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- .- - 1~5\ UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY iC 3; PROFESSIONAL PAPER 1115 PIJ\TE 2 (SHEET 1 OF 2) 1< ~; j,l A 0' , /' , ?'{ '" '" ~ \\ '.,\\ '", ,\. / ~ "'- , ~ \ \,I{ '- ,,1, ,).. .1 EROSION AND DEPOSmON ON SLOPES GULLJES--Cut in thick sandy slope wash deposits on grassy slopes and In thin stony coDuvium over bedrock on forested slopes. Gullying most extensive along dirt roads, roadside drainage ditches, and in preexisting 9UIlles. As largE: as about 600 ft long, 7 h deep, and 20 h wide on gentle grassy slopes and commonly cut to bedrock (generally less than 6 h) on steep forested slopes. Small gullies not shown In densely forested areas LANOSUDES--Most1y developed in thin colluvial mantles over bedrock. prlmarUy on north- to northwest-facing slopes of about 60 to 85 percent. Includes: rockslides (RS), rockfalls (RF), debris slides (OSl, debris f\()l.l.IS IOF), debris avalanches lOA). and undifferentiated landslides (LS). TaU on lriangle Indicates mapped upslope extension of deposit or associated erosional scar :.J SI-lEE1WASH DEPOSITS-CoI I mthapo<<d4 1~t1y thof,_very. Local1fine to very "OO=ud"" pebbly sand, common y ess n nl,.l1es..... Y may I e thicker, coarser grained deposits near the mouths of gullies and small gulches. Usually eroded from steep forested slopes and deposited on adjoining gentler grassy slopes. Areas of sheet erosion, which are mostly limited to forested slopes, are not shown Deposits of sand to pebbly sand that accumulated In areas near the mouths of guUiesand small gukhes, where the mode of flow changed from confined to unconfined and in areas where the flow was impeded by obstructions such as fallen trees. road embankments, and fences. LocaUy may Include some coarser gmined deposits with a small amount of cobble-size material and some sheetwash deposits. Usual]y less than 5 It thick Areas 01 varied erosional and depositional features too small, discon- tinuous, or indistinct 10 map Individually. Includes one or more of the following: ShaUOIN guUies, sheetwash deposits, areas of bent grass, or gravelly l~ deposits EROSION AND DEPOSmON ]N TRIBUTARY GULCHES MINOR EROSION AND DEPOSmON--Characterized by dlscontlnuous 10 continuous shallow channel scour and deposition of sandy to cobbly mate. rial eroded from the bottom and sides of the gulch. Bedrock floor of gulch not exposed. May include short segments with moderate erosion and deposition. Overbank sediments are mostly sands to pebble gravels. CoJ-. ored ared represents approximate extent of flooding: short-dashed red line \used where channel is too narrow to show actual width EXPLANATION r -1 , ~ \ "" :/ ~ ,I, " ,~ " s/' t;/ "'-=, \' "- "" -B4 'f' 'I' r~ 1 MODERATE EROSlON AND DEPOSmON--Characterized by continuous channel scour and deposition of sandy to bouldery material eroded from the bottom and sides of the gulch. Bedrock floor of gulches locaUy exposed. Includes short segments with minor erosion and deposition or major erosion and local deposition. Overbank sediments are mostly sands to pebble ' gravels. Colored area represents approximate extent of flooding, long- dashed red line used where channel is too narrow to show actual width ) j MAJOR EROSION AND LOCAL DEPOSITION-Characterized by ( continuous deep channel scour and by local deposition of bouldery gravel mostly allnsides of sharp bends, Much of the bedload and bank materials less than about 3 ft in diameter commonly washed out of the gulches. ( Bedrock floor of gulches is exposed; locally mantled by thin discontinuous flood deposits and lag boulders. Overbank sediments are mostly sands to pebble gravels that locally contain some cobbles and boulders. Colored area represents approximate extent of floodlng: solid red line used where channel is too narrow to shO\Al actual width ,I, ~ i'u .. ~ ~ ~ ~,\: . ili I I .. \ \ " '^ ----- \, ~ ,IV..' ., \" \ , , ,\ I ,f,\\ Ill" " 'V 'c ~ "'- ~ -' \ "- ~" l / ~ ';c Ii 'I , L ) \ " \ - " '" '^, \( ~..... /) A, ;:, "..~~:<ND/~D/9/5 ' ...._... ft -, .",/ ND/ND/20/6 ..~~ ) 'I " .' c , \ < - (, \ " ~ ./"- ~=~ --~ - ~ ~ "" "4;0.:: ~ ,', ,"' ~11"1~~ ~ ~ ~ .(~ " ~ , (, .0\ -6- EROSION AND DEPOSITION ALONG MAIN STREAMS Minor to moderate channel scour within floodways of Big Thompson River and North Fork: intensive scour restrlcted to outsides of relatively sharp bends and areas along constricted reaches_ Channel deposits range from sand to boulder gravel: owrbank sand to pebbly sand occW"s ]ocaIly. Colored areas represent approximate extent of flooding Widespread deposition of sand to pebbly sand. Indudes some small deposits of pebbly 10 cobbly gravel. Doned red line used along North Fork above ,) G]en Haven where channel Is too narrow to show actual width Roe stipple Indicates areas of widespread deposition of pebbly to cobbly gravel; Includes some small deposits of pebbly sand and cobbly to bouldery gravel. Coarse stipple indicates widespread deposition of cobb]y to bouldery gravel: includes some small deposits of pebbly to cobbly gravel Loca1 areas of intense lateral scour Extensive channel scour within floodways of Big Thompson River and North Fork: deposition of cobble to boulder gravel. Bouldery gravel bars common, especially along insides of bends. Overbank sands to boulder gravels occur locally. Colored areas represent approximate extent of floodlng. Roe stipple indicates areas of widespread deposition of cobb]y to bouldery gravel: includes some small depostts of pebbly to cobbly gravel. Coarse stipple indicates widespread deposition ofbouldery gravel: includes some small deposits of cobbly to bouldery gmvel Intensive channel scour throughout ftoodways of Big Thompson River and North Fork; local deposition of cobbly to bouldery gravel. Much of the sandy to bouldery material scoured from the channel was deposited farther downstream along reaches with lower gradients_ Overbank sands to boulder gravels occur locally. Colored areas represent approximate extent of flooding. Coarse stipple Indicates local deposition of bouldery gravel Segments of highway severely eroded or destroyed by floodwater Boulder-measurement site-Number after letter B corresponds to river mileage of site. Sizes of largest boulders are summarized in tables 7 and 81n text High water and scour measurements on intermittent and perennial streams-Numbers, left to right, represent width of floodwater, height of floodwater above present floor of gulc:h or present stream level, postflood width of channel, and postfIood depth of channel. All measurements are In feet. Letters ND in place of measurement indicate not determined. Letters br after depth of channel indicate that the channel was scoured to bedrock Peak-discharge measurements (In cubic feet per second) by Water Resources Division of the U.S. Geological Survey lsohyets (in Inches) for July 31-August 2, 1976 storm, slightly modified from unpublished data provided by the National Weather Service Mileage marker-Indicates distance in miles along riverbed 5' r '> y \, \, . II '!J! :-:--: " L ~ .;s. :.~ " 7,. 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II.. .~.~ ~ .~, ~ih.- ~"" '"'~.~,.~ JW" I . ')," , ~ ~','p::~" 'I&~ '" <0' 0' ~J';';:t,:. )) "it ~I' :~- /~. ["~"7/1,.,%~~, :-".-~ '<~g ~ '~'''-,~ - " ' 'j" " ,.. "'.~. ~ ,'" ~ >'>!, ,. - -"":'.o..l!- 0-/ III '-, '9- ,jt" - . \ ., I Ii i": ~. - ._-.':'M ~ " 7i'i..""-.."aL'I'" --- ~ ,-' ,...,.... -. " ,'-~.".."'" '/'- _--- NOTE-_'n", .... ~' l,;""": Much of the mapping on plate 2A-C is based on the interpretation of postflood --',~----.' stereographic aerial photographs, including black and white imagery of the area along the Big Thompson and North Fork Big Thompson Rivers (approxi. mate scales 1 :3,500-1 :8.000 by Kucera and Associates, Denver, CO, and / ~ 1:6,000 by Hogan/Olhausen, Loveland. CO) and infrared color transparenCIes o;r: ~- . of 'h, moo,,"'",", port 0' 'h, "udy ".. loop",lm". ,.." ,,24,000 by iI\ ~~- Intrasearch. Denver, CO). Aerial-photograph interpretation was supplemented //, '-""" \.'Iii by field observations mostly along the main streams. in some of the major and _ ~>~_~ II minor tributary gulches, and in the Estes Park area. _ .~'~) , .7200, \\..6 ~. '. ,'u'''' :~,'- '-:=","'\ " ~\ .M\~ -- ~ - / , I r . I I , v. ~ It 31 , " I "'5' \ y I I", '- ~I 'I' I r I " 'J. \ \~ ,,\ "'/':~'~ N .' ~'\.,. , 'I ~ ~. 4 " - -fi: '\, - -,L I -II y ,I "'Y"'~ F.- J~ 1 j ) .. , r I" I I , 'I , / I / II " ,/ " ~ v= ,I , .. " " , 1i / ~ \1 ~ - ~ ~ -,- 1 , " '., \ I. :' '" , , _..~ ..... 'Ie " II" ? ) I' ""'\ ,I ... k ) \ "., r I, \ ,,' 1 " ~ \. \ :.. -- I -~ )'. ',\. , 6 b I i 7 I \ b, , 1 l ~ 4 '\ '""'10, ".~ <, J j 1- , ,I \. ( ( , I, ." r t I J , ) '- "- (, , \ ... ~ -I. I,/, f Cf~~ I :)S' cS j .L '\ ,) ., \. l' p" -ii:. ~."'" 'I ;, ',t \; , , '\ f j 'I ,~ " Extli'nt of mapping ,,'j \ ~tf'\'" , , ,,~ "\\' :--- ,): . . ~ 1 " ::<' 1 " ... , ~ " r / I I, I (~ J ,0 , .." . v . ., ,\ . ~ + . <, l~ ,\ I \ \ \ 11 ~ ]' , , \It, ./ ,"" 1:: / l v ,I I, f " l " \ ~I I . ~' . /, ]{ o o( 1\ t i- 1 , \ "", t 'J' ) I 1 f 1 T, n. . . , "'-,') 1:~':: 22'- " ,II", " I l" - l";\q.; J , ,I ", Base from U_S. GeologicalSl6'o'8Y, Orakel962.EstesPark.1957.levisedlOOl; GlenHaven.1002.longsPeak.1%7.revisedl00l: Pilnot'ama Peak. 1002; ard /'itIe'NOOd Lake. 1962 fJ A, BIG THOMPSON RIVER FROM ESTES PARK TO DRAKE AND NORTH FORK BIG THOMPSON RIVER FROM GLEN HAVEN TO DRAKE EJ Flood effects mapped by P,W, Scl'rnidt andR.R.Sllfoba.lg]6 GEOLOGIC AND GEOMORPHIC EFFECTS OF THE 1976 STORM AND FLOOD, BIG THOMPSON RIVER AREA, COLORADO QUADJ'lANGLELOCATION """"",,-...~..... 010......,...... 1 ~ . SCALE 1:24000 o 1 MilE ~ ~ 1 .5 0 .....- --. .......... --. --. 1 KILOMETER CONTOUR INTERVAL 40 FEET NATDlAL GEOOfTC\IlAl1fAI. OAruM OF 1929 *u.&. GOV!~..Mt.... ..'...'.... OffICI, "1\I--<ln.(J2O,~