced with a closed s y s t e m except at roadway crossings. © Roadway culverts and bridges shall be designed to pass the design flow under open channel hydraulic analysis with a minimum freeboard as specified in the attached freeboard chart. Multiple span road crossings shall have minimum clear spans of 30 -feet, unless otherwise permitted by the Chief Engineer. Where possible, the road- way shall be designed to form a sag vertical curve with a low point at the waterway crossing with minimum grades to confine and control overflow at the crossing.. Roadway culverts and bridges shall be designed to include only deck and roadway. Fill material shall not be used to meet roadway elevations above the deck. OOutlets for enclosed drains emptying into open channels shall be designed to point downstream at an angle of 45 °. OSubsurface drains shall be installed wherever recommended by the Design Engineer, or Chief Engineer, where ground water is en- countered, or may be present during wet weather. © Lots abutting streams and open channels with a drainage area greater than 100 acres shall be graded to drain towards the waterway. Pl 2. DESIGN COMPUTATIONS The following data shall be submitted to the Chief Engineer by the Design Engineer: HYDRAULIC DESIGN DATA. 1. Computations for runoff, conduit and channel sizes, slopes, losses, hydraulic gradient and other hydraulic characteristics and informa- tion pertinent to the system. Computations shall be properly arranged and presented in such a manner that they may be readily checked. 2. The following data shall be shown on the construction plans. a. Design flow (Q), watershed area (A), rough- ness coefficient (n), and velocity (v), for all conduits and channels. b. Hydraulic grade lines. c. Water surface elevation at each manhole and catch basin. d. Building setback lines, where required. 0 STRUCTURAL DESIGN DATA. I. Structural design computations for all drain- age structures other than pipes used within the limits of current loading tables and struc- tures shown in the "Standard Details" of the County of Hawaii Department of Public Works. 2. Information pertinent to the design, such as boring data, soils report, etc. 3. Upon the completion of construction of major structures, submit pertinent data such as pile driving logs, pile tip elevations, etc. 3. CLOSED CONDUITS SIZES AND GRADIENTS 1. The size and gradient will be determined by the Manning formula: Q = A 1.486 R2-13 S11'2 n Q = flow, in cfs R = hyd. rad. in ft. A = area, in sq. ft. S = slope, in ft. /ft. n = roughness coefficient (Manning's) A direct solution of this formula for pipes are found on pages 23 to 31. 2. The following limitations apply — a. Minimum size pipe: 18 inches inside diameter b. Minimum velocity: 2% feet per second c. In general, pipe sizes shall not decrease in the direction of the flow. OMATERIALS AND "n" VALUES The following pipes are acceptable for storm drain construction together with the roughness coef- ficient to be used in the solution of the Manning Formula. Materials n Concrete ................... .013 Cast iron ........ ........ .013 *Corrugated metal pipe (CMP) Unpaved ................. .024 25% paved invert ........... .021 Lower 50% paved ........... .018 100% paved ........... .013 *Use of CMP shall be permitted only when specif- ically approved for an installation by the Chief Engineer in writing. ® LOADING 1. Reinforced Concrete Pipes: Reinforced con- crete pipes shall be constructed to ASTM Specifications and currently classified as Class I, Class II, Class III, Class IV, and Class V pipes. a. Minimum pipe cover in roadways, drive - ways and other areas with vehicular traffic (based on the current, "Standard Speci- fications for Highway Bridges," AASHO) shall be as follows: ASTM Pipe Minimum Classification Diameter Pipe Cover Class III Pipe Less than 48" 2' -6" Class III Pipe 48" and above 2' -0" Class IV Pipe All sizes 2' -0" Should there be a need for a pipe cover of less than 2' -011, the design engineer shall submit a structural design for review and approval. The decision to allow such de- sign will be made by the Chief Engineer. 7 b. Minimum pipe cover in easement areas without vehicular traffic shall be 1'_0,1. c. Maximum permissible depth will be deter- mined from current loading tables in pipe handbooks for the respective pipes, using 110 lbs. per cu. ft. as the weight of earth. d. All pipes shall be installed using a first class bedding trench condition. Proper foundations shall be provided for pipes. Pipes on unstable ground or fresh fill shall be supported by a method acceptable to the Chief Engineer. e. Drain pipes installed along the longitu- dinal axis of the roadway shall be located in the pavement area between curbs. 1. Other Closed Conduits. There shall be no minimum cover or maximum permissible depth requirements for closed conduits other than pipes except that such structures shall be designed to support all loads that it shall be subjected to. O MANHOLES AND INLETS 1. Manholes: a. Location. Manholes shall be located at all changes in pipe size and changes in alignment or grade and at all junction points. b. Spacing. Maximum manhole spacing shall be 250 feet for pipes 36 inches or less in diameter, or box drains with the smallest dimension less than 36 inches. Maximum manhole spacing for larger pipes and box drains shall be 500 feet. c. Special Details. Bottoms of manholes and inlets serving as manholes shall be shaped to channelize flow and sloped with slope of pipe as shown in "Design Details." 2. Inlets (Catch Basins) a. Location. Inlets shall be located at the upstream side of intersections, in sumps and where required by quantity of flow. b. Spacing. Maximum spacing shall be 500 feet. c. Types. For gutter grades up to 4 %, stand- ard 10 -foot curb inlets with a depressed gutter shall be used. For grades 4% and greater, 10 -foot long deflector inlets shall be used. d. Capacity. Inlet capacities as follows are acceptable: 8 Type Gutter Grade cfs (1) Std. depressed 0.4% 6 gutter inlet 4.0% 4 sump 10 (2) Deflector Inlet 4.0% 4.5 12.0% 5.5 Greater than 12.0% 6 max. e. Gutter Flow. The gutter flow shall not exceed a width of 8 feet. ® PIPE SYSTEM ANALYSIS Generally speaking, the pipe system shall be analyzed by sections, that is, outlet to manhole, manhole to manhole or manhole to inlet. The analysis shall start at the lowest point of flow and continued upstream. The design flow shall be used in determining whether the pipe will flow full or partially full. Full consid- eration of- the tailwater, entrance and critical flow conditions shall be made. 1. Pipe Flowing Full. If the conditions show that the pipe section will flow full, the prin- ciples of flow of water in closed conduits shallbe use . The water surface elevation of the upstream manhole is determined by adding the pipe friction and manhole losses to the water surface elevation of the down- stream manhole or the beginning elevation as previously stated. 2. Pipe Flowing Partially Full. If the condi- tions show that the pipe section will flow partially -full, the principles of flow of water in open channels shall be used. The pipe partially -full condition maybe determined from the Pipe Flow Charts on pages 23 to 31. The tailwater condition must also be considered in this determination. 3. Manhole Losses a. For junction conditions such as drop man- holes, or where the outflow line deflects more than 10° with any inflow line, the hydraulic grade shall be- determined by applying the Entrance Control loss and C & D losses (where applicable), or A, B, C & D losses, whichever is greater. b. For junction conditions where the outflow line deflects 100 or less with the inflow line, the hydraulic grade shall be deter- mined by applying the A, B, C & D losses. © HYDRAULIC GRADIENT COMPUTATIONS The hydraulic gradient is (1) a line connecting points to which water will rise in manholes and inlets through- out the system during the design flow or (2) the level of flowing water at any point along an open channel. It shall be determined starting at the downstream end of the proposed drainage system and proceeding up- stream by adding the friction losses and manhole losses of the system. The hydraulic gradient for the design flow shall be at least one foot below the top of the manhole cover, or 1 foot below the invert of catch basin inlet opening. 1. Beginning Elevation The elevation of the hydraulic gradient at the downstream end shall be selected according to the following conditions: a. Connection to existing drainage system — determined from the hydraulic gradient computations of the existing drain; b. Discharge into a stream — determined from the flow conditions of the stream; c. Submerged tailwater condition — begin at the tailwater elevation; and d. Freefall condition (conduit) — begin at the crown of the proposed drain. 2. F-ritti h f = S{ (L), where: hf = head loss due to friction Sf = friction slope from Manning's formula, (n V)2 2.208 R 4/3 L = length of pipe or channel The friction loss shall be calculated for the condition of the design flow, that is, pipe flowing full or partially full. 3. Manhole Losses Manhole losses shall be as shown on the charts, "Head Losses in Manholes ", (Plate 17 & 18, pg. 32). The losses shall be eval- uated with pipes flowing full in the vicinity of the manholes; and therefore the velocity shall be for the pipe flowing full. The curves on the charts show the various losses: a. A curve — loss due to entrance and exit b. B curve — velocity head (1) Where the downstream velocity ex- ceeds the upstream velocity, the head loss shall be difference in velocity heads. velocity head loss shall be zero. c. C curve —loss due to change in direction, taking the worst case for branches at a manhole. d. D curve — loss due to incoming volume. O SPECIAL DETAILS The following structures shall be installed where re- quired: 1. Headwalls, aprons and cut -off walls at drain inlets and outlets. 2. Energy dissipators at outlets. 3. Debris — control structures. 4. Guard rails at headwalls and inlets, where they present a hazard to vehicular traffic or pedestrians. 4. OPEN CHANNELS O CHANNEL SIZE Use the Manning's Formula to determine the required waterway areas where uniform flow can be assumed. 1.486 R 2/3 S v2 Q - AV and V= n A = area of flow, in square feet V = velocity, in feet per second n = roughness coefficient ( Manning's) R = hydraulic radius, in feet S = slope of the energy gradient, in feet per feet The channel depth shall include design water depth and minimum freeboard allowances. Design water depth shall include rise in water surface caused by curves and junctions. OCHANNEL RIGHT -OF -WAY The channel width shall be sufficient to provide the required waterway area for the design storm as deter- mined bythese standards. The total right -of -way shall include a 15 -foot wide maintenance road along both banks where the top width of channel exceeds 50 feet, and along one bank where the top width is 50 feet or less. The maintenance road along the channel shall be topped with 6 inches of crushed coral or base course and treated with bituminous material. In lieu of a maintenance road, for normally dry channels, access ramps or other suitable alternative measures to facili- tate maintenance may be provided. (2) Where the downstream velocity is OPERMISSIBLE VELOCITIES AND "n" VALUES less than the upstream velocity, the Following is a list of "n" values for open channels 9 and maximum permissible velocities. Maximum velo- cities 4. Total depth of channel lining will include shall be based upon design flow quantities. design water depth and freeboard. Manning Maximum Unlined Channels "n" 5. Attention shall be given to construction de- Velocity(fps) Side Slopes tails of linings such as thickness, reinforce - Rock,smooth and uniform 035 15 2: I ment, expansion and construction joints, cut - Rock, jagged and irregular .040 15 1: I Ledge coral orlime stone off walls, water -tight joints, placement of .025 10 I : I Earth, no vegetation 5 reinforcement, etc. Where the channel dis- .025 I: I Earth, grass, some weeds 5 charges into streams or other channels out - .030 1 2: I Earth, dense weeds side of the limits of a development, velocity .035 5 I Lined Channels reducing and transition structures shall be constructed to minimize erosion and over - Conc., trowel finish 013 No limitation topping of banks and subsequent flooding of Conc., smooth wood forms .015 No limitation downstream areas. Gunite 020 20 6. Where velocities are supercritical, rectangular Grouted Rip -rap & CRM channels shall be used, unless otherwise (Cement Rubble Masonry) .025 20 permitted by the Chief Engineer. Asphaltic Concrete .015 20 7. Earth channels shall be planted with vegeta- Corrugated Metal Flumes tion, such as grass of a species not suscep- Part- circle Sections .021 25 tible to rank growth. ® FREEBOARD. 1. Maximum design velocity for channels cut in earth shall not exceed 5 feet per second. The In designing open channels, freeboard must be pro - velocity shall be determined by using the vided to allow for surface roughness, wave action, tural exi f�e nasting slope o waterway with- air - bulking-,_and- splash - and - spray. The -se phenomena out utilizing grade transition structures to depend on the energy content of the flow. For water control the maximum slope for a given unlined flowing at velocity v and depth d, the energy per foot channel cross - section and design flow. of width per second is equal to (wvd) (v2 /2g) = wdv3 /2g, 2. Velocities betwee 5 f where w is the unit weight of water. e n et per second and 15 feet per second will be permitted in materials such as cemented gravel, hard pan, or mud rock depending upon its hardness and resist- ance to scouring. Borings and samples shall be submitted for evaluation before velocities exceeding 5 feet per second will be permitted. G CHANNEL LINING I. Earth channels shall be fully lined when ve- locities exceed 5 feet per second, unless otherwise permitted as noted in Section C -2 above. 2. All fill sections shall be lined. This lining shall be a complete lining including side slopes and invert with appropriate cut -off walls. If the invert.of the channel is in a cut section the invert slab may be omitted and appropriate cut -off walls provided at the toe of the side slope lining. . 3. Where linings are required or used, the linings shall be continuous. Lining of fill sections without continuing the lining out through cut sections in a channel will not be allowed un- less adequate- provisions are made to reduce the velocity from the lined section to meet the allowable velocity for the unlined section. Lue Thus, this kinetic energy can be converted to potential energy to lift the water surface when flow is stopped or changing direction as a function of depth and velo- city of flow. The U.S. Bureau of Reclamation has developed an empirical expression to express a rea- sonable indication of desirable free board in terms of depth and velocity as follows: Freeboard in feet = 2.0 + 0.025.3 d where v is the velocity in feet per second and d is the depth of flow in feet. The velocity of flow can be computed by dividing the design discharge by the cross - sectional area of flow. For convenience of ap- plication, the above expression is shown graphically in Plate 7 (pg. no. 21 ). For discharges less than 30cubic feet per second use channel size design of 100% greater capac- it than the design capacity. JUNCTIONS Junctions shall be designed to channel both flows as nearly parallel as possible to reduce velocity and momentum components, deposition of debris and ero- sion of banks. 0BENDS AND SUPERELEVATIONS Changes in the direction of flow shall be made with smoothly curved channel walls allowing for super - elevation in water surface. Curves will nearly always require additional depth. Trapezoidal channels for supercritical velocities are not recommended. Curve radii should be sufficiently great to limit supereleva- tion of the water surface to one foot above computed depth of flow or 107a of water surface width, which- ever is the least. The amount of superelevation for simple curves may be determined as follows: 1. Trapezoidal Channels: Subcritical velocity: e =V2b +2zd) (g R -2zV 2) 2. Rectangular Channel: Subcritical velocity: e =V26 gR Supercritical velocity: e = 2V2 gR Supercritical velocity — compound curve: e c Y b gR The compound curve is a simple curve of radius R preceeded and followed by a section of simple curve with radius of 2R, and length of b , where sin B = �m ton B V Where: e = maximum difference in elevation of water surface between channel sides (ft) z = Co- tangent of bank slope d = normal depth (ft) b = channel bottom width (ft) R = radius of curve to centerline (ft) g = acceleration due to gravity (fps2) V = normal velocity (fps) dm =mean depth 11 P .i l WS i .. ' b Water: Surface Superelevation Showing, "e A. 11 P .i l OTRANSITIONS I. The maximum angle between channel center- line and transition walls should be 12.5'. 2. Sharp angles in alignment of transition struc- tures should be avoided. ODEBRIS BARRIERS Debris barriers should be provided upstream of the intake to prevent clogging. Where required, boulder basins shall be provided upstream of the debris barrier. OENERGY DISSIPATORS Energy dissipators shall be used to dissipate energy where necessary, and to transition the flow from a lined channel to a normal flow in a unlined channel. Z, Energy dissipators may be any of the following types such as the SAF basin, baffled chute, dentated sills, buckets, impact, hydraulic jump, or other approved designs. j SAF BASIN A , - - ;.1'4111/. IIIItlUllltil BAFFLED CHUTE 31111 '11 I'l 11111mall R J i i'm 7V. V. Reference: "The SAF Stilling Basin" U. S. Sail Conserva Conservation -TP-79, May 1949 and "Hydraulic Design of Service Report SCS t Stilling Basins and Energy Dissipators" U. S. Bureau of Re- IMPACT TYPE OUTLET CIO-ation, Engineering Monograph No. 25. 12 Design Charts Table GUIDE FOR THE DETERMINATION OF RUNOFF COEFFICIENTS FOR BUILT -UP AREAS* WATERSHED 8 -11% 12 -15% 1.0 CHARACTERISTICS EXTREME HIGH MODERATE LOW INFILTRATION NEGLIGIBLE SLOW MEDIUM HIGH 6.0 0.20 0.14 0.07 0.0 STEEP HILLY ROLLING FLAT RELIEF (�-25 %) (15 -25 %) (5 -15 %) (0 -5 %) 0.08 0.06 0.03 0.0 VEGETAL NONE POOR GOOD HIGH (< 10 %) (10- 500/6) (50 -90%) COVER 0.07 0.05 0.03 0.0 INDUSTRIAL HOTEL - DEVELOPMENT a BUSINESS APARTMENT RESIDENTIAL AGRICULTURAL TYPE 0.55 0.45 0.40 0.15 i ire ur�igi, t 111[7e77t c must result prom a total 01 the values for all four watershed characteristics of the site. APPROXIMATE AVERAGE VELOCITIES OF RUNOFF FOR CALCULATING TIME OF CONCENTRATION TYPE OF FLOW OVERLAND FLOW: Woodlands Pastures Cultivated Pavements OPEN CHANNEL FLOW: Improved Channels Natural Channel* (not well defined) VELOCITY IN FPS FOR SLOPES (in percent) INDICATED 0 -3% 4 -7% 8 -11% 12 -15% 1.0 2.0 3.0 3.5 1.5 3.0 4.0 4.5 2.0 4.0 5.0 6.0 5.0 12.0 15.0 18.0 Determine Velocity by Manning's Formula 1.0 3.0 5.0 8.0 *These values vary with the channel size and other conditions so that the ones given are the averages of a wide range. Where. ever possible, more accurate determinations should be made for particular conditions by Manning's formula. 14 1 Table 2 156 000' 45 30' IS' 153°00' sa 4, Up lu Point ob 3 3 1s' �\ Wai io Bay Honokaa Kawaihae 20 1 — — —��— r�� SCALE IN MILES 00 1 \ 1 \ �\ 20 1.5 i O � A� I 1 1 45' ' 1 H I I a Kailuo 2 2.5 , 5 4 ` 10 o 4 i i 1 30' Kealakekua Bay : I M NA L A i Pahoa i 30' \ •`�� •• IF-.< /ter �...•• /' Pohala 16� � 1 , r , 2 `%\ COUNTY OF HAWAII Intensity of 1 -hr Rainfall (Inches) 19 ° � oo' LEGEND ° Tm_ 10 00. y� '---- Principal 2 Roads --•••'•••• Other Roads Kalae 156000, 45' 30 . IS I55000' f Plate 1 15 j>• 166 000' 45 30' 15' 2Up lu Point 15 l" 3 1.5 wai io Bay Hongkoa Kawalhae 20 00' �\ �.� N Wal ms• `. 2 i 45' .5 1 LA1 Kailua 2 30' Kealakekua Bav ISS°00' 't 40 Q� ob o 16 II 2 0 2 4 6 6 SCALE NA I 1 1 Hilo 6 �11 0 0 4 � \ � woo ,...... ,: \\ 5 M NA L i� Pahoa %D -• -<-' 2 5 � 15' Pahi 2.5 19C 3 oo' LEGEND 2.5 -- - -- Principal Roads •••••••••• Other Roads Kalae 156000' 45' 30' 16 -20 00 i45 ii —mom IS' 4 COUNTY OF HAWAII Intensity of 1 -hr Rainfall (Inches) Tm' 50 yr- 00 15' 156 000' Plate 2 2000 1000 900 Soo 700 600 500 400 300 W W LL 200 Z FE fn 100 Q 80 _J 60 50 x F 40 0 Z W 30 20 10 0 Z O (7 IL O cr W U Q 2 U .■ir i■ ME������� 9- O U 6 F- W J 7 Z 6 5 6 Plate 4 " " "'•' ■ ■ ■►"• ■■■.. ��..%.......'. In�uiiiiiiiiiiii iiGGGGiGiiiiiii....._ir■Ciiiii RAINFALL FOR DURATI(IltS- W 2 Z 1 J J LL Z Q n O 35 30 N W PAVED 2s z BARE 20 U SOIL P late 3 W (POOR GRASS d Ld SURFACE Z O 0.5 Ld AVE. J U) -GRASS 1•p 15 SURFACE F- F Z 2.0 WDENSE Overland GRASS d 5.0 U F_ a: Q 10 W 20 a Z Flow z W 50 10 z Chart .■ir i■ ME������� 9- O U 6 F- W J 7 Z 6 5 6 Plate 4 " " "'•' ■ ■ ■►"• ■■■.. ��..%.......'. In�uiiiiiiiiiiii iiGGGGiGiiiiiii....._ir■Ciiiii RAINFALL FOR DURATI(IltS- W 2 Z 1 J J LL Z Q n O 4 1 2 4 6 8 10 20 40 60 80 100 VALUES OF "K" IN THOUSANDS L= Maximum length of travel in feet H - Difference in elevation between most remote point and outlet in feet. S - Slope H/L K= L - H3 graph from Hunter Rouse "Engineering Hydraulics." 18 200 400 400 200 100 N 80 d C 60 'E 40 "U h- LL 20 H- Z _O F- Q e I— Z 6 LU V Z O 4 U 2 1000 Plate 5 Time of Concentration ( OF SMALL AGRICULTURAL DRAINAGE BASIN ) Plate s DESIGN CURVE FOR PEAK DISCHARGE VS. DRAINAGE AREA SEE PLATE bA (more than 100 acres) FOR RUNOFF ZONES CURVES ARE FOR STREAM CHANNELS AND DRAINAGE STRUCTURES APPROXIMATE 100 YEAR RECURRENCE INTERVAL 60 4a N 10( U 8( 0 0 6( z c� W 4C o: a U 2C Y a W a IC 8 6 5 4 U 1w cU ou 4u ou 60 80 100 200 300 600 DRAINAGE AREA IN 100 ACRES 19 Munn 1111111105 PAR i38�� IN MEN memo Memel Noun a noun =ME MEN Hong ==on loop 111 0011111 no 11111 no U 1w cU ou 4u ou 60 80 100 200 300 600 DRAINAGE AREA IN 100 ACRES 19 Ils' _ 0 145 mm 156 000' 45' 30' IS' 155 000' OQ Upolu Point , 1 waipio Bay . `� ;_ Honokaa awaihae 2 0 2 4 6 8 SCALE IN MILES aimea 2C oc _- . -_- - -~ A K A ,- 1 �oo ' i Hilo - - — ALAI D ``� - - -- 45 Kailua 8000 1000 i \. Kealakekua Bay \ M A Pahoa%p -.,� -- � 30' ;4 Tahalo 15� 1 , RUNOFF ZONE MAP 190 00' 19° LEGEND 00' ' ---' Principal Roods /'I�1�i A A Other Roads Kalae Plate 156 600' 45 30' IS' I55 000' FREEBOARD ALLOWANCES Plate 7 FREEBOARD IN FEET:(ForQ >3Ocfs) 2.0 +0.025 V Vd Where V = Velocity, in feet per second d = Depth of flow, in feet NOTE: For discharges less than 30 cfs, channel shall be designed for 100% greater capacity than the design discharge. 2 4 6 8 10 20 DEPTH OF FLOW IN FEET 6 t- W W 5 LL z 0 o: a 0 4 m W W m LL 3 40.. ' ' ' ' '6O �u L'�80 Pipe Flow Charts The following pipe flow charts have been derived by the U. S. Public Roads Administration, Division Two, Washington, D. C. These charts are designed to enable direct solution of the Manning formula for circular pipes flowing full and for uniform part -full flow in circular pipes. The "n" scales of 0.013 and 0.024 have been inserted to facilitate the use of these charts for storm drainage systems in Hawaii. The following examples will help to explain the use of the pipe flow charts. EXAMPLES A. Determine the depth and velocity of flow in a long 30 -inch pipe, n 0.013, on a 0.5- percent slope (So = 0.005) discharging 25 cfs. Enter the 30 -inch diameter chart at Q = 25 on n = 0.013 scale, follow up to intersection with line for slope So 0.005, and read normal depth do = 1.8 feet and normal velocity V = 6.6 fps. To find criti- cal depth, enter chart at Q = 25 on n = 0.013 scale, and read critical depth do = 1.6 feet at intersection with dotted critical curve. Also critical velocity Vc = 7.6 fps. (Note: Critical depth and velocity would be the same, regardless of pipe roughness.) B. Determine friction slope for a 30 -inch corrugated metal pipe, n = 0.024, on a slope So = 0.008 ft /ft with a discharge Q = 25 cfs. Enter the 30 -inch diameter chart at Q = 25 on n = 0.024 scale. Note that this ordinate falls to the right of the 0.008 slope line, therefore, the pipe will flow full. Read friction slope Sf = 0.012 at the line for depth equal to pipe diameter. (Note: Q = 25 x 0.024 =40 cfs on the Q -scale for n = 0.015.) 0.015 22 24 111 e�n��� ►. � «u.:. • . IN mik MISS eye■ . e����c���r�►■�.0 � ���►. u .. ,, • I n■. n ■u �, i��� . r 24 • , I 25 It MAN 1��1�►�'1 - Ion 1 ice■ �►� �►��. u,��� V . 1 laBlu his ►N1�01,11 ► � ..,..., . WK 25 • NINE 1 1 1 1 . '�� \� ►1111 !► , � � � MN a 11 1►� 1 � � �' / i 1 01 1 p_. Ob 00. oy &\.00p ,I o00 0 I !t. If oOC"o o, oo�oo_ V h u SdJ - A - .(jloo7.gA N N 26 N Q 0 o 2, o ao R O o 0 m N O 1 O PEI o •rq �o `' - -`°o N Ro h t� ion o II ��• o� N V Cd Q N � b r � u O ho CO th r-4 aw I m N Q 0 DI AT[ in m O Y tQ.1 O V' 4 r V ul POO * = U 27 J j Q o •r-1 A o a � U o . o 0 co cl r ° N - 0 o c 'v fm 0 v Q 1 I N Q Q H r F+y �p u 0 h a� �o ,1 A ��C�r►ii���. v OEM \lii�. � � � ��1�a � i �a��l� u�a ■die . m O Y tQ.1 O V' 4 r V ul POO * = U 27 J j Q o •r-1 A o a � U o . o 0 co cl r ° N - 0 o c 'v fm 0 v Q 1 I N Q Q H r F+y �p u 0 h a� �o m O Y tQ.1 O V' 4 r V ul POO * = U 27 J 28 mom � loll n■ ��,� .. . , Mill .�r�rc�,�a ■■■ ��. �•,,, ■ �' M�a>>��ra�r. loll •• - ���►��►���► ���, ►�. , INN , �� , loll ski • - �►aI►��A�o���,� ��a� ��� .. ' �■ Its ,. ;►;� Now= RUN lw logo ■■mom �■�� ►a►�.►,��, 28 20 FT 2 .4 6 +.8 1.0 H.2 1. 4�s 6 �N 8 EE 20 2.2 2.4 2.6 2.8 3.0 3.2 3.4 18 - _ _ --- -- , , ■■■■■ttt■tttt■tt■, • ■ � ■ O ■ t ■ ■ ■ ■tt ■ttt ■t ■t ■� . ■ tt■■t ■ i,t�� t .eNONE ttttttt. ■ et � -- -��tN■ ■■NON .■ e �e ■ ■■eoN ■eee ■ e■■NOOeo■NNN ■ ► ■i tt ■ ■■tie. eee ■ tt�t, ■■Ne ■ ■■ ■Noe ■ �. ���ee ■ ■eee■ttttttttttttttttN ■■ ■Nome ■ - ■ ■��■e.�me ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■Nee ■ mom ■ ■MEMO ■ ■ ■ ■■N .,� t ttt■ ■ 32 SOURCE: BALTIMORE COUNTY DEPARTMENT OF PUBLIC WORKS Example: Analysis & Solution 4 • • i i # # SOLUTION GIVEN: Pipe size, Q, Velocity and * "A" LOSS (ENTRANCE & EXIT LOSS) Direction of flow. 1. Use worst case and determine degree of bend. 1. Determine higher velocity between V, and VZ 2. With higher V, or V2, use Curve "C" and deter- * # 2. Use Curve "A" or "C" depending on pipe size # a. For 00 to 22%2° bends, h,, shall be 0.67 times h. and determine hA (Ex. Prob. hA =0.16) # # "B" LOSS (VELOCITY HEAD LOSS) c. For 450 to 900 bends, he shall be 2.00 times h 1. Use Curve "B" and determine h� for V, and V2 36" # hc= 2x0.16 =0.32) a. If V2 is lower than V,, then hB shall be 0. Q = 40.0 1 V, = 5.8 "D" LOSS (LOSS DUE TO INCOMING VOLUME) 42 "*# b. If VZ is higher than V , then hB shall be 1. Add total branch volume and determine ratio of QZ 70.0 hB2- hgl V2= 7.ii 2. Use appropriate curve and determine h0 with 3 (Ex. Prob. hB = 0.87 and hB = 0.53 24" * 2 . 1 hB = 0.87 - 0.53 = 0.34) * CIO TIONAL CHANGE LOSS) V3= 10.0 *# 1. Use worst case and determine degree of bend. # 2. With higher V, or V2, use Curve "C" and deter- # mine head loss (h) a. For 00 to 22%2° bends, h,, shall be 0.67 times h. # b. For 22%2° to 45° bends, he shall be 1.00 times h. * c. For 450 to 900 bends, he shall be 2.00 times h (Ex. Prob. h = 0.16 hc= 2x0.16 =0.32) "D" LOSS (LOSS DUE TO INCOMING VOLUME) 42 "*# 1. Add total branch volume and determine ratio of QZ 70.0 branch volume to upstream volume. V2= 7.ii 2. Use appropriate curve and determine h0 with 3 higher V, or V3 # (Ex. Pro b. Q 3 = 30 = 75% Q 1 40 * * * hD = 0.64) LEGEND # TOTAL LOSS: Q,= Upstream Volume, cfs 1. Add hA, hB, h0 and hD I' Q2= Downstream Volume, cfs * (Ex. Pro b. hT = 0.16+ 0.34 + 0.32 + 0.64 Q3= Incoming Volume, cfs * hr = 1.46) • Losses Vj= Upstream Velocity, fps # A = 0.16 V2= Downstream Velocity, fps B 0.87 -0.53 = 0.34 =: �P V3= Upstream Branch Velocity; fps # ; C 2 (0.16) = 0.32 p h„ =Head Loss, in It. +*� = 0.64 `•' ;: Total Loss 1.46 ft. 3 ; NOMOGRAPH FOR CONCRETE PIPE CULVERTS WITH ENTRANCE CONTROL PLATE 19 34 To use scale (2) or (3), project horizontally to scale (1), then use 180 10,000 straight inclined line through D illustrated. and Q scales, or reverse as 168 (1) ( 7) (3 ) 8,000 156 6, 000 EXAMPLE 6.0 144 5,000 D -42 inches (3.5 ft) 6.0 Q -120 cfs 5.0 132 4,000 6.0 5.0 H H j 3,000 D* feet 5.0 - 4.0 120 (1) 2.5 8.8 4.0 2,000 (2) 2.1 7.4 108 (3) 2.2 7.7 4.0 *D in feet 3.0 3.0 96 1,000 3.0 800 84 600 2.0 2.0 W 500 72 400 mlo 2.0 Z E 300 U) cn 1.5 60 IL 200 p U l- 1.5 54 z W W 48 Cr 1 W > J 80 Z U 42 W - ¢ 50 1.0 1.0 LL O = 40 W 1.0 x 36 c_Un H SCALE ENTRANCE W 9 •9 33 0 TYPE 9 FW W (1) Square edge with W 2 30 headwall Q Q (2) Groove end with 3 •8 •8 0 headwall •8 27 (3) Groove end Q W 10 projecting 2 24 8 .7 .7 .7 6 21 5 4 3 .6 .6 18 .6 2 15 1.5 1.0 .5 .5 12 (U.S. Bureau of Public Roads.) 34 12 NOMOGRAPH FOR BOX CULVERTS WITH ENTRANCE CONTROL 11 PLATE 20 10 400 9 300 8 200 5 7 4 0 3 6 100 = 80 \ O 2 0-5 CY 60 I W 50 = W W W F 40 O Z -LL O F Q Z 3 30 O Z LL W W O W O o (L 1.0 J O p 1L W W U Z 0.9 LL 3 � — W W J 0- 10 3 < EXAMPLE O 0'8 Cr Given: 4'x 2' Box Culvert _ tun) - N Carrying 40 C.F.S. (Q /b 10) O 2.5 LL. 8 Read: H/a W Q�.� U F- wO For Square Edged z 6 W —0.7 LL Entrance =1.10, H=2.2 _ J W 5 Z - 0 z 2 Q of p 0.6 b = o v N 3 Q W C1 T 0.5 a 2 1.5 0.4 1.0 0.8 0.6 1.0 .0, 5 0.3 I I 35 15 11K BUREAU OF PUBLIC ROADS Plate 21 36 .5 .5 61 NOMOGRAPH FOR C. M. PIPE CULVERTS WITH ENTRANCE CONTROL ISO 10,000 168 8,000 EXAMPLE 156 6,000 D =36 inches (3.0 feet) (2) 5,000 0.66 cfs 6• 144 4,000 132 Hw* Hw 5. 6. 3,000 0 (feet) 120 (1) 1.8 5.4 4 5. 6. 2,000 (2) 2.1 6.3 5. 108 (3) 2.2 6.6 4. *0 in feet 3. 4. 96 1,000 3. 800 3. 84 600 500 2• 72 400 - N LLJ 300 2. x Z 1.5 60 tJ 200 1.5. 1.5 54 p / H W Ir > 48 0: 80� _Q J Q O 60 _Z 0 42 �/0 50 = 1.0 1.0 w / 40 a LU 36 30 ENTRANCE ILI •9 .9 1.0 W w SCALE Ir a33 _ D TYPE 20 ~ .9 30 (1) Headwall .8 .8 (2) Mitered to conform Q 27 to slope = LLJ 8 10 (3) Projecting 8 •7 7 . 24 6 .7 21 5 To use scale (2) or (3) project 4 horizontally to scale (1), then use straight inclined line through 3 .6 ,6 18 0 and 0 scales, or reverse as illustrated. ,6 2 15 11K BUREAU OF PUBLIC ROADS Plate 21 36 .5 .5 61 00 0 co 0 ri (1) F- 0 ir 0 0 (1) LLJ 6 cr > < J Ljj Z) Z < F- ui a2 . u- 0 o (f) F- 0 2 Ld z cr- 0 0 < F- u- F- Ir 0 cr- u- < cr LLJ CL 0 0 O. F- 0 to -5-' Z re) w ti 2 Z Z 0 ,j > Z w W 0 LL Z 0 w ir 06 ON It, Z W 2 Z 0 -J Z Z W C) 0 w 0 oq 0 LL. cr) 0 V) 0 F- co i N 14 cr- w E 0 3 II w 0 LLI 0- in a. W 0 0 0 > z w W -i 0— x X -i Z .7 w U) YEARS TO PERFORATION-16 GAGE METAL CULVERT 0 0 O c0 V) E co i N 14 cr- E 0 3 II LL 0 LLI in a. 0 0 0 > z w 0 -i X cr 0 45; LL CL 2) 00 co c� Ir 0 C) 0 0 w 0 0 N 0 L<L U.) 0 Lf) V re) YEARS TO PERFORATION-16 GAGE METAL CULVERT 0 0 O c0 0 E co i 14 cr- E 0 3 II 0 in a. u- 0 0 0 > z w 0 cr 0 45; LL 00 co c� Ir 0 C) 0 0 w N L<L N >. Z C 03 — W z W (n 0 < W w a. (D o z �- �- LL — w < L) -j ir ir CD L,)I< =) L-i 0 < LL 2 a- LL. 0 o2 IF Appendix PIPE Figure 1 SYSTEM ANALYSIS M W V EXAMPLE OF COMPUTATION MH4 20 Cfs 9M H3 100' N W V 0 C44 30 Cfs MH2 30 Cfs MH1 250' 200' Given: Runoff quantities, n, manholes and outlet condition as shown in Figure 1. Determine: Pipe sizes and Hydraulic gradient. SOLUTION USE PLATES 8 TO 20 (pg. 23 to 35) AS AID TO ANALYSIS. Make preliminary determination of pipe sizes for the data given using pipe flow charts. This is shown in Figure 2. Using the pipe 'sizes and slopes of pipes as de- termined above, compute hydraulic gradient for the system. This is shown in Figure 3. 1. Controlling grade at M.H. #1 is 100.00 as shown in Figure 1. Study conditions of flow between manholes or inlets to determine if entrance control or losses govern hydraulic gradient. 2. With the selected pipe size between M.H. #1 and M.H. #2, 24" diameter pipe -at S - 0.010, compute the head loss in the pipe by the for- mula h = SL or hf - SfL, whichever controls. h = elevation head loss hf = friction head loss S — slope of the pipe Sf = friction slope (used when pipe flow- ing full) L — length.of the pipe or channel 38 Since the pipe is flowing full, as determined by the pipe flow chart using 24" diameter, the friction slope 0.018 must be used. The head loss in the pipe is: hf = SfL hf = (0.018) (200) = 3.60 feet The downstream hydraulic gradient at M.H. #2 is equal to the controlling grade at M.H. #1 plus the head loss or 100.00 + 3.60 = 103.60 3. Since the pipe is flowing full, and there are no bends or drops, compute the upstream hy- draulic gradient at M.N. #2 by adding the man- hole losses to the downstream hydraulic gradient at M.H. #2. These values are ob- tained from charts on manhole losses. From the charts: A = 0.47 B = 0.00 (since the velocities are equal) C = 0.00 D = 0.00 0.47 ft. (Total M.H. losses) The upstream hydraulic gradient at M.H. #2 is: The upstream hydraulic gradient at M.H. #3 is: 103.60 + 0.47 = 104.07 110.0 + 1.49 + 4.70 = 116.19 4. With the selected pipe size between M.H. #2 dt, - 1.3 Figure 2 M.H. #4, 18" diameter pipe at S 0.038, com- 18" @ 0.010 pute the head loss in the pipe: h = SL V = 5.7 h = (0..040) (250) = 10.00 feet do :1.5 d„ : 1.2 dn -2.0 18 , @ 0.038 / 24 @ 0.040 24" @ 0.010 V =11.3 V : 9.5 MHz MH1 V =9.5 4 MH3 100.00 + 10.00 + 1.20 = 111.20 V. 113.80 Tdn INV. 110.00 INV. 100.00 INV. 98.00 : 1.5 MH #4, compare losses and use the higher HGL. manhole losses and entrance control losses @ 0.020 for open channel flow. Only manhole losses B -0.00 D =0.00 V =11.3 C =0.80 (0.40x2) 0.80 NOTE: Velocities shown are for pipe flowing full D a 0.00 C = 2 (0.40) = 0.80 (90e Bend) which are to be used to calculate the manhole losses. The upstream hydraulic gradient at M.H. #2 is: The upstream hydraulic gradient at M.H. #3 is: 103.60 + 0.47 = 104.07 110.0 + 1.49 + 4.70 = 116.19 4. With the selected pipe size between M.H. #2 6. With selected pipe size between M.H. #3 and and M.H. #3, 24" diameter pipe at S = 0.040, M.H. #4, 18" diameter pipe at S 0.038, com- compute the head loss elevation in the pipe: pute the head loss in the pipe: h = SL hf = Sft h = (0..040) (250) = 10.00 feet h f - (0.038) (100) - 3.80 feet Since the pipe is -1oc flowing full as deter- _The downstream hydraulic gradient at M H mined by the pipe flow chart, the elevation #4 is- head loss and the normal depth must be added 116.19 + 3.80 = 119.99 to the invert of M.H. #2. Therefore, the down- stream hydraulic gradient at M.H. #3 is: since the tailwater condition of the pipe is 100.00 + 10.00 + 1.20 = 111.20 submerged. 5. Compute the upstream hydraulic gradient at 7. Since there is a bend greater than 100 at M.H. #3 by adding to the invert elevation the MH #4, compare losses and use the higher HGL. manhole losses and entrance control losses A =0.66 C =0.80 for open channel flow. Only manhole losses B -0.00 D =0.00 "C" and ''D" need be considered. C =0.80 (0.40x2) 0.80 From the charts: D a 0.00 C = 2 (0.40) = 0.80 (90e Bend) 1.46 H /D= 3.2 H = 4.80 D = 0.69 119.99+1.46=121.45 i 113.80+4.80+0.80=119.40 1.49 ft. (Total M.H. losses) Entrance control loss for Q =30 cfs, D'= 24 "is: H/D = 2.35 H = 4.70 feet The upstream hydraulic gradient at MH #4 is 121.45 Adjust pipe sizes if warranted by the hydraulic gradient as computed above. 444 121.45 I HYDRAULIC GRADIENT 119.99 116.19 113.80 111.20 MH4 110.00 MH3 F704.071 103.60 100.00 PIPE INVERT 100.00 Figure 3 MN2 INV. 9MH1 39 i (t i 40 O 1 0 a o. v O v. d f E .0 N .G O a a 0 z N W E V Q: 7 . j N a wv= LL1 Y w a Y V Om � PC o % O rw F w I Im < °u6 w� 0 M V � Y I m i � s F s. Q � D V � o 47 u` i C >o e� fr7 V a z Q N a a Y V N" h �4 ip 7 e � 'r u O< V 4 u r w H z V a w y a a 9 40 O 1 0 a o. v O v. d f E .0 N .G O a a 0 z N W CULVERT DESIGN PROJECT: COMPUTED BY: DATE: CHECKED BY: HYDROLOGY CHARACTER OF GROUND L= Tc = L H= K = S = = Design Frequency= Years Save.= STORM DURATION I= C= Q =CIA= cfs PRESSURE LINE EL= HW H �H� AEL So = 2 ' _ D ho EL � '� EL Site Index No. _ I 100 So UNSUBMERGED OUTLET SUBMERGED OUTLET CULVERT IDENTIFICATION CAPACITY CHART INLET CONTROL OUTLET CONTROL NOMOGRAPH TYPE MATERIAL SIZE HW (FT.) HW(FT.) Ke H D,1l — do ho -Sot HW dc= D H = Head in feet Ke or Ce = Entrance loss coefficient ho = d 2 D D = Diameter of pipe in feet n = Mannings roughness coefficient - HW = H + ho SoR ,C = Length of culvert in feet SUGGESTED LAYOUT OF COMPUTATIONS FOR Q = Design discharge rate in cfs CULVERT DESIGN TO BE SUBMITTED FOR dc= Critical depth in feet APPROVAL. ho =Pressure head in feet So =Slope of pipe HW =Head water in feet - FOR USE WITH CULVERT CAPACITY CHARTS OF U.S. BUREAU OF ROADS 41 Drainage Plan Showing Design Data to be Submitted on Drawing w OS.L Co :E ° , . ,;1• C N MOOD 0 W � � ^• ,�� W p OS•S W In .7rc m a. m 0 d o -- N ^OOOLA - V J �o C MCI - -O O. �- N 1 p a 00 • E 2 >'' M 00 y pa0 Cw> / CO o ^ s 00 L Ln N '' . LU � '�„� ° m "-rte j o ? •f' c 4) �•�� i C'4 _MO' II ry W ..� IL . .. r pQ rn> 0:< Cy Cvl> —.. 0040 Y ' .gin