CENTRAL OREGON STORMWATER MANUAL CHAPTER 8 CONVEYANCE

Transcription

1 CHAPTER 8 CONVEYANCE Chapter Organizatin 8.1 Intrductin Design Flw Cnstructed Channels Channel Analysis Minimum Requirements fr Cnstructed Channels Channel Design Preservatin f Natural Lcatin f Drainage Systems Culverts Culvert Analysis Minimum Requirements fr Culverts Strm Drain Systems Pipe Analysis Minimum Requirements Pipe Design Gutters Gutter Analysis Gutter Design Drainage Inlets i Chapter 8 Cnveyance

2 8.6.1 Minimum Requirements Grate Inlet Design Cntinuus Grades Curb Inlet Design Cntinuus Grade Cmbinatin Inlet Design SAG Cnditin Curb Inlet Design SAG Cnditins Appendix 8A Example Calculatin: Nn-Flded Width... 8A - 1 Appendix 8B Example Calculatin: Nn-Flded Width... 8B - 1 Appendix 8C Example Calculatin: Grate Inlet Capacity Cntinuus Grade... 8C - 1 Appendix 8D Example Calculatin: Grate Inlet Capacity Cntinuus Grade... 8D - 1 Appendix 8E Example Calculatin: Curb Inlet Capacity Cntinuus Grade... 8E - 1 Appendix 8F Example Calculatin: Curb Inlet Capacity Cntinuus Grade... 8F - 1 Appendix 8G Example Calculatin: Cmbinatin Inlet Capacity SAG... 8G - 1 Appendix 8H Example Calculatin: Curb Inlet Capacity SAG... 8H ii Chapter 8 Cnveyance

3 8.1 INTRODUCTION A cnveyance system includes all natural r cnstructed cmpnents f a strm drain system that cllects strmwater runff and cnveys it away frm structures in a manner that adequately drains sites and radways, minimizing the ptential fr flding and ersin. Cnveyance facilities cnsist f curbs and gutters, inlets, strm drains, catch basins, channels, ditches, pipes and culverts. The placement and hydraulic capacities f strm drain structures and cnveyance systems, while taking int cnsideratin the ptential fr damage t adjacent prperties, shuld als attempt t reduce the degree f risk t traffic interruptin due t flding within the traveled radway. The cnveyance system shall als prvide discharge capacity sufficient t cnvey the design flw at velcities that are self-cleansing withut being destructive t the cnveyance facilities. These bjectives are achieved by designing all cnveyance facilities utilizing the design strm event specified fr the given facility and by adhering t varius parameters such as minimum and maximum velcity, freebard, cver, etc. A prperly designed cnveyance system als attempts t maximize the hydraulic efficiency by utilizing the prper material, slpe and size. Open cnstructed cnveyance systems shuld emulate the natural, pre-develped cnditins t the maximum extent feasible. Natural drainageways must be preserved and prtected; filling them in r building n tp f them is nt acceptable practice. It may be necessary t set aside sme drainageways r land features fr reginal use (see Sectin fr criteria). Inflw t, and discharges frm, the cnstructed system shall ccur at the natural drainage pints in the same manner as the existing cnditins as determined by tpgraphy and existing drainage patterns. Strmwater discharge shuld nt be diverted int irrigatin canals withut apprval frm the irrigatin district and any ther applicable regulating agencies. Existing drainage patterns shuld be discussed in the Drainage Reprt and reviewed in the dwnstream analysis. (See Sectin 3.4.5) DESIGN FLOW The design flw, and verflw requirements fr each type f cnveyance system is utlined belw. Either the NRCS Hydrgraph Methd r the Ratinal Methd can be used t size the cnveyance system. These requirements are cnsistent with thse listed in Chapter 2. Additinal design criteria and analysis requirements are utlined in the remaining sectins f this chapter. Cnstructed Channels Cnstructed channels shall be designed with sufficient capacity t cnvey and cntain, at a minimum, the depth f the 50-year peak flw plus an additinal 30 percent, assuming develped cnditins fr nsite tributary areas and existing cnditins fr any ffsite tributary areas. 8-1 Chapter 8 Cnveyance

4 The design shall safely bypass strm events that exceed the abve criteria and shall prvide an verflw path, with the capacity t cnvey the 100-year strm event, assuming develped cnditins fr nsite tributaries and existing cnditins fr any ffsite tributaries. The verflw shuld drain tward the natural discharge pint f the cntributing basin. The verflw path must be capable f cnveying the 100-year strm event and shuld drain tward the natural discharge pint f the cntributing basin, away frm adjacent buildings, residences, etc. (Nte: Per Oregn Drainage Law, verflws leaving the prject site cannt exceed natural flw rates withut agreement frm the dwnstream prperty wners.) Culverts New culverts shall be designed with sufficient capacity t cnvey the 50-year design strm assuming develped cnditins fr the nsite basin and existing cnditins fr any ffsite cntributing basins. Increase culvert size t pass the 100-year event if a safe verflw fr flws abve the 50-year event cannt be prvided. Strm Drain Systems and Inlets New enclsed systems and inlets shall be designed with sufficient capacity t cnvey peak flw rate fr the 25-year design strm event with at least six-inches f freebard between the water surface and the prpsed adjacent grund surface. Enclsed systems may surcharge r vertp drainage structures fr strm events that exceed the 25-year event, s lng as a safe verflw path is prvided. The verflw path must be capable f cnveying the 100-year strm event (assuming develped cnditins fr nsite tributaries and existing cnditins fr any ffsite tributaries). The verflw shuld drain tward the natural discharge pint f the cntributing basin, away frm adjacent buildings, residences, etc. (Nte: Per Oregn Drainage Law, verflws leaving the prject site cannt exceed natural flw rates withut agreement frm the dwnstream prperty wners.) Gutters Gutter flws in radways shall allw fr the passing f vehicular traffic during the 25-year design strm event by prviding nn-flded znes. Fr paved radways, the nn flding width requirement varies with the classificatin f the rad. See Table 8-8 fr nn-flded width requirements. Drainage Inlets Drainage inlets shall be designed with sufficient capacity t cnvey the 25-year design strm assuming develped cnditins fr the cntributing area. 8-2 Chapter 8 Cnveyance

5 8.2 CONSTRUCTED CHANNELS CHANNEL ANALYSIS A channel analysis shall be perfrmed fr all cnstructed channels prpsed fr the prject and fr all field verified existing natural drainageways/channels present nsite. Channel analysis may be perfrmed by hand calculatins, spreadsheets, r using any f a number f widely available sftware prgrams. The fllwing items shall be included in the drainage reprt and the rad and drainage plans, when applicable: Cmplete channel calculatins that state the design peak flw rates and design infrmatin, such as channel shape, slpe, Manning s cefficient (Table 8-4). Calculatins shall be prvided fr each distinct channel sectin (i.e. if the slpe, shape r rughness change significantly); The velcity, capacity, and Frude number shall be calculated whenever the gemetry f the channel changes; The centerline and directin f flw fr all cnstructed drainage ditches r natural channels lcated within the prject limits, are t be clearly shwn in the cnstructin plans and basin map. Fr all prpsed channels, lcating infrmatin shall be prvided at all angle pints; and, Channel prtectin shall be prvided when velcities exceed permissible velcities (See Table 8-1). The calculatins shall justify the prtectin area, thickness, material size and gradatin, and filter blanket reinfrcement, if needed. This infrmatin shall be included in the plans; TABLE 8-1 PERMISSIBLE CHANNEL VELOCITIES MAXIMUM PERMISSIBLE VELOCITIES (ft/sec) SOIL TYPE OF LINING (EARTH; NO VEGETATION) CLEAR WATER WATER CARRYING FINE SILTS WATER CARRYING SAND & GRAVEL Fine Sand (nn-cllidal) Sandy Lam (nn-cllidal) Silt Lam (nn-cllidal) Ordinary Firm Lam Vlcanic Ash Fine Gravel Stiff Clay (very cllidal) Graded, Lam t Cbbles (nn-cllidal) Chapter 8 Cnveyance

6 TABLE 8-1 CONTINUED Graded, Silt t Cbbles (cllidal) Alluvial Silts (nn-cllidal) Alluvial Silts (cllidal) Carse Gravel (nn-cllidal) Cbbles and Shingles Shales and Hard Pans Surce: Special Cmmittee n Irrigatin Research, American Sciety f Civil Engineers, Based n unifrm flw in cntinuusly wet, aged channels with erdible linings. The Frude number shall be checked near the beginning and near the end f a channel that has significantly different grade changes t determine if a hydraulic jump ccurs (Frude number changes frm <1 t >1, r vice versa). Since it is difficult t crrelate the lcatin f a hydraulic jump t the actual lcatin in the field, the Engineer shall prpse evenly spaced riprap berms, checkdams, r ther prtective measures t ensure that the jump des nt erde the cnveyance facility. When gesynthetics are used fr channel stabilizatin, fllw ODOT prcedures fr design and material specificatin. The plans shall clearly specify fabric type, placement, and anchring requirements; and, The plans shall specify seed mixture and irrigatin, as applicable, if grass-lined channels are prpsed MINIMUM REQUIREMENTS FOR CONSTRUCTED CHANNELS Slpe Minimum grades fr cnstructed channels shall be the fllwing: ½ percent (0.005 feet/feet) fr cement cncrete; 1 percent (0.010 feet/feet) fr asphalt cncrete; and, ½ percent (0.005 feet/feet) fr graded earth r clse crpped grass; and 1 percent (0.010 feet/feet) fr rip rap lined channels. Nte: Nn-structured alternatives are preferred ver asphalt and cncrete channels whenever pssible. Side Slpes Ditches may be V shaped r trapezidal. Hwever, V-ditches are nt recmmended in easily erdible sils r where prblems establishing vegetatin can be anticipated. The side slpe f radside ditches shall cnfrm t the requirements fr clear zne f the lcal jurisdictin and/r ODOT design standards. Ditches r channels shall nt have side slpes that exceed the natural angle f repse fr a given material r per Table 8-2: 8-4 Chapter 8 Cnveyance

7 TABLE 8-2 MAXIMUM DITCH OR CHANNEL SIDE SLOPES TYPE OF CHANNEL SIDE SLOPE HORIZONTAL: VERTICAL Firm Rck Vertical t ¼:1 Cncrete-Lined Stiff Clay ½:1 Fissured Rck ½:1 Firm Earth With Stne Lining 1½:1 Firm Earth, Large Channels 1½:1 Firm Earth, Small Channels 2:1 Lse, Sandy Earth 2:1 Sandy, Prus Lam 3:1 Surce: Civil Engineering Reference Manual, 8 th Editin Lcatin Cnstructed channels cannt be placed within r between residential lts. Ditches and channels shall be lcated within a drainage tract r within a brder easement. Large lt subdivisins (lts 1 acre) may be allwed t have ditches r channels traverse thrugh the lt(s) and cnsideratin may be given as t placement within an easement versus a tract. The lcal jurisdictin will review these prpsals n a case by case basis. Depth The minimum depth f pen channels shall be 1.30 times the design flw depth (ft) r ne ft; whichever is greater. This prvides a minimum 30 percent freebard depth abve the design flw water surface. Velcity Table 8-1 lists the maximum permissible mean channel velcities fr varius types f sil and grund cver. If mean channel velcities exceed these values during the design flw, channel prtectin is required (see Sectin 8.2.3). In additin, the fllwing criteria shall apply: Where nly sparse vegetative cver can be established r maintained, velcities shuld nt exceed 3 fps; Where medium density vegetatin can be established by seeding, velcities in the range f 3 t 4 fps are permitted; Where dense sd can be develped quickly r where the nrmal flw in the channel can be diverted until a vegetative cver is established, velcities f 4 t 5 fps are permitted; and, On well established sd f gd quality, velcities in the range f 5 t 6 fps are permitted. 8-5 Chapter 8 Cnveyance

8 8.2.3 CHANNEL DESIGN Channel Capacity Open channels shall be sized using the fllwing iteratin f Manning s frmula, equatin A R S Q = VA = (8-1) n Where: Q = rate f flw (cfs); V = mean velcity in channel (ft/s); A = crss-sectinal area f flw in the channel (ft 2 ); n = Manning s cefficient (See Table 5-4); S R = channel slpe (ft/ft); and, = hydraulic radius (ft) = Area/wetted perimeter Nte: The Manning equatin will give a reliable estimate f velcity nly if the discharge, channel crss sectin, rughness, and slpe are cnstant ver a sufficient distance t establish unifrm flw cnditins. Strictly speaking, unifrm flw cnditins seldm, if ever, ccur in nature because channel sectins change frm pint t pint. Fr practical purpses, hwever, the Manning equatin can be applied t mst pen channel flw prblems by making judicius assumptins. Mst hydraulics handbks cntain tables that simplify the calculatins, and cmmercially available sftware is ften used fr channel design. Energy Dissipatin Design An energy dissipater is useful in reducing excess velcity, as a means f preventing ersin belw an utfall r spillway. Cmmn types f energy dissipaters fr small hydraulic wrks are: hydraulic jumps, stilling wells, riprap utfall pads, utlet aprns, and gabin weirs. Channel Prtectin Channel velcities shall be analyzed peridically thrughut the channelized rute, particularly at the fllwing lcatins: At the first pint that the strmwater runff becmes cncentrated int a natural r cnstructed channel; At any significant change in channel cnfiguratin (grade, sideslpes, depth, shape, etc.); and Any significant change in flw (i.e. immediately dwnstream f an utfall) If channel velcities are fund t exceed the limits in Table 8-1, then channel prtectin shall be prvided. Channel prtectin material shall be selected based n the revetment and armring capabilities. The Manning s n value shall be analyzed 8-6 Chapter 8 Cnveyance

9 in the given channel cnfiguratin t determine if the material prpsed will reduce the velcity t a manageable speed. If the calculatins reveal that cmmn materials such as matting r riprap are nt the best slutin t prtect the channel frm ersin, strnger prtectin such as gabins and/r stilling pls may be necessary. Nnstructural ptins, such as vegetatin and wdy debris, shuld als be cnsidered. Riprap Prtectin at Outlets If the flw velcity at a cnduit utlet exceeds the maximum permissible velcity fr the sil r channel lining, utlet prtectin is required. The prtectin usually cnsists f an ersin resistant reach, such as riprap, between the utlet and the stable dwnstream channel t prvide a stable reach at the utlet in which the exit velcity is reduced t a velcity allwable in the dwnstream channel. The design f such prtectin is based n the design strm runff event. If prtectin is needed at the utlet, energy dissipatin shall be prvided. The ability f riprap revetment t resist ersin is related t size, shape and weight f the stnes. Mst riprap lined channels require either a gravel filter blanket r filter fabric under the riprap. Where very large riprap is used it is smetime necessary t use tw gravel filter layers between the subgrade and the riprap. Aprn Dimensins The length f an aprn (L a ) as shwn in Figure 8-1, is determined using the fllwing empirical relatinships that were develped fr the U.S. Envirnmental Prtectin Agency (1976): Or 1.8Q La = + ( 7DO ) 3 / 2 D fr O D TW O (8-2) 2 3Q D La = + ( 7DO ) 3 / 2 D fr TW < O (8-3) O 2 Where: D = maximum inside culvert width (ft); Q = pipe discharge (cfs); and, TW = tailwater depth (ft) at the utlet pipe. When there is n well-defined channel dwnstream f the aprn, the width, W, f the aprn utlet as shwn in Figure 8-1, shall be as fllws: Or W = 3 D O L a fr W = 3 D O + L a fr D TW O (8-4) 2 D TW < O (8-5) Chapter 8 Cnveyance

10 When there is a well-defined channel dwnstream f the aprn, the bttm width f the aprn shuld be at least equal t the bttm width f the channel and the lining shuld extend at least ne ft abve the tailwater elevatin. The width f the aprn at the culvert utlet shuld be at least 3 times the culvert width. The minimum thickness f the riprap layer shall be 12 inches, D max r 1.5D 50, whichever is greater. Figure 8-1 Riprap Revetment at Outfall Schematic Aprn Materials The median stne diameter, D 50 is determined frm the fllwing equatin: D 50 4 / Q = (8-6) TW ( ) D O 8-8 Chapter 8 Cnveyance

11 Where: D 50 = the diameter f rck, fr which 50 percent f the particles are finer. The riprap shuld be reasnably well graded, within the fllwing gradatin parameters: D 1.25 max 1.50 D 50 Where: D15 and = D 50 Dmin and = D D max = the maximum particle size; D min = the minimum particle size; and, D 15 = the diameter f rck, fr which 15 percent f the particles are finer. A filter blanket under the riprap is nrmally needed. If a gravel r sand filter blanket is used, then it shall cnfrm t the gradatin parameters listed in Table 8-3. The size f the filter blanket material is designated d xx, the size f the riprap is designated D xx, and the size f the subgrade is designated d xx. The thickness f each filter blanket shuld be ne-half that f the riprap layer. If it is fund that D 15 /d 85 < 2 then n filter blanket is needed. Where very large riprap is used, it is smetime necessary t use tw filter blanket layers between the subgrade and the riprap. 50 TABLE 8-3 CRITERIA FOR GRAVEL OR SAND FILTER BLANKET GRADATION PRIMARY CRITERION D 15 < 5d 85 Recmmended Secndary Criteria 5d 15 < D 15 < 40d 15 D 50 /d 50 < 50 Guidelines fr Strmwater Management, Spkane Cunty, February PRESERVATION OF NATURAL LOCATION OF DRAINAGE SYSTEMS New develpment shall be designed t prtect natural drainage features including drainageways, fldplains (Sectin 7.7.2), wetlands and streams (which include DSL stream channels) (Sectin 7.7.3), natural clsed depressins (Sectin 7.7.4) that stre and/r allw water t infiltrate int the grund, and ther natural features and existing drainage/strmwater facilities. These features are cllectively referred t as the Natural Lcatin f Drainage Systems (NLDS). Preserving the NLDS will help ensure that strmwater runff can cntinue t be cnveyed and dispsed f at its natural lcatin. Preservatin will als increase the pprtunity and ability t utilize the mre predminant systems as reginal strmwater facilities. 8-9 Chapter 8 Cnveyance

12 Prtectin Sme prtins f the NLDS fall under the jurisdictin f Oregn Department f Fish and Wildlife (ODFW) and/r the DSL and/r ther state r federal agencies. The prject Engineer is respnsible fr: Determining which prtins f the develpment site are under state r federal jurisdictin, and Obtaining prper permits fr activities in jurisdictinal drainage systems. In general, n cuts r fills are allwed in state r federally regulated NLDS except fr perpendicular crssings f driveways r rads with engineering plans shwing apprpriately sized culverts r bridges. Such prjects must meet the requirements and gain apprval frm Oregn Department f Fish and Wildlife (ODFW), DSL, and ther lcal, state, r federal agencies. Nn-regulatry prtins f the NLDS within develpments cntaining lts ne acre r smaller may be relcated within the develpment prvided that it is demnstrated that the drainageway will enter and exit the site at the pre-develped lcatin and that discharge will ccur in the same manner as prir t develpment. Since sme nn-regulatry NLDS may be useful fr managing reginal strmwater, crdinate with the lcal jurisdictin t determine if the facility that is relcated shuld be increased in capacity (i.e. larger pipe r cnveyance channel). Fr all NLDS, the width r size f the tract r easement within which the drainageway will be cntained shall be determined based upn an analysis f the prpsed strmwater flws directed t these drainage systems and the extent f the resulting water surface. Maintenance and access requirements fund in this Manual shall als be cnsidered. At a minimum, the tract r easement width shall be n less than 20 feet wide. All new develpment cntaining lts that are ne acre r smaller shall be required t set aside the drainageway as pen space in a separate tract. Fr new develpment cntaining lts that are greater than ne acre, the drainageway may be set aside in either a tract r an easement. N part f an identified drainageway shall becme part f a residential building lt. 8.3 CULVERTS A culvert is a pipe under a radway r embankment used t cnvey flw frm ne prtin t anther f a natural r cnstructed drainage channel. A culvert shall cnvey flw withut causing damaging backwater flw cnstrictin, r excessive utlet velcities. In additin t design flws and the hydraulic perfrmance f culverts, ther factrs can affect the ultimate design f a culvert and shall be taken int cnsideratin. These factrs can include the ecnmy f alternative pipe materials and sizes, hrizntal and vertical alignment, envirnmental cncerns, fld prtectin, existing channel gemetry, and fish passage Chapter 8 Cnveyance

13 8.3.1 CULVERT ANALYSIS Culvert analysis is cmplex and is typically perfrmed using cmmercially available cmputer sftware. If hand calculatins are prpsed, example calculatins can be fund in several technical publicatins and pen channel hydraulics manuals. When applicable, the fllwing items shall be included in the drainage reprt, r rad and drainage plans: Cmplete culvert calculatins that state the design peak flw rates, velcities at the inlet and utlet, flw cntrl type (i.e. inlet r utlet cntrl), flw depth, and design infrmatin fr the chsen culvert such as size, slpe, length, material type, Manning s cefficient (See Table 8-4); Headwater depths and water surface elevatins fr the design flw rate; Radway crss-sectin and radway prfile; Lcatin infrmatin fr each f the culvert inverts and invert elevatins; Type f end treatment (fr example, wingwall, flared end sectins, etc); and, Wall thickness. TABLE 8-4 MANNING'S ROUGHNESS COEFFICIENTS (n) FOR CULVERTS OR CLOSED SYSTEMS MATERIAL TYPE n 1 Cncrete Pipe Ductile Irn HDPE CMP AWWA C ASTM D3034 PVC The n values presented in this table are the Nrmal values as presented in Chw (1959). Fr an extensive range and fr additinal values refer t Chw (1959) Additinal r value infrmatin is ften prvided by pipe manufactures MINIMUM REQUIREMENTS FOR CULVERTS Peak Flw Rate Culverts shall be sized t handle the 50-year peak flw rates assuming develped cnditins fr the nsite basin and existing cnditins fr any ffsite cntributing basins. These peak flws are calculated using the methds described in Chapter 5. In additin, the culvert shall be checked fr high flw damage during the 100-year strm event Chapter 8 Cnveyance

14 Allwable Headwater Elevatin Headwater is the depth f water at the culvert entrance at a given design flw. Headwater depth is measured frm the invert f the culvert t the water surface. Culverts shall be designed t carry the design runff with a headwater depth less than 2 times the culvert diameter fr culverts 18 inches and under, r 1.5 times the culvert diameter fr culverts greater than 18 inches. In additin, culverts shall be designed such that the water surface elevatin fr the design strm event des nt exceed the elevatin f the base curse f the radway t avid saturatin f the rad base. Velcity and Slpe T avid siltatin that reduces culvert capacity, the minimum velcity fr culverts shall be 4 feet per secnd during the design strm event and the minimum slpe shall be 0.5 percent. Fr grades greater than r equal t 20 percent, anchrs are required unless deemed nt necessary by calculatins and the manufacturer s recmmendatins. Diameter The minimum culvert diameter shall be as fllws: TABLE 8-5 MINIMUM CULVERT SIZES CULVERT LOCATION MINIMUM SIZE (inches) Under Public Rads 18 Under Private Rads 12 Under Driveways/Appraches 12 Material Pipe material listed in Table 8-4 can be used fr culverts. Check with the lcal jurisdictin fr specific material restrictins r preferences. Placement/Alignment Culverts shall be placed n the same alignment and grade as the drainageway, whenever pssible. Cnsider raising intakes slightly abve the flw line t allw fr sedimentatin, but avid cantilevered utfalls that may cause te ersin. Drp inlets r manhles may be used t reduce exit velcities n steep terrain. Cnsideratin shuld als be given t changes f cnditins ver time. Chapter 8 Cnveyance 8-12

15 Angle Pints The slpe and alignment f a culvert shall remain cnstant thrughut the entire length f the culvert. Hwever, in situatins where existing radways are t be widened, it may be necessary t extend an existing culvert at a different slpe. The lcatin where the slpe changes is referred t as the angle pint. If the new culvert sectin is t be placed at a flatter grade than the existing culvert, a manhle shall be prvided at the angle pint t facility the remval f debris and sediment. A manhle is nt required where the new culvert sectin is t be placed n a steeper grade than the existing culvert. Outfalls Outfalls shall cnfrm t the requirements f all federal, state, and lcal regulatins. Ersin cntrl shall be prvided at the culvert utfall. See Sectin fr additinal infrmatin regarding utfall prtectin. Culvert Debris and Safety The Engineer shall evaluate the site t determine whether debris prtectin shall be prvided fr culverts. Debris may cnsist f sil depsits (i.e. silt, sand, gravel, and bulders), limbs, sticks, lgs, and trees. In areas where heavy debris flw is a cncern, fr example dense wded areas, debris prtectin shall be prvided. Methds fr prtecting culverts frm debris prblems include: upsizing the culvert, debris deflectrs, debris racks and debris basins. Safety bars shall be prvided fr culverts with a diameter greater than 36 inches. Safety bars must be prvided n bth the upstream and dwnstream ends f the culvert. The clear space between bars shall be 4 inches maximum. An example f an utlet rack fr safety r debris prtectin is shwn in Figure 8-3. When prpsing a debris rack r safety bars, the area upstream f the culvert area shall t be evaluated t determine what wuld happen if debris plugged the culvert pening. Cnsideratin shuld be given t the ptential degree f damage t the radway and adjacent prperty, ptential hazard and incnvenience t the public, and the number f users f the radway. Structural Design Fr culverts under radways, the amunt f cver ver the culvert is defined as the distance frm the tp f the pipe t the bttm f the pavement. It des nt include asphalt r cncrete paving abve the base. The minimum amunt f cver is 2 feet fr culverts unless the manufacturer recmmends therwise. The minimum cver fr culverts under private driveways is 1 ft frm the tp f the pipe t the finish grade f the driveable surface. If the depth f cver is shallw (less than 1 ft) and truck wheel lads are present, it will be necessary t prpse a design t prevent structural damage t the pipe r prvide manufacturer s recmmendatins. Als, extreme fill heights (20 feet r 8-13 Chapter 8 Cnveyance

16 greater) may cause structural damage t pipes and will require a special design r adherence t the manufacturer s recmmendatins. The strength f the pipe depends upn its bed design, backfilling methds, and the quality f the backfill sil. In material incapable f develping adequate supprt, excavatin and backfilling with granular material shall be perfrmed t a width sufficient t prvide the necessary supprt. End Treatments The type f end treatment used n a culvert depends n many interrelated and ften cnflicting cnsideratins. The fllwing discusses different end treatments: Prjecting Ends is a treatment where the culvert is simply allwed t prtrude ut f the embankment. This is the simplest and mst ecnmical. There are several disadvantages such as susceptibility t fltatin, ersin, safety when prjecting in the clear zne, and aesthetic cncerns; Beveled End Sectins cnsist f cutting the end f the culvert at an angle t match the embankment slpe surrunding the culvert. Beveled ends shuld be cnsidered fr culverts 6 feet in diameter r less. Structural prblems may be encuntered fr larger culverts nt reinfrced with a headwall r slpe cllar; Flared End Sectins are manufactured culvert ends that prvide a simple transitin frm culvert t a drainage way. Flared end sectins are typically nly used n circular pipe r pipe arches. This end treatment is typically the mst feasible ptin in smaller pipes up t 48 inches in diameter. Safety cncerns generally prhibit their use in the clear zne fr all but the smallest diameters; Headwalls are cncrete frames pured arund a beveled r prjecting culvert. They prvide structural supprt and eliminate the tendency fr buyancy. Fr larger diameter pipes (i.e. greater than 10 feet in diameter), a slpe cllar is recmmended. A slpe cllar is a reinfrced cncrete ring that surrunds the expsed culvert end; r, Wingwalls and Aprns are cmmn n larger reinfrced cncrete bx culverts. Their purpse is t retain and prtect the embankment, and prvide a smth transitin between the culvert and the channel. Fish Passage Culverts lcated in waters in which native migratry fish are currently r were histrically present must address fish passage requirements and receive an apprval, waiver, r exemptin frm ODFW. Laws regarding fish passage may be fund in ORS thrugh 910 and in OAR 635, Divisin 412. Specific design criteria are utlined in the ODFW Fish Passage Criteria dated Octber 22, Chapter 8 Cnveyance

17 8.4 STORM DRAIN SYSTEMS A strm drain system is a netwrk f pipes that cnvey surface drainage frm catch basins r ther surface inlets, thrugh manhles, t an utfall. The design f strm drain systems shall take int cnsideratin runff rates, pipe flw capacity, hydraulic grade line, sil characteristics, pipe alignment depth, pipe strength, ptential cnstructin prblems, and ptential impacts t dwnstream prperties PIPE ANALYSIS Strm drain system analysis can be perfrmed using cmmercially available cmputer sftware r spreadsheets. If hand calculatins are prpsed, example calculatins can be fund in many technical publicatins and design manuals. The ODOT Hydraulics Manual is a gd reference that includes detailed sample calculatins. When applicable, the fllwing items shall be included in the drainage reprt, r rad and drainage plans: A basin map shwing nsite and ffsite basins cntributing runff t each inlet, which includes a plan view f the lcatin f the cnveyance system; Cmplete pipe calculatins that state the design peak flw rates, full pipe capacity, and design infrmatin fr each f the pipe runs (size, slpe, length, material type, manning cefficient); Velcities at design flw fr each f the pipe runs; The hydraulic grade line at each inlet, catch basin, manhle, angle pint, and utlet; and, A prfile f the main line strmwater system (and cnnectins, where applicable), shwing size, material type, lengths f pipes (r culverts), and invert elevatins, rim/finished grade elevatins fr manhles, catch basin, and ther structures. Nte: Fr lateral pipe cnnectins t strm drain lines in existing rights-f-way, fixed invert elevatins are preferred but nt required. Only a minimum depth frm finish grade t pipe invert and the minimum pipe slpe necessary t satisfy the freebard and self-cleansing velcity requirements must be prvided n the design plans. This allwance is made t accunt fr ptential cnflicts with existing utilities in the ROW MINIMUM REQUIREMENTS Peak Flw Rate Clsed pipe systems shall be sized t handle the design peak flw rates utlined in Sectin These peak rates can be calculated using the methds described in Chapter Chapter 8 Cnveyance

18 Hydraulic Grade Line The Hydraulic Grade Line (HGL) represents the free water surface elevatin f the flw traveling thrugh the strm drain system. Pipes in clsed systems will be sized by calculating the HGL in each catch basin r manhle. A minimum f 0.50 feet f freebard shall be prvided between the HGL in a catch basin r manhle and the prpsed grund elevatin during the 25-year design flw. Demnstrate that the water surface elevatin will nt back up int crawl spaces r fld ther structures. Pipe Velcities and Slpe Strm drains shall be designed t maintain a self-cleaning velcity f 3 feet per secnd (fps) r greater during the design flw. Table 8-6 prvides the minimum slpes required fr varius pipe sizes in strm drains flwing full. TABLE 8-6 MINIMUM PIPE SLOPES IN STORM DRAINS FLOWING FULL PIPE SIZE (inches) MINIMUM SLOPE (ft/ft) n= Surce: FHWA, Hydraulic Engineering Circular N. 22, Secnd Editin Pipe velcities shuld nt be excessively high since high flw velcities (appraching and abve 10 fps) cause abrasin f the pipes. When the design velcities are 10 fps r greater, manufacturer s recmmendatins demnstrating that the pipe material can sustain the prpsed velcities shall be prvided. When the grade f a strm pipe is greater than r equal t 20 percent, then pipe anchrs are required at the jints, at minimum. A pipe anchr detail is shwn in Figure 8-2. Pipe anchr lcatins are t be defined in the plans, and a pipe anchr detail shall be referenced r prvided. Table 8-7 shws minimum pipe anchr requirements. Chapter 8 Cnveyance 8-16

19 PIPE SLOPE TABLE 8-7 MINIMUM PIPE ANCHOR SPACING MINIMUM ANCHOR SPACING Percent 35 feet Percent 25 feet > 50 Percent 15 feet Material Pipe material shall meet the lcal jurisdictin requirements fr strm sewer pipe. Pipe Diameter and Length The minimum pipe diameter shall be 12 inches; except fr single pipe segments less than 50 feet lng, which may be 8 inches in diameter. The maximum length f pipe between junctins shall be n greater than 300 feet. Pipe diameters cannt be dwnsized fr dwnstream runs. Inlets All lines cnnected t strm sewers r drywells (with the exceptin f drywells in swales) must be designed per the lcal jurisdictin standard plans. Placement and Alignment N strm drain pipe in a drainage easement shall have its centerline clser than 5 feet t a private rear r side prperty line r 10 feet frm building fundatins r ther structures. Cnsult lcal jurisdictin fr additinal setback requirements. Fr a strm drain lcated under the rad, the strm drain shall be placed in accrdance with the lcal jurisdictin requirements r standard plans. If it is anticipated that a strm drain system may be expanded in the future, prvisins fr the expansin shall be incrprated int the current design. Outfalls Pipe utfalls shall be placed n the same alignment and grade as the cntributing strm drain system. Outfalls shuld discharge at the same elevatin as the existing grade. Outfalls shall cnfrm t the requirements f all federal, state, and lcal regulatins. New utfalls t the Deschutes River, Crked River, r ther water bdies designated as waters f the United States require regulatry agency apprval. Ersin cntrl shall be prvided at the strm system utfall. See Sectin fr additinal infrmatin regarding utfall prtectin Chapter 8 Cnveyance

20 Figure 8-2 Pipe Anchr Typical Detail 8-18 Chapter 8 Cnveyance

21 Strm Drain Debris and Safety The Engineer shall evaluate the site t determine whether debris prtectin shall be prvided fr strm drain systems. Debris may cnsist f sil depsits (i.e. silt, sand, gravel, and bulders), limbs, sticks, trash, r ther landscaping materials. In areas where heavy debris flw is a cncern, fr example dense wded areas, debris prtectin shall be prvided. Methds fr prtecting the strm drain systems frm debris prblems include: debris deflectrs, debris racks and debris basins. Fr an enclsed strm drain system lcated in urban lcatins, safety bars shall be prvided fr utfalls with a diameter 18 inch r greater t prtect frm unauthrized individuals entering the strm drain system. Outfalls within a fenced area are nt required t have safety bars. The clear space between bars shall be 4 inches maximum. An example f an utlet rack is shwn in Figure 8-3. Ntes: 1. CMP r CPEP smth interir end sectin shwn; 2. All steel parts must be galvanized and asphalt cated (Treatment 1 r better). Figure 8-3 Outlet Rack Typical Detail 8-19 Chapter 8 Cnveyance

22 Structural Design The amunt f cver ver the pipe is defined as the distance frm the tp f the pipe t the bttm f the pavement. It des nt include asphalt r cncrete paving abve the base. The minimum amunt f cver is 2 feet unless the manufacturer recmmends therwise. If the depth f cver is shallw (less than 1 feet) and truck wheel lads are present, it will be necessary t prpse a design t prevent structural damage t the pipe r prvide manufacturer s recmmendatins. Extreme fill heights (20 feet r greater) may als cause structural damage t pipes and will thus require a special design r adherence t the manufacturer s recmmendatins. The strength f the pipe depends upn its bed design, backfilling methds, and the quality f the backfill sil. In material incapable f develping adequate supprt, excavatin and backfilling with granular material shall be perfrmed t a width sufficient t prvide the necessary supprt. Inverts at Junctins Whenever tw pipes f the same size meet at a junctin, the dwnstream pipe shall be placed 0.1 feet belw the upstream pipe invert. When tw different sizes f pipes are jined, pipe crwns shall be placed at the same elevatin. The exceptin t this rule wuld be at drp manhles. Exceptins may be allwed by the lcal jurisdictin when tpgraphic cnditins will significantly impact the depth f the dispsal lcatin. Cmbined Systems Cmbined sanitary and strmwater sewer systems are prhibited PIPE DESIGN T analyze the cnveyance capacity f a clsed pipe system, the fllwing general steps may be fllwed when steady flw cnditins exist, r cnditins can be accurately apprximated assuming steady flw cnditins: 1. Estimate the size f the pipes assuming a unifrm flw cnditin, using equatin 8-1. Refer t Table 8-4 fr Manning s cefficient fr different pipe materials. 2. Fr the trial pipe sizes chsen, determine unifrm flw depth and critical flw depth; 3. Determine if upstream (accelerated flw) r dwnstream (retarded flw) cnditins exist. Subcritical flw ccurs when dwnstream cnditins cntrl, supercritical flw ccurs when upstream cnditins cntrl. Then by cmparing unifrm flw depth, critical flw depth, and initial flw depth, determine what flw regime will ccur. Identify hydraulic jump lcatins, and where any ther discntinuity f flw depth will ccur. 4. Cnduct a mre detailed analysis by cmputing the hydraulic grade line. The direct step methd r standard step methd is ften used t calculate the hydraulic grade line. Fr supercritical flw, begin at the upstream end and cmpute flw 8-20 Chapter 8 Cnveyance

23 sectins in cnsecutive rder heading dwnstream. Fr sub-critical flw, begin at the dwnstream end and cmpute flw sectins in cnsecutive rder heading upstream. The analysis f clsed pipe systems is cmplex and is typically dne using cmmercially available cmputer sftware packages. If hand calculatins are prpsed, example calculatins can be fund in several technical publicatins n pen channel hydraulics, such as: Handbk f Hydraulics, by Brater and King; and Open-Channel Hydraulics by French. 8.5 GUTTERS A gutter is a sectin f pavement adjacent t the radway which cnveys water during a strm runff event. Gutter flw calculatins are necessary t establish the spread f water nt the shulder, parking lane, r travel lane. Radways shall have an adequate nnflded width that allws fr the passing f vehicular traffic during the 25-year design strm event. The nn-flded width (L) is shwn in Figure 8-4 and the minimum nnflded widths fr varius rad classificatins are utlined in Table 8-8. Figure 8-4 Nn-Flded Rad Width (L) TABLE 8-8 NON-FLOODED ROAD WIDTH REQUIREMENTS ROAD CLASSIFICATION NON-FLOODED WIDTH (L) 1 Private Rad 12 feet Lcal Access 12 feet Cllectr Arterial, 2 Lane 16 feet Minr Arterial, 2 Lane 24 feet Other Rad Types Per lcal jurisdictin 1 During the 25-year design strm. Nn-flded width and flw depth at the curb are ften used as criteria fr spacing pavement drainage inlets (curb r grate inlets). Drainage inlets shall be spaced s that the nn-flded width requirements are met and strmwater des nt flw ver the back f the curb. Spacing shall nt t exceed 300 feet regardless f flded width and flw depth cmpliance Chapter 8 Cnveyance

24 8.5.1 GUTTER ANALYSIS When applicable, the drainage reprt shall include cmplete gutter calculatins that state the design peak flw rates, design flw depth, rad crss slpe, rad grade, and nn-flded width. The equatin fr calculating gutter flw is a mdified versin f Manning s equatin S x S L T Q = (8-7) n Where: Q = flw rate (cfs); n = Manning s cefficient (Table 8-9); S L = lngitudinal slpe f the gutter (ft/ft); S x = crss slpe (ft/ft); and, T = spread in ne gutter (ft) TABLE 8-9 MANNING'S ROUGHNESS COEFFICIENTS (n) FOR STREET & PAVEMENT GUTTERS TYPE OF GUTTER OR PAVEMENT n Cncrete Gutter, Trweled Finish Asphalt Pavement Smth Texture Rugh Texture Cncrete Pavement Flat Finish Brm Finish GUTTER DESIGN Surce: FHWA, Hydraulic Engineering Circular N. 22, Secnd Editin Unifrm Gutter Sectin Unifrm gutter sectins have a crss slpe which is equal t the crss slpe f the shulder r travel lane adjacent t the gutter. The spread in a unifrm gutter sectin can be calculated using equatin 8-7 and slving fr T (spread) r using the fllwing frm f that equatin: S x S L Q n T = (8-8) 8-22 Chapter 8 Cnveyance

25 Figure 8-5 Unifrm Gutter Sectin An example calculatin fr determining the nn-flded width and the depth f flw fr a unifrm gutter sectin is prvided in Appendix 8A. Cmpsite Gutter Sectin Gutters having cmpsite sectins are depressed in relatin t the adjacent pavement slpe. That is, the paved gutter has a crss slpe which is steeper than that f the adjacent pavement. The design f cmpsite gutters requires cnsideratin f flw in the depressed segment f the gutter. The spread (T) in cmpsite gutter sectins cannt be determined by a direct slutin; rather an iterative apprach fllwing the prcedure utlined belw shall be used. An example calculatin fr determining the spread fr a cmpsite gutter sectin is included in Appendix 8B. Figure 8-6 Cmpsite Gutter Sectin 1. Assume a flw rate bypassing the depressed gutter sectin, Q s; 2. Cmpute Q w using the fllwing: Where: Q = Q w Q s (8-9) Q w = flw rate in the depressed sectin f the gutter (cfs); Q = design flw rate (cfs); Q s = flw rate in the gutter sectin beynd the depressed sectin (cfs); 8-23 Chapter 8 Cnveyance

26 3. Cmpute the gutter crss slpe (if it is nt given), S w, using fllwing equatin: S w = S x + a W (8-10) Where: S w = crss slpe f the depressed gutter (ft/ft); S x = rad crss slpe (ft/ft); W = gutter width (ft); and, a = gutter depressin (ft). 4. Cmpute E, the rati f flw in a chsen width (the width f a depressed gutter r grate) t the ttal gutter flw, using the fllwing equatin: Qw E = Q (8-11) 5. Slve fr T using fllwing equatin: S w S x T = W 1+ (8-12) 3 8 S w E S x 1 E 6. Cmpute T S using fllwing equatin: = T W (8-13) T S 7. Use equatin 8-7 t determine Q s fr T S and cmpare t estimated Q s frm step 1. Steps 1 thrugh 6 shall be repeated until the estimated and cmputed Q s are apprximately the same. 8.6 DRAINAGE INLETS Drainage inlets are used t cllect runff and discharge it t a strm drainage system. They are typically lcated in gutter sectins, paved medians, and radside and median ditches. Inlets mst cmmnly used in Central Oregn are as fllws: Grate Inlets cnsist f an pening in the gutter r ditch cvered by a grate. They perfrm satisfactrily ver a wide range f lngitudinal slpes. Grate inlets generally lse capacity as the rad/gutter/ditch grade increases. A majr advantage f grate inlets is that they are installed alng the radway where strmwater is flwing. Curb Inlets are vertical penings in the curb. They are mst effective n flat grades, in sags, and where flws are fund t carry significant amunts f flating debris. Curb inlets lse interceptin capacity as the gutter grade increases; therefre, the use f curb inlets is recmmended in sags and n grades less than 3 percent Chapter 8 Cnveyance

27 Cmbinatin Inlets cnsist f bth a curb-pening and a grate inlet. They ffer the advantages f bth grate and curb inlets which result in a high capacity inlet. There are many variables invlved in designing the number and placement f inlets, and in determining the hydraulic capacity f an inlet. The hydraulic capacity f a strm drain inlet depends upn its gemetry as well as the characteristics f the gutter flw. Inlet capacity gverns bth the rate f water remval frm the gutter and the amunt f water that can enter the strm drainage system. Inadequate inlet capacity r pr inlet lcatin may cause flding n the radway resulting in a hazard t the traveling public. Appendix C f Chapter 13 in the ODOT Hydraulics Manual includes additinal infrmatin guidance in selecting apprpriate inlets fr a given cnditin and includes standard dimensins fr varius inlet types. Lcal jurisdictins may als have their wn design specificatins fr grates and inlets MINIMUM REQUIREMENTS Peak Flw Rate Drainage inlets shall be designed and lcated with capacity t carry the 25-year peak flw event. The design flw can be calculated using the methds described in Chapter 5. Structures Catch basins, inlets and strm manhles shall cnfrm t the standard plans f the lcal jurisdictin, r ODOT s design guidelines when lcal jurisdictin standards are nt available. Catch basins, inlets, and strm manhles shall be placed at all breaks in grade and hrizntal alignments. Pipe runs shall nt exceed 300 feet fr all pipe sizes. Structure lcatins shall cnsider maintenance access and future cnnectin needs. Grates All grate inlets cnstructed at lw pints f radways shall be cmbinatin inlets. The mst cmmnly used cmbinatin inlet is a bar r vaned grate with a hded curb cut area. Grate inlets n grade shall have a minimum spacing f 20 ft t enable any bypass water t reestablish its flw against the face f curb between inlets. Als, drainage inlets shall nt be lcated in frnt f pedestrian access ramps r in crsswalks. Grates shall be depressed t ensure satisfactry peratin; the maximum depressin is 2 inches. Curb Inlets Cncrete curb inlets (i.e. aprns) shall be required at the entrances t all strmwater facilities and are prvided in rder t aid strmwater cnveyance int the facility and t suppress vegetatin grwth at the inlet Chapter 8 Cnveyance

28 The maximum length f a curb inlet shall nt exceed 6 feet and shall have a 2 inch depressin at the curb line. The finish grade f the swale/pnd sideslpe, where the cncrete curb inlet aprn ends, shall be a minimum f 2 inches belw the finished elevatin f the cncrete curb aprn extensin. The intentin is t allw strmwater runff t enter the swale/pnd unbstructed, withut backing up int the street and gutter due t vegetatin vergrwth at the inlet. Curb inlets shall be placed at the mst upstream and dwnstream pint alng the rad adjacent t the treatment r dispsal facility, regardless f the flw directed t curb inlet; i.e. the capacity f the inlets may exceed the design flw rate entering the facility. In many cases, when a lng drainage facility is prpsed, and the engineering calculatins supprt it, additinal intermediate curb inlets may be required. Overflw structures, such as drywells r catch basins, shall be lcated away frm the pint r pints where runff flws int the facility. When the verflw structure is lcated within the facility, slpes arund the inlet shall be n greater than 4: GRATE INLET DESIGN CONTINUOUS GRADES The capacity f an inlet n a cntinuus grade can be fund by determining the prtin f the gutter discharge directly ver the width f the inlet. On cntinuus grades (assuming that the grate has the capacity t intercept the entire flw rate directed tward it), the amunt f strmwater intercepted by a grate is equal t the amunt f strmwater runff flwing directly ver the grate plus the amunt that flws in ver the side f the grate thrugh the slats/bars. The fllwing prcedure is mst accurate when velcities are in the range f 3 t 5 ft/s at a 2 r 3 percent lngitudinal slpe. Fr instances where the velcity is fund t exceed 5 ft/s, additinal intermediate inlets can be added, cntributing basins redefined, and the assciated velcities recalculated. While adding inlets is ne slutin t reducing the velcity, mre infrmatin may be fund regarding the affect f sideflw by cnsulting the FHWA Hydraulic Engineering Circular N. 22 (HEC- 22), Sectin 4.4 Drainage Inlet Design. Nte that cmmercially available sftware may be used t determine grate inlet capacity. The capacity f a grate inlet n a cntinuus grade may be calculated using the prcedure utlined belw: 1. Determine the runff frm the cntributing basin at the high pint t the first inlet. This is the amunt f runff that culd be intercepted by the first inlet. 2. Select an inlet and nte the grate width (GW) in the calculatins 1 ; 3. Analyze the mst upstream inlet. The width f flw (T) is calculated using the prcedure described in Sectin Verify T is within the allwable limit 1 ODOT lists standard inlet design parameters in Table B f Chapter 13, Appendix C f the ODOT Hydraulics Manual. Additinal inlet parameters can be fund in the manufactures literature Chapter 8 Cnveyance

29 (Table 8-7), then determine the amunt f flw intercepted by the grate (basin flw bypass flw). 4. The inlet bypass flw n a cntinuus grade is cmputed as fllws: 8 3 ( T GW ) Q BP = Q ( ) (8-14) T Where: Q BP = prtin f flw utside the grate width (cfs); Q = ttal flw f gutter appraching the inlet (cfs); GW = grate inlet width perpendicular t the directin f flw (ft). Zd T Q d V 1 S S x GW Figure 8-7 Typical Grate Inlet Crss-Sectin 5. The velcity shall fall belw 5 ft/s. The velcity f flw directly ver the inlet is calculated as fllws: Where: Q QBP V 1= (8-15) (GW) [ d 0. 5(GW)(S )] x V 1 = velcity ver the inlet (ft/s); S x = crss slpe (ft/ft); and, d = depth f flw at the face f the curb (ft), given by: d = T * (8-16) S x If the nn-flded rad width des nt meet the minimum criteria, an additinal inlet shuld be placed at an intermediate lcatin and the prcedure repeated. If the velcity exceeds 5 ft/sec then side flw shall be cnsidered using the methd utlined in HEC Chapter 8 Cnveyance