Headwater elevation water surface elevation just. Tailwater elevation water surface elevation just

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: Culvert Hydraulis Bob Pitt University of Alabama and Sirley Clark

used in roadway rossings and detention pond outlets.

Tailwater elevation water surfae elevation just downstream of te ulvert

ulverts needed to pass a design disarge Hydrauli apaity of existing

resulting from a speifi disarge rate Hydrauli performane urves for a

1 : Culvert Hydraulis Bob Pitt University of Alabama and Sirley Clark Penn State - Harrisburg Culvert Flow Culvert Systems Culverts typially used in roadway rossings and detention pond outlets. Headwater elevation water surfae elevation just upstream of te ulvert Tailwater elevation water surfae elevation just downstream of te ulvert Analysis typially for: Size, sape and number of new or additional ulverts needed to pass a design disarge Hydrauli apaity of existing ulvert system Upstream flood level at an existing ulvert system resulting from a speifi disarge rate Hydrauli performane urves for a ulvert system (wi are used to assess ydrauli risk at a rossing or as input for anoter ydrauli or ydrologi model

3 From: FHWA. Hydrauli esign of Higway Culverts. From: FHWA. Hydrauli esign of Higway Culverts. From: FHWA. Hydrauli esign of Higway Culverts. 3

4 Culvert Hydraulis: Control Type Culverts at as a signifiant onstrition to flow and are subjet to a range of flow types, inluding bot gradually varied and rapidly varied flow. Simplify by ontrol type: Outlet Control Assumption: Computes te upstream eadwater dept using onventional ydrauli metodologies tat onsider te predominant losses due to ulvert barrel frition Also inludes minor entrane and exit losses. Tailwater ondition as important effet on ulvert system. Inlet Control Assumption: Computes upstream eadwater dept resulting from onstrition at te ulvert entrane Neglets ulvert barrel frition, tailwater elevation and oter minor losses. Te ontrolling eadwater dept is te large of te omputed inlet and outlet ontrol eadwater depts (sine a single ulvert may at times operate under ea of te two ontrol types. Culvert Hydraulis: Outlet Control Headwater dept is found by summing te tailwater dept, entrane minor loss, exit minor loss and frition losses along te ulvert barrel. Energy basis for solving te outlet ontrol eadwater (HW) for a ulvert under inlet ontrol is given by te basi energy equation, rewritten for ulvert terms. V V HW 0 g g u d TW H Were HW 0 eadwater dept above outlet invert (lengt) V u approa veloity (lengt/time) TW tailwater dept above outlet invert (lengt) V d exit veloity (lengt/time) H sum of all losses (entrane minor loss [H E ] barrel frition losses (H F ) exit loss [H O ] oter losses), (lengt) Culvert Hydraulis: Outlet Control Culvert Hydraulis: Outlet Control Wen te ulverts onnet ponds or oter waterbodies wit negligible veloity on te upstream and downstream, te equation simplified to: HW 0 TW H Culverts are often ydraulially sort (meaning tat uniform dept will not be aieved during water s passage troug te ulvert). Solved using te gradually-varied flow analysis teniques. 4

5 Culvert Hydraulis: Outlet Control Entrane losses due to ontration of flow as it enters te ulvert. Entrane losses are a funtion of barrel veloity ead just inside te entrane, wit te smooter entranes aving te lowest entrane loss oeffiients. Entrane losses expressed using te following equation: H E k e V g Were H E entrane loss (lengt) k e entrane loss oeffiient V veloity just inside barrel entrane (lengt/time) g gravitational onstant (lengt/time ) From: FHWA. Hydrauli esign of Higway Culverts. From: FHWA. Hydrauli esign of Higway Culverts. From: FHWA. Hydrauli esign of Higway Culverts. 5

6 Culvert Hydraulis: Outlet Control Culvert Type Pipe, Conrete Entrane Type and esription Projeting from fill, soket end (groove-end) Entrane oss Coeffiient, k e 0.3 Projeting from fill, square ut end Headwall or eadwall wit wingwalls Soket end of pipe (groove-end) Square edge Rounded (radius / ) itered to onform to fill slope End-setion onfirming to fill slope Beveled edges, 33.7 o or 45 o levels 0. Side or slope-tapered inlet 0. Culvert Hydraulis: Outlet Control Culvert Type Box Culvert Entrane Type and esription Headwall parallel to embankment (no wingwalls) Square-edged on 3 edges Rounded on 3 edges (to radius of / barrel dimension or beveled edges on 3 sides) Wingwalls at 30 o to 75 o barrel Square-edged at rown Crown edge rounded (to radius of / barrel dimension, or beveled top edge) Wingwall at 0 o to 5 o to barrel Square-edged at rown Wingwalls parallel (extension of sides) Square-edged at rown Side or slope-tapered inlet Entrane oss Coeffiient, k e Culvert Hydraulis: Outlet Control Culvert Type Pipe or Pipe Ar, Corrugated etal Entrane Type and esription Projeting from fill (no eadwall) Headwall or eadwall and wingwalls square-edge itered to onform to fill slope, paved or unpaved edge End-setion onfirming to fill slope Entrane oss Coeffiient, k e Beveled edges, 33.7 o or 45 o levels 0. Side or slope-tapered inlet 0. Culvert Hydraulis: Outlet Control Exit loss is an expansion loss. Funtion of ange in veloity ead tat ours at te disarge end of te ulvert. Exit losses expressed using te following equation: d H O.0 V g Were H O exit loss (lengt) V d veloity of outfall annel V veloity just inside end of ulvert barrel (lengt/time) g gravitational onstant (lengt/time ) V g Wen disarge is negligible, exit loss equal to barrel veloity ead. Typially solved using gradually-varied flow analysis. 6

7 Culvert Hydraulis: Inlet Control Wen operating under inlet ontrol, ydrauli ontrol setion is ulvert entrane. Typially, te frition and minor losses in te ulvert are not as signifiant. Critial dept normally ours at or near te inlet, and flow downstream of te inlet are superritial. Tree types of inlet ontrol: For low disarge onditions, te ulvert entrane ats as a weir. Wen te ulvert is fully submerged, te inlet operates as an orifie. Transitional Region just above te unsubmerged zone and below te fully submerged zone. Culvert Hydraulis: Inlet Control Flow Two equations possible (typial to use te nd one for and als). : HW H Q A i 0. 5 S : HW Q 0. 5 A Were HW i eadwater dept above te ontrol setion invert (lengt) interior eigt of ulvert barrel (lengt) itered inlets: H speifi ead at ritial dept, y V /g (lengt/time) use slope Q ulvert disarge (lengt 3 /time) orretion fator A full ross-setional area of te ulvert barrel (lengt ) of 0.7S instead S ulvert barrel slope of -S, onstants from table Culvert Hydraulis: Inlet Control Culvert Hydraulis: Inlet Control Flow for submerged (orifie) flow: HW Q i 0. A 5 S itered inlets: use slope orretion fator of 0.7S instead of -S Were HW i eadwater dept above te ontrol setion invert (lengt) interior eigt of ulvert barrel (lengt) H speifi ead at ritial dept, y V /g (lengt/time) Q ulvert disarge (lengt 3 /time) A full ross-setional area of te ulvert barrel (lengt ) S ulvert barrel slope, onstants from table, onstants from table for submerged flow appliable wen Q/A i

8 Sape and aterial Cirular Conrete Cirular CP Cirular Sape and aterial Box Box, ¾ Camfers Coeffiients for Inlet Control esign Inlet Edge esription Square edge wit eadwall Groove end wit eadwall Groove end projeting Headwall itered to slope Projeting Beveled ring, 45 o bevels Beveled ring, 33.7 o bevels Coeffiients for Inlet Control esign Inlet Edge esription ¾ amfers, 45 o skewed eadwall ¾ amfers, 30 o skewed eadwall ¾ amfers, 5 o skewed eadwall 45 o bevels; 0 o -45 o skewed eadwall 45 o non-offset wingwall flares 8.4 o non-offset wingwall flares 8.4 o non-offset wingwall flares, 30 o skewed barrel Sape and aterial Box Box Box Sape and aterial Box, Top Bevels C Boxes Horizontal Ellipse Conrete Coeffiients for Inlet Control esign Inlet Edge esription 30 o to 75 o wingwall flares o and 5 o wingwall flares 0 o wingwall flares 45 o wingwall flares d o to 33.7o wingwall flare d o eadwall wit ¾ amfers 90 o eadwall wit 45 o bevels 90 o eadwall wit 33.7 o bevels Coeffiients for Inlet Control esign Inlet Edge esription 45 o wingwall flares offset 33.7 o wingwall flares offset 8.4 o wingwall flares offset 90 o eadwall Tik wall projeting Tin wall projeting Square edge wit eadwall Groove end wit eadwall Groove end projeting

9 Sape and aterial Vertial Ellipse Conrete Pipe Ar 8 Corner Radius C Pipe Ar 8 Corner Radius C Sape and aterial Elliptial Inlet Fae Conrete Conrete Coeffiients for Inlet Control esign Inlet Edge esription Square edge wit eadwall Groove end wit eadwall Groove end projeting o eadwall itered to slope Projeting Projeting No bevels o bevels Coeffiients for Inlet Control esign Inlet Edge esription Tapered inlet - beveled edges Tapered inlet - square edges Tapered inlet tin edge projeting Tapered inlet troat Side tapered less favorable design Side tapered more favorable design Slope tapered less favorable design Slope tapered more favorable design Coeffiients for Inlet Control esign Sape and aterial Pipe Ar 3 Corner Radius C Inlet Edge esription Projeting No bevels 33.7 o bevels Ar C 90o eadwall itered to slope Tin wall projeting Cirular Smoot tapered inlet troat Roug tapered inlet troat Hydrauli Operation of Culverts: Simplified Hydraulis of ulverts an be lassified into four ategories:. inlet and outlet. inlet wit full flow but free disarge at te outlet 3. inlet wit partially full pipe flow 4. inlet 9

10 Hydrauli Operation of Culverts: Simplified Culvert Operation: Inlet and Outlet for eadloss in tis ulvert type in a irular ulvert: gn 8Q k e 4/3 4 R π g Were Q disarge diameter R ydrauli radius of te ulvert barrel ( /4 for full-flowing barrel) Culvert Operation: Inlet and Outlet Culvert disarge is primarily affeted by tailwater elevation (TW) and te ead loss of te ulvert (regardless of ulvert slope). Culvert flow an be treated as pressure pipe flow. Headloss is sum of ulvert ead loss and exit and entrane losses. for eadloss in tis ulvert: k e V g n R V Entrane oeffiient, k e, approximately for a squareedged entrane and 0. for a well-rounded entrane. anning s n: n 0.03 for onrete; n 0.04 for orrugated metal pipe. 4/3 V g Culvert Operation: Inlet wit Free Outlet isarge If te disarge arried in a ulvert as a normal dept larger tan te barrel eigt, te ulvert will flow full even if te tail water level drops below tat of te outlet. isarge is ontrolled by eadloss and level of eadwater. are same as for te submerged inlet and outlet. 0

11 Culvert Operation: Inlet wit Partially Full Pipe Flow If te normal dept is less tan te barrel eigt, wit te inlet submerged and free disarge at te outlet, a partially full pipe flow ondition will normally result. Te ulvert disarge is ontrolled by te entrane onditions (ead water, barrel area, and edge onditions), and te flow is under entrane ontrol. isarge alulated by te orifie equation: Q C d A g Were ydrostati ead above te enter of te pipe opening A ross-setional area C d oeffiient of disarge (C d 0.6 for squareedged entrane and C d.0 for well-rounded entrane) Culvert Hydraulis: Example A orrugated steel pipe is used as a ulvert tat must arry a flow rate of 5.3 m 3 /se and disarge into te air. At te entrane, te maximum available ead water is 3. m above te ulvert invert. Te ulvert is 35 m long and as a square-edged entrane and slope of etermine te diameter of te pipe. Culvert Operation: Inlet Wen te ydrostati ead at te entrane is less tan., air will break into te barrel. No longer pressure pipe flow. Culvert slope and barrel wall frition will ditate flow. ue to a sudden redution of water area at entrane, flow usually enters te ulvert in superritial ondition. Critial dept takes plae at te entrane of te barrel. If frition is suffiient, dept of flowing water inreases. epending on tailwater elevation, superritial flow may onvert to subritial flow troug ydrauli jump. Water surfae profile alulated using gradually-varied flow equations. Culvert Hydraulis: Example Of te four types of ulvert ydraulis, determine te type. Not unsubmerged inlet. Not submerged outlet. Cek for submerged inlet wit partially full flow and pressurized pipe flow. Assume full pipe flow: H 3. k e gn R g S o 4/3 (0.003)(35 (0.04) ( / 4) π 4/3 8 m (35 ) Q g m ) (5.3 π m 3 / g se) 4

12 Culvert Hydraulis: Example Assume full pipe flow: m.4 m g (0.04) ( / 4).5.5 4/3.3 4 (35m ) 4/3 8(5.3 m π 3 /se) 4 g Culvert Hydraulis: Example Assume partially full pipe flow: isarge ontrolled by entrane ondition only. Orifie ula (and substituting for ): Q C d 5.3 m 3 / A.4 se m g (0.6) π 4 g 3. Resistane to flow in te pipe limits te flow. Terefore, use te diameter alulated wit tis assumption (submerged inlet and full pipe flow)..4 m Culvert Hydraulis: Example Assume partially full pipe flow: isarge ontrolled by entrane ondition only. Head is measured above enterline of pipe m Summary of Culvert Flow Conditions: Prasun 987

The Basics of Culvert and Inlet Design

PDHonline Course C619 (8 PDH) The Basics of Culvert and Inlet Design Jerry D. Morrow, PE 2013 PDH Online PDH Center 5272 Meadow Estates Drive Fairfax, VA 22030 6658 Phone & Fax: 703 988 0088 www.pdhonline.org