347:
17:
418:
1091:
1329:
265:
104:
51:
201:
616:
803:
860:
1098:
1408:
Every dam needs some form of energy dissipation in its discharge structure to prevent erosion and scour on the downstream side of the dam, since these phenomena can result in dam failure. Plunge pools (also called stilling basins) and impact boxes are two examples of energy dissipators used on dams.
358:
could be used to obtain C from H. For a given depth at the spillway crest, the flows calculated using the USBR method are higher than those from the NRCS method because of the higher discharge coefficients. C increases with H under the USBR method, whereas C is assumed to be constant with respect to
384:
is classified as either nappe flow or skimming flow. Nappe flow regimes occur for small discharges and flat slopes. If the discharge is increased or the slope of the channel is increased, a skimming flow regime can occur (Shahheydari et al. 2015). Nappe flow has pockets of air at each step whereas
436:
1399:
When cavitation occurs on a spillway, it can cause severe damage. This is especially true when the velocities exceed 25 m/s. Therefore, protection is needed at these velocities. Cavitation can be prevented by decreasing the flow velocity or by increasing the boundary pressure.
848:
Under a skimming flow regime, water flows in a coherent stream down the step. Water skims the top of each step as it flows down the chute. Recirculating vortices are developed between each step which allow the water to flow over the top of the vortices and skim over each step.
623:
1086:{\displaystyle {\frac {\Delta H}{H_{max}}}=1-{\frac {\left({\frac {f}{8\sin(\alpha )}}\right)^{\frac {1}{3}}\cos(\alpha )+{\frac {1}{2}}\left({\frac {f}{8\sin(\alpha )}}\right)^{-{\frac {2}{3}}}}{{\color {red}{\frac {2}{3}}}+{\frac {H_{dam}}{d_{c}}}}}}
111:
Design guidelines for these spillways are limited. However, research attempts to assist engineers. The two main design components are the inception point (where flow bulking first occurs—increased flow depth) and the energy dissipation that occurs.
1383:
is the formation of a void, such as a bubble, within a liquid. A fluid passes from a liquid state to a vapor state due to a change in the local pressure while the temperature remains constant. In the case of a dam spillway, this can be caused by
1324:{\displaystyle {\frac {\Delta H}{H_{max}}}=1-{\frac {\left({\frac {f}{8\sin(\alpha )}}\right)^{\frac {1}{3}}\cos(\alpha )+{\frac {1}{2}}\left({\frac {f}{8\sin(\alpha )}}\right)^{-{\frac {2}{3}}}}{\frac {H_{dam}+{\color {red}{H_{0}}}}{d_{c}}}}}
1395:
Cavitation occurs within the body of flow of a given distributed roughness. However, the exact location where it will occur cannot be predicted. In the case of chute spillways, cavitation occurs at velocities between 12 and 15 m/s.
1687:
11. Shahheydari, H., Nodoshan, E. J., Barati, R., & Moghadam, M. A. (2015). Discharge coefficient and energy dissipation over stepped spillway under skimming flow regime. KSCE Journal of Civil
Engineering, 19(4), 1174-1182.
67:
through the steep slope of an open channel. There are four main components of a chute spillway: The elements of a spillway are the inlet, the vertical curve section (ogee curve), the steep-sloped channel and the outlet.
217:
The coefficient, 3.1 varies for different entrance conditions. The value of the coefficient is slightly higher if the conveyance channel has a greater width than the inlet. The value 3.1 is based on the assumption that
1412:
Many USBR dams use energy dissipating blocks for chute spillways (also called baffled aprons). These blocks help induce a hydraulic jump to establish subcritical flow conditions on the downstream side of the dam.
611:{\displaystyle {\frac {\Delta H}{H_{max}}}=1-{\frac {0.54\left({\frac {d_{c}}{h}}\right)^{0.275}+1.715\left({\frac {d_{c}}{h}}\right)^{-0.55}}{{\color {red}{\frac {2}{3}}}+{\frac {H_{dam}}{d_{c}}}}}}
1678:
Peterka, A.J. (1984 (Eighth
Printing)). Hydraulic Design of Stilling Basins and Energy Dissipators (Engineering Monograph No. 25). United States Department of the Interior – Bureau of Reclamation.
134:
Side channel spillways are typically used to discharge floods perpendicular to the general direction of flow by placing the control weir parallel to the upper portion of the discharge channel.
798:{\displaystyle {\frac {\Delta H}{H_{max}}}=1-{\frac {0.54\left({\frac {d_{c}}{h}}\right)^{0.275}+1.715\left({\frac {d_{c}}{h}}\right)^{-0.55}}{\frac {H_{dam}+{\color {red}{H_{0}}}}{d_{c}}}}}
1524:
78:
Proper spillways help with flood control, prevent erosion at the ends of terraces, outlets, and waterways, reduce runoff over drainage ditch banks and are simple to construct.
152:
produced handbooks on dam design. In the
National Engineering Handbook, Section 14, Chute Spillways (NEH14), flow equations are given for straight inlets and box inlets.
372:
The flow coming into the spillway is subcritical. The slope of the chute causes the flow velocity to increase. Typically, supercritical flow is maintained in the chute.
1416:
The steps on stepped spillways can be used for energy dissipation. However, they tend to be effective only at dissipating energy at low flows (i.e. skimming flow).
42:. They can function as principal spillways, emergency spillways, or both. They can be located on the dam itself or on a natural grade in the vicinity of the dam.
81:
However, they can only be constructed at sites with natural drainage and moderate temperature variation and have a shorter life expectancy than other spillways.
126:
However, few design guidelines are in place and stepped spillways have only been successful for small unit discharges where step height can influence the flow.
155:
NEH14 provides the following discharge-head relationship for straight inlets of chute spillways, which is given by the flow equation for a weir:
1562:
249:(In this case, freeboard is the vertical distance from the water surface to the dam crest when the water surface is at a lower elevation.)
354:
For the NRCS computations, the mean velocity of approach was assumed to be zero. For the USBR computations, it was assumed that linear
430:
For the nappe flow regime, a partially or fully developed hydraulic jump occurs as a result of the jets created between each step.
346:
148:
Different agencies have different methods and formulas for quantifying flows and conveyance capacities for chute spillways. The
149:
273:
100:
stepped spillways have become increasingly popular because of their use in rehabilitating aged flood control dams.
16:
1477:
1455:
1705:
181:= specific energy head in reference to the crest of the inlet, or the head over the crest of the inlet (ft)
1669:^ Kells, J.A. Smith, C.D. (1991). Canadian Journal of Civil Engineering, 1991, 18:358-377, 10.1139/l91-047
92:
are used to dissipate energy along the chute of the channel. The steps of the spillway greatly reduce the
1657:
Chanson, H. Design of
Spillway Aeration Devices to prevent Cavitation Damage on Chutes and Spillways.
1569:
120:
97:
119:
levels downstream of a dam, aid wastewater treatment plants for air-water transfer of gases and for
1503:
1568:(3rd ed.). United States Department of the Interior – Bureau of Reclamation. Archived from
1478:"Energy Dissipation on Flat-Sloped Stepped Spillways: Part 2. Downstream of the Inception Point"
276:
also uses the weir formula to quantify flow over a chute spillway. The USBR flow equation is:
1679:
1593:"Comparison of energy dissipation between nappe and skimming flow regimes on stepped chutes"
1592:
1546:
208:
If the flow rate per unit width is defined as q = Q/W, then the equation can be written as:
8:
343:
Example: For a spillway crest length/width of 25 ft, Q will vary with H as follows:
140:
However, it can cause a sudden increase in reservoir level if the channel is submerged.
1700:
75:, the slope of the spillway must be steep enough for the flow to remain supercritical.
64:
1658:
1481:
116:
35:
1638:
1611:
1607:
1435:
381:
292:
H = elevation difference between the reservoir water surface and the spillway crest
89:
417:
1520:
1504:"Hydraulics of Stepped Spillways for RCC Dams and Dam Rehabilitations. PAP-596"
1480:. American Society of Agricultural and Biological Engineers. pp. 111–118.
123:
removal and reduces the spillway length or eliminates need for stilling basin.
93:
72:
1694:
1485:
355:
350:
Discharge as a function of water surface elevation for NRCS and USBR formulas
1545:
United States
Department of Agriculture – Soil Conservation Service (1985).
1525:"Historical Development of Side-Channel Spillway in Hydraulic Engineering"
39:
229:
NEH14 also provides the following relationship for side channel inlets:
1385:
1380:
1462:. United States Department of Agriculture – Soil Conservation Service.
385:
skimming flow does not. The onset of skimming flow can be defined as:
226:
are measured at a location that exhibits subcritical flow conditions.
264:
1643:
1626:
1509:. United States Department of the Interior – Bureau of Reclamation.
1430:
188:= mean velocity of approach at which the depth H is measured (ft/s)
103:
31:
200:
50:
1389:
137:
It offers low flow velocities upstream and minimizes erosion.
174:
H = depth of flow over the crest (or floor) of the inlet (ft)
115:
Stepped spillways are useful for flood control, increasing
1425:
255:
H = height of the sidewalls above the spillway crest (ft)
28:
1680:
http://www.usbr.gov/pmts/hydraulics_lab/pubs/EM/EM25.pdf
413:= the critical depth of the onset of skimming flow (m)
1348:= free surface elevation above the spillway crest (m)
1101:
863:
822:= free surface elevation above the spillway crest (m)
626:
439:
1659:
http://staff.civil.uq.edu.au/h.chanson/aer_dev.html
295:
C = discharge coefficient, which varies as follows:
20:
Spillway channel example at the Colt Crag
Reservoir
1323:
1085:
797:
610:
1692:
96:of the flow and therefore reduce flow velocity.
38:to convey impounded water in order to prevent
1341:= dam crest head above the downstream toe (m)
815:= dam crest head above the downstream toe (m)
247:= discharge capacity without freeboard (ft/s)
150:Natural Resources Conservation Service (NRCS)
1624:
1519:
1625:Chatila, Jean G.; Jurdi, Bassam R. (2004).
1627:"Stepped Spillway as an Energy Dissipater"
1560:
1475:
274:United States Bureau of Reclamation (USBR)
1642:
289:L = spillway crest length (or width) (ft)
129:
1471:
1469:
416:
345:
263:
199:
102:
49:
15:
1590:
1586:
1584:
1582:
1497:
1495:
1403:
843:
1693:
1551:, Section 14, Chute Spillways (NEH14).
1541:
1539:
1537:
1466:
1453:
1447:
852:
259:
252:L = length of the spillway crest (ft)
1579:
1492:
171:W = width of the chute or inlet (ft)
84:
1561:Blair, H. K.; Rhone, T. J. (1987).
1534:
1501:
375:
13:
1105:
867:
630:
443:
367:
14:
1717:
1476:Hunt, S.L.; Kadavy, K.C. (2010).
1292:
1034:
766:
559:
195:
58:
45:
1631:Canadian Water Resources Journal
421:Image of nappe and skimming flow
1672:
1663:
362:
121:volatile organic compound (VOC)
98:Roller-compacted concrete (RCC)
34:that utilize the principles of
1651:
1618:
1612:10.1080/00221686.1994.10750036
1554:
1513:
1243:
1237:
1201:
1195:
1168:
1162:
1005:
999:
963:
957:
930:
924:
1:
1600:Journal of Hydraulic Research
1441:
1375:
425:
168:Q = discharge of inlet (ft/s)
143:
1355:= maximum head available (m)
7:
1419:
10:
1722:
1362:= critical flow depth (m)
359:H under the NRCS method.
1591:Chanson, Hubert (1994).
1460:Engineering Field Manual
1563:"Design of Small Dams"
1530:. Brisbane, Australia.
1523:; Phister, M. (2011).
1325:
1087:
799:
612:
422:
392:)=1.057*h - 0.465*h/l
351:
269:
205:
130:Side channel spillways
108:
63:Chute spillways carry
55:
25:Open channel spillways
21:
1326:
1088:
836:= critical flow depth
800:
613:
420:
349:
267:
203:
117:dissolved oxygen (DO)
106:
53:
19:
1706:Hydraulic structures
1548:Engineering Handbook
1099:
861:
844:Skimming flow regime
624:
437:
211:q = Q/W = 3.1 = 3.1H
71:In order to avoid a
1368:f = friction factor
857:Un-gated spillway:
402:l = step length (m)
399:h = step height (m)
191:g = 32.16 ft/s
1404:Energy dissipation
1392:in flowing water.
1371:α = channel slope
1321:
1305:
1083:
1045:
853:Energy dissipation
795:
779:
608:
570:
433:Ungated spillway:
423:
352:
302:For H = 1 ft
270:
268:Side channel inlet
260:Side channel inlet
206:
109:
65:supercritical flow
56:
22:
1365:H = head loss (m)
1319:
1318:
1265:
1247:
1215:
1186:
1172:
1128:
1081:
1078:
1043:
1027:
1009:
977:
948:
934:
890:
839:H = head loss (m)
793:
792:
728:
690:
653:
606:
603:
568:
541:
503:
466:
341:
340:
90:Stepped spillways
85:Stepped spillways
36:open-channel flow
1713:
1682:
1676:
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1517:
1511:
1510:
1508:
1499:
1490:
1489:
1473:
1464:
1463:
1454:Beauchamp, K.H.
1451:
1436:Stepped spillway
1330:
1328:
1327:
1322:
1320:
1317:
1316:
1307:
1306:
1304:
1303:
1302:
1287:
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1270:
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1267:
1266:
1258:
1252:
1248:
1246:
1223:
1216:
1208:
1188:
1187:
1179:
1177:
1173:
1171:
1148:
1140:
1129:
1127:
1126:
1111:
1103:
1095:Gated spillway:
1092:
1090:
1089:
1084:
1082:
1080:
1079:
1077:
1076:
1067:
1066:
1051:
1046:
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950:
949:
941:
939:
935:
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910:
902:
891:
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888:
873:
865:
829:= total head (m)
804:
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685:
676:
665:
654:
652:
651:
636:
628:
620:Gated spillway:
617:
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607:
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604:
602:
601:
592:
591:
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571:
569:
561:
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537:
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527:
514:
513:
508:
504:
499:
498:
489:
478:
467:
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464:
449:
441:
382:stepped spillway
380:The flow over a
376:Stepped spillway
299:
298:
107:Stepped spillway
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1644:10.4296/cwrj147
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989:
984:
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979:
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905:
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878:
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828:
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408:
391:
378:
370:
368:Chute spillways
365:
286:Q = flow (ft/s)
280:
262:
248:
246:
237:
235:
225:
221:
215:
214:
198:
187:
180:
162:
161:
158:Q = 3.1W = 3.1H
146:
132:
87:
61:
48:
12:
11:
5:
1719:
1709:
1708:
1703:
1684:
1683:
1671:
1662:
1650:
1637:(3): 147–158.
1617:
1606:(2): 213–218.
1578:
1575:on 2014-02-22.
1553:
1533:
1512:
1502:Frizell, K.H.
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94:kinetic energy
86:
83:
73:hydraulic jump
60:
59:Chute spillway
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54:Chute spillway
47:
46:Spillway types
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3:
2:
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1234:
1231:
1228:
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1204:
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1117:
1113:
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1093:
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1069:
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1021:
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986:
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974:
971:
966:
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945:
942:
936:
927:
921:
918:
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906:
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895:
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879:
875:
870:
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838:
831:
824:
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805:
787:
783:
773:
769:
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747:
738:
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730:
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710:
705:
702:
697:
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687:
682:
678:
672:
667:
661:
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645:
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638:
633:
618:
598:
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582:
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572:
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548:
543:
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533:
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510:
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468:
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431:
419:
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398:
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386:
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373:
360:
357:
356:interpolation
348:
344:
336:
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328:
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309:
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118:
113:
105:
101:
99:
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91:
82:
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69:
66:
52:
43:
41:
37:
33:
30:
26:
18:
1686:
1674:
1665:
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1634:
1630:
1620:
1603:
1599:
1570:the original
1556:
1547:
1515:
1459:
1456:"Structures"
1449:
1415:
1411:
1407:
1398:
1394:
1379:
1332:
1094:
856:
847:
806:
619:
432:
429:
394:
387:
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371:
363:Flow regimes
353:
342:
281:
271:
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216:
207:
163:
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125:
114:
110:
88:
80:
77:
70:
62:
24:
23:
1521:Hager, W.H.
40:dam failure
1695:Categories
1442:References
1386:turbulence
1381:Cavitation
1376:Cavitation
426:Nappe flow
144:Flow rates
1701:Spillways
1486:2151-0032
1255:−
1241:α
1235:
1199:α
1193:
1166:α
1160:
1137:−
1106:Δ
1017:−
1003:α
997:
961:α
955:
928:α
922:
899:−
868:Δ
736:−
662:−
631:Δ
549:−
475:−
444:Δ
32:spillways
1431:Spillway
1420:See also
1390:vortices
305:C = 3.2
1333:where:
807:Where:
395:Where:
282:where:
279:Q = CLH
239:where:
236:= 3.1Lh
164:where:
1484:
1596:(PDF)
1573:(PDF)
1566:(PDF)
1528:(PDF)
1507:(PDF)
706:1.715
698:0.275
519:1.715
511:0.275
411:onset
222:and v
1482:ISSN
739:0.55
668:0.54
552:0.55
481:0.54
337:3.8
329:3.7
321:3.6
313:3.4
272:The
27:are
1639:doi
1608:doi
1426:Dam
1388:or
1353:max
1339:dam
1232:sin
1190:cos
1157:sin
994:sin
952:cos
919:sin
827:max
813:dam
29:dam
1697::
1635:29
1633:.
1629:.
1604:32
1602:.
1598:.
1581:^
1536:^
1494:^
1468:^
1458:.
405:(d
388:(d
334:5
326:4
318:3
310:2
245:mi
234:mi
1647:.
1641::
1614:.
1610::
1488:.
1360:c
1358:d
1351:H
1346:0
1344:H
1337:H
1314:c
1310:d
1300:0
1296:H
1289:+
1284:m
1281:a
1278:d
1274:H
1263:3
1260:2
1250:)
1244:)
1238:(
1229:8
1225:f
1220:(
1213:2
1210:1
1205:+
1202:)
1196:(
1184:3
1181:1
1175:)
1169:)
1163:(
1154:8
1150:f
1145:(
1134:1
1131:=
1124:x
1121:a
1118:m
1114:H
1109:H
1074:c
1070:d
1064:m
1061:a
1058:d
1054:H
1048:+
1041:3
1038:2
1025:3
1022:2
1012:)
1006:)
1000:(
991:8
987:f
982:(
975:2
972:1
967:+
964:)
958:(
946:3
943:1
937:)
931:)
925:(
916:8
912:f
907:(
896:1
893:=
886:x
883:a
880:m
876:H
871:H
834:c
832:d
825:H
820:0
818:H
811:H
788:c
784:d
774:0
770:H
763:+
758:m
755:a
752:d
748:H
731:)
726:h
721:c
717:d
711:(
703:+
693:)
688:h
683:c
679:d
673:(
659:1
656:=
649:x
646:a
643:m
639:H
634:H
599:c
595:d
589:m
586:a
583:d
579:H
573:+
566:3
563:2
544:)
539:h
534:c
530:d
524:(
516:+
506:)
501:h
496:c
492:d
486:(
472:1
469:=
462:x
459:a
456:m
452:H
447:H
409:)
407:c
390:c
243:Q
232:Q
224:a
220:e
218:H
213:e
186:a
184:v
179:e
177:H
160:e
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