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<br />
<br />34
<br />
<br />TECHNIQUES OF WATER-RESOU~ES INVESTIGATIONS
<br />
<br /> 1.60 1.00 I -1- _
<br /> 0,96,_ ,
<br /> - /~ ,- ~ l---1
<br /> .;- 1 -t-
<br /> ~ 0,88
<br /> 0: 1.40 l' IJD
<br /> 0 0,84
<br /> t- - "r "So
<br /> (J
<br /> " 0,80
<br /> .. 1.20 -->-- Datum
<br /> Z ,76
<br /> 0
<br /> i=
<br /> (J 1.00 ---
<br /> UJ ,,~ 0:
<br /> 0:
<br /> 0: ,--, --,---
<br /> 0 ;:s
<br /> (J
<br /> 0,80 I 3
<br /> ~3~ ~4~~ ............ ---I 2
<br /> 0,60 1
<br /> 0 1 2 ......---
<br />l~ 10 ~\,oO 1 0
<br /> 29n2l
<br />00 9 Ro, ......- 9
<br />.::s t---
<br />0 8 ,// 8
<br />i=
<br />" 7 // ---- 7
<br />0:
<br />UJ 6 - -,- ------, 6
<br />'" ./
<br />0: 5 u__ ,+-- -- ---- ---- --,- 5
<br />"
<br />:I: ./
<br />(J 4
<br />Vl / 4
<br />0 3 , I' 3
<br /> ~
<br /> 1.0 1.5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 -_
<br /> hi
<br /> -15-
<br />
<br />Figure 17,-Relation bdween head and discharge for type 6 flow.
<br />
<br />gradient upstream to the headwater ele-
<br />vation using the computed discharge. If
<br />the computed and known elevation there
<br />do not agree, 8.S8ume another critical depth
<br />and rapea t the procedure.
<br />2. For types 3 and 4 flow (flow with backwater),
<br />the discharge is assumed. Then starting
<br />with the known tailwater elevation, the
<br />ener!(y !(radient is routed upstream to the
<br />headwater elevation. If the computed
<br />headwater elevation differs from that
<br />known, repeat the computations using
<br />other assumed discharges until agree-
<br />ment is reaehed.
<br />~, For type 5 flow (flow under high head), the
<br />controlling feature is the entrance geom-
<br />etry. The routing procedure cannot be
<br />applied here.
<br />4. For type 6 flow (flow under high head), the
<br />same procedure is followed as for type 3,
<br />except that the starting point for the pie-
<br />
<br />zometric head (h,) must be estimated in
<br />some manner. In type 6 flow, h, is not
<br />measured to the water surface.
<br />(1) For box culverts the line of piezometric
<br />head at the outlet may be considered
<br />to lie sli!(htly below the centerline
<br />for high Froude numbers, gradually
<br />increasing to a level about halfway
<br />between centerline and top 01 barrel
<br />for a Froude number approachin~
<br />unity. An average h, of O.65D may
<br />be used for the range of Froude num-
<br />bers ordinarily encountered in cul-
<br />vert flow in the field.
<br />(2) For pipe culverts of circular section it
<br />is known that the piezometric head
<br />usually lies between o.5D and 1.0D,
<br />An average h, of 0.75D may be used
<br />for the range of Froude numbers
<br />ordinarily encoun tcred under field
<br />conditions, A more exact value, based
<br />
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