~~~~------·· MADISON RIVER_. MONTANA REPORT ON FLOOD ·EMERGENCY MADISON RIVER SLIDE ( .• VOLUME I MAIN REPORT U. S. ARMY ENGINEER DISTRICT-, OMAHA CORPS OF ENGINEER:S OMAHA, NEBRASKA • SEPTEMBER 1960 • .. ~ --·------··-- -------·------ ------- - ----------------- MADISON RIVER, MONTANA REPORT ON FLOOD EMERGENCY MADISON RIVER SLI-DE VOLUME I SEP!'EMBER 1960 PREPARED BY U. s. ARM!' ENGDJEER DISTRICT, GARRISON CORPS OF EIGINEERS RIVERDALE, NOR'l'H DAKO'l'.A EDI'l'ED Aim PUBLISHED BY U. s. ABMI ENGIBEER DISTRICT, OMAHA COBPS OF ENGINEERS OMARA, NEBRASKA MADISOX RIVlm1 IIOIT.ANA :REPORT 01' FLOOD l!MBRGDCY MADISON RIVER SLIDE SEP.riMBER 196o VOLU.ME I - RAm REPORT TABLE OF CONTDTS SUbject Paragraphs P!ges The Earthquake 1- 2 1 Madison River Valley 3 - 5 1-2 Hebgen Dam and Lake 6- 9 2 Madison R1 ver Slide 10- l2 2 - 3 13 - 14 3 Request for Corps Assistance 15 - 16 4 P.re11miD.ary' Investigations 17 - 19 5 Initial Activities 20 - 23 5 - 6 !l.'eehnical studies 24- 30 6- 8 Maps and surveys 31- 32 8 33 - 34 8 B)'draul.ic Design 35 - 36 9 Equip;ant 37 - 38 9- l2 Construction 39 13 Initial Spillway 4o- 45 13 - 14 Maintenance of Initial Spillway 46- 49 14 - 15 Board of Consultants 50 - 53 15 - 16 LcM!riDg the Spillway 54 - 61 16 - 3.8 .Aggradation 62 3.8 Consultants Meeting 63 - 64. 18 - 19 VOLUME I - MAIB REPORT TABLE OF CON1'l5ltrS ( Cont 'd. ) SUbject ParagraE!!s Pages Working Hours 65 19 Materials and StabUity Investigations 66 19 Test Roles 67 20 l~terials in Channel 68 20 MOvement Surveys 69 20 Slll!ID8rY of Explorations 70 20 Possible Additional Slides 71 - 73 21 Communications 74 21 Emergency Warning System 75 - 79 22 HYdrologic Reports 80 23 HYdraulic Studies 81- 82 23 Real Estate 83 - 86 24 Log Boom 87 24 ~rsonnel 88 24 Reports and Public Information 89 - 91 25 Cooperation of Other Agencies 92- 95 25 - 26 Quantities 96- 97 26 Costs 98 27 Conditions Subsequent to Close of Construction Activities 99 - 100 27 Comments 101 - 107 28 (Volume II contains appendixes consisting of detailed technical reports.) (, ( ( ' • ( ... Photo 1. About 2) August 1959. 2 days :following earthquake. USDA - F'orest Service photo. lo The Earthquake.. On 17 August 1959.9 at about llg38 .P•ll•1 one ot the most seve~e earthquakes in the history of the United states atru.ek the Rocky Mountain region in the vicinity of Yellowstone BatiODal. Park. ~e shock was recorded at the University of California Seismological Station at Berkeley, Cali:f'ornia.9 with a magnitude of 7 o5 to 7. 75 on the R;tchter sca.leo Several af'~r-shocks, ranging in magnitude frca 5·5 te 6. 75 on the Richter scale, were recorded at Berkeley in the next 24 hours~ Many more shocks and tremors of lesser and decreasing magnitude were felt in the area. for weeks af'terwardo The epicenter was estimated to be in the southwestern part of Yellowstone National Park. Damage was particularly heavy in the upper Madison River valley in Montana. Nine lives are Qown to have been lost and nineteen other persons known or thought to have been in the area have not been accounted tor, and are presumed to have :perished under the slide at the mouth of the Madison Canyon(! 2o Tb.:ts report covers the activities of the Corps of Engineers, under ·the authority of Public Law 99, 84th Congress, lst Session, in appraising the situatio:n and in removing the hazard to l.ife and the threat of flood d.amage caused by the earthquake o 3 o Madison R1 ver Valleyo 'l!b.e Madison River heads in Yellowstone National Park and flows northwest~ then northward to the vicinity of Three Forks, Montana» where it joinS the Gallatin River on the east and the Jefferson River on the west to form the Missouri Rivero See the general map Plate lo Hebgen Dam~ a water storage project of the Mont&Da Power Company:; is located at the entrance to Madison Canyon in the Madison Mountain RSDge o From the dam, the river flows west about eight miles to the mouth of the canyon, where it begins. curving northward i.nto a broadJI open valleyo Hebgen Lake formed by Rebgen Dam in a wide valley above the canyon~ has a capacity of 345,000 acre-teet. '!he area from the west boundary of Yellowston.e National Park to and in­ cluding the mouth of Madison Canyon is within the boundaries of the GaLlatin National Forest~ 4o Hebgen Lake and the Madison River valley have been very popular with vacationers e The Madison~ River has been known for mrmy years as one of the best trout-fishing streams in the nation., Montana Highway 287 extends :f'rt)Dl its junction with Uo So 191 about eight miles north of West Yellowstone, Montana, along the north shore of Hebgen Lake$ through :Madison Canyon and generally down~ the Madison River to $ junction with Uo So 10 So about ten miles west of' IJ!lree Forks9 Montanao During the summerJ the highway normally is heavy with tourist traffic and many resorts» cabin camps, and campgrounds are operated for the traveling publico Ma.ey vacationers pitch their tents or park their trailers at convenient spots along the river:; particularly in the reach through Madison Canyono 1 5. The Madison River valley below the canyon is devoted largely to stock-raising. Several large ranches and a number of motels and lodges have extensive developments in the flood plain. The town of Ennis, with a population of about 600, and the village of Jeffers, with a population of about 4o, are situated on the flood plain about 40 miles downstream from Madison Canyon. Between Madison Canyon and nu-ee Forks there are ll highway or road bridges, two railroad bridges, and many miles of high­ ways, secondary roads, and railroads. 6. Hebgen Dam and Lake. The earthquake caused major faulting along the right bank of Hebgen Lake and along the mountain slope north of the lake. The right side of the lake dropped several feet and the left shore was . left exposed. It is still uncertain whether the left side of the lake bed was uplifted, or whether the recession of the lake from the shore was a result of the subsidence of the right side. Several sl.ides along t ..he right side of the lake severely damaged the highway. Surveys made by the Coast and Geodetic Survey show that some areas along the right side of Bebgen Lake dropped as much as 19 feet. 7. The disturbance in Hebgen Lake sent a series of water waves, reported to be at least three feet high, over the dam, causing erosion of the downstream slope and toe and putting out of operation a small generator u.sed for station service. The dam is an earth and rock fill, with a concrete core wall founded on bedrock, except the north end, where the spillway has a cutoff wall extending about 15 feet below the bottom of the structure. 8. At the right abutment of the dam the crest of the embankment on the downstream side dropped about four feet with respect to the core wall, believed ·to be due largely to compaction of the terrace founda­ tion. The upstream crest of the embankment dropped as much as six feet below the top of the core wall. The core wall itself was cracked in several places, mostly near the spillway, the largest crack being about five inches wide; at two breaks lateral displacement of one to three inches occurrede The spillway and chute were seriously damagedJJ to the extent that replacement is planned by the owner. 9· Immediately after the quake, considerable seepage was reported issuing from the natural terrace slope just downstream from the dam. Since the seepage decreased to a small amount after the spill.way dis­ charge was stopped by placing of the stop logs, it was concluded that most of the seepage came from the spillway channel and not through the dam. 10. Madison River Slide. A massive slide, see frontispiece, covered Highway 287 and completely blocked the Madison River just up­ stream from the mouth of Madison Canyon. The slide originated on the south or left canyon wall and moved across and up the valley, forming a natural dam from 200 feet to 400 feet in height and about three-fourths 2 of a mile in width at the 'baseo '!be leading edge of the slide mass came to rest high up on the north. canyon wall.o The lowest portion a£ the mass formed a sadd.le approximately over the old river cbATJnel. ll. The slide destroyed an undeveloped c~ampground located on the right side of the valleyo Separate families or groups of campers aJ.so were caught in or alo;pg the edges of the slid.e. Latest report• pl&ee . the number of known li~s iost in tlie Hebgen Lake .- .Madison caD:yon area at seven, with an additional -19_ missing persc'ns possibly buried under the slide. 12. ~e pre~nce at the slide in M&diSQDL Canyon and the \Ulknown but apparently weake:aed c5)nditio:n of Bebgen Ilam posed a serious threat of disastrous fl~odi.ng in the Madison River Yalley. If' Bebgen DUl shoul.d fail, the release of stored water without doubt would cause a devastating flood down the entire valley and probably along the Missouri River as well. Even if Hebgen did not taU, the rising waters in the .new l.ake formed by the slide, if permitted tc:• overtop the slide, could cut a cb.annel so rapidly that serious floodi.Ilg would result all the way down the Madison River valleyo Rough estimates indicated that failure ·at Bebgen BalD eou.ld ~ause flood damage as hi.@;h as $15,000,000.