,, ..
EAST FORK DAH FONTEN ELI.E OAH East Fork of Tuckasegee River Green River Tuckasegee, Horth Carolina LaBarge, Wyoming 1955, Rocl
FONTENELLE OIIM EAST FORK DAM 1965, Earthf Ill 1955 , Rock fill 1965 , Acc ident, Type 2 1982, Acc ident, Type 1 26 Mar~h 1979, Major repa ir Cause - Granite foun dat ion cracked Cause - Incidents 1 and 2 both \ during construction and worsened with resulted from seepage th rough frac subsequent freeze/thaw action tured foundation rock (note: surface of fractured rock left untreated during construction) I I ,. ' 78 79 FONTENELL E DAM FONTENELLE DAM 1965 , Earthfill 1965, Earthfi 11 "firm foundation" rock . Fo r over 3,000 feet (900 m) of the embankment noticed i n 1982 , had risen over 10 feet whi le the reservoir remained length, it was decided that the "firm foundation" rock was too frac constant . As the pressure in the piezometer cont inued to r ise and tured, so a secondary cutoff trench was excavated from 5 to 7 feet (1.5 investigations indicated it was valid, t'he dl!cis ion was made t~ lower to 2. L m) into the fractured rock. A single-row grout curtain was deve the reservoir an additional 38 feet (1 1. 6 m) , mak ing it 63 ft (19.2 m) loped from a grout cap constructed from the bottom of the cutoff trench. be low normal water surface elevation. DESCRIPTION OF INCIDENTS: REMEDIAL MEASURES: Incident 1 : Incident 1: ~ In May 1965 , Fontenelle Reservoi r was filling for the f irst t ime and The reservoir was lowered as rapi dly as possible. The eroded portion ·of seepage and sloughing was observed in the backf ill on the left side of embankment that needed t o be repl aced was 345 feet (105 m) long at the . the sp i l lway (which is near the right side of the embankment). A drain crest and 65 fee t (19.8 m) high. The foundati on treatment prior to pipe wa s Install ed along the spillway to remove the seepage , but the repl ac i ng t he ~mbankment consisted of 1) redoi ng a port ion of the origi s louyllluy ..:or1ll nuet.l . In early Septe111ller 1g55, the reservoir was about nal left and r tght abutment grout curtains and extendi ng them further - ~ 2 feet (0 . 6 m) over the spi llway crest and seepage increased r apidly into both abutments and 2) blanket grouting the upstream rock beneath from about rnidheight of the dam near the right abutment. The seepage the failed embankment area . rapidly eroded about 10,50D yd3 (8 ,000 m3) of embankmen t ; loss .of the total reservoir wa s prevented only through high releases from the outlet Inci dent 2: '"'ork s .
· ; ~:·.::~.-~ . " Reservoi r restrictions were initiated. Fol l owi ng the concl usion that· The eros ion at Fo ntenelle Dam was believed ·to...,be caused by the rock the fou nd at ion treatment for Fontenelle Dam was such that a fai lure f rom cond it ions at the site and their treatment. La'rg~.. . up t o 6 inches piping could occur anywhere along the length of the dam, construction (150 nun) stress relief j oints in the left abutment that. were partially al ternatives were considered. The alternative selected was an unrein fi l led wlth natural de bri s were treated ~Y grouting. It i s believed forced continuous concrete cutoff wal l that woul d extend essential ly for t hat the grouting was not ful ly effective in thi s area both because of the length of the dam from near t he crest down throug h t he e••bankment the natural debris In t he joints and because grouti ng cannot rea l isti and through the fractured foundat i on rock. The 2-foot (0.6-m) wide ca lly be expected to work perfectly. It is also believed that the cutoff wall is be i ng constructed by excavat i ng the emba nkment and rock pressures from grouting in the right abu t men t area may have sp li t open with a rock mill that supports the excavation wit h slurry. Fol lowi ng some of t he exist ing rock layers. Surface treatment at the emban kment excavat ion of the leng th des ired for a segmen t of the wall, gene rally abutmen t contact, in addi't ion to the grouting, could have been benef i- about 30 feet (g m), the slurry is displaced by concrete starting from cia 1. -...... the bottom of the trench. A successful test section was constructed in , 1985-86 and the repairs should be comp leted in 1989 . Inci dent 2: BIBLIOGRAPHY: Following the completion of embankment repa irs in lg66, the reservoir wa s opc•·a ted normally for a number of years. In late 1982 , a small "final Sa'(ety Evaluat ion of Fontene l le Dam", Seedskadee Project, amoun t of prev iously unobserved seepage was seen at the toe of the dam Wyomi ng, 'Bure au of Reclamation, Denver, Col orado, July 1ga4 near both the left abu tment and the central port ion of t he dam. Study of the des ign and construction of the embankment indicated inadequa~e Bellport, B. P., Bu reau of Reclamat ion Experience in Stab il izing foundat ion treatment and the reservoir was restricted in 1983 to 10 feet Embankmen t of Fontenelle Dam , "!COLO," 9th Congress, Volume I, pp 67-79, (3m) bel ow normal. Investigation of t he left side of the embankment in September 1967 JgOJ ind icated there were numerous very soft ar e ~ s near the emban kment fou ndati on con tact . As a result of f ind ing thesd soft areas, t he reser CONTACT: Bureau of Rec lamation voir was restricted to 25 feet (7 .6 m) below norma l and consideration of Engineeri ng and Research Center repair al ternat ives was begun . PO Box 25007 Denver , Colorado 80225-0007 In early 1985 , it wa s observed t hat the water pressure in a piezometer, near the central portion of the emban kme nt where seepage had been
80 81 ,. l GLEN CANYON DAM GLEN CANYON DAM Colorado River 1964, Con crete arch hge, Ar izona 1g54, Concrete arch from be ing overtopped, the outlet work s and powerpl ant were operated at full capac ity and both spillways we re used ' from June 2 to July 23, lg83. ,, . DATA: The operation of the waterways is summarized in figure 1. \lithin 3 days ,. after the left spillway began operation, rumbli ng noi ses were hear d from Ju ne 2 to Ju ly 23, }g83, Severe damage to concrete lini ng of the spil lway tunnel aod port ions of t he t unnel lini ng were seen in t he Acc ident , Type 1 (Al) left and right sp illways from cavi ta di scharging water . The left spil lway gates were then briefly closed for tion an d erosion an inspection of the tunnel and th e right spillway continued operat ion\ World Reg ister of Dams Not 1 i sted The inspect ion revealed that cavitation and erosion damage were taking U. S. Register of Dams 1963 , page 138, line 2 place in the vertical bend at the lower portion of the tunnel with Height 710 feet (216. 4 m) approx im ately 50 yd3 (38m3 ) of 'conc rete l ining removed. Flood flows Re servoir 27 ,000,000 acre-ft (33,304,000 x tol continued to f ill t he reservoir requir i ng both spillways to be operat ed Pu rpose Long-term regulatory storage, power continuous ly for almost 2 mont hs with a peak discharge of 32,000 ft3;s generation, flood control, recreatioa (906 m3;s) in the right spillway. After the flood inflows had subs ided, Geology The dam and spil lways are founded the sp i llway gates were closed an d the tunne l dewatered. Dama ge in t he en t irely on Navajo Sandstone. le ft spillway cons isted of a ho le 35ft (10.7 m) dee p, 134ft (41 ml - .• long, an d 50 ft (15 m) wi de excavated into the sandstone at t he DESCRIP TION OF DAM: downstream end of the vertical bend, extensi ve damage to the concrete l ining upstream fr0111 the "big ho le , " removal of three-fourths of the Gl en Canyon Dam is a 710-foot-high (216. 4 m) concrete arch dam wi th a tunnel li ner circumference i n the immediate area , and deposition of a cres t length of 1560 feet (475 m) . Th~ c ~hi ckness of the dam at t he large amount of the excavat ed mater ial at t he downstream end of the tun crest is 25 feet ( 7.6 m), the max imum b a's-l!~<.t h.lckn ess is 300 feet (91 m) ne l. Damage i n the right spillway was less extensive than in the left and the dam contains 4,900,000 cubic yards (3,750.t000 m3) of mas s spillway and primarily consisted of a hole, 175 ft (53 m) long and 12 ft concrete. A separate spi llway is constructed in each abutment. Ea ch (3.6 m) deep, at the downstream end of the vertical bend. spil lway consists of an intake structure with t wo 40- by ' 52.5-foot (12.2- by 16.0-m ) radial gates and a concrete-lined t unn el. Eac h RE MEDI AL MEASURES : spillway t unnel has a mi nimum diameter of 41 feet (12.5 m). The ou tlet works near the left abutment of the dam consist s of four g6-inch (2.4-a) Remedial meas ures taken for the spillway damage at Gl en Canyon Dam con diameter pipes. Each outlet is controll ed by one g6- i nch (2.4 -m) .r ing sisted of two parts: ... follo11er ga te an d one g6-inch (2 .4-m) hollow-jet va l ve . The comb1ned .. river outlet works capac ity is 15,000 ft3;s (425 m3; s). ·Meas ures taken du ri ng sp illing to mini mi ze damages to the , spillways and protect the safety of the dam. •' The powerplan t at the toe of the dam consists of eight ·r 18 , 750-ki1 . ge ne rators. Eight 14 -foot (4.3-m) penstocks through the dam convey wa ~~-Me a sures taken after spilling t~ ensure the spi llways would to the turbines. The total discharge capacity of the powerplant Is ~ not be damaged during future spi llway operat ions .
ap proximately 26, 000 ft3/s (736 m3Js). I •, On ce It was ~now n that t he spillways were being damaged by cav itat ion DESCRIPTION OF INCIDENT : and erosion, '~pillw a y operations wer.e developed that min imi zed the I -~ ~~ ! . discharges through the spi llways, espec ial ly the r i gh t spillway. The ".. I Rapid snowmelt and heavy rainfal l in the Upper Co lorado River Basi n powerpl ant and river outlets were operated at near capaci ty for the ; I c r cat~d a r~co r d flood runof f Into Lake Powell dur ing the spring and duration of t he flood. Ei ght -foo t (2 .4-m) high steel f lashboards were ~:, su nvner of 1903. To control the r ising reservo ir and preve nt t he dall added to t he top of the spi l lway gates to permit smaller releases ...:-..: , through the spillway, increase flood surcharge storage in the reservo i r ~ by 1.25 x 106 acre- ft (1. 5 x lDg m3) , and allow the spillway gates to be GLEN CANYON DAM;,_ . closed several weeks early so spil lway repa irs co uld beg in as soon as l964, Co ncrete arch possible. Spi llway discharges were kept as low as possible in the right June 2 to Ju ly 23 , 1983, spi llway to limit damages because the area of danage in the right Acci dent, Type 1 spillway was further up stream t han tha t in the left sp i l lway. It was Cause - High spillway discharges ~ . ne~ded to pass the 1983 f l ood on }i::j Colorado River . ~... ~· . - ~
84 85 GLEN CANYON DAM GLEN CANYOfl DA~I 1964, Concrete arch 1964, Concrete arch felt there was a greater chance of damage in the right spillway propa gating upstream far enough to allow an uncontrolled release of the reservoir. The right spillway was also being kep t in reserve in case , the f lood forecasts were in error or a large thunderstorm was to occur. I Once the spillway gates were closed on July 23, 1983, construction acti vities began on repairing the tunne ls to ensure they would be available should another flood occur in 1984. To prevent cavitation damage from occurring during future spillway operations, the construction activities of late 1983 and early 1984 included the addition of aeration slots in the upper po t ion of each spillway tunnel. The successful design and construction of the aeration slots and tunnel repairs were verified in protQtype tests conducted in Au gust 1984. BIBLIOGRAPHY:
"Fi na l Construction Report on Repair Spil1~1ay Tunnels, Glen Canyon Dam, Co lorado River Storage Project , "U.S. Bureau of Reclamation, Denver, Co lorado, December 1984.
Burgi, P. H.; l~oyes B. M.; Gamble, T. W., · •Opj~tion of Glen Canyon Dam Spillways - Sunmer 1983," Water for Resource de\i'~ ·l.Qpment, American " Soc iety of Civil Engineers, New York, NY, 1984. -~~
Burgi, P. H.; Eckl ey , M. S.; "Repairs at Gle n Canyon Dam," Concrete International: Design and Construction, American Concrete Institute, Detroit, Mi chigan, March 1987. CONTACT: Bureau of Rec l amat ion Engineering and Research Center PO Oox 25007 Denver, Colorado 80225-0007
Figure~l . - Operation of waterways - May/August 1983
···. 'r
86 87 GLEN CANYON DAI1 GLEN FLINT LAKE DAM 1964, Concrete arch Li ttle Walnut Creek Greencastle, Indiana 1975 , N/A OATA: ; 1976 , Major repai r (MR) Sl ide ga t e stem buckled during closure ~ or ld Reg ister of Dams Not li sted U.S. Register of Dams Not 1 is ted \ lfei ght 67 ft (20.4 m) Reser voi r 15,231 acre-ft (1,879 x 103m3) · Purpose Flood control and recreation Geology N/A DESCRIPTION OF DAM: The dam was constructed in 1975. Reservoir releases are made through a 42-inch (1,060-rrrn) diameter reinforced concrete conduit with a 30-inch (760-nrn) reinforced concrete pipe drop in let spi llway and a low-level slide gate . The sl ide gate, located with in the wet wel l of the inlet structure , is a 24- by 30-inch (610 by 760-mm) seating head type, f lat backed, heavy duty Armco sluice gate wi th a non-ri sing, 1.125-inch (28 .5-mm) diameter, stem. The gate i s operated with a "T"-handled, square head, wre nch. Mou nted in the wall between the we t and dry well, 28 ft (8.5 m) above the ga te, is a 3-inch {76-rrrn) drawdown gate valve ~h i ch is also operated with the "T"-wrench. Runn i ng In to the base of the dry we ll is a 6-i nch (150-mm) pipe covered by a fl ap gate. Th e nor ~a l pool elevat ion is elevation 759.6. The invert of the gate i s at elevat ion 719.5. OESCR IPTIOrl OF INCIDEIH: The sli de gate was operated satisfactori ly prior to the in i tial f illing of ~he da~ in 1975. The sl ide gate was opened when the pool was at nor mal )ool elevation for shoreline maintenance in 1976. Wh en the gate was , closed, the stem buckled. Th e st em was replaced, but aga in buckled on · closure of the $lide gate. 'i REMEDIAL MEASURE\: Sa nd bags were placed i n t he wet well to tempo rarily seal the opening vhen the slide gate would not close. The sl i ~e gate and stem we re rep laced with self-·contal ned s 1 ide gate and stem having a minimum length ~f stem in comp ression.
F igurc 2. - Example of sp illway tunnel damage GLEN FLINT LAKE DAM 1975, N/A 1976, Major repai r • • .r Cause- Inadequate design
88 89 MOOSE CREEK DAM NAVAJO DAM 1980, Ear thf il 1 San Juan River Farmi ngton, New Mexico DESCRIPTION OF INCIDENT: 1963 , Zoned earthf ill Piezometer readings and observations of r elief well flow i ndi cated DATA: higher than an t icipated upli ft pressures at the downst ream toe In some areas. Subsequent subsur face explorations revealed a mass of permafrost 1963-1985, Major repair (MR) Signi f icant increase In seepage and creating a cut-off j ust downstream of the ma in embankment. wetting of down stream shell , ' World Register of Dams 1984, page 30, line 14 A pl an view of the project and typical cross sections in permafrost U.S. Register of Dams 1963 , page 140 , line 4 areas are attached. Height 402 ft 022.5 m) Reservoi r 1, 708 ,600 acre-ft (2,108 x 1Q6 m3) REMED IAL MEASURES : Purpose Irrigation ~ Geology ~ed r. o~k . at Nav~jo Dam is sediment ary \ No emergency measures were t aken . The de sign of ad di tional relief wel ls 1n or1g1n and 1s nearly flat lying be tween the dow nstream t oe and the "perma fro st cu t -off" is under way. with no fo lding or fau l ting. The rock cons ist s of sandstones , with To avo id such incidents ~n the fu t ure, extens ive explorations will be inter beds of sil tstones and shales. requi red In areas of disconti nu ous permafrost. Th e abrupt changes in The sandstones are mo de r ately to ..... ver t ica l and hori zontal boundaries of permafrost masses within the highly permeable. Weather ing, in the unfrozen soi ls must be def ined. form of iron staining, extends about 200 ft (65 m) deep in to both abut 11 I BLI OGRAPIIY : ments. On the right abutment, weathering is more intense iucreasing Chena River Lakes Project , Le tter'iReport 21, Permafrost Effects on the per~ab il ity of the roc ~. Shale Seepage (draft), u.s. Army Corps of E'nglne~rs, Al aska District, July and si ltstone beds range from thin 1985 ''<::...... _ l ami na te to beds 20 feet (6.1 m) _ ...... - thick. The sha le and si lt stone beds l CONTACT: Corps of Engineers are unaffected by we athering and Al ask a District essenti ally impermeab le, direc ting PO Box 898 water laterally into the more per Anchorage, Al ask a ggS06-0898 ~ i ous over lyi ng sandstone and al ong Intermi ttently open beddi ng planes. As a result of rive r downcutting joints and cracks have formed t n'the rock parallel t o the canyon walls. These open joints are pr esent in both abutmen t s, bu t are mor e extens ive in the left abut men t. Also. open \ ho ri zont al bedding pl anes exist \ inte1·mi tten t ly along the contacts between the sandstone and sha le beds of both abutment s. lfAVAJO DAM 1963 , Zoned earthfi ll 1963-85, Major repair Cause - Signif icant inc rease in seepage and wetting of downst ream she 11
r ; 134 c..,;.. • 135 NAVAJO DAM NAVAJO DAM 1963, Zoned earthf ill 1963 , Zoned earthfi ll UESCR IPTI ON Of DAM: the contact areas , part icularly in t he left abutmen t, increase the suscep t ibility to erosion of embankmen t mater ial adj acen t to untreated Uavaj o Dam has a s tructural height of 402 feet ( 122.5 m) , a crest length joints and cr ac ks . j of 3,640 feet {1,112 m) , a max imum base width of 2, 566 feet (782 m) , I and crest width of 30 feet (9 .1 ). The total embankment vo l ume is Joints and cracks cons t itute a ma j or seepage path throug h the l eft abut 26,840,000 yd3 (20 ,520,700 m3). The embankment consi sts of three zones me nt . A s imilar condition exists in the cliff areas of the r ight abut of material. Zone 1, the impervious co re of the dam, cons ists of a mi x ment. Th e fl ow r ate in these joints is cons idered suffi cient to causej \ lure of cl ays an d silt s of l ow plast icity. Zo ne 2 consists of coarse erosion of impe r vious embankment material if the cracks and joints are sand, grave l , and cobbles. The zone 3 portion of the da rn emb ankment adjacent to the embankment. consists of a mi xt ure of cl ays, si lts, sands, and gravels not suitabl e for use in zones 1 and 2. Th e up st ream fac e of the dam has a 3-foot Due to the steep configuration of the left abutment, there is ext ens ive \ (0.9-m) layer of r iprap which provides slope protection from the crest j oi nting and cracking of t he abutment rock . Because removal of. t he to elevat ion 5985 feet ( EL 1824 m). maj or sys t em of near-vertical j oi nts wou ld have required ex tens 1ve rock excavation , i t was de termined du r ing cons truction that excavat ing on ly _. DESCR IPTION Of INCIDENT : the overburden on the abutmen t and treat ing the joints by blanket grout ing through risers would be mo re app~op ri ~ t e . Embankment m at~ rial Secpagn at Navajo Dam was f irst observed on 5 June 1963 , abou t 1 year was placed against the abu tment surfaces 1mmed1ately after excavat1on. dl Lt!r the ouLiet gates were closed for the in it ial filling of the The crack s and joints were then grou ted by riser pipes extended up . reservoir. Seepage has increased dur ing the l ife of the dam , wi th total throu gh the fill t o reduce foun dation uplift and movement. The sealinj meas ured seepage f rom both abu tmen t s c urre~t1y averaging about of near-surface cracks with this type of grout ing, which was pract iced 1,800 gal/m in (6.8 m3/m i n) . ·-.·,,...,_ ....._ at the time the dam was constructed , is not cons idered adeq uate by ~ ..... ~~- present-day standards. Al so , with this type of grout ing operat ion, i t Studies indica te there i s a hi gh pr·ob ab il ity of s e~p"aQe' · fl o wi n g along is difficult to assess the effectiveness of the near-surface j oin t seal the emba nkme nt-abu t ment contact which will erode the core mater ial into obtained . the un trea ted j oi nts an d cracks. This erosi on will eventua l ly cause failure of t he structure. For th is erosion or pip ing to occur, several REMED IAL MEASURES: condi t ions must exi st : ( 1) the embankment co re mater ial mu st be erod ible; CZ ) the f l ow rate along the in terface must be suff ic ient to Left Abutment Concrete Diaphragm Cu toff Wa ll - The installation of a cause eros ion; (3) open joint! and cracks mus t ex i st at the conc rete wa ll wi thin the embankment and extendi ng into the abutmen t was embank~~ent - abutmen t contact; and (4) the core ma teri al must be ab le to selec ted for the left abutment . The 2. 7-ft (0 . 8-m) thick wa ll wou ld escape from the emba nkment through unf il tered, open pathways in t he extend vertically from the cres t of t he dam i nto t he foundat ion rock. embankment or the founda t ion. All of these conditions exiSt.at Navajo Th)s wa ll wil l cut off all seepage at or near the abutment contacts. Dam . Construction l abor atory t est reports show tha t t he ernbankmen t core ' mater ial at Navaj o Dam is predom inan t ly lean to sandy clays and silts of On the left abutment, the concrete diaphragm wall would be abou t 450 ft low plas ticity. Mater ials of th !s type are ge nerally highly erosi ve. (1 37 m) long with a depth ranging from approxim atel y 60 to 400ft (18 t o 122 m). The Jail woul d extend 50 to 2DO f t (15 to 61 m) hor izontally in Th e excava ted surface of the left ab~tme n t and the cli ff areas of the the abut ment w~ c h wo uld prov ide an impermeable barrier bel ow the leve l ri ght abu tment were extremely steep with several vert ical -to-overhangi ng of any sig n i f i c~n t relief jointing . · fdces left In pl ace . Embankment materia l was compacted agai r1st these sur fa ces . Emban kmen t pl acement aga inst vert ical or overhang i ng faces Right Abutment D~aina g e Tunne ls- A mo~ i f i ca t i on.a l te rn ati~e i nvo lving res ul ts In an inabil ity to achieve proper f il l densi ty and contact at t he inst allat ion bf a tunnel and a dr a1n sys t em 1nto the r1 ght abu tment the embankment-abutment' interface, and increases the potential for at Navajo Dam was selected. The tunnel and f i ltered dr ain system essen crack ing of the f i ll adjacent to the abutment due to Uifferentia1 tially eliminates the potential for uncontrolled piping by di recti ng the settlemen t of the f i 11 or arching of the stresses in the emb ankment seepage away from the embankment-abutme nt contact. result ing in lower dens i t ies near these discontinuit ies . Bl anket grout ing through riser s used in the left abut~ent hydraulically frac The drainage system wi l l reduce the saturation of the downstream s ~ell t ured the embank men t, caus ing zones of grout intrusion into t he embank of the emba nkment by i ntercepting and contro lling the seepage . Th1 s ment and between t he emba nkment-abutmen t contact . These condi t ions at ·.-~ ill · in crease embankmen t stab il ity to an acceptable leve l and remove the threat.of dam fa i lure from an unstab le embankment .
·~o 136 137 IIAVAJO DAM NEWTON FALL S PAPER HI LL LAGOON NO. 4 1963 , Zoned earthfill Barrel Creek Newton Falls, Hew York The r igh t abutment drai nage scheme would include instal lat ion of a 1965 , Earthfi 11 1,045-ft (318.5-tn) long , 10-ft (3,000-nm l diameter tunnel w~th 11 !700 ft (3 ,566 m) of 4- inch (1 00-mm) diameter drai n holes and a gro1n dratn. DATA: I BIBLI OGRAPiiY: 6 October 1984 , Fai lure, Breaching of embankment and emptying Type 2 (f2J of lagoo n Hone World Reg ister of Dams Not l isted U. S. Reg ister of Dams Hot l isted \ CONTACT: Bureau of Recl amation Height 30 ft(9. 111) Eng ineering and Research Ce nter Reservoir 306 acre-ft (377 x 103 m3) PO Box 25007 Purpose Waste treat11ent Denver, Co lorado 80225-0007 Geology N/A DE SCRIPTION OF DAM: Th e di ke for the Newton Falls Paper Mill l agoon No. 4 is approxim ately 30 ft (9.1 m) high wi th a cres t length of 300 ft ( 91 m). The dike is a zoned earthfill with an Impervious core and sand fi l ter. Both faces of the dike slope at 2.5: 1 (H:V l. The top of the di ke is 13 ft (4 m) wide. The lagoon is a waste treatment pond for a paper mi ll. DE SCR IPTION OF INCIDENT:
When i t bec ame ne cessary t o lower t h~ l ag oon to install a f low moni toring sys t em; · it was disco vered that no me ans had been provided to drain it. Therefore the follow i ng steps were taken: 1. The original drawi ngs were checked to veri fy t he type of embankment construction. 2. The construction was also checked wi th the mill yard supervisor wh en the dam was constructed. He verified that cl ay wa s used in the construct ion of the dam. The procQdure decided upon t o l ower the level of the dike wa s to slowly skim off~he horizon tal top surface of the di ke for a length of approx i ma~tlY 60ft (18 . 3 m) so that a wide spi llway with min imum flow at any one ~o i nt was created. Th1s was considered to be safe as the dike was constructed wi th an impervious core. Also, the dike was considered to be heavily compacted as the crest of t he darn was actually us ed as a roa.dway for heavy trucking for many years.
NEWTON rALLS PAP(R M I L~ kAOOOH HO, 4 \ 1965, Eartfi~lll 6 October 1984 , Fa ilure, Ty pe 2 Cause - Wh ile a spillway was being cut in t he enbankment to lower the reservoir, the outflow eroded the emban kmen t.
138 139