382:
the reservoir – the upper part and the lower part – the upper part gets filled with sand and coarse sediments and the lower part, which is the deep river channel, gets deposited with fine sediment on its terraces which needs to be flushed by reservoir operation (a high concentration of sediments was noted near the power intake). However, for seven years after the project was commissioned, the reservoir was not desilted, which resulted in trapping of 82% of the sediment inflow into the reservoir and which moved towards the body of the dam and interfered with diversion of flow through the power intake in the body of the dam for power generation. The dam is provided with one scouring sluice at the bottom in the main river channel adjacent to the intake screen of the power intake that draws water for power generation. To keep the reservoir in a serviceable condition to derive planned power benefits, it became obligatory to drain the reservoir to its lowest level (though it caused an inevitable economic loss in power generation during the filling stage every year) and flush the deposited sediments downstream so that the intake does not get choked and allows sediment flow into the turbines. The first flushing operation was carried out in three well defined stages in 1973 and thereafter repeated every year till 1990. The downstream impact on the river regime as a result of the silt flushed from the reservoir was also studied when a peak concentration of 400 grams/litre were noted in the form of turbid water not only on the flood plains but also where the river merged with the
Atlantic Sea. It was expected that these deposits would be flushed during the flood season. However, as a result of the silt flushing, some detrimental effect on the
323:; out of this, the reservoir created by the Cachi Dam intercepts the upper catchment area of 919 square kilometres (355 sq mi). The annual precipitation in the entire river basin varies from 1,200 to 8,000 millimetres (47 to 315 in). In 80% of the total catchment area, the relief varies distinctly, with mountains which have slopes between 20 and 85 degrees. The average annual water inflow into the reservoir is at the rate of 104 cubic metres per second (3,700 cu ft/s). The gross storage capacity of the reservoir is 51 million m (1.8 billion cu ft). The design flood discharge is 3,500 cubic metres (120,000 cu ft)/sec. The reservoir has a water spread of 324 hectares (800 acres) which stretches over a length of 6 kilometres (3.7 mi) with maximum water depth of 69 metres (226 ft). Sixty percent of the reservoir's catchment is forested, the remainder is agricultural land. Density currents are formed in the reservoir on account of a combination of temperature gradients and high sediment concentration.
49:
390:
dam to flush the sediment deposits in the reservoir are effective given the "duration and degree to which the reservoir is drawn down and on the discharge capacity of the sluices" and also the shape of the reservoir, which in the case of Cachi is in a narrow gorge. Studies indicated that the average diameter of the sediments deposited in the reservoir was of the order of 0.04 mm. It was also noted that on the terraces of the reservoir flushing was not very effective since they were covered with
332:
356:
units of 34 MW (which would also operate under overload conditions) capacity. They are of vertical type
Francis Turbine units which are designed to operate under heads varying between a maximum of 246 metres (807 ft) and a minimum of 221 metres (725 ft). The first two units of the power plant were commissioned in 1966 and 1967, the third in 1978. The project was implemented with soft loan funding provided by the
955:
56:
398:
The Cachí reservoir is now flushed of sediment deposits on an almost yearly basis. The field studies on the flushing operation carried out in 1996 indicated that about 250,000 tonnes were deposited within the reach between 10 kilometres (6.2 mi) and 30 kilometres (19 mi) downstream from the
381:
deposits (flushed through low level sluice provided in the body of the dam), 21% getting deposited on the terraces, 18% flowing out through the spillway by gate operation and power intake through turbines and 7% trapped as bed load in the reservoir. This process is witnessed in two distinct parts of
346:
The project was planned, designed and executed by ICE, with support for the design of the arch dam, and for supervision of construction provided by Dr. Laginha
Serafim, the Portuguese consultants. The construction of the arch dam was undertaken after extensive explorations of the geological features
318:
as it flows in from the northeast winding through the steep-sided valley. The river has a total drainage area of 3,000 square kilometres (1,200 sq mi) in an elevation range varying from 3,432 metres (11,260 ft) above mean sea level at its highest point to the lowest outflow point into
338:
The Cachi dam is a thin double-arch concrete structure (stated to be one of the thinnest such dams in the world)) built to a height of 80 metres (260 ft) above the deepest foundation. It is located in a narrow gorge and has a crest length of 70 metres (230 ft), impounding 51 million cubic
389:
The effectiveness of the flushing operations has been studied over the years by hydrographic surveys of the reservoir using turbidimeters, side scan sonar, sub-bottom profiler, repeated echo sounding, sediment coring and X-ray techniques. The studies have indicated that the sluices provided in the
355:
The water from the reservoir is diverted through a 5,942-metre (19,495 ft) long pressure tunnel, a surge tank, a 566-metre (1,857 ft) long penstock including a 116-metre (381 ft) long pressure shaft (steel-lined tunnel) and a power house. The power house has an installation of three
286:
provides multiple benefits through the three dams built on it. Out of the three dams, Cachi Dam, not only provides power generation benefits but also controls floods, and offers recreational facilities in the Lake Cachi. The Rio Macho project on the upstream provides hydroelectric power and the
363:
The output of the hydroelectric power plant at Cachí will increase from 100 megawatts to 160 MW. The expansion of the power plant will include a new 40 MW generator. An existing generator will also be upgraded. The work is scheduled to begin in 2012. The project should be finished by 2015,
407:
The dam takes advantage of the head available in the river, which for some 65 kilometres (40 mi) creates white water suitable for rafting. Surrounded by mountains, the lake was created when the
Instituto Costariccense de Electricidad built the dam across the river to supply
364:
according to the Costa Rican
Electricity Institute (ICE). Once expanded, the Cachí power plant will be able to supply the electricity needs of 330,000 people. The project is being funded by a $ 140 million loan from the Central American Bank for Economic Integration (CABEI).
343:, the dam did not suffer any damage even though the epicentre was 86 kilometres (53 mi) away from the dam. However, there was a temporary suspension of power generation at the powerhouse located 12 kilometres (7.5 mi) away, due to dislocation of the transformers.
347:
confirmed the suitability of the site. During construction, two diversion tunnels with gated controls, designed for a discharge of 600 cubic metres (21,000 cu ft)/sec were constructed to divert water away from the work site of the dam foundation.
367:
Power evacuation from the switch yard of the power station was planned with step-up substation equipped with three-phase step-up transformers and evacuated through double circuit 132 kV transmission lines connecting Cachi with the Rio Macho power plant.
33:
394:
which had trapped the sediments. The old river channel also had indicated a deposit rate of about 2 metres (6 ft 7 in), which, however, is now regularly flushed out by opening the scouring sluice.
376:
The annual sediment load into the Cachi reservoir estimated at 0.81 million tons, which amounts to 1% storage volume of the reservoir, had been assessed at the planning stage to be distributed at 54% as
784:
1010:
928:
611:
759:
290:
The reservoir, in the Rio
Reventazón, is an important supplier of electrical power to Costa Rica. It is operated by Instituto Costarricense de Electricidad (ICE).
636:
48:
788:
834:
Brandt, S. Anders; Swenning, Joar (1999). "Sedimentological and
Geomorphological Effects of Reservoir Flushing: The Cachí Reservoir, Costa Rica, 1996".
1000:
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projects in Costa Rica. It has an installed capacity of 102 MW with three units of 34 MW capacity each (Vertical
Francis turbines).
95:
682:
559:
503:
438:
582:
995:
914:
282:
The project became operational with the first unit commissioned in 1966, the second unit in 1967, and the third unit in 1978. The
466:
964:
1005:
643:
287:
downstream Birris power project also provides drinking water (40% of the metropolitan city’s water supply needs).
969:
260:
409:
307:
340:
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331:
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264:
137:
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672:
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was noted by local people of the area in the downstream reaches of the river below the dam.
315:
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283:
268:
244:
158:
144:
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dam. Of these, 82% were channel-bed deposits while 18% were deposited on the river banks.
391:
383:
320:
176:
166:
989:
847:
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127:
275:, away from the east bank of the lake. Built in the 1970s, it was one of the first
470:
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730:
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32:
906:
357:
252:
81:
110:
97:
885:
705:
812:
526:
378:
303:
138:
152:
910:
760:"Appraisal Of Power And Telecommunications Projects Costa Rica"
937:
706:"Turbidity currents in Cachi Hydropower Reservoir, Costa Rica"
495:
Human security and the environment: international comparisons
314:
in the
Ujarras valley. The lake is created by the dam on the
330:
302:) in the northeastern part of the lake, near the village of
548:
Miranda, Carolina A.; Penland, Paige R. (1 November 2004).
725:
723:
527:"The Cachí Reservoir:Investigation of Flushing Efficiency"
339:
metres of inflows of the
Reventazon River. During the
642:. desastres.unanleon. pp. 94–95. Archived from
230:
222:
214:
206:
198:
190:
186:
175:
165:
150:
136:
126:
87:
77:
21:
226:51 million cubic metres (41,000 acre⋅ft)
55:
836:Geografiska Annaler: Series A, Physical Geography
612:"Appraisal of the Fifth Power Project Costa Rica"
88:
922:
218:80 metres (260 ft) to deepest foundation
8:
1011:Buildings and structures in Cartago Province
765:. Worldbank.org. 18 June 1963. pp. 5–10
666:
664:
606:
604:
171:919 square kilometres (355 sq mi)
929:
915:
907:
498:. Edward Elgar Publishing. pp. 269–.
433:. Fodor's. 12 September 2000. p. 58.
18:
807:
805:
754:
752:
750:
674:Evacuation of sediments from reservoirs
631:
629:
461:
459:
457:
420:
7:
677:. Thomas Telford. pp. 197–200.
492:Edward Page; M. R. Redclift (2002).
467:"Hydroelectric Plants in Costa Rica"
813:"The Cachí reservoir in Costa Rica"
360:in two stages after due appraisal.
298:Lake Cachi contains the Cachí Dam (
251:) is an artificial lake in central
866:. Lonely Planet Publications. 2004
16:Artificial reservoir in Costa Rica
14:
708:. NTNU –Institute for Vasshygging
953:
848:10.1111/j.0435-3676.1999.00069.x
54:
47:
31:
585:. cafevolio.com. Archived from
583:"Cachí" Dam ¬ Cartago Province"
229:
221:
213:
205:
197:
189:
554:. Lonely Planet. p. 149.
1:
1001:Geography of Cartago Province
671:Rodney White (January 2001).
469:. industcards. Archived from
310:in the middle reaches of the
76:
614:. Worldbank.org. 21 May 1975
263:, to the east-southeast of
1027:
412:with hydroelectric power.
255:created by the Cachí Dam (
234:970 metres (3,180 ft)
948:
42:
30:
996:Reservoirs in Costa Rica
863:Lonely Planet Costa Rica
259:), an arch dam north of
202:324 hectares (800 acres)
732:Engineering news-record
430:Fodor's Costa Rica 2001
210:69 metres (226 ft)
194:70 metres (230 ft)
335:
248:
890:coastsmountainscr.com
372:Sedimentation studies
341:1991 Limon earthquake
334:
261:Tapantí National Park
892:. Cartago,Costa Rica
886:"Lakes Destinations"
132:Artificial reservoir
111:9.82722°N 83.81667°W
735:. McGraw-Hill. 1967
271:. The main town is
161:into Atlantic Ocean
107: /
1006:Dams in Costa Rica
336:
116:9.82722; -83.81667
37:View of Lake Cachi
983:
982:
684:978-0-7277-2953-8
649:on 1 October 2011
561:978-1-74059-775-3
529:. Hydroconulst.se
505:978-1-84064-458-6
440:978-0-679-00542-1
238:
237:
231:Surface elevation
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942:Reventazón River
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787:. Archived from
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316:Reventazon River
312:Reventazon River
284:Reventazon River
269:Cartago Province
257:Represa de Cachí
159:Reventazon River
154:
153:Primary outflows
145:Reventazon River
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473:on 19 July 2009
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392:water hyacinths
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300:Represa de Cach
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179: countries
139:Primary inflows
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65:Represa de Cach
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25:Represa de Cach
24:
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842:(3): 391–407.
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815:. homeswipenet
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327:Cachi arch dam
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321:Atlantic Ocean
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167:Catchment area
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791:on 2012-02-15
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277:hydroelectric
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249:Lago de Cachí
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207:Average depth
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894:. Retrieved
889:
880:
868:. Retrieved
862:
856:
839:
835:
829:
817:. Retrieved
793:. Retrieved
789:the original
785:"Tico Times"
779:
767:. Retrieved
737:. Retrieved
731:
710:. Retrieved
700:
688:. Retrieved
673:
651:. Retrieved
644:the original
616:. Retrieved
591:. Retrieved
587:the original
577:
565:. Retrieved
550:
543:
531:. Retrieved
521:
509:. Retrieved
494:
487:
475:. Retrieved
471:the original
444:. Retrieved
429:
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375:
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299:
297:
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256:
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239:
223:Water volume
199:Surface area
62:
22:
637:"Lifelines"
351:Power plant
191:Max. length
114: /
89:Coordinates
990:Categories
975:Reventazón
795:2012-02-15
551:Costa Rica
416:References
403:Recreation
358:World Bank
306:along the
253:Costa Rica
241:Lake Cachi
215:Max. depth
182:Costa Rica
82:Costa Rica
63:Lake Cachi
23:Lake Cachi
970:Angostura
294:Geography
102:83°49′0″W
99:9°49′38″N
410:San José
308:225 road
78:Location
965:La Joya
940:on the
896:26 June
870:25 June
819:26 June
769:26 June
739:26 June
712:26 June
690:26 June
653:26 June
618:26 June
593:26 June
567:25 June
533:16 June
511:26 June
477:26 June
446:25 June
379:thalweg
304:Ujarras
265:Cartago
245:Spanish
681:
558:
502:
437:
960:Cachí
763:(PDF)
647:(PDF)
640:(PDF)
384:biota
273:Cachí
177:Basin
938:Dams
898:2011
872:2011
821:2011
771:2011
741:2011
714:2011
692:2011
679:ISBN
655:2011
620:2011
595:2011
569:2011
556:ISBN
535:2011
513:2011
500:ISBN
479:2011
448:2011
435:ISBN
319:the
128:Type
844:doi
267:in
992::
888:.
840:81
838:.
804:^
749:^
722:^
663:^
628:^
603:^
456:^
247::
930:e
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657:.
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597:.
571:.
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481:.
450:.
243:(
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
