Document o9oO4J3R5eQ9X3e3y7XdqMO27

| IA GRANDE DAM. .5 mile* do*nttf*om from Alder It cfett length, 500 It; bate thickness, 145 ft. Atsumir^ JJ4 * essentVohy o diversion lor Vo Grande tunnel. Height, 215 ft; operating rongs, dam form* )060-aCre-h regulating mtnbk 1`AIDER DAM ond powerhouse form largest single unltln Nls- crate structure, 330 ft high, 1500 ft long, (20 ft thick at quallyNo, 3 development. Th* dam, o vorioble-rodiui con- base, forms 0 storage reservoir of 210,000 ocro-ft copoelty Redeveloping Old Hydro Project Ups | Output From 150 to 500 Million Kwhr Duittnc the $4 years that Tacoma. Wash, has operated Ita electric power When Tacoma, Wash, needed mere power it redeveloped its site system, the Capacity has grown 10 238,000 kw. Of this amount, 204,000 kw on Nisqually River by installing 90,000-kw more capacity in ere In four hydroelectric plants, and two plants and adding water storage that more tbon tripled 34.000 kw In two steam plants, the letter being held is cold emergency kwhr generation. Units connect direct to stepup transformers- reserve. Latest additions ore the 40,* 000-kw La Grande end SQ,Q00-kw Alder plants, which are jointly known os Nisqually Mo. 2 power development. The fast generator was placed in op eration Moy 5, 1947. Teeomq's Hydro System. Before conidering this profeet, here's a general picture of the city's hydro system and how U tics into the Northwest power network. Tacoma is fortunately lo cated in regard to hydroelectric power. All four of its plants have been devel oped within a radius of 33 miles from the center of load, which Is one reason why the city enjoys the lowest power rates In the lj. S. This system ties into the Northwest ern power poo] that Includes eleven of the largest private, municipal and fed eral government utilities in the five Northwestern states of Washington, Oregon. Idaho, Montana and Utah. When the generating equipment on or der for this pool is Installed it will hare a capacity of nearly 5,000,000 kw. Surplus energy of ooo system is made available for sole 10 the others, thus reducing the use of high-cost power from fuel-burning plants. At various timet, because of insuf ficient hydroelectric capacity, the city has purchased power for part of its load, which has had a continuous growth, averaging 10% per year. Coat 0/ power bought from other utilities is higher than that produced by the city's awn plants. Purchase (s economical up to a given point, however, because of . the savings in investment and operating costs. Because of continued demands for low-cost power, engineering recom mendations made in 1938 favored ex pansion of the city's hydroelectric ca pacity. Studies o! several sites culmi nated in the selection end jerelopmefii ' of what Is now known ss NisquallT Ns-, 2 power development. Contracts were . let for the construction of this project , in April and June 1942, but because ol the war the first generator did flat p Into service until late in 1946; constme- t/on was completed In April 1947. Tbit addition makes the capacity prsttio- . ally sufficient to supply the city's laid ol 900 million kwhr per year. The site of the new development 1* (hat of the old 24,000-kw U Grande / plant built In 1912, 30 miles southeast ') of Tacoma. This plant has four fiOOO-kv horizoflfal.gha/t units driven bf 800Obp ,- fnaeti turbines operating under a t)5-li head. Redeveloping this alto cbinges La Grande from 0 stream-flow to storage plant otid Increases its out* `pat, ineluding that of tbe Alder units, from 150 kwhr to 500 million kwhr per . year. Alder Dam. As shown In Fig. 3Aeld Ls Grande development included a lew diversion dam ond intake about two .miles up river (ro'm the power plant. .The dam diverted water into a 2-mIlo lonnel and pipeline leading to a tegu. (sting reservoir. From this reservoir . lour penstocks, led to an equal number - f main generating units fn the power . plant and one penstock served tbe two smite units. Fig. 3C. lo the new development. Fig. 3A and B, Alder Dam floods out the old La Grinds diversion dam end forms a , ^servoir ol 210.000 ecre-fl storage caWhy, 0) which 158,300 are usable on W-h drawdown. Maximum normal res- moir elevation is 1200 ft with extreme ferigo flood level el 1207. This dam, the largest jingle unit in tbe project. Is a variable-redius atruo- tore containing 420,000 cu yd of con crete. It is 330 ft high, 1500 ft long, 120 ft thick at its base, and 15 ft thick at the top. Here there is an ll.ft road and walkway. An overflow spillway with (our taintcr gates, each 32 ft long by 23 It high, provides flood protection. Rated 75,000 efs, the spillway haa a capacity equal to three times maximum recorded flood. Alder powerhouse, immediately downstream from (he dam, Fig. 2, 30 and 4, haa two Pelttm 34,500-hp frauds, vertical-shaft turbines designed for a 178- to 273-ft head range. Each con nects to the upstream face of the dam, at center-line elevation 985, by a 10-ftdiameter Mecl penstock. A fi-S-ft river outlet pipe with its upstream center line ot elevation 972.5 also passes through the dam near ita base. Fig. 4. Discharge from this pipe b controlled by a regu lating valve below the downstream face of the powerhouse. Penstocks and out let pipe ere protected bf emergency bulkhead gates and trash racks at the dam's upstream face and each turbine's scroll ease connects to iu penstock by a 10-ft butterfly valve. la Grands Dam. Downstream )J5 miles from Aider, La Crande Dam, Fig. 1 end 3A, is 'essentially a diversion for La Grande tunnel, ft forms a regulat ing reservoir of 1060 acre-fl capacity, assuming 25-(t operating range. This dam, 215 ft high with 500-ft crest length Is 164 (t thick at ita base, 12 ft at its crest and contains 85,000 cu yd of eoncrate. Of gravity design, the dam curves lightly at Its top to converge the water flowing over the spillway to it won't slop over the training walls. Located in the dam's center portion, the-aplUway is controlled by four tainter gates also of 75,000-c/i capacity. A 14.5-ft concrete-lined tunnel, 6500 (l tong, leads from above the dam to the new poweriiouse that forms an ex tension to the old one, Fig. 3A and O. Trash racks operated with traveling hoists protect the tunnel's entrance, and caterpillar gates regulate water flow into it. Near the lower end oi the tunnel a. steel-lined 14.5-ft surge shaft rises 280 ft vertically to a plate-steel differential surge tank, 40 it in diameter and 1133 ft high. This tank is sunk for half its height into the bluff's lop, 400 ft above