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1:tt }J.s 1 to 111tot:her- oubtattdittB _g:r1tdrtate stttdt:itt · t}i.t ikivt f ot ratfL1tf ;>JiJb1 l)ttlu11t. UNIVERSITY OF MINNESOTA
This is to certify that I have examined this bound copy of a master's thesis by
Scott James Carney
and have found it is complete and satisfactory in all respects, and that any and all revisions required by the final examining committee have been made
HOWARD MOOERS Name of Facility Advisor
Signature of Facility Advisor
Date
GRADUATE SCHOOL PALEOHYDROLOGY OF THE WESTERN OUTLETS OF GLACIAL LAKE DULUTH
A THESIS SUBMITIED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY
Scott James Carney
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE
September, 1996 ABSTRACT
Glacial Lake Duluth occupied the western end of the Lake Superior Basin, dammed between the retreating Superior lobe and a series of moraines. Lake Duluth is identified by a series of discontinuous strandlines observed throughout the western portion of the lake basin. Two prominent outlets have long been recognized, the Portage outlet in Minnesota, which drained southward along the Kettle channel, and the Brule outlet in Wisconsin, which drained along the St. Croix channel. However, the relative role of each outlet in the drainage of the lake has never been adequately explained. The Brule and Portage outlets formed early during ice retreat and they drained small ice marginal lakes. Further ice retreat allowed the small lakes to coalesce forming Lake Duluth. Because of isostatic tilting, the Lake Duluth strandlines rise about 0.5 meters per kilometer eastward between the Portage and Brule outlets from 323 m to 335 m. After adjustment for rebound, the Brule outlet is estimated to be about 10 m below the elevation of the Portage outlet. The paleodischarge of the outlets and their associated channels was estimated using the U.S. Army Corps of Engineers water surface modeling package, HEC-2. Inputs to the model included topographic cross-section of the outlets and channels constructed at 1500 meter spacing from the lake outlets to a distance of 60 km downstream. Analysis of glaciofluvial sediments were used to estimate a range of Manning's roughness coefficients. The model was run with various discharges to construct stage/discharge relations. Maximum lake discharges were detennined by minimum channel cross sections. To check the validity of the discharge estimates, an atmospheric energy-balance approach utilized to estimate potential maximum meltwater availability. Peak channel discharges estimated using
HEC-2 and peak summer meltwater production form the energy-balance approach are in remarkably close agreement, ranging from 30,000- 45,0000 m3/s. The Brule outlet served as the primary drainage channel for Lake Duluth. Stage/discharge relations indicate that the Portage outlet could only have been active during the peak of seasonal meltwater
II production or because of extraordinary inputs of water.
III TABLE OF CONTENTS
TI1LE ...... I ABS'fRACT ...... II TABLE OF CONTENTS ...... IV LIST OF FIGURES ...... VI LIST OF TABLES ...... IX LIST OF APPENDICES ...... X ACKNOWLEDGMENTS ...... XI
INTRODUCTION ...... 1
Late Quaternary Glacial history of the Western Lake Superior Basin ...... 5
METHODS OF INVESTIGATION Geomorphic Analysis ...... 21 Field Investigation ...... 21 Laboratory Methods Channel Geometry ...... 22 Paleohydrological Analyses The Manning Equation ...... 23 Largest Clast Discharge Calculations ...... 24 Development of Stage/Discharge Rating Curves ...... 27 Water-Surface Profile Modeling (HEC-2) ...... 27 Specified Variables for HEC-2 Modeling ...... 30 Correction for Differential Rebound ...... 32 Independant Confirmation of Estimated Discharge...... 32
RESULTS ...... 35 General Geomorphology and Channel Geometry St. Croix Channel characteristics Geomorphology of the Island Lake quadrangle ...... 37 Geomorphology of the Webb Lake quadrangle...... 41 Channel geometry relationships ...... 44 Channel sediment descriptions ...... 46
Kettle Channel characteristics General geomorphology and channel geometry ...... 46 Channel geometry relationships ...... 48 Channel sediment descriptions Kettle Channel sediments...... 51 Pre-Lake Duluth channel sediments ...... 55 Paleohydrologic calculations ...... 55 The Manning Equation ...... 55 Largest clast calculations ...... 57 Energy Balance discharge ...... 60 Isostatic adjustment ...... 60 HEC-2: Water surface profile modeling ...... 63 DISCUSSIONS ...... 65 Channel history St. Croix Channel...... 66 Kettle Channel...... 70
CONCLUSIONS ...... 75
REFERENCES
APPENDIX A APPENDIXB APPENDIXC
PLATE 1 LIST OF FIGURES
1 Geography Of Field Area ...... 2 2 Geographic locations of the study area ...... 3 3 Phases of glaciation in Minnesota
3a Bedrock topography ...... 6 3b Deposition of Hawk Creek till ...... 6 3c Deposition of Granite Falls till...... 6 3d Hewitt phase of the Wadena lobe ...... 6 3e St. Croix phase ...... 7 3f Erosion of tunnel valleys by subglacial streams ...... 7 3g Deposition of eskers in tunnel valleys ...... 7 3h Automba phase ...... 7 3i Spilt Rock-Pine City phase ...... 8 3j Bemis phase ...... 8 3k Nickerson-Alborn phase ...... 8 31 Formation of Lake Agassiz ...... 8 4 Phases of glaciation in Wisconsin
4a Tiger Cat advance ...... 9 4b Hayward advance ...... 9 4c Swiss advance ...... 10 4d Airport advance ...... 10 4e Lake Ruth advance ...... 11 4 f Porcupine advance ...... 11 4g Lake View advance ...... 12
5 Channelized outwash of the Minong Quadrangle ...... 14 6 Drainage Sequence of Lake Koochiching and Lakes Aitkin II and Upham II ...... 15 7 Lake Superior Region ...... 18 8 Water level curves in the Lake Superior Basin ...... 19
9 Channel dimension measurements ...... 25 10 Total conveyance for a cross section ...... 30
11 Glacial lake shoreline features ...... 31 12 Melt rates calculated from the energy balance model ...... 34
VI 13 Incision of the Bois Brule river ...... 36 14a St. Croix channel bottom elevations ...... 38 14b St. Croix channel width vs. distance from the outlet...... 38
14c St. Croix channel gradient vs. distance downstream from the outlet ...... 39 14d St. Croix channel first derivative of slope vs. Distance dwonstream from outlet ...... 39
15 Swiss Surface features ...... 40 16 Four erosional surfaces of the Webb Lake Quadrangle ...... 42 17 Four erosional surfaces of the Webb Lake Quadrangle ...... 43 18 Quaternary Geology of the Kettle Channel ...... 47 19 Confluence of the Scanlon Channel with the Portage outlet channel ...... 49 20 Uncollapsed and collapsed Willow River Outwash plain ...... 50 2 la Kettle channel bottom elevations ...... 52 21 b Kettle channel width vs. distance from outlet ...... 52 21c Kettle channel gradient vs. distance downstream from outlet ...... 53 21d Kettle channel first derivative of slope vs. Distance downstream from outlet...... 53
22 Brule outlet bankfull discharge as calculated by the Manning equation ...... 54 23 Portage outlet bankfull discharge as calculated by the Manning equation ...... 54 24 Spillway maximum discharge calculations for all methods ...... 56
25 Outlet stage I discharge curves 25a Manning's n = 0.03, outlet elevation 315 m ...... 58 25b Manning's n = 0.1, outlet elevation 315 m ...... 58 25c Manning's n = 0.03, outlet elevation 323 m ...... 59 25d Manning's n = 0.1, outlet elevation 323 m ...... 59
26 St. Croix channel bottom elevations and water surface profiles 26a Discharge= 15,000 m3/s, Manning's n = 0.03 ...... 61 26b Discharge= 15,000 m3/s, Manning's n = 0.1...... 61
27 Kettle channel bottom elevations and water surface profiles
27a Discharge= 5000 m3/s, Manning's n = 0.03 ...... 62 27b Discharge= 5000 m3/s, Manning's n = 0.1 ...... 62
VII 28 Wave washed topography of the Brule Quad ...... 77
VIII List Of Tables
1 Meltwater Production Of The Superior Lobe ...... 34
2 Manning's Roughness Coefficents Calculated from Largest Clast Analysis ...... 57
3 Discharges Calculated From Largest Clast Analysis ...... 58
IX List Of Appendices
Appendix A Discharge calculation from the Manning Equation A) St. Croix Channel B) Kettle Channel
Appendix B Cross Sections For The St. Croix Channel
Appendix C Cross Sections For The Kettle Channel
x ACKNOWLEDGMENTS
There have been many moments when I thought that I would never finish this thesis.
Usually during these times inspiration would come to me in one form or another. There have been many people who have helped through this thesis and I would like to take a moment to thank them.
First and foremost is Howard Mooers. Howard not only helped formulate the initial subject matter, but assisted and supported me and my ideas in ways too numerous to list here. Thank you Howard never turning my questions away and for always seeing the bright side when I could not see it.
Thank you Charlie. Frequently when I became overwhelmed or frustrated Charlie would tell me "It's just a thesis". Somehow this had a way of putting everything in perspective. I was a pleasure to work with you side by side in the classroom and the field.
Without the support of the UMD Geology Department this would not have been possible. I would thank all those responsible for giving me a chance to be a student and teacher in this fine institution.
Thank you Mom. You helped me through many tough times (which usually included money). More importantly I thank you for the love and emotional support which you have blessed me with over the past 27 years. Thank you for your never ending confidence and friendship.
Thanks to my extended family, where ever they may be. I thank them for all the love and support they have given to me throughout my life. They are a true blessing and they are always close to my heart
To Lyn, I thank you for being my friend through the past several years and giving me a push at the end. Although you probably never knew, you were a big inspiration to me to keep going and moving forward. I look forward to enjoying your company over the years to come.
XI Last, but not least, I thank God for giving me a healthy body and mind that can think, learn question, and comprehend. I thank him/her for giving me all the opportunities and experiences I have been blessed with.
XII INTRODUCTION The Lake Superior basin underwent a complex evolution throughout the Pleistocene Epoch as the Superior lobe advanced and retreated. The glacial history is recorded by a complex stratigraphy and surface morphology. With the final retreat of the Superior lobe a new phase of landscape evolution commenced with the formation of the first of series of proglacial lakes. Initially, water was ponded in numerous small basins each with a separate outlet through ice-cored moraines. As recession of the Superior lobe continued, these small basins coalesced forming progressively larger lakes. The record of many of the small lakes was subsequently destroyed by ice meltout and sediment collapse. The larger lakes are recorded by wave-washed topography, beaches and bars, and prominent outlet channels. Two of these larger lakes left significant geomorphological and stratigraphic records. Glacial Lake Nemadji occupied the extreme western end of the Superior Basin dammed between the ice margin and the Thomson and Nickerson moraines (Upham, Leverett, Wright) (Fig. 1). Along the Wisconsin shoreline, Glacial Lake Brule formed in a similar fashion dammed on the south by the Porcupine moraine (Clayton, 1984) (Fig. 1). Lake Nemadji drained via the Portage outlet, which then joined the Kettle channel at Moose Lake, Minnesota (Fig. 2). Lake Brule drained through the Brule outlet and continued along the present course of the Bois Brule and St. Croix Rivers (Clayton, 1984) (Fig. 2). With the continued retreat of the Superior lobe, Lakes Nemadji and Brule merged forming Glacial Lake Duluth, which stabilized at an elevation between 331m (Farrand, 1960) and
323m (Clayton, 1983). It is generally accepted that Glacial Lake Duluth drained via the Brule outlet, which lies approximately 8 meters lower than the Portage outlet Continued ice retreat opened lower outlets in the eastern portion of the Superior Basin, which resulted in the abandonment of the Lake Duluth level (Drexler, 1981; Farrand and Drexler, 1985). These post-Duluth lake levels and their outlets are discussed in detail by Farrand (1969), Drexler (1981) and Farrand and Drexler (1985). At approximately 10,000 years B.P., the readvance of the Superior lobe during the Marquette phase of glaciation
1 MOOSE LAKE
CHENGWATANA 'ST. CROIX SURFACE CHAI\TNEL
+ffi CLOQUET MORAINE I< I PORCUPINE AND OTHER MORAINES O 40 80 KILOMETERS
0 25 50 MILES
Figure 1. Geography of field area. Showing the locations of channels, extent of Lake Duluth and approximate position of moraines and Lakes Aitkin I and Upham I. Scale is approximate.
2 FROM LAKE BRULE! DULUTH
BRULE OUTLET TO LAKE NEMADJI
MODERN DIVIDE ,,,,.. BLACKHOOF CHANNEL MOOSE LAKE UPPER KETTLE--...._ CHANNEL
HINCKLEY•
• GRANTSBURG CHENGWATANA SURFACE 90
Figure 2. Geographic locations of the study area. Showing Lake Duluth channels: Kettle channel, Portage outlet channel and St. Croix channel. Pre-Lake Duluth channels include: St. Louis, Blackhoof, Scanlon, and Upper Kettle. Numbers indicate miles downstream from outlet. Italic print indicates water source/ destination. Scale is approximate. \.J.J resulted in the blockage of lower outlets and re-establishment of the water level in the western end of the Lake Superior basin at the Lake Duluth level. Following the Marquette phase, water levels in the basin again underwent stages of lowering. Although Glacial Lake Duluth has been the focus of several investigations over the past
100 years, significant questions remain regarding early lake history and outlet I stage relationships. Farrand (1960) conducted reconnaissance-level mapping in the western end of the Superior basin, however, Zarth 's (1977) examination of the shoreline features of the extreme western end of the Superior basin remains as the only detailed investigation of the early stages of Lake Duluth since the mapping of Leverett (1928) . In particular, the timing of the origin of the outlets and channels; whether the Brule and Portage outlets functioned simultaneously at the Duluth Stage; reconstruction of the Brule outlet (which has been extensively modified by post-glacial incision of the Boise Brule River); and a reexamination of possible differential rebound between the Portage and Brule outlets require attention. This investigation summarizes the results of detailed descriptions of the geomorphology and channel geometry of the Brule and Portage outlets and their respective channels, mapping of former shoreline features between the Portage and Brule outlets to examine differential isostatic rebound, identification and quantification of potential meltwater sources, estimation of paleodischarge of the outlets and channels, and the development of stage/discharge relationships for Glacial Lake Duluth.
4 Late Quaternary Glacial historv of the Western Lake Superior Basin
The glacial history of the Lake Superior basin in Minnesota is summarized by Wright
(1965, 1970, 1972) and glacial events in adjacent northwest Wisconsin have been studied in detail by Clayton (1984). Little is known about glacial events prior to the Late Wisconsin
Stage (Baker et al., 1981, 1984; Mickelson et al., 1984). Wright (1964, 1972) and Wright and Ruhe ( 1965) recount the history of the Superior lobe as a series of phases. The first and most extensive Late Wisconsin advance of the Superior lobe is the St. Croix phase, during which ice advanced out of the Superior basin to form the St. Croix moraine in central Minnesota (Fig. 3e). Wright and others (1970) suggest that the Superior lobe had reached its maximum by about 20,000 B.P. (Wright, 1972) a date that Clayton and Moran
(1982) suggest is too old. The St. Croix phase is also recognized in Wisconsin (Johnson,
1986; Clayton, 1984). Details ofthis advance are documented by Mooers (1988), Wright
(1972), Wright and Watts (1969), Johnson (1986), and Wright and others (1970).
The retreat of the Superior lobe from the St. Croix moraine was punctuated by numerous readvances, possibly surges (Wright and others, 1973). The next phase of the
Superior lobe, the Automba phase, is marked by an advance of the Superior lobe into the
Mille Lacs region of east-central Minnesota (Fig. 3h). The extent of this advance is defined by the Mille Lacs moraine, which lies on the western edge of Mille Lacs Lake, and extends to the northeast as the Wright and Cromwell moraines to the Highland moraine (Fig. 1).
The Automba Phase correlates with the Tiger Cat Advance in Wisconsin (Clayton, 1984)
(Fig. 4a). While the Superior lobe stood at the Mille Lacs moraine, meltwater ponded in north-central Minnesota creating Lakes Aitkin I and Upham I (Fig 1). Any shoreline features that may have developed, were erased by the subsequent advance of the St. Louis sublobe during the Culver Phase (Fig. 3h). Evidence for these lakes is preserved in a thin, red and gray, stone-poor till deposited by the St. Louis sublobe after overriding the former lake plain (Ballantyne, 1991).
5 / I I I I \
/ ' ' ' / ...... _...... /
r 0 l> ,.,,CD ,.,,0 z l>
\ c. d . \ ' ' I ' I ' I ', I ' ---- /'
Figure 3 a-d. Phases of glaciation in Minnesota. Large arrows show direction of ice movement, small arrows show direction of drainage, groups of dashes indicate drumlins. a) Bed-rock topography; b) Deposition of Hawk Creek Till by Superior lobe; c) deposition of Granite Falls till by Wadena lobe; d) Hewitt phase of Wadena lobe (Alexandria moraine and Wadena drumlin formation). (From Wright, 1972)
6 L. Aitkin I '
h .
Figure 3 e - h); e) St. Croix phase. Advance of Superior and Rainy lobe to St. Croix moraine and advance of Wadena lobe to Itasca moraine. (Approx. 20,000 B.P.); f), erosion of tunnel valleys by subglacial streams beneath Superior and Wadena lobes; g) deposition of eskers in tunnel valleys; h) Automba phase of Superior and Rainy lobes, formation of Lakes Aitkin I and Upham I. (from Wright, 1972)
7 -.:. ii Little \ ·.Falls k . :;;
MINNEAPOLIS•··. .. ManKato
Figure 3 i - l); i) Split Rock-Pine City phase of the Grantsburg sublobe and Superior lobe, formation of Lake Grantsburg (approx. 16,000 B.P.); j) Bemis phase of Des Moines lobe, formation of Anoka sandplain, wastage of Grantsburg sublobe (approx. 14,000 B.P.); k) Nickerson-Alborn phase, advance of Superior lobe to Nickerson moraine (approx. 12,000 B.P.); I) formation of Lake Agassiz (draining through Warren river outlet) formation of Lake Aitkin II and Upham II (draining through the St Louis river to diversionary channels). (from Wright, 1972)
8 / / .,. I /S UPERIOR •o· I I I ll.PQ57lf;/ I / / 'S: , ,' '' " r•:i 47' I -1 I I I I I I I I / o
46 '
Figure 4a Tiger Cat Advance, during the last part of the Wisconsin glaciation. Line with tick marks indicates ice margin. Arrows show possible ice-flow direction. Small arrow heads show direction of drainage. Correlative with Automba phase. (From Clayton, 1984)
-----I I 4 7· I I
I
I . . ,. '· ·'" :
Figure 4b. Hayward Advance, formation of Lake Grantsburg. Diversion of meltwater from Chippewa river to Namekagon river. Approximately correlative with pre-Split Rock phase. (From Clayton, 1984)
9 I SUP[RIOR / oo · / I / ·s / I ,'!::=="=="'" ==5'":· I 1" ·; / I I I ·. ii I I
. : ., ... I ...... PRICE
Figure 4c. Swiss Advance, formation of the Swiss Surface. Correlative with the Split Rock phase. (from Clayton, 1984)
I / .,. / I I I APosTlt ,. I !/ 47' -': #.:J l ,t) f) I }.-" '! 0 r·:1 I I I I ... I ,·j BURNETT I __ !..) I. - 192° I I Figure 4d. Airport Advance, approximately 12,300 B.P.. Correlative with Nickerson - Alborn phase. (from Clayton, 1984) 10 ./ 01 • I S UPERIOR /; I I I I / ,. / ·,. · / 0 !() lP"" . •s, I / 0 ... ' i<.: . ·i·-··. l ,.,.folh I ,. ·. . ', '. ) .. ! Il . ..._., .- ·-· PRICE .' 91• i""' Figure 4e. Lake Ruth Advance, approximately 11,500 B.P .. Correlative with Nickerson - Alborn phase. (From Clayton, 1984) J PINE -· ..,: .. I .. ' ------1 .', I i ,. I ' : VILAS - _____-,---· •.. · BURNETT ······· · ! - ! ..- PRICE Figure 4f. Porcupine Advance, approximately 11,000 B.P.. Flow from Lake Ontonagon along the southern margin of the Superior lobe to the St. Croix channel. (from Clayton, 1984) 11 .,. SUPERIOR ./ •o ./ ./ , · / I .,. ST. LOUIS _ ·· .. i . ;_.·. i_', " ;·····. .,. Figure 4g. Lake View Advance, between approximately 9,500 and 10,000 B.P.. Correlative with Marquette Advance. (from Clayton, 1984) Following the retreat of ice from the Automba margin the history of glacial lakes in the Superior Basin began. Wright (1969) hypothesizes that lacustrine sediments were deposited in a proglacial lake, which formed in front of the retreating Superior lobe. The existence of this lake is based on observations of clayey tills associated with the Split Rock phase and are presumed to be the result of the incorporation of these lake sediments into the ice (Wright, 1969). The Hayward Advance (Clayton, 1984)(Fig. 4b), which is not recognized in Minnesota, occurred prior to the Split Rock Phase. The main event of this advance is the / diversion of outwash from the Chippewa River to the Namekagon River (Fig. 4a and 4b). The Spilt Rock-Pine City phase saw the readvance of the Superior lobe to the Cloquet I moraine and the overriding of the St. Croix moraine by the Des Moines lobe (Wright, 1972)(Fig. 3i). During the Pine City phase (Fig. 3i) the Grantsburg sublobe, an extension of the Des Moines lobe, effectively dammed the southward drainage of meltwater from the Superior lobe, forming the short-lived Glacial Lake Grantsburg (Cooper, 1935). 12 The Split Rock-Pine City phase has been correlated with the Swiss Advance in Wisconsin by Clayton (1984). The most notable landform created during the Swiss Advance is an expansive outwash surface that borders the southern bank of the St. Croix spillway called the Swiss Surface (Fig. 4c). (Clayton, 1984). Subsequent erosion incised this surface. Evidence of this erosive period is seen in areas of collapsed, channelized outwash located on the Gordon and Minong Flowage 7.5 Min. Quads in Wisconsin (Fig. 5). During the Nickerson-Alborn phase, the St. Louis sublobe, an eastward extension of the Des Moines lobe, invaded north central Minnesota forming the Culver moraine at it's maximum (Fig 3k). Contemporaneously, the Superior lobe advanced out of the Superior basin as a narrow lobe, forming the Nickerson-Thompson moraine (Fig. 3k). With the retreat of the St. Louis sublobe, glacial Lakes Aitkin II and Upham II formed, presumably dammed between the ice margin and the Culver moraine. With the continued retreat of the St. Louis sub lobe, Lakes Aitkin II and Upham II merged and were drained at first by the St. Louis River, and later by the combination of the St. Louis and Snake Rivers (Fig. 6e). While the Superior lobe was still at the Nickerson-Thomson moraine, water flowed eastward through the St. Louis River to a series of diversionary channels, which led the water around the western edge of the Nickerson-Thompson moraines (Wright and others, 1970) (Fig. 1). These channels then fed into the channel currently occupied by the underfit Kettle River (Fig. 6e). The western Wisconsin equivalent of the Nickerson-Alborn phase is the Airport Advance (Attig et al., 1985). During the Airport Advance, the ice margin was located between Lake Nebagamon and Solon Springs, Wisconsin (Fig. 4d). The definition of this glacial stage is based on observations of an outwash surface within the entrenched Swiss surface (Clayton, 1984). As the Superior Lobe retreated from the Nickersonffhomson moraine, the St. Louis River occupied lower diversionary channels. The lowest of the diversionary channels was 13 Figure 5. Channelized outwash of the Minong Quadrangle. Channelization occurred prior to complete melting of buried ice, evidenced by collapse depressions within the channels. Scale is I :24,000. Area shown is approximately 3.2 km wide. 14 Ice front ;' Outwosh plains and channels WO Km '------' j Ice front j Ice front Glacial lo•e Glacial lake Poth of melt water s Poth of meltwoter F 1 Ice front j Ice f rent Glacial lake Glacial lake Poth of meltwoter Poth of meltwoter s \ WO Km ._____,WO Km Ms Figure 6. Drainage sequence of Lake Koochiching and Lakes Aitkin II and Upham II. a) late glacial setting; b) early Mizpah stage; c) late Mizpah stage; d) Gemmel stage; e) Upper Train stage; f) Lower Trail stage. Channel abbreviations relevant to this study; de = diversionary channels; K = Kettle River; Po = Portage River (Portage Outlet); SL= St. Louis River (from Hobbs, 1983). 15 beheaded when the St. Louis River breached the Thompson moraine near Thomson, Minnesota. Flow then entered the Superior Basin into Lake Nemadji, which by this time had breached the Nickerson moraine forming the Portage outlet (Hobbs, 1983) (Fig. 6t). The Lake Ruth Advance (Fig. 4e) is correlative to the later stages of the Nickerson- Alborn phase and is recognized by two fluvial deposits termed the Iron River and Lost Lake Surfaces (Clayton, 1984). Along the southern rim of the Superior basin, the Porcupine Advance (Fig. 4t) followed the retreat from Lake Ruth margin around 11,000 B.P. (Clayton, 1984). Clayton (1984) suggests that during the Porcupine Advance, the St. Croix channel was enlarged by a sudden input of meltwater. According to Clayton ( 1984 ), the source of this water was Lake Ontonagon, which was located in the Upper Peninsula of Michigan (Fig. 7). Apparently Lake Ontonagon drained suddenly, flowing to the west through a proglacial channel and entering the St. Croix channel near Brule, Wisconsin (Clayton, 1984) (Fig. 4f). According to Clayton (1984), Lakes Brule and Ashland existed simultaneously and were linked by proglacial channels to proglacial lakes in the upper peninsula of Michigan. As the ice margin continued to retreat, these proglacial lakes coalesced with lakes along the Minnesota shore to form one contiguous lake along the western and southern margins of the Superior basin. The name given to this lake is Lake Duluth and used only for lake stages that correspond to the Duluth beaches. The Lake Duluth beaches lie at an elevation of 323 m (1060 ft) (Clayton, 1982) near the Portage outlet and can be traced to a higher elevation at the Brule outlet The discrepancy in beach elevations between the two outlets can be explained by differential isostatic rebound, which is discussed in detail in following sections. 16 As the lake level within the Superior basin continued to drop in response to the retreating Superior lobe, many minor shorelines developed and have been subsequently named. These include the Highbridge, Moquah, Washburn, Manitou, and the Beaver Bay (Fig. 8). A detailed chronology of the lower lake levels is found in Farrand and Drexler (1985). The position of ice margins also influenced the water level of Lake Agassiz. At approximately 10,800 B.P. the Superior Lobe had wasted back to a position which allowed Lake Agassiz to drain to the east lowering the lake from the Campbell to the Moorehead level. Clayton (1983) and Farrand and Drexler (1985) suggest that this water flowed east to the Lake Nipigon basin (Fig. 7) in southern Ontario, which then flowed through the Superior Basin and then east into Lake Huron. If this is correct, the water level in the Superior Basin must have been at the Minong level or lower, meaning that the eastern outlets of Superior must have been ice free (Clayton, 1983). This drainage configuration was short lived as the ice advanced a final time during the Marquette advance. The Marquette phase represents the final advance of glacial ice into the Superior basin. The ice sheet moved from an unknown position in Ontario to moraines in northern Wisconsin (Clayton, 1984) and the upper peninsula of by approximately 10,000 years B.P. (Farrand and Drexler, 1985). The advancing ice of the Marquette Phase (9900 B.P.) cut off the eastern outlets for both the Lake Agassiz and the Superior basins, resulting in reoccupation of the Campbell (Emerson Phase) and Duluth stages, respectively (Clayton and Moran, 1982). Once again, the burden of draining the Superior basin shifted to the Brule and Portage outlets, as the ice margin lay to the north and east of the Brule outlet (Clayton, 1983). Lake Duluth must have remained at or slightly above the Duluth level until sometime prior to 9700 B.P. (Teller and Thorleifson, 1983) 17 LAKE NIPIGON-· : :: :: A R I LAKE GRANTSBURG WISCONSIN .. Figure 7. Lake Superior region. Showing location of glacial lakes outside of the Superior Basin and other ..... landmarks. Scale is approximate . 00 Mississippi outlets 1085- /DUL \ \ I 1000- \ ·1, --1 I f ·,·fost Duluth Lakes > lLJ .....J lLJ I I <1 _J I I w lLJ I ' I Cf) en 800 - I i I ., Proto- ' -250 lLJ \ :j-St. Marys_..____ St. Marys Strait---' St. Marys R. 0 > OJ 0 River c:i: CD \ : I <1 I : I (/") I ------W BB ------:- -200 Nip - : Soult w 600-Po"lt:! Post Minong --- Alg. I :Houghton MIN I _,. -150 / I -' I /" 400- ,,,,,.,, / / ,," / / /Qj I Io· , , I I I I I I I I I 12 10 6 4 2 0 1000 yrs B. P. Figure 8. Water level curves in the Lake Superior basin. The spike at 10,000 B.P. occurred only in the western basin, while the eastern basin was at the Minong level. DUL= Duluth, POST-ALG =Post-Algonquin, MIN= Minong, W =Washburn, BB= Beaver Bay, NIP= Nippissing. (From Farrand and Drexler, 1985) 19 With the final retreat of ice in the Superior basin at approximately 9700 B.P. the eastern outlet of Lake Agassiz was reopened, releasing a discharge in excess of 100,000 m3/S (Teller and Thorleifson, 1983) which flowed east into Lake Nipigon (Fig. 7). A series of five channels then conveyed this deluge into the Superior Basin, which presumably had returned the Minong level (Teller and Thorleifson, 1983). Farrand and Drexler (1985) suggest that this flooding might have consisted of a series of five floods, based on the fact that there are five well defined channels and a corresponding number of lower lake stages between the Minong and Houghton level. Detailed descriptions of the Post-Marquette lake stages are offered in Saarnisto (1975), Clayton (1985), Farrand and Drexler (1985), and Hansen and Mickelson (1988). 20 METHODS Geomorphic Analysis A geomorphic analysis was conducted on the western portion of the Lake Duluth Basin and the St. Croix and Kettle Channels with the aid of 7.5 minute topographic maps and aerial photos. This analysis served as an introduction to the study area and included the identification of landforms within the channels, landforms affecting the course of the channels, constraint of channel geometry and identification of potential exposures. Mapping within the channels focused on geomorphic features such as spillway banks, terraces, scoured surfaces, erosional remnants, and pendant and alcove bars. In an effort to improve the correlation of outlet elevations, former shoreline features were mapped. These features consisted of beaches, spits, deltas, and wave washed topography. Features were delineated on 7.5 minute topographic maps and the elevations of the discontinuous beach features were plotted against distance along a line between the Portage and Brule outlets. Information in geomorphically complex areas was supplemented by aerial photo examination (where coverage was available). This information was added to topographic base maps. When completed, the spillway landform information was then converted to a digital format through digitizing of the base maps (plate 1). In order to clarify stratigraphic and geomorphic relationships in the field, glacial landforms adjacent to the spillway were outlined on U.S.G.S. 1:100,000 maps based on mapping of Hobbs and Goebel (1982), Wright and Watts (1969), and Clayton (1984). Field Investigation Field work was conducted during the summer of 1994 to describe channel sediments for paleodischarge calculations and hydraulic modeling. Initially, field work consisted of reconnaissance mapping to locate exposures of channel sediments and to establish relationships between sediment types and landforms. The sites identified during 21 initial mapping, were then reexamined and described in detail. Detailed sedimentary descriptions were made at 32 sites in the St. Croix Channel, and 35 sites in Kettle Channel and tributaries. The number of sites is reflective of the sediment exposures found within the channels. Sedimentary descriptions focused on the matrix or clast supported nature of the sediments, sedimentary relationships, lithologic composition of the clasts, sedimentary structures, and median grain size of matrix and clasts. With this information, an environment of deposition was hypothesized and noted. Lack of access roads, high water tables, and thoroughly excavated gravel pits hampered attempts to observe the stratigraphic structures and relationships of exposures through much of the study area. For exposures within the channel margins a largest clast analysis was conducted to determine the clast size (clast size in the 90th percentile), which would later be used in discharge calculations. Largest clast analyses involved collecting the largest clasts in the exposure. The long and intermediate axes were then measured using a caliper for clasts under 20 cm (8 in) and tape measure for those greater than 20 cm. Bedrock outcrops within the channels were described by lithology and areal extent. In several areas with poor sediment exposures, a Gidding soil probe with a 10 cm (4 in) auger was used to determine geomorphic relations and subsurface stratigraphy. In reaches of the channels where peat accumulation obscured the channel bottom, channel bottom elevations were determined by finding the peat thickness with a peat probe. The thickness of peat deposition was determined by measuring depth at which sands or fine gravel were first encountered. Laboratory Methods Channel Geometry In order to accurately calculate paleodischarge channel geometry must be constrained. Channel geometry was defined by the construction of cross sectional profiles at selected sites along the length of both channel systems (Appendices A and B). During initial work 22 cross sections were measured at 2 mile intervals. Later, modeling with HEC-2 required more frequent cross section spacing in reaches that exhibited significant variability in cross sectional geometry that could not be accurately modeled. Channel geometry measurements were made along cross sectional lines and included width, depth and bottom elevation. Cross sectional spacing and channel curvature were also measured to fulfill requirements for HEC-2 modeling. All measurements were made with respect to the criteria illustrated in Figure 9. The resulting cross sections are found in appendices A and B. Channel gradients were reconstructed based on the correlation of stream terraces, abandoned channels, and channel bottom elevations. Channel width and depth were plotted with respect to distance downstream from the outlets. The first derivative of the slope was calculated to illustrate the change in gradient along the channels. Paleohydrological Analyses Following the compilation of channel cross-sections, the Manning equation was used to estimate minimum, maximum, and average bank-full channel capacities. For areas where channel bed sediments had been described, the largest clasts contained with stratified sequences were used to estimate maximum bed shear stress, flow depth, and discharge. However, rigorous analysis of stage/discharge relationships and channel capacities were accomplished using HEC-2. The Manning Equation Initial discharge estimates were computed using the Manning equation: (1.1) where V is velocity, Um is a unit conversion factor which equals 1 when R and V are in meters and equals 1.49 when R and V are measured in feet. Manning's coefficient (n ) is dimensionless (Chow, 1959). R is the hydraulic radius, for which depth can be substituted 23 for channels with a width to depth ratio greater than 100 (Tinkler, 1981). All of the spillway cross sections examined exceeded the width to depth ratio specified above. S 0 is stream gradient. In order to calculate the cross sectional area (A ) of the channels, the cross sectional profile was considered to be rectangular. Width and depth dimensions were measured assuming bank full conditions (Fig. 9). With A and V known, discharge (Q) can be calculated: Q=VA (1.2) Velocity and discharge calculations were computed at cross sections that were representative of a uniform reach, or where there was a significant change in either cross sectional area or gradient. Initial calculations used two values of Manning's n, 0.1 and 0.03 (Dingman, 1984), to constrain reasonable channel conditions. These n values were selected by matching observed channel conditions to descriptions for these values found in Chow (1959). These computations were made at 40 sites along the St. Croix channel and 22 sites on the Kettle channel. Results are found in Appendix C. Largest Clast Discharge Calculations The collection of largest clast data was used to calculate the shear stress required to transport the D90 clast size. The calculated shear stress then allows the constraint of paleodischarge. This process assumes that D90 is representative of the largest clasts the stream was able to transport (Church, 1978). The calculation employs Shield's relationship as follows (all units are metric): * Tc T =----- (1.3) c (P. - p,JgD where;< =Shield's stress (0.014) (Heller and Paola, 1989) (dimensionless) Tc =shear stress required to move clast of diameter (D) [F/A] Pw =water density [M/v] 24 Dl D2 FLOW OUT OF PAGE DATUM= SEA LEVEL DEPTH = ELI - EL2 WIDTH=Dl -D2 CROSS SECTION LINE l CROSS SECTION LINE 2 CROSS SECTION LINE 3 LIMIITOF SPILLWAY INCISION LOB= LEFT OVERBANK LENGTH ROB = RIGHT OVERBANK LENGTH I Figure 9. Channel dimension measurements. Upper diagram shows cross sectional view. Lower diagram shows map view. 25 p s = clast density [M/v] 2 g =acceleration due to gravity (9.81 rn/s ) D = diameter of D90 clast [L] Shield's relationship is then rearranged to solve for Tc : Tc = (Q.Q14({ps - Pw)gD) (1.4) Tc is then substituted into the following expression : h = _!_s_ (1.5) p"'gS' where: h = flow depth [L], S = stream gradient (dimensionless), Specific discharge is then calculated by the relationship for universal velocity distribution in open flows: q = h.jihS Ln(_!: - 1J (1.6) K Z0 where: K =Von Karman's Constant= 0.4 (Chow, 1959) .z;,, = Roughness length which is calculated by: K .z;,,=-s (1.7) 3D Total discharge can then be calculated by: Q=qB (1.8) where: Q = total discharge [Vff] B = channel width [L] 26 Largest clast data were also used to compute the bed roughness of the channels following the work of Church (1978). Bed roughness is computed by: I 6 0.0926(R ) n=------1.16 + 2.0(log( RI Dg )) 4 (1.9) where: n = bed roughness R = hydraulic radius (depth) Dg4 = diameter of the 84th. percentile clast Development ofStage/Discharge Rating Curves Stage/discharge rating curves illustrate the dependence discharge on water level (stage) (Bedient and Huber, 1992). Once lake outlet and channel geometry are defined, stage/discharge relations can be determined. The construction of stage/discharge relationships allows for the comparison of known lake stages with calculated outlet and channel discharge capacity. During this investigation stage/discharge rating curves were constructed using outlet water surface elevations specified by HEC-2 (discussed in detail below). Water-Surface Profile Modeling (HEC-2) In order to accurately estimate the stage/discharge relationship water elevations at the lake outlets must be correlated with outlet discharge. This task was accomplished through the modeling of discharge and water surface profiles using HEC-2. HEC-2, developed by the U.S. Army Corps of Engineers, calculates water surface profiles for steady and gradually varied flow in natural or artificial channels (Hydrologic Engineering Center, 1990). The program is based on an iteration (also known as the step standard method) of a one dimensional energy equation, with energy losses due to friction computed by the Manning equation. Both subcritical and supercritical flow can be modeled. Basic input 27 parameters of HEC-2 include a starting water elevation, cross-sectional channel geometry, discharge, energy loss coefficients, and channel and overbank reach lengths. Energy losses are represented by Manning's n , and expansion or contraction coefficients to account for energy losses between adjacent cross-sections. A water surface is determined with HEC-2 by completing the following procedure (Hydrologic Engineering Center, 1990): 1. Specify a water surface elevation at the downstream cross section (subcritical flow) for a given reach. 2. Based on the specified water surface elevation, determine the corresponding total conveyance and velocity head. Total conveyance is found by the summation of the incremental conveyances (Fig. 10) calculated for each subdivision. Conveyance for a subdivision is found by: k = 1.486 (l.10) ll ' where k is conveyance, n is Manning's roughness coefficient, a is the cross sectional area and r is the hydraulic radius. Velocity head ( V,,) is determined by: av2 V=- (1.11) " 2g ' where a is the velocity coefficient, which ranges from 1.05 to 1.40 for most cross sections and is an indication of the velocity distribution across the cross section (Bedient and Huber, 1992). Water velocity is represented by V and g is the acceleration due to gravity. 3. With values for conveyance and velocity head, compute S1 : ( 1.12) 28 S1 is the representative friction slope, Q1 and Q2 represent discharge at the beginning and end of the reach, Ki and K2 are the conveyance at the end points of the reach. With S1 from 1.12, he, the elevation head can be computed by 1.13: (1.13) where C is the expansion or contraction coefficient. Contraction and expansion coefficients are typically 0.1and0.3, respectively, for minor changes in channel geometry. For abrupt changes, values as high as 0.6 (contraction) and 1.0 (expansion) may be employed (Bedient and Huber, 1992). L is the discharge-weighted reach length, determined by equation 1.14 L = L,ollioh + LchQch + LroJ:loh (1.14) Q/ob + Qch + Qob where Lioh• Leh• andLrob are reach lengths specified for flow in the left overbank, main channel and right overbank, respectively. Q10b, Qc,,, Qrob =arithmetic average of flows at the ends of the reach for the left overbank, main channel, and right overbank, respectively. 4. With the values from steps 2 and 3, solve Equation 1.15 for water surface elevation a y2 a y2 WSi + _2__L = w.s; + _1_1 + h (1.15) 2g 2g e where: WSi and w.s; are the water surface elevations at the upstream and downstream ends of the reach, respectively. V1 and V2 are mean velocities (total discharge/ total flow areas) at ends of the reach. The computed value of W S 2 is compared with the value assumed in step 1. The interation continues until the values agree to within 0.01 meters (or 0.1 feet). 29 Figure 10. Total conveyance for the cross section is obtained by the summation of the incremental conveyances. (Modified from HBC, 1990) Specified Variables for HEC-2 Modeling Multiple water surface profiles were modeled in order to constrain discharge in both the St. Croix and Kettle channels over a variety of conditions. Final profiles for the St. Croix Channel were modeled for multiple discharges, ranging from 2500 to 25,000 m3/s, at increments of 2500 m3/s. The upper end of this range was determined by HEC-2 as the bankfull discharge. The Kettle Channel was modeled similarly, with discharges ranging from 1000 to 12,500 m"3/s, at an interval of 2500 m3/s. Again the highest discharge modeled represents bankfull conditions. Each discharge value was run as subcritical flow, for three different Manning coefficients of 0.1, 0.03 and 0.065. Initial starting elevations were correlated with terrace elevations, whereas, upstream reaches used starting elevations obtained from the last modeled cross section from the previous reach. The channels were subdivided into reaches ranging from 10 to 36 miles to simplify data entry and editing. The portion of the St. Croix Channel from the modern divide (mile 18) to the Brule outlet (mile 0), is now occupied by the north-flowing Bois Brule River. Headward erosion has excavated the bottom of the former channel. In order to reconstruct discharge for this 30 Shoreline Features Between the Portage and Brule Outlets Beach ...... Wave Washed Top09rophy - ·- ·- -- Outlet Sills ----- Lake Duluth Level 1160 ...... 1180 . ······ .. . . . - 1140 1120 - 1120 ...... -. . . - - lrOO ------1100 1080 -- 1080 - =-- -- -: =--=- ---- _:-__;.. - _- --_ "- _------_. =:_.:. . • - .:- - i!c;l IOBlJ 1060 104-0 - - - -- ·- HUO 1020 I I I I I I I I I I I 1020 0 5 10 15 20 25 JO JS 40 45 50 55 Miles East of the Portage Outlet Figure 11 . Glacial lake shoreline features of the southern highland of the Superior Basin between the Portage and Brule outlets. Elevations ore uncorrected for differential isostatic rebound. Outlet sills between miles 50 and 55 represent two modeled Brule outlet elevations. Lower sill between miles 0 and 8 is the elevation of the Portage outlet, the upper sill represents the elevation of the rim of the Lake Duluth basin. V.)- reach an estimate of the channel gradient was made. This was accomplished by assuming that the gradient for the reach between miles 0 and 18 was similar to the reach between miles 18 through 30, as the latter reach appears to have been relatively unaffected by modern erosion. The gradient for miles 18-30 is 1.89 x 10-4 and by extrapolating this gradient from the modern divide upstream to the outlet an uncorrected outlet elevation of 315 m (1035 ft) is obtained. Following the detailed examination of beach and outlet features, later models used a gradient defined between an outlet terrace at 323 m (1060 ft) and the modern divide 311 m (1020 ft). Correction for differential rebound To more accurately model the interaction of the Lake Duluth level with the Portage and Brule outlets, it was necessary to correct the outlets for isostatic rebound. Lake Duluth is defined by a well developed, but discontinuous series of strandlines which lie at an elevation of about 323 m (1060 ft) near the Portage outlet (Fig. 11). Near the Brule outlet the best developed strandlines lie at a elevation of 335 m ( 1100 ft). Through the delineation of beach and other shoreline features between the outlets, a trend of increasing elevations was observed. In order to clarify the differential rebound of the Lake Duluth shoreline, all features below the lowest possible Brule outlet (315 m) were eliminated as were features assumed to be remnants of earlier higher glacial lakes. Independent Confirmation Of Estimated Discharge Calculation of the energy availible to melt ice allows for the estimation of ice melt rates and meltwater production within the Superior basin watershed during glaciation. This energy balance concept illustrates the relationship between available energy and glacial ice melt rates, from which meltwater discharge can be calculated. For this study the author used a series of energy balance curves developed for Lake Agassiz (Fig. 12) (J.B. Swenson, unpublished data). Each melt rate curve represents the meltwater production for 32 a specified equilibrium line position during the hypothetical melt season which extends from about June 26th to November 16th, with the peak melt reached on August 25th. For the purpose of this model the drainage basin of the Superior lobe was estimated at 130 km using the ice configuration reconstructions of Dyke and Prest (1986) at 10,000 B.P. 33 250 ----· 200 150 100 ,r·------./,,.-:_----.__---·,.._, 40 kPa .... - '""'-...... 50 ...... ,.. ·, ·--·----·---·--so-l Figure 12. Showing melt rates calcuated from energy balance model. Curves account for variation in melt rates for different ablation zone lengths. Melt season begins on June 26 and ends on November 16. Peak melt rate on August 25 (Modified from Swenson, 1994) SHEAR STRESS (kPa) ELEV ATI ON LINE PEAK MELTW ATER POSIDON(KM) DISCHARGE (m"3\s) 10 590 35,360 20 295 17,693 30 200 10,888 40 150 8,847 50 120 7,078 Table 1. Meltwater production from the Superior Lobe. Discharge calculations based on a glacier width of 130km. Estimated from Dyke and Prest (1986). 34 RESULTS The Kettle and St. Croix Channels have been altered by geomorphic processes during the Holocene. The extent of this modification is, however, difficult to quantify. Most of the post-glacial.modification is incision by modern streams but the primary meltwater channel characteristics are readily identified. The Kettle and St Croix Channels have a complicated history and are the result of erosion from Lake Duluth discharge, but meltwater discharge from retreating glacial ice and the drainage of Pre-Duluth glacial lakes. Although channel modification resulting from individual discharge events is difficult to distinguish, general observations of channel characteristics can be made about the Lake Duluth chapter in the channel's history. ST. CROIX CHANNEL CHARACTERISTICS GENERAL GEOMORPHOLOGY AND CHANNEL GEOMETRY The St Croix Channel is a prominent geomorphic feature of northeastern Wisconsin. With a maximum width of 6759 m and a maximum depth in excess of 30 m, the St. Croix Channel dwarfs the modern, underfit Upper St. Croix River. The St. Croix Channel can be divided into two parts, upper and lower, separated by the modern drainage divide between the Bois Brule and St. Croix rivers (Fig. 2). From the Lake Duluth outlet south to the modern divide, the St. Croix Channel is a straight, steep sided, deeply incised channel with poorly-developed terraces. Post-glacial headward erosion has reversed the slope of the channel bottom allowing the modern Bois Brule to flow to the north erasing much of the original channel bottom. An example of the extent of modern erosion is located just north of Brule, Wisconsin where the Bois Brule has incised over 37 m (120 ft) (Fig. 13). This form gives way to a significantly wider and shallower, meandering, flat bottomed channel near Solon Springs, Wisconsin (plate 1). Downstream 35 Figure 13. Showing the incision of the Bois Brule river, about 8.0 km northwest of Brule, Wisconsin. Note wave topography in section 22. Scale is 1:24,000. From U.S.G.S. 7.5 minute Oulu Quadrangle. Area shown is 2.40 km wide. 36 from the divide the channel widens in response to a decrease in slope (Fig. 14b and c). The next 32 km of St. Croix channel is composed of straight, incised reaches intermixed with broad and meandering sections (plate 1). The wider, lower gradient reaches are characterized by features such as erosional remnants, abandoned channels, terraces, and longitudinal bars (discussed below). Downstream from Danbury, Wisconsin the spillway consists of a deep narrow valley that evolves into a broad channel that has been tentatively named the Chengwatana Surface (M.D. Johnson, 1994, pers. comm.) (plate 1). As previously discussed, channel cross-sectional shape is highly variable. This variability can be attributed to changes in many variables including slope and bank materials. In order to illustrate this variability, two contrasting reaches of the St. Croix Channel were chosen to illustrate similarities and differences in channel geomorphology observed throughout the study area. Geomorphology of the Island Lake Quadrangle The portion of the St. Croix Channel depicted on Figure 15 is located 9.6 km south of the Lake Duluth outlet (plate 1). The channel is bordered by a portion of a moraine formed during the Porcupine Advance (Clayton,. 1984). The topographic expression of this moraine is in stark contrast with the Swiss Surface (Clayton, 1984) (Band A, respectively on Figure 15). The channel in this location is approximately 1040 m wide with a maximum depth of 40 m. The true depth and gradient of this portion of the spillway is difficult to determine because of modem incision by the Bois Brule River. The cross sectional profile of this reach consists of an asymmetrical, narrow, steep sided channel (Fig. 18). A point bar/cutback relationship is suggested by the differences in slope between the eastern and western banks of the channel (Fig. 15). A number of gullies, which have eroded through the channel banks, must have developed soon after deglaciation as many of the gullies are headed by closed depressions that can be attributed to the melting 37 310 300 290 280-t------\:------1 270 260 ...... zoNE.4 ...... ZONE2 ZONE3 250 _. _._._._.,._._._._._._._._._._._._._.._._._._._._._._.,._._._._._._._._._._._._. .• _.,.,._._._.,. _._._.,. .._. _._._._. _. _. _._. _. _._._. H•..,._.n_._._._._.,u_._. _. _._.,u_. ,.._._._._._._._._._._._.,_._.n _.,._.._._._._._._._._.._._._.._.._._. ,._._._.H _. _. _._._._.._._._.u_.,. .n ._.. _. _._. . _.;,.,. •.• _._._._._._. _.,_._._,._.,. _. 0 10 20 30 40 50 60 70 80 90 100 MILES DOWNSTREAM FROM OUTLET Figure 14a. St. Croix channel bottom elevations 4500 4000 3500 ...... -...... 3000 ... ·················································...... ·································· 2000 1500 1000 500 ...... ZONE I >f< ZONE 2 >I< ZONE 3 > 0 10 20 30 40 50 60 70 80 90 100 MILES DOWNSTREAM FROM OUTLET Figure 14b. St. Croix channel Width vs. Distance from outlet 38 fc- ZONE3 -0.0015 -0.0020 ZONE 2 --->I -0.0025 ZONE4 -0.0030 -+---.---.-..--.---.----.-...--r----..---..-...--r---.-.....--.---.---.-..--.---t 0 10 20 30 40 50 60 70 80 90 100 MILES DOWNSTREAM FROM OUTLET Figure l 4c. St. Croix channel gradient vs. distance downstream from outlet 4.00e-7...------. 3.00e-7 f- c; 2.00e-7 -< l.OOe-7 0 O.OOe+O -t-+<...... _-_,_...,..,_..,-.._,_,..,, --...... --+-<..-,. ---..-1-++1 ...... =--···-·-·············...... ___- ____- ___- ___ ZONE3 ZONE4 -4.00e-7 -5.00e-7 -6.00e-7 -+---.--.....--.---.-...--.---.-...---.----,-.....--,---,.--r---r-r---.---.--f 0 10 20 30 40 50 60 70 80 90 MILES DOWNSTREAM FROM OUTLEf Figure 14d. St. Croix channel first derivative of slope vs. distance downstream from outlet 39 Figure 15. Showing the Swiss Surface (A), Porcupine moraine (B), Post-glacial gully (C), and the St. Croix channel (D). Scale is 1:24,000. From U.S.G.S. Island Lake Quadrangle. The area shown is approximately 3.8 km wide. 40 of buried ice (Con Figure 15). This relationship implies that this portion of the channel must have been in existence prior to, or contemporaneous with deglaciation. Geomorphology of the Webb Lake Quadrangle The portion of the St. Croix Channel on the Webb Lake quadrangle is geomorphically complex (Figures. 16 and 17), when compared to the Island Lake reach. This reach is characterized by a maximum width of 2775 m, maximum depth of 24 m, and an average gradient of 7.9 x 10-4. The surface geology of this region is dominated by the Swiss outwash surface, which lies at an elevation of approximately 305 m (1000 ft) and slopes to the southwest. There are four distinct surfaces within the margins of the St. Croix Channel on the Webb Lake quad, three of which can be attributed to postglacial erosion. The highest surface, found at an elevation of 308 m (1010 ft) , slopes to the southwest. It is a portion of the outwash surface created during the Swiss Advance (Clayton 1984) (A on Figure 16). Three other surfaces, B, C, and D (Fig. 16) represent incision of the Swiss Surface. Evidence for this erosion can be seen in the form of a small channel in eastern 112, sec. 18, T. 42 N, R. 14 W and by an erosional remnants in the NE 1/4, NW 1/4, sec. 26, T. 42 N, R 15 W (A on figure 18b) and SE 1/4, sec. 31, T. 42 N, R. 15 W (Fig. 16). The first surface attributable to spillway erosion lies at an elevation of approximately 296 m (970 ft) (Bon Fig. 16). This extensively developed, fairly uniform surface is thought to represent the first stabilization of the St. Croix Channel bottom incised into the Swiss surface. Examples include; N 1/2, sec. 26, T. 42 N, R. 14 W, NE 114, NE 1/4, sec. 35, T. 42 N, R. 15 W (Bon Figure 16), and sec. 29, T. 42 N, R. 14 W (Bon Figure 16). The next period of erosion resulted in the downcutting of the 296 m surface to a level of approximately 280 m (920 ft) (Con fig. 16). This interpretation is based on the existence of a number of prominent channels (SW 1/4, sec. 24, T.42 N., R. 15 W. (C on Figure 17) 41 Figure 16. Showing four erosional surfaces (A, B, C, D) of the Webb Lake Quad. See text for description. Scale is 1:24,000. From the U.S.G.S. Webb Lake Quadrangle. Area shown is approximately 3.8 km wide. 42 Figure 17. Showing the four erosional surfaces (A, B, C, D) of the Webb Lake Quad. See text for description. Scale is 1:24,000. From the U.S.G.S. Webb Lake Quadrangle. Area shown is approximately 4.3 km wide. 43 and NE 1/4, sec. 29, T. 42 N, R. 14 W.) (Con Figure 16) whose bottoms lie at this level. As a result of this incision, several erosional remnants were created such as Big Island and those located in the N 1/2 sec. 25, T. 42N, R. 15 W (Fig. 17). Another interesting feature is the valley occupied by the modern Namekagon River, which grades into the St. Croix channel at this level (Con Fig. 16). This valley apparently formed contemporaneously with the 280 m surface because both are graded to the same elevation. The last distinct period of erosion, formed an incised channel, occupied by the course of the modern St. Croix River (D on figures 16 and 17). The most likely source of water for this erosional event is Lake Duluth water, because the channel is too large to have been formed by erosion of the modern St. Croix. This erosional surface beheads a number of the channels and contains several erosional remnants whose maximum elevation reflect earlier surfaces ( for example NE 1/4, sec. 34, T. 42 N, R. 15 W and SE 114, NE 1/4, sec. 25, T. 42 W, R. 15 W) (Fig. 16). CHANNEL GEOMETRY RELATIONSHIPS In theory, river width and slope dimensions should be inversely related, as should width and depth. Assuming a constant discharge, increasing slope should yield a decrease in the width, and vice versa Similarly, assuming constant discharge and slope, river width should decrease as depth increases, and vice versa With these relationships in mind, channel dimensions were examined. The St. Croix Channel can be divided into four zones, based on general trends in channel bottom elevation (Fig. 14a). Upon further examination, slope and width characteristics of the spillway, tend to exhibit similar trends within these boundaries (Figs. 14b, 14c). Zone 1 is a fairly uniform reach with mild slopes, averaging 2.0e-4 (Fig. 14c). The uniformity of the slope from miles 0 to 18 is an artifact of slope reconstruction as headward erosion of the Bois Brule has modified the former channel bottom, necessitating the 44 estimation of the paleoslope. This estimation was accomplished by inferring a uniform slope between the modem divide (311 m) and the lowest terraces at the outlet (315 m), which assumes that this terrace was formed by lake Duluth outlet erosion. Zone 1 channel bottom elevations were corrected for isostatic rebound, as were the rest of the elevations for the St. Croix channel. The uniformity of the slope is illustrated in figure 14d, by the low amplitude of the first derivative of the slope. Small periodic variations in the channel bottom elevation (Fig. 14a) channel gradient (Fig. 14c) and 1st derivative of channel gradient (Fig. l 4d) are because of rounding off elevations to the nearest contour elevation. Channel width exhibits more variability, generally decreasing from 4000m at the outlet to a minimum of 700 mat mile 10 (Fig. 14b). From this point the channel width gradually increases, with some minor fluctuations to 3400 m at mile 34. The boundary between zones 1 and 2 is defined by an abrupt change in slope at mile 35. The gradient in zone 2 increases to an average of approximately 1.0 x 10·3 and exhibits the most variability in gradient of the four zones as illustrated in figure 14 a, c, and d. Channel width generally decreases, with the exception of the area centered on mile 53, where the width briefly increases (Fig. 14b). Sixty-five miles downstream from the outlet the channel gradient decreases to value of approximately 1.0 x 10·4, marking the beginning of zone 3 (Fig. 14a). This zone is characterized by relatively constant gradients and steadily increasing width. Maximum channel width, within this zone, approaches 5000 mat mile 84 (this maximum does not include the Chengwatana surface because this surface was determined not to have been utilized during the lake Duluth events). Zone 4 encompasses the last 13 miles of the study area, and is defined by a significant drop in bottom elevation (Fig. 14a). Here average gradient approaches values of 1.0 x 10-3, and as with zone 2 the gradient exhibits greater variability than the more gently sloping zones (Fig. 14d). Width decreases in a downstream direction, in response to the increasingly steep gradient. 45 CHANNEL SEDIMENT DESCRIPTION The type and nature of the sediments found within the channels is variable from reach to reach, reflecting the factors that control the depositional environment. These variables include: grain size and composition of the eroded material, flow regime, bedrock influences, and channel geometry. The bank materials of the St. Croix Channel are dominated by sand sized sediment as this is the predominant sediment type found in the Swiss surface. Sand from the Swiss Advance, as well as others, also makes up the majority of deposits observed within the St. Croix Channel. Although sands derived from the Swiss Advance and other glacial episodes dominate the sedimentary history of the St. Croix Channel, gravel deposits were scattered throughout the channel. The majority of channel deposits in the St. Croix channel consist of moderately to well sorted, massive, loose gravel. Gravel deposits were generally matrix supported with moderately to well rounded clasts averaging 5 - 25 cm in diameter (2 - 10 in). Clasts in excess of 60 cm (24 in) were observed in a few channel sediment exposures and also scattered through the channel bottom in a number of localities. Most depositional exposures were in the form of longitudinal and alcove bars, while erosional exposures were predominately located on terrace surfaces. KETTLE CHANNEL CHARACTERISTICS GENERAL GEOMORPHOLOGY AND CHANNEL GEOMETRY The Kettle Channel has a maximum width of 8095 m, reached at the confluence with the St Croix Channel, and a maximum depth of 33 m. These dimensions are not representative of an average reach of the Kettle Channel, which in general, is significantly shallower and narrower. From the lake outlet to Sturgeon Lake, Minnesota (Fig. 2), a distance of 19 km, the Portage Outlet Channel and Kettle Channel are bordered by the Nickerson moraine and 46 LJ Ground Moraine (Cloquet Association) Ground Moraine (Mille Lacs Association) Ground Moraine (St. Croix Association) LJ End Moraine (Undifferentiated) Lv:vj hp = Holocene Peat so Outwash (Undifferentiated) Stagnation Complex (Cloquet Moraine) L::j td = Holocene/Pleistocene Terraces Figure 18. Quaternary Geology of the Kettle Channel. Modified from Hobbs (1982). 47 ground moraine associated with Automba phase of glaciation (Hobbs, et al., 1982) (Fig. 18). The banks along much of this reach have been affected by post-glacial collapse of stagnant ice, and complicate definition of the channel. A number of gravel bars and scoured surfaces are also found within this reach. North of Moose Lake, the Kettle Channel truncates the prominent Scanlon channel (Fig. 19), which is a meltwater channel formed by the drainage of Lakes Aitkin II and Upham II (Wright et al., 1970)(Fig. 2). At Sturgeon Lake, the modem Moose Hom River enters the modem Kettle River. This also marks the point of confluence between the Kettle and Upper Kettle Channels (Fig. 2), the latter being formed during the early stages of discharge from Lakes Aitkin II and Upham II. South of this confluence, the collapsed topography of the western bank of the Kettle Channel has been modified by subsequent channel erosion, creating a number of erosional remnants (Fig. 20). On the eastern side of the Kettle Channel the collapse topography has been subdued by burial beneath the Willow River outwash plain (Fig. 20). Near the community of Willow River, Minnesota, the Kettle Channel increases in width (Fig 2lb) as slope decreases (Fig. 21c) Near Rutledge, Minnesota, the Kettle Channel evolves into wide, shallow, flat bottomed channel. A few kilometers south of Rutledge, the channel narrows to a distance of only several hundred meters forming a steep sided gorge (Fig 2lb). South of Sandstone, Minnesota, the channel gradually widens (Fig. 21B) and shallows as it encounters the Chengwatana surface. Coinciding with the expansion of the Kettle Channel is a distinct increase in the number of terraces, gravel bars and erosional remnants. CHANNEL GEOMETRY RELATIONSHIPS .. The Kettle Channel can be divided into three zones based on criteria similar to those used for the St. Croix Channel. The three zones are miles 0 - 21, miles 21 - 34, and miles 34 -45 (Fig. 21a). 48 Figure 19. Showing the confluence of the Scanlon Channel (A) with the Portage Outlet channel (B). From the U.S.G.S. Moose Lake Quadrangle. Area shown is approximately 3.6 km wide. 49 ... , . ·, ..-·•• ·.·- > ,f ' ! : - ·-' l ' ;,,,-.....' : \- A.- 1 :.:.:' :.: / • ···•·· , I: ·,;,:, -d i.- Figure 20. Showing uncollapsed (A) and collapsed Willow River Outwash plain (C). Note streamlined erosional remnant (B). Dashed line approximates the limits of the Kettle channel. From the U.S.G.S. Willow River Quadrangle. Area shown is approximately 4.0 km wide. 50 Zone 1 is characterized by a gradually increasing gradient that averages less than 5.0 x 4 10- • Width is variable and increases slightly from 305-610 meters. Along zone 2 the gradient of the channel increases dramatically. This change in gradient is illustrated in figure 21d, as the plot of the first derivative of elevation vs. Distance. Along zone 2 there is a dramatic change in spillway geometry. This reach is narrow with a steep slope and is deeply incised (Fig 21a, b) Zone 3 marks the transition from the narrow, deeply incised channel found in zone 2, to a modest channel incised into the extensive Chengwatana surface. The gradient here 4 average 5.0 xl0- , and are the most consistent of the three Kettle Channel zones. Width increases to a maximum of nearly 8000 m on the Chengwatana surface. Unlike the St. Croix Channel, the Chengwatana surface was included in the width dimensions of the Kettle. This decision is based on the fact that, although it is unlikely that this surface was created by waters originating from Superior basin glacial lakes, it may have been partially inundated during the drainage of these lakes . CHANNEL SEDIMENT DESCRIPTION Kettle Channel Sediments Although 35 sites were investigated along the Kettle Channel, only 11 were to be determined to be candidates for deposition by channel discharge. The criteria used to these sediments were elevation, grain size, sedimentary and geomorphic relationships and topographic expression. The majority of the gravel deposits observed within the Kettle channel are characterized by well sorted, moderately to well-rounded clasts supported by a moderately to well-sorted sand. Kettle channel gravel deposits are typically massive to weakly bedded. Average D90 clast diameter is 3-8 cm with composition being dominated by the Thomson formation and volcanic and sedimentary lithologies derived from the Superior basin. The majority of channel sediment exposures were associated with longitudinal bars. 51 1040 ,..... 1030 1020 980 --...... - •. - ...... - ...... - ...... 970 ...... 960 ...... 950 ····--········-··-··----·--···-········--··················-···-··-·-··-··-···-··-·······-· ...... ::±L ...... - 0 5 10 15 20 25 30 35 40 45 MILES DOWNSTREAM FROM OUTLET Figure 21a. Kettle channel bottom elevations 8000 7000 ,..... 6000 ...... ::r: !:--< 5000 -Ci >- 4000 < ....l 3000 ....l p.. -en 2000 1000 0 5 10 15 20 25 30 35 40 45 MILES DOWNSTREAM FROM OUTLET Figure 2lb. Kettle channel width vs. distance from outlet 52 0.0000....------.-.....------.------.... -0.0005 ...... ZONE! :.: ...... jc--- ZONE3 -0.0015 ------·------·-+----+------! -0.0020 ·····························································································...... ························································· -0.0025 5 10 15 20 25 30 35 40 45 MILES DOWNSTREAM FROM OUTLET Figure 21c. Kettle channel gradient vs. distance downstream from outlet 2.00e-7....------. l.50e-7 ZONE3 -1.00e-7 -l.50e-7 10 15 20 25 30 35 40 45 MILES DOWNSTREAM FROM OUTLET Figure 21d. Kettle channel first derivative of slope vs. distance downstream from outlet 53 800000 700000 ,-.. en 600000 <- N=0.03___. 6 500000 tl.l 0 400000 < 300000 :I:: u en 200000 -Q 100000 0 0 10 20 30 40 50 60 70 80 90 100 MILES DOWNSTREAM FROM BRULE OUTLET Figure 22. Bankfull discharge as calculated by the Manning equation. The minimum discharge for n=O. l is 13,724 m"3/s, for n=0.03 minimum dishcarge is 45,747 m"3/s. Both minimum discharge values were computed at mile 48. 350000 300000 ,-... ti) 250000 < -8 '-' tl.l 200000 0 150000 <:I:: u en 100000 -Q 50000 0 5 10 15 20 25 30 35 40 45 50 MILES DOWNSTREAM FROM THE PORTAGE OUTLET Figure 23. Bankfull discharge as computed by the Manning equation. The minimum discharge for n=0.1is12,010 m"3/s, for n=0.03 minimum discharge is 40,034 m"3/s. Both minimum values were computed 14.5 miles downstream from the Portage outlet. 54 Pre-Lake Duluth Channel Sediments In order to constrain the influence of discharge from the Portage outlet on the preexisting channel system, the diversionary channels described by Wright (1970) were investigated to characterize their deposits. This characterization was done in hope of being able to separate Lake Aitkin II and Upham II drainage events from similar events originating from the Superior Basin. A longitudinal bar 1.76 km in length is located in the Scanlon channel approximately 5 miles northeast of Moose Lake, Minnesota . This bar offers many excellent exposures that are representative of the deposits found in the diversionary channels. PK-27 (SE 114, NW 1/4, sec. 11, T. 46 N., R. 19 W.) is one such exposure, which displays approximately 7.5 m of massively bedded, matrix supported gravel interbedded with thin (20 cm), discontinuous, course sand lenses. Gravel clasts at this site averaged 7 - 14 cm and were dominated by local lithologies of the Thomson formation and rocks associated with the Superior basin. PALEOHYDROLOGIC CALCULATIONS Paleodischarge is difficult to estimate because of problems in accurately estimating slope, water depth, and channel geometry, variables that are essential to discharge calculations. In order to estimate discharge as accurately as possible, this study employed a number of methods to constrain the volume of water the channels could accommodate. THE MANNING EQUATION Bankfull discharge estimates made using the Manning equation are found in Appendix A. Figures 22 and 23 illustrate the variability in bankfull discharge capacity for the St. Croix and Kettle channels, respectively. Maximum bankfull discharge for the St. Croix Channel is 1,265,533 m3/s and 379,660 m3/s for Manning's roughness coefficients of 0.03 and 0.1, respectively (Fig. 22). These maximum values represent the bankfull discharge 55 50,000 45,0001::::: 146,000 er:, - 37,500 < il\111 '-' 35,000 %130 000 ::::::: C,!) , < 27,500 27,500 =: ·=:·:- u 25,000 er:,.... Q 20,000 11,500 rn 17 ,500mu14,000 14,000 1 12,0001 12,500 12,500 12,0001]: 10,000 I 7000 ':::::: 0 u.l u.l :i :i 0 e, 8 QI QI e, u.l °' C'I u.l - Figure 24. Spillway maximum discharge calculations for all methods. Light column indicates values calculated for the Kettle channel. Dark column indicates values calculated for the St. Croix channel. Maximum Ul discharge column shows reasonable maximum discharge range for each channel. 0\ Miles Downstream from Station Depth D90 Manning'sn Brule Outlet Number (meters) (meters) 17 BS-33 15.23 0.169 0.029 18 BS-32 16.76 0.158 0.028 19 BS-21 24.38 0.212 0.030 20 BS-23L 15.24 0.115 0.027 20 BS-23U 15.24 0.172 0.029 32 BS-24 21.33 0.38 0.033 33 BS-25 27.43 0.134 0.028 33 BS-26U 27.43 0.086 0.026 33 BS-26L 27.43 0.086 0.026 48 BS-9 24.38 0.062 0.025 52 BS-10 24.38 0.18 0.029 56 BS-7 16.76 0.307 0.032 78 BS-27 30.48 0.139 0.028 Average 0.028 Miles Downstream from Station Depth D90 Manning'sn Portage Outlet Number (meters) (meters) 2 PK-27 13.72 0.124 0.027 2 PK-27 13.72 0.124 0.027 3 PK-22 15.24 0.139 0.028 4 PK-26 16.76 0.091 0.026 7.5 PK-7 18.29 0.11 0.027 8 PK-4 15.24 0.12 0.027 10.6 PK-12 12.19 0.081 0.026 13 PK-24L 9.14 0.171 0.029 13 PK-24U 9.14 0.085 0.026 19.5 PK-20 12.19 0.182 0.029 25 PK-19B 30.48 0.185 0.029 Average 0.027 Table 2. Manning's roughness coefficients as calculated from largest clast analysis. U behind station numbers indicates upper formation in the exposure. L behind station number indicates lower formation in the exposure. 57 Miles Downstream from Station Discharge Brule Outlet Number (m3/s) 17 BS-33 155,149 18 BS-32 180,511 19 BS-21 80,325 20.3 BS-23L 53,991 20.3 BS-23U 98,072 32.5 BS-24 50,005 33 BS-25 11 ,747 33 BS-26 6,633 47.5 BS-9 20,027 52 BS-10 63,507 56 BS-7 178,850 78.2 BS-27 11,903 Miles Downstream from Station Discharge Portage Outlet Number (m3/s) 2 PK-27 7,908 2 PK-27 14,986 3 PK-22 22,938 4 PK-26 986 7.5 PK-7 19,366 8 PK-4 19,992 10.6 PK-12 16,358 13 PK-24 12,666 13 PK-24L 35,556 19.5 PK-20 56,764 25 PK-19 2,293 Table 3. Discharge calculated from largest clast analysis. U behind station numbers indicates upper formation in exposure. L indicates lower formation in exposure. 58 at mile 98. The average discharge is calculated to be 1,129,018 m3/s and 206,198 m3/s for roughness coefficients of 0.1and0.03, respectively. Using the same Manning's coefficients the minimum discharge was calculated to be 45,747 m3/s and 13,724 m3/s at mile 48 (Fig. 23). Because the maximum discharge of a channel is limited by the lowest capacity cross section, the minimum discharge values define the upper limit of potential channel discharges values. Appendix A(b) shows the bankfull discharge values calculated for the Kettle Channel, and figure 23 illustrates these values. Maximum discharge for the Kettle Channel is reached at mile 32, with values of332,671 m3/s and 99,801 m3/s, for n values of 0.03 and 0.1 respectively (Fig. 23). The average discharge is calculated to be 119,361 m3 /sand 35,808 (for n = 0.03 and 0.1 respectfully). The minimum discharge values were calculated 3 3 at mile 14.5, and equal 40,034 m /s (n = 0.03) and 12,010 m /s (n = 0.1), which as previously stated, defines the upper limits of channel discharge. To summarize, the maximum discharge that could be accommodated by the St. Croix channel is controlled by the channel geometry of mile 48. Bankfull discharge at this point is calculated to be 45,747 m3 /s (n = 0.03) and 13,724 m3 /s (n = 0.1). The maximum discharge capacity of the Kettle channel is limited by mile 14.5 to 40,034 m3 /s (n = 0.03) and 12,010 m3 /s (n = 0.1). LARGEST CLAST CALCULATIONS The largest clast data collected from channel deposits were used to estimate bed roughness (Table 2) and discharge (Table 3). St. Croix Channel discharge ranges from 3 3 178,850 m /s (BS-7) to 40,284 m /s (BS-26). BS-7 is also the site of the highest D90 (90th percentile clast size), with a diameter of 0.308 m, and the highest bed roughness of 0.032. The lowest D90 and bed roughness are located at BS-9, with values of 0.062 m and 0.025, respectively. The average bed roughness is 0.028. 59 - - BRULE STAGE CURVE 0 5000 10000 15000 20000 25000 30000 DISCHARGE (M"3/S) Figure 25a. Outlet stage I discharge curves. Manning's n =0.03, Brule outlet elevation is 315m. Dashed line indicates interpolated curve. Lake Duluth level is approximately 325m. ---- 325 BRULE STAGE CURVE 315 0 5000 10000 15000 20000 25000 DISCHARGE (M"3/S) Figure 25b. Outlet stage I discharge curves. Manning's n=O. l, Brule outlet elevation is 315m . Dashed line indicates interpolated curve. Lake Duluth level is approximately 325m 60 PORT AGE STAGE CURVE §E-< 3 25 ...... ' .. < B 320 ...... < ::::> (/J ffi E-< < 0 5000 10000 15000 20000 25000 DISCHARGE (M"3/S) Figure 25c. Outlet stage I discharge curves. Manning's n=0.03, Brule outlet elevation is 323m. Lake Duluth level is approximately 325 m. PORTAGE STAGE CURVE ------·-·------··-·----·------ 325 BRULE STAGE CURVE 315 ...... 310-+-...-.,....-,...... 0 5000 10000 15000 20000 25000 DISCHARGE (M"3/S) Figure 25d. Outlet stage I discharge curves. Manning's n=0.1, Brule outlet elevation is 323m. Lake Duluth level is approximately 325m. 61 320 310 300 ,.-... '-' 290 z 0 280 -E-< > 270 u:i 260 250 240 0 20 40 60 80 100 MILES DOWNSTREAM FROM BRULE OUTLET Figure 26a. St Croix channel bottom and water surface profiles. Elevations corrected for rebound. Q = 15,000 m"3/s, n = 0.03 340 330 320 ,.-... 310 '-' 5 300 -E-< 290 > 280 u:i 270 260 250 240 0 20 40 60 80 100 MILES DOWNSTREAM FROM BRULE OUTLET Figure 26b. St. Croix channel bottom and water surface profiles. Elevations corrected for rebound. Q = 15,000 m"3/s, n = 0.1. 63 330 325 320 315 ,-.., 310 ...._, z 305 0 E=: 300 > 295 290 285 280 275 270 0 5 10 15 20 25 30 35 40 45 MILES DOWNSTREAM FROM PORTAGE OUTLET Figure 27a. Kettle channel bottom and water surface profiles constructed for a discharge of 5,000 m"3/s and Manning's n = 0.03 340 335 330 325 ,-.., 320 ...._, 315 z 310 0 305 E-< - 300 > 295 290 285 280 275 270 0 5 10 15 20 25 30 35 40 45 MILES DOWNSTREAM FROM PORTAGE OUTLET Figure 27b. Kettle channel bottom and water surface profiles constructed for a discharge of 5000m"3/s and Manning's n = 0.1 64 and St. Croix Channels for HEC-2 modeling, a more localized measure of the differential rebound is required. Figure 11 illustrates the magnitude of the isostatic adjustment of strandline and beach features between the Brule and Portage outlets. A clustering of well developed beaches forms a topographic high east of the Portage outlet at an elevation of 324 m (1065 ft). Those beaches, although discontinuous, can be traced to the Brule outlet where they lie at an elevation of 335 m ( 1100 ft). A regression line plotted with respect to beach elevation represents the former plain of the Lake Duluth water surface. HEC-2: WATER SURFACE PROFILE MODELING In order to correlate discharge estimates with the Lake Duluth beach level, HEC-2 was employed to reconstruct the water surface elevations within the spillways. More importantly, a relationship between lake level and channel discharge is developed. Stage I discharge curves developed to examine the relationship between lake level and discharge through the outlets. For a spillway bed roughness of 0.03 and an uncorrected Brule outlet elevation of 315 m (1035 ft), a discharge in excess of 30,000 m3 /sis required for the water level at the Brule outlet to approximate the level of Lake Duluth (Fig. 25a) . Under these conditions the Portage outlet would be below accepted lake stage and functioning in conjunction with the Brule outlet, discharging about 2500 m3 /s. Figure 25b illustrates conditions identical to those used in Fig 26a with the exception of spillway roughness, which is 0.1. The increased bed roughness decreases the discharge requirements for the water level in the outlets to reach the Lake Duluth level. In this configuration a discharge of approximately 20,000 m3 /sis required for the lake to reach the Duluth level, of which 19 ,000 m3 /s would flow out of the Brule outlet. Figures 25c and 25d illustrate the discharge I stage relationship between the Portage and Brule outlets with the elevations of the St.Croix Channel increased to correspond to a Brule outlet elevation of 323 m (1060 ft) (uncorrected for isostatic rebound). With a roughness of 0.03 a discharge of approximately 35,000 m3 /s is required to raise the water level in the Brule outlet to the 65 Duluth level (Fig. 25c), whereas a bed roughness of 0.1 (Fig. 25d) requires discharge of only 16,000 m3/s to reach the same level. The final configuration for the stage diagrams features the 323 m outlet elevation with a roughness coefficient of 0.065 (Fig. 25e). With these parameters a discharge of roughly 25,000 m3 /s is required to raise the water level in the Brule outlet to the Duluth level. Figures 26a and b illustrate changes water surface and bottom elevation profiles for the St. Croix Channel caused by a change in Manning's roughness coefficient. Figures 27a and b illustrate similar changes for the Kettle Channel. The most reasonable scenario is represented by that illustrated by figure 25e for a number of reasons. 1) The predicted discharge of 25,000 m3 /s may be representative of equilibrium conditions since it is well below the predicted bankfull discharge as predicted by the Manning equation; 2) discharge falls into ranges predicted by the Manning equation; 3) discharge is sufficient to evacuate all but the highest predicted by the energy balance model and 4) it employs an outlet height which corresponds to the best developed terrace found in the Brule outlet 66 DISCUSSIONS Although the interaction between ice margins, glacial lakes of the Superior Basin and their corresponding outlets has been examined in detail for over 100 years, problems remain concerning the relationship between lake levels and the outlets. One such problem concerns the relationship between the glacial lakes of the Superior Basin and the two westernmost outlets, the Brule and the Portage and their respective channels. The first proglacial lake in the Superior Basin for which direct evidence is still observed followed the Nickerson Phase and Porcupine Advance of eastern Minnesota and northern Wisconsin, respectively. Following the final ice retreat from the western portion of the Superior Basin, Lakes Nemadji and Brule formed along the southern rim of the Superior basin. Near the Portage outlet, wave-modified glacial topography (marked by the transition from hummocky to planar topography) is observed up to an elevation of 351 m (1150 ft) and represents the former surface of Lake Nemadji. This shoreline is generally weakly developed, but, locally wave built terraces, sand spits, deltas, and beach remnants remain. Former shoreline features of Lake Brule can be seen in a wave washed surface whose upper limit lies at approximately 369 m (1210 ft) (Fig. 28). Some minor beaches can be observed at an elevation of 360 m (1180 ft) in Section 5 and 6, T. 46 N., R. 9 W., but overall beach development is poor. The poorly developed nature of the shoreline features may reflect the short amount of time the lake existed. These shoreline features indicate that the outlet was below 369 m when the wave washed surface was fonned, and suggest the outlet level must have dropped at least 9 m before the minor beaches formed. During the early stages of Lakes Nemadji and Brule, ice must have separated the two lakes because these wave modified surfaces are not continuous between the two outlets. During this time the Portage and Brule outlets functioned simultaneously, draining the separated Lakes Nemadji and Brule, respective! y. With the continued retreat of the Superior lobe, Lakes Nemadji and Brule, as well as a number of other minor proglacial lakes, coalesced forming Lake Duluth. The name Lake Duluth is derived from the well developed beaches located in Duluth, Minnesota which lie at an elevation of 67 approximately 335 m (1100 ft). This former shoreline is traceable to a point near the Canadian border along the north shore of Lake Superior, and into the Upper Peninsula of Michigan along the southern shore. Near the Portage outlet, in the extreme western portion of the Superior basin, the Duluth beaches lie at an elevation of 323 m (1060 ft). Tracing this strandline east to the Brule outlet, the elevation of the Duluth beach increases to 335 m (1100 ft) (Fig. 11). This 12 m increase in elevation is attributed to differential isostatic rebound, a value that is consistent with previously published values for the region (Johnson, 1946; Farrand and Drexler, 1985). It has been suggested that the Duluth beaches owe their well developed nature to the fact that this level was occupied twice; once upon the retreat of the ice following the Nickerson Phase and again during the Marquette phase (Farrand and Drexler, 1985). CHANNEL HISTORY ST. CROIX CHANNEL A number of studies on glacial spillways (Clayton, 1983; Matsch, 1983; Teller and Thorleifson, 1985; Baker, 1987; Lord and Kehew, 1987) have concluded that the formation of these spillways was the result of infrequent, high magnitude floods. Clayton (1984) suggests a similar origin for the St. Croix Channel based on a comparison of channel size and catchment area dimension (Matsch, 1983). The findings of the current study are that the St. Croix Channel apparently evolved through the late Wisconsin through a number of distinct periods of downcutting. The processes responsible for the establishment of the St. Croix Channel appear to have been a mixture of long term erosion punctuated by episodic flood events. Portions of the modern drainage system were intact as early as the Hayward Advance, when outwash drainage systems shifted from the Chippewa River to the Namekagon River (Clayton, 1984). During the end of the Swiss Advance the Swiss Surface underwent a period of incision and channelization (Clayton, 1984). This erosional episode may have been one of the initial events that defined the course of the Upper St. Croix. These channels were reoccupied and enlarged by meltwater produced by subsequent advances, further establishing the regional drainage 68 system. Evidence for the reoccupation of these channels is found in the form of an outwash surface within the entrenched Swiss Surface. This surface has an elevation of 332 m (1090 ft) in Sec 13, T. 44 N., R 12 W., south of Solon Springs, Wisconsin. Following the Lake Ruth Advance, ice in northern Wisconsin retreated into the Superior basin, allowing the formation of Lake Brule. The formation of Lake Brule must have closely followed the retreat of the Superior lobe from this position because of the presence of collapse depressions within the wave smoothed topography. Melting of buried ice may have allowed the passage of water over the moraine, and with subsequent erosion of the sandy sediment, establishment of the Brule outlet. This water would have been the first water to utilize the full length of the St. Croix Channel. The Duluth level beaches clearly grade to the Brule outlet, suggesting that the Brule outlet controlled this lake stage (Figure 11 ). A number of outlet variables may have influenced the increasing importance of the Brule outlet in the drainage of Lake Duluth. These factors include outlet elevation, outlet composition, lake levels and discharge capacity. The majority of the drainage of Lake Duluth was accomplished by this lowest outlet. The discharge capacity of the Brule outlet, in its modem form, is also greater than that of the Portage (Figures 25a-e). This higher discharge potential, when combined with the sandy drift that composes the Brule outlet area (the Portage outlet area is composed of clayey till), suggests that the Brule would have downcut more rapidly than the Portage for a given discharge. Clayton (1984) suggests that the St. Croix channel was downcut approximately 30 m during the retreat of the Superior Lobe through a single or a couple of catastrophic glacial lake discharges. Although there was not significant evidence for such floods observed during this study, the sedimentary record indicates large flows did take place during the history of the St. Croix Channel. With this in mind, events affecting the Superior basin prior to and after the formation of the St. Croix Channel must be investigated. Several potential sources for catastrophic flood events existed in the Superior basin during the Late Wisconsin. These include increases in lake level caused by glacial surging, discharges of meltwater in the form of jokulhlaups, and input of meltwater from other glacial lakes, particularly 69 Lake Agassiz. Clayton and others (1985) suggest that glacial surging occurred in the southwestern portion of the Laurentide Ice Sheet between 12,300 and 10,800. Little information is available in the Superior basin regarding the position of the ice margin during this period due to the presence of Lake Superior. Many authors (Bindschadler, 1983; Weertman, 1957; Alley, 1989; Kamb, et al., 1985) believe the main requirement for surge initiation is the presence of pressurized subglacial water, which decreases the bed resistance between the glacier and basal sediment. Clayton and others (1985) suggest that the impermeable nature of lake sediments found in the Great Lakes region, could result in increased water concentrations beneath the Superior lobe. An additional factor that was not mentioned is the potential of ice advance into existing bodies of water, more specifically the advance of the Marquette phase into Lake Minong, which occupied the Superior basin prior to the Marquette advance. With the presence of a body of water of sufficient depth, the ice of the Marquette advance may have been lifted from its base, accelerating its advance. In either case surging could have resulted in the rapid increase in lake levels in the Superior Basin. fokulhlaups are rapid discharges of ponded glacial meltwater, which could have either a subglacial or supraglacial source. These events offer an additional mechanism by which flood magnitude discharges could be accounted for. A series of jokulhlaups have been suggested as a triggering mechanism for the catastrophic flooding of Lake Missoula in the Late Wisconsin (Waitt, 1985). Although many jokulhlaups have been documented (i.e. Bjornsson, 1974, Atwater, 1983, Thorarinsson, 1957), no known evidence exists for their occurrence within the Superior basin. The complex interaction between the drainage of glacial lakes of the Great Lakes region and the lakes of the Superior basin is well documented (see previous sections). It is not the purpose of this section to summarize the chronology of these interactions, but to suggest whether these drainage events could have influenced the formation of the spillways in question. The earliest input of glacial lake water from a source outside of the Superior basin is the input received from the drainage of Lake Upham II. As discussed above, this event was probably involved in the initiation of the Portage outlet, but did not affect the Brule system because the outlets drained separate 70 basins. Later events involving the post-Marquette catastrophic eastward drainage of Lake Agassiz drastically altered the geomorphology of southern Ontario (Teller and Thorleifson, 1983, 1985, 1987b). Although the Portage and Brule outlets were ice free at this time, Clayton (1983) suggests that these floods occurred while the lake level in the Superior basin was well below the Duluth stage, and thus did not pass through the westernmost outlets. It is also unlikely that even the combined bank full capacity of the Brule and Portage spillways could accommodate floods of the magnitude generated by these events, which were on the order of 100,000 m"3/s (Teller and Thorleifson, 1983). Clayton (1984) discusses the formation of the Brule spillway, stating that if a flood is required to produce the dimensions of the Brule spillway, an external source of water must be sought. Clayton concludes that the most likely source of this flood would be Lake Ontonagon (Fig. 7); and he further postulates that the lake drained suddenly, flowed westward through a proglacial channel, which joined the Brule spillway at Brule, Wisconsin. Clayton claims that this flood might have been large enough to form the Brule channel. The author disagrees with this hypothesis based on discharge calculations for a channel constriction two miles east of the town of Brule. Using the Manning equation a maximum discharge of about 600 m3 Is was calculated for this constriction. This discharge was determined with the following parameters, Manning's n = 0.03, width= 365 m, depth (hydraulic radius)= 10.67 m, and slope was assumed to be 1 mlkm. Clearly, unless the flow through this constriction was supplemented with water from another unidentified channel, Lake Ontonagon flow cannot be responsible for the majority of the erosion found along the Brule/St. Croix spillway. Based on the previously cited work, major floods originating outside of the Superior basin cannot be held accountable for the formation of the Brule spillway. The stage I discharge curves illustrated in figures 25a-e were constructed in order to determine whether the Portage and Brule outlets functioned simultaneously at the Duluth level and to constrain the discharge requirements for the outlets at this level. The stage I discharge curves were constructed over a range of variables to account for the Brule outlet elevation and bed roughness. Bed roughness is a critical parameter, necessitating consideration of a range of bed roughness 71 values from 0.03-0.1. These values agree with bed roughness coefficients commonly used in spillway paleohydrologic reconstruction (Matsch, 1983; Lord and Kehew, 1987; Teller and Thorleifson, 1987b). Largest clast analysis was used to confirm the bed roughness coefficients used in HEC-2 modeling. The calculated values fall within this range (table 2). Figure 25e was constructed to represent water levels at an intermediate bed roughness. The elevation of the Brule outlet is a critical variable in an accurate description of the relationship between both outlets and their interaction with lake stages. Although the actual elevation of the Brule outlet is unknown because of erosion, the lowest terraces incised by the Bois Brule lie at an elevation of 315 m ( 1035 ft), suggesting that the youngest outlet was higher than this level. A more reasonable level for the bottom of the outlet is defined by a well developed terrace at 323 m (1060 ft). Since the actual elevation of the Brule outlet is not easily determined, it was modeled at the two outlet elevations discussed above (315 m and 323 m). Figure 25e presents a reasonable scenario. Estimated discharges are within calculated values, and the water surface elevation of the Brule outlet approximates the Duluth level. In this configuration the Brule spillway would convey approximately 25,000 m3/s when the water surface was at the Duluth level. Similarly, the Portage would have a discharge of 1000 m3/s. Based on these results, the Portage and Brule could have functioned simultaneously, but probably only during large flows such as the peak of the summer melt season. Given seasonal flows as great as 25,000 m3/s, a catastrophic flood is not necessary in order to account for the formation of the Brule spillway. KETTLE CHANNEL Although the effects of Lake Duluth on the Kettle Channel have not been examined in detail, Hobbs (1983) suggests that Wright's diversionary channels and the Kettle Channel played a significant role in the drainage of the glacial lakes of north central Minnesota. The course of the Kettle Channel was most likely determined prior to the drainage of these lakes, following ice retreat from the Spilt Rock phase. Wright ( 1972) states that a portion of the meltwater flowed south into 72 Lake Grantsburg, while the remainder flowed north into Lakes Aitkin I and Upham I. At this time the system probably consisted of outwash channels laden with sediment which were later reoccupied and enlarged by lake discharge forming the Kettle Channel. The early stages of spillway formation appear to be contemporaneous with the development of the Chengwatana surface (discussed previously). The dramatic increase in the channel width (Plate 1), which signifies the northern extent of the Chengwatana surface, can be explained by a change in the composition of the bank material. Schumm ( 1977) states that the composition and grain size of the bank material influences the shape of the cross sectional profile. Channels incised into material composed of high percentages of clay and silt tend to be narrow and deep. Conversely, channels incised into more coarse, less cohesive sediments tend to be wide and shallow. These ideas are demonstrated by the southern end of the Kettle Channel, which is deeply incised into the clayey till of the Split Rock phase glaciation. Approximately 40 miles downstream from the outlet the composition of the bank material changes to outwash, which corresponds with the dramatic increase in width associated with the northern boundary of the Chengwatana surface. Despite the fact that later channel events may have destroyed or obscured evidence for the event that formed the Kettle Channel and Chengwatana surface, there are several events that could have been of sufficient magnitude to form these features. The list of possibilities include: 1) the lake that Wright suggests formed in the Superior Basin prior to Split Rock phase glaciation; 2) drainage of Lakes Nemadji and Duluth; 3) Lake Koochiching; 4) Lakes Aitkin II and Upham II. Drainage from Wright's pre-Split Rock phase lake can be discounted because the Kettle Channel cross cuts the moraine and outwash plain formed during this advance, suggesting that the drainage of this theoretical lake must have preceded the formation of the Kettle Channel (Fig. 19). Drainage from Lakes Nemadji and Duluth are not likely candidates for the formation of the Kettle Channel and Chengwatana surface because the Portage Outlet Channel has a lower discharge capacity than the adjoining Scanlon channel. During the early stages of development, the Portage Outlet Channel must have been significantly smaller than its present day dimensions. Assuming this, during the Lake Nemadji stage, clearly not enough water could be discharged from the lake to 73 form the Chengwatana surface or significantly erode the Kettle Channel. In order to form the Kettle Channel and the Chengwatana surface, a larger volume of water and a channel to accommodate this water is required. The Scanlon channel is the most likely candidate. During the Gemmell stage, Lake Koochiching (a predecessor to Lake Agassiz) drained through the Prairie Channel into Lakes Aitkin II and Upham II. Hobbs (1983) suggests that this drainage was routed through the Scanlon Channel. During the formation of the Scanlon Channel, passage into the Superior basin was not possible because of the continued presence of stagnated ice within the Nickerson - Thomson moraine. This conclusion is based on the topographic expression on the eastern bank of the Scanlon channel, which is much steeper than the western bank and also shows evidence for ice collapse. The Scanlon channel dimensions and topographic expression match those of the Kettle Channel below Moose Lake, suggesting that the discharge event that formed the Scanlon Channel also formed the Kettle Channel. The event responsible for the majority of the erosion of the Kettle Channel and the formation of the Chengwatana surface was likely meltwater emanating from Lakes Aitkin II and Upham II, with potential contributions from Lake Koochiching. The flood was routed through the St Louis River valley then redirected along the western edge of the Thomson moraine, eroding the Scanlon channel and the Kettle Channel. This hypothesis is further supported by the cross cutting relationships of the Scanlon, St. Louis and Portage Outlet Channels. The lowest stage of the St. Louis Channel must have formed as a result of the final drainage of Lake Upham II since it was the last major erosional event to affect the channel. The Scanlon Channel clearly predates this final drainage of Lake Upham II because the lowest terrace level of the St. Louis Channel is lower than the head of the Scanlon Channel. Similarly, the Portage Outlet Channel truncates the southern edge of the Scanlon channel, indicating that occupation of the Portage Outlet Channel must have followed, or at least continued later, than that of the Scanlon channel. These relationships suggest that the Scanlon channel (and thus the Kettle Channel) was formed prior to, or during the final draining of Lake Upham II and the formation of the Portage Outlet Channel. According to Hobbs (1983) the Scanlon channel was eroded solely by Lake Upham II waters, 74 as the water level had dropped to a sufficient level as to divide Lake Aitkin II from Upham II. Discharge from Lake Upham II breached the Nickerson - Thomson moraine near Carlton, Minnesota and supplemented meltwater produced by the Superior lobe, raising lake level enough to overtop the Nickerson I Thomson moraine a second time in the vicinity of Moose Lake, Minnesota. This second breach initiated the downcutting of the Portage outlet. The present elevation of the Portage outlet is 318 m ( 1044 ft) after modem sedimentation has been accounted for (E. J. Bacig, 1996, pers. comm.). Apparently the Portage outlet and Portage Outlet Channel downcut to this level prior to the formation of the main Lake Duluth beaches because the beaches formed east of a sill, which water would have had to overtop in order to exit via the Portage outlet. The conclusions of this study, supplemented by previous work, suggest the Kettle Channel was formed by a series of events prior to the formation of Lake Duluth. These individual events are not easily recognized in the channel, for a number of reasons including: lack of terrace development, incomplete sedimentary record and topography effected by ice collapse. The most significant of these is the lack of sedimentary exposures attributable to channel deposition. Although the sedimentary record is discontinuous, observed exposures offer insight into the depositional history of the channel. Lord and Kehew (1987) state that the existence of poorly sorted, homogenous gravel within a glacial spillway is strong evidence for catastrophic flooding, although they note that there is a general lack of channel sedimentation in this type of spillway. These characteristics are reflected in the Kettle and Scanlon channels. The vast majority of sediments observed in the Kettle channel were composed of glacially deposited materials, which had been exposed through scouring of the surface by water through the channel. Spillway deposits similar to those described by Kehew and Lord were observed in the Scanlon channel (see previous discussions) as well as portions of the Kettle Channel. These similarities with the spillways described by Kehew and Lord suggest that large magnitude floods have inundated the Kettle and Scanlon channels, although they most likely did not originate in the Superior Basin. The former statement is based on the matching channel cross sections and sedimentary similarities with the Scanlon Channel, which formed from the 75 drainage of Lakes Aitkin II and Upham II. 76 CONCLUSIONS The Portage and Brule outlets formed during distinctly different periods, during the late Wisconsin, apparently by contrasting methods. The Kettle Channel formed during the drainage of Lake Koochiching in north central Minnesota (Hobbs, 1983). This flood which may have occurred catastrophically, was routed through Lakes Aitkin II and Upham II, through the St. Louis Channel and the Scanlon Channel, and entered the Kettle Channel at Moose Lake, Minnesota. Discharge originating from the late stages of lake Upham II breached the Thomson moraine and mixed with ponded Superior lobe meltwater called lake Nemadji. The level of Lake Nemadji rose with the addition of the lake Upham water and overtopped the Nickerson!fhomson moraine, initiating the downcutting of the Portage outlet and the Portage Outlet Channel. Following the formation of Lake Duluth, the role of the Portage outlet and the Kettle Channel diminished to intermittent occupation by small discharges during peak melt season or other times when meltwater input into the basin exceeded approximately 25,000 m3/s. The course of the St. Croix Channel formed initially during the Swiss advance of the Superior lobe. Incision of this system at the end of the Swiss Advance and reoccupation by subsequent advances further established the regional drainage system along the course of what would become the St. Croix Channel. This theory may be supported by the fact that many reaches of the St. Croix Channel have discharge capacities much higher than the maximum channel discharge defined at mile 48. Progressively later events may have enlarged the existing channel cross section through lateral erosion and downcutting, which then would not allow the channel to flow at bank full capacity, given a constant discharge. Upon the retreat of the Superior lobe into the Superior basin, a number of interconnected proglacial lakes formed along the southern ice margin. Although it has been suggested that some of these lakes may have drained catastrophically into the St. Croix Channel, this study found little evidence to support the theory of a major flood entering the channel at any point except the Brule outlet. The Brule outlet incised the Lake Ruth and 77 Porcupine advances in a manner similar to the Portage outlet. There exists evidence for two pre-Duluth lakes at elevations of 372 m (1220 ft) and 350 m (1150 ft) (Fig. 28). Initiation of the Brule outlet presumably occurred during the drainage of the former lake, because no other outlets have been identified. This lake was named Lake Brule and was contemporaneous with Lake Nemadji. The stabilization of this lake level was controlled by the downcutting of the Brule outlet to an unknown level. Following the formation of Lake Duluth, the Brule became the major outlet for the basin. This was due to either the fact that the Brule outlet was already lower than the Portage, or that the Brule downcut faster than the Portage. In either case the majority of the Lake Duluth water discharged through the St. Croix Channel with the Portage outlet being used only during periods of high meltwater production in the basin. As shown in figure 24, reasonable estimates of maximum discharge for the Kettle Channel fall between 12,000 and 17,500 m3 /s. Discharges of this magnitude could have been potentially reached only during the drainage of Lake Koochiching, Lakes Aitkin II and Upham II, or Lake Nemadji since discharges of this magnitude could not have been reached during the Lake Duluth stage. Based on geomorphic relationships of the Kettle, Scanlon and Portage Outlet Channels, discharges in this range were most likely reached during the drainage of either Lake Koochiching or Lakes Aitkin II and Upham II. Calculated discharges for the St. Croix suggest that the maximum discharge fell between 14,000 and 27,500 m3/s. This range in discharge coincides with the discharge predicted by modeling of the relationship between the St. Croix Channel and Lake Duluth, suggesting that the St. Croix spillway functioned at a stage lower than its bankfull capacity. 78 Figure 28. Wave washed topography of the Brule Quadrangle. Dashed lines indicate approximate limits of wave modification. Some evidence visible for modification to an elevation of 372 m (1220 feet). Solid line indicates limit of modern erosion into the 323 m (1060 foot) terrace. Scale is 1:24,000. Area shown is approximately 3.2 km wide. 79 REFERENCES Alley, R.B., 1989, Water pressure coupling of sliding and bed deformation: I. 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Appendix A Discharge calculations from the Manning Equation (A) St. Croix Channel Appendix A (a) St. Croix channel manning discharge .tvliles Downstream from Discharge 013/s Discharge m3/s Portage Outlet (n=O.I) (n = 0.0.3) 4 428,536 128,561 6 168,605 50,582 7 113,027 33,908 8 123,780 37,134 10 175,4% 52,649 13 200,375 60,113 14 282,257 84,677 15 472,688 141,806 17 313,708 94,112 18 256,135 76,841 21 141,052 42,316 23 161,181 48,354 24 203,236 60,971 27 166,794 50,038 29 89,933 26,980 31 98,545 29,563 36 169,597 50,879 40 203,948 61,184 42 402,462 120,739 43 99,029 29,709 46 249,690 74,907 48 45,747 13,724 49 99,413 29,824 51 185,592 55,678 55 655,718 1%,715 57 308,226 92,468 58 367,536 110,261 61 100,560 30,168 62 343,073 102,922 64 202,797 60,839 67 173,628 52,089 69 58,059 17,418 72 160,162 48,049 77 164,166 49,250 81 74,206 22,262 84 179,630 53,889 87 402,481 120,744 93 122,244 36,673 96 1,170,952 351,286 98 1,265,533 379,660 (B) Kettle Channel Appendix A(b) Kettle channel Manning discharge Miles Downstream from Discharge m3/s Discharge m3/s Portage Outlet (n =0.1) (n =0.0.3) -6.7 18,787 7,515 3 10,852 4,341 4 8,308 3,323 5 18,114 7,245 5 19,298 7,719 7.5 13,110 5,244 9 6,459 2,584 9 4,622 1,849 13 10,922 4,369 18 8,515 3,406 21 15,658 6,263 21 11,477 4,591 29 8,460 3,384 29 20,570 8,228 33 57,499 22,999 33 6,712 2,685 39 86,675 34,670 39 2,188 875 44 30,542 12,217 44 27,642 11,057 Appendix B Cross sections for the St. Croix channel MILE-16 MILE-17 1170 1L"U 1150 :::::::r::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::::::::::::::::::::::: 1150 mo ·············································••········•············ 1130 1110 -••••••fr-••• n •-··-·· •••·•• ••••••• •••• •••••••••-•••••••·•••••••••••••••••••••-••••·••- 1110 1090 · •••'!-••••·••••••••• • •• • ••••• • ••••••••• ••• •••• • ••••• •• •• ••••• ••• •• •••••••••••• • ••••••••• • 1090 1010 1070 1050 1(1;0 1030 tCllO 1010 1010 990 990 9i"O ···························································-······-············-·····-······· 970 ·································································-··························· 9SO 950 ····················-········································································ 930 ·-·········································································· ················· 9:)0 ···· ·············-··············--··················· ·········· ············ ··· ············· ··· 910 910 ···········-················································································· 890 890 810 g,-o ·•••••••••·•••••·••·••••••••·•••••·•••·••···•·•··•··••·•··•••••••••••·••··••••·••••··•········ 850 850 830 ------··------···---··-·--···-··-·--·---········--········-··-·····---·-···---· 630 ···········-················································································· ····-··············· ···· ···························································· ··-······ 8 10 •···•···•••·•·•••····•·••·••••••••••••••··•·•••••••• ····•·•··••••••·••••••••••••••••·••••••·· 810 500) moo 25000 l!lXll 15000 HORIZONTAL DISTANCE (FT) HORJZONTAL DISTANCE (Fl) MI LE -15 MILE-14 1190 1170 1110 1150 1150 mo 1130 1110 1110 1090 ·········· ··············-···············-··································· 1090 1070 ·····-····--·-·{;:--··-·-·-·····-···---·-··-··--···-·-·--·····-·-·-·--·-··--·····-···-··-···· llliO Ja;Q ·········· ...... f=: la;() uno ------·--·-----··---·------·····---·--···------·------··--!;:, 1000 1010 z 1010 990 ············ ··:r ········································································· 0 990 f= 970 ...... :.-.-:.-:::::.-.-.-:::.-.-.-...... :.-:.-.-:_ < 9SO : G'.i 930 ..J 930 UJ 910 ·---.------··- ·············· ···········------··--· 910 890 ····················-········--··················--·············-----···············----····· 890 850""' ···••··••••••••••••·•••·•··••••••••••••·••• •···················•···•·•·•••····•···········••· ""'650 8$0 ·····················································-···································-··· 800 8 10 810 ...... 190 SCDl 1000l 15000 5000 1000l 15001 HORJZONTAL DISTANCE (Fl) HORJZONTAL DISTANCE (FT) MILE-12 MILE-JO 1190 1190 1170 mo 1150 1150 1130 :.·:::::.·.·::.-.-.-::::::::::::.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-:::::::::::.-.-.-.-.-.-.-.-.-.-.-:.-.·:.-.-.-.- rno 1110 ••••••• O! 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S HORIZONTAL DISTANCE (Ff) HORIZONTAL DISTANCE (Ff) MILE6 MILE4 lliU 1170 ·····\:!··················-·············- ·-················································ 11 50 -··ti-::······················································································ 11 50 mo 1130 1110 1110 lOiU 1070 1050 1050 ·:::r::::::::::::-_":::::::::::::::::::::::::::::::·::::::::::::·:::::::::::::::·:::::::·:·:·::::::: 1000 1000 z 1010 1010 0 ..., (:::: 99J ------····-··--···-.. --·-·-············- -·-··-··········------·------·--·------·--- --·------.- < 9i'O ••.•••..••...... ••.••.•••..••.•. . •.••••.•...... •••...... •. •.•...... 9i1) ······· ··········-·-·········· ············································· 950 950 [;; ...J 9)() ················-·····------····-·· ········· ········ ·--············ ······· ..... •...... 930 ...... ••...... - ...... 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J l MI LE20 MILE22 1170 ··•····•••·····················•·•·····••·····••·······•·••···••··••···•··•···•••············ mo mo ...... ·················-···--·-····· ll50 11'0 ... :::::...... ·················...... mo 1110 ···················&!········································································ 1110 1090 1m to'i'O ···-···············t1····················-··················································· r:: lCISO . ···············ti······································································· """lClSO z 1000 z 1010 0 0 ;:::: :: ;:::: < 970 ------··------< 910 950 .••.•.•••••. ••••••••.•••••.••.•••..•.•.••••••.•••••••••••.••••••• . ••••••••••••••••••••.•••••• >UJ 950 [;; ...J ...J 930 ------········------.----········ ..··· ·········--.---····· UJ 9>0 UJ 910 ···························-········· ·······························-························ 910 890 ····························································································· 890 S7'0 ····-·-················-·······------·--·····-···············--······················ 810 850 . •••••••••.•.•••.•••...•...••. ••••••••••.•••••••••.••..•.•••..•••••••••••••.••• . ••....•••.•.. a.so 830 ·······- ···------············- ··········································-····--······· SIO -···························································································· 810""' ...... 10000 25000 ""' 10000 HORIZONTAL DISTANCE (FT) HORIZONTAL DISTA NCE(FT) M1LE24 MILE26 1170 1150 lJi'O ·························•·····••············································•• ········ 1130 1150 ···········-················································································· 1110 ll!K) ············ ·········································-······································· uro 1110 1090 1(170 1(170 lffiO ·f ·-···------·-·------······························--·------···············- ····---- 1'60 UDO ·""·························································································· 1000 .5. ..••...... ••...... z 1010 z 0 m 0 1010 !== m < 970 [;'; 115() > ...J <110 ...J 9JO ...... •. •...•• ...... ••...... • . .•••. •...... 910 "'UJ "' 890 910 -·-···--·- ····--···--················--······----·-···--·-················-··· ············· ·· ··········-·····----·-···---··--·······------·-·····-······--·-··········--·····-·········· 870 890 550 870 ··········-·································································-················ 830 6SO ···········-················································································ 830 ...... --··········· ...... ············. 610 810 ·············-····-·····---·····-----·······-··············-· ··········-······-········-·-· ""' 10000 15000 HORIZONTA L DISTANCE (CIV!) HORIZONTAL DISTA NCE (FT) MILE28 tvDLE 30 n90 llllO n m 1170 lll HORIZONTAL DISTANCE (Fl) HORIZONTAL DISTANCE (Ff) MILE32 MILE33 1190 nllO 1110 n m 1150 115() mo mo 1110 11JO ,... 1070""" 1'""'om g 1050 11l50 ! WO z lOJO z 1010 0 1010 0 990 990 <( < m 950 G; 95() >Ul """ _, _, 900 Ul Ul 910 ""'910 800 890 810 sm &50 &50 "'o 810 ""'810 7'JO 190 10000 15000 10000 HORIZONTAL DISTANCE (Fl) HORIZONTAL DISTANCE (Fl) MILE34 tvULE35 11 90 1170 1170 115() 1150 mo 11-'0 1110 1110 1090 ,... 105()'""' 1000 z 1010 0 990 5000 10000 15000 2500l 0 10000 15000 25000 HORIZONTAL DISTANCE (FT) HORJ ZONTAL DISTANCE (Fl) MILE41 MILE40 mo,------mo lli'OUSO llSO 1"0 mo 1110 1110 uro lO'Xl 1050""" ··················································· 1050"'"' .....::::.·:::::: .·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·:.·.·:.·.·.·.·.·.·.·.·.· z llllO 0 r: .·:::::::::::g: ·:::::::::::::::::::::::::::.·.·:.·:::::::::::::::::::::::::::::::::::::::::::::. < 910 $0 iii 930 -' 930 Ul 910 9l0 890 890 870 870 650 sso ···················································-··················-····················· 8l0 ----····------·-·----·--··········-·-,.·------·-······-·-·-·-····· ·- ···-······-···-· 810 ••·•••••·••••• •••·•· ••••••••·•••••••••· ••••••••······• ..••••••.....•..••.•.••••.••.••..•..•• ...... 10000 15000 2500) 5000 10000 15000 HORIZONTA L DISTANCE (Fl) HORIZONTAL DISTANCE (FT) MILE42 .. -.. -.. -.. -..- ..- .. -.. -.. -.. -.. -.. -.. -.. -.. -.. -.. -.. -.. -.. -.. -.. -.. -.. -.-.. -..-.. -.. -.. -.. -.. -..- .. -...- ..- ..- ..- ..- ..- ..-.. - ..- ..-.- .. 1170 1150 1150 1"0 1130 1110 1110 ll1>0 l l1>0 10'70 c 1070 ll'.60 1050 lCll-0 :::::::::::::::::r::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 1000 z z 0 lOlO 0 uno i== 990 :::::::::::::::::l::::::::::··:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: i== 990 ··········-@I· ············································································· < < 910 iii $0 -' iii Ul Ul-' 930 9l0 890 2 E 6iO ·············································· ······---································ ····· 850 ---··--·-······--····------·-··-----·-··················-·············-······-······ 850 ················ ········••·••·······•••••········••·••···································•··· 830 a.,,{)····-··························-························································ 810 ······-······-·····-···-·····-····--·-···----··-· ··--·-···········-···-·-·-·············---- 810 •·•••••••·••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• ...... 0 15000 10000 15000 2500l HORJWNTAL DISTANCE (Fl) HORJWNTAL DISTANCE (Fl) MILE46 MI LE48 1170 lli\l 1150 1150 1130 mo 1110 1110 ···················-H·········-······--··········-········-··-·--··························· 1090 111.iU ...... §...... 1070 ···············································-··-··-················ ······················· ! !OOJJ I S HORIZONTAL DISTANCE (Fl) HORIZONTAL DISTANCE (Fl) MILESO MI LE 52 1190 1170 11 10 1150 !ISO mo 11 10 "'"ll10 1090 ;;?. •••• •••••••••••••••••••• ••• •••• ••• . ••••• •••••••••• ••••• ••••• ••• •• •• •• ••••• ••••••••• ••• •••• 1090 !()]() 1<170 G !IBO g !IBO z 1030 1010 z 0 0 f::: 990 < 970 950 ....l r··········· ··t······ ·····-···································-·························· UJ 910 ....l 910 UJ 690 870 a.so a.so 830 830 · ·············-·························-···················································· 610 SlO •·••••••••••••••••••••••••••··••••··•···•···••••••••••·••••••••·•••···••••••••••••••·•••••••• ?90 !OOJJ !S HORI ZONTAL DISTANCE (Fl) HORIZONTAL DISTANCE (Fl) MILES; MI LE 56 1170 1170 1150 1150 mo 11 10 11"'"10 1090 1090 ! ()]() 1()70 g ! IBO ! IBO z g IQIO 0 z 1010 f::: Q 990 ············??····--··············----·-----··············-·-···········-······-············· : .-.-----.-.-_-_·_-_·:.·.·_·_·.-.·_-_-_-_-_-_·_-g .-.-:.·.-_·.-_-.-_-_·_·_·:.·_-.-.-.-_·_-_-_-_-_-_-.-.-_-_·_·_·:.-.-.-.-.-.-.-.·.·.·.·.·.-.-.-.-.-.-.-.-.-.·_-_·_·_·_·_·_·_·.-.·.·.· f- < 970 ·········································································· 950 ...... u ...... 950 -----·-----e--- . ··············- --··························-··············-············· ....l >UJ UJ 910 ...•••.•. •••. 17. •...•••..•...••••.....•...... •• .•••...... l 910 UJ 910 890 : ::::::::::::::.-.::·:::.J 870 850 ·-·---··------·----·-···--·-·········------·--·-········----·-········· 850 ··-----···········-·······························-··--······································ 830 -----·------···--· 830 810 ································· ································ ········-··················· 810 ································································-···························· SCXXl IOOJJ IS HORI ZONTAL DISTANCE (Fl) HORI ZONTAL DISTANCE (Ff) MILE58 !v!ILE59 ]]90 1170 1170 1150 1150 rno IUD 1110 1110 1090 1090 1070 1070 1000 1000 z 1000 z 1000 0 1010 0 1010 990 990 ••••••••••••• .C!.x •• ·-··················--···········································-········· < 970 < 911) ··············£ ············································································· 9SO ••••••••••••••••••••••• 15 ...... •...... iii 9SO ··············V·······-···········•··························•···•·····••·······--··--····· iii..J ..J UJ "30 UJ "30 910 910 890 ""'870 sso 830 ·······················································-····································· 8JO BIO 810 790 SOJO ]()(XX) 15000 2SOOJ HORIZONTAL DISTANCE (Fl) HORIZONTAL (FT) MILE60 MILE62 1190 1190 1170 1170 1150 1150 1130 1130 1110 1110 1090 1090 i::: 1070 1070 1000 i::: 1000 z 1000 !;, 1000 ""0 1010 z 1010 990 0 990 < 911) ··········s························-----···············································--·-·· <: '170 ··ll························································································· 950 -·········o···············...... 950 .. t) ..•...... •..•...... •...... iii..J w 900 ...... iii_, 9'0 .. ,t;...... 910 UJ 910 890 890 870 870 sso sso 830 8JO 610 610 790 790 ]()(XX) ]SOJO 200lJ SCXXJ ]SOJO 200lJ 2500) HORIZONTAL DISTANCE (Fl) HORIZONTAL DISTANCE (Fl) MILE64 MILE66 1190 ltiO 1110 1150 ]]50 1130 1130 1110 1110 1090 1090 tO'iO 1070 1000 1000 1000 z 1000 0 1010 1: 990 970 •••••••!j ...... 911) 950 9SO iii..J 9lD UJ "30 910 890 : 870 850 ...... sso EDD ·····································•·····································•···••·••··•••·••· 8JO SID .....•...... •...... •...... •...... •.•...... • BIO 790 0 ]SOJO 200lJ 2SOOJ UXlll ] SOJO HORI ZONTAL DISTA NCE (FT) HORIZONTAL DISTANCE (Fl) MILEo7 !V!ILEo8 Jli'O 11ro 1150-+------1150 mo 1130 1110 1110 1090 1090 1070 1070 1(60 J(l;O lCllO lCllO 1010 9'0 ···············-·············-·····················lli······································· 970 950 930 ···················································tr··· ...... 910 . ... ··············································i;;··· ...... : :·::·:·:·:·:·:·:·:·:·:·:·:::::::::.·.·.·.·.·_·:·:·:·:·:·:·:·:·:·:·:·:·_·.·.·_·:·:._._._._._l-._·_::·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:· 830 ·-··········· .. ·--·--··--·----·-··-··-······--·-·-··-·-······---·-·······--·········--·--- 83.() ••• ••••• . ••••••••.•• ••.. •••••.•.••••••••••. ••••••. ••• ••••• .••• •••••. . ••••.•••••••••• • ••. •••• • 810 •••••..•..••....•...••.....••..••..••.••...... •.. ••.••...•.•..•. •.•••. ••..••....••••.•.•.• 810 0 lOOll lSOOJ 2500J HORIZONTAL DISTANCE (FT) HORIZONTAL DISTANCE (Fl) MJLE70 !V!ILE71 1190 1170 1150 USO""' mo mo 1110 1110 1090 1090 1070 1070 ...... •.•...... •...... (; 1a;o ](!;() •••••••• • ••• •• •••••• • ••••• •• ••••••••••• • ••••••• •• ••••• ••••• •• •••••••.•••••••••• •••••••••••••• z lCllO lCllO 0 1010 f:= 990 <'. 9'0 > 950 ..J "' 9:10 "' 910 690 870 sso ""'810 810 •••••••••••• ••••••••. . ••••• . •••.• .••. ••••••••••••. ••••••••••••••••••••••••••••••• . ••••••••••• 790 lOCDJ 1500J 200lJ 5llXl lOOll 1500J 200lJ 2500J HORIZONTAL DISTANCE (Fl) HORIWNTAL DISTANCE (Fl) MILE 72 !V!ILE73 1190 1170 nro 1150 ------1150 mo 1130 1110 1110 1090 1090 1070 1070 l(l;O 1a;o z llDO 0 1010 != 9lO <( > 970 950 ..J "' 900 910 •••••••• "' 910 ""'671) fil _:::::.:.:: .. :.::::::::::::::::.:·::::r::::.. a>O 810 ...... •.....•...... •....•...... ••..•.....•...... • ...... •..•.....•.....•. ""'810 790 lOOll 1500J 2500J HORIZONTAL DISTANCE (Fl) HORIZONTAL DISTANCE (FT) MILE74 1190 ,--______rv_n_LE_7o_ · ------1190 1110 1170 nso llSO 1130 lJJO 1110 1110 1090 111)() 1070 1070 lffiO r:: lffiO 10\0 z llllO lmo 0 lmo i== 990 < 970 ..J w ""'900 910 890 870 8SO 830 830 SIO 810 790 0 10000 lSOOJ HORIZONTAL DISTANCE (F1) HORIZONTAL DISTANCE (F1) MILE BO MILE78 """r------llS5-p...... - ..-. .- ..-. .- ..-. .- ..- mo 1165 1150 11-1.5 lllO 1125 1110 1105 llES 1065 ""° 11>15 :: 11125 1005 11'5 965 9<5 ,..."''905 865 S ""Q1S 5000 10000 lSOOJ 5000 10000 lSOOJ HORIZONTAL DISTANCE (F1) HORI ZONTAL DISTANCE (F1) Appendix C Cross sections for the Kettle channel MILEB8 MILEB7 ll'll 1170 1170 1150 1150 1130 1130 1110 1110 1000 .·.·::::.·.·.·::::.·:.l .·-·_·_·_·_·:::.·.·:::.·:::.·.·_·_·_·:.·:.·.·.·_·_·_·.-.·.·:.·.·.·_·_·:::.·.·_·_·_·_·_·::.·:.·.·_·_·::::.·.·:.·:.·.·_·::: 1000 - 1070 1070 lCEO ::::::::::::::::r::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: f; 1050 z JWD ... ••••••• . . . . . • :C ...... •.•...... •...... z l MILE B6 MILE BS !I'll 1190 ,------, mo ltiD 1150 1150 mo mo 1110 1110 lO'IJ 1000 >:: 1010 :::::::::::::::::.t ::::::::::::::::::::::::::::::::::::::::::::::::::::::.·:::::::::::::::.·:: 1070 <::. 1050 f; 1050 z l OlO z l HORIZONTAL DISTANCE(Fl) HORIZONTAL DISTANCE (Ff) MILE B4 MILEB3 119.J 1190 lJ '° 1110 1150 1150 1130 mo 1110 11 10 lO'IJ 1000 10?0 r::: ]IJi'Q 1050 <::. 1050 z z uno 0 10'""'10 0 1010 != 990 990 < 970 > G; ""'950 UJ %0 ·:::_::::::::::::::::::::::::::::l::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ..J ..J UJ 930 UJ 930 ·································e-························································· 910 910 ·········-···········-·········Z······-·····-·········································· .... 890 810 870 :::::::::::::::::::::::::::::::.:·l:::::::::::::::::::::::::::::::::::::::::.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- 850 sso 830 8'0 SID ····························································-································ 810 ...... 190 0 500J JCOXI 1SQD 2 HORIZONTAL DISTANCE (Fl) HORIZONTAL DISTANCE (FTJ MILEl MlLE2 1190 11;o 1170 1150 1150 1130 1130 1110 1110 1090 1000 1070 - 1070 1050 t; lCM z UllO ::::r:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 1000 0 1010 1010 I= 990 ...... ••...... •...... •..•...... •....••...... ••.....•...... < 990 > 970 970 ·------·------·--·--···------··--·-·· DJ_, 950 950 ·····---·--··---··--···-···-····-----·------·-·-····-···------·--········-·--············ DJ ino sea ...... 910 ..•• .•.. ••.•.•....••••.....••....•••...••..•....•...•.•.•.••••.•...... •.....•..••••••••• 910 ·•·············••·•· ••• ·•••••• ·•··••••· •••••····················•········•······•••·····••·••· 890 .•..•.••• ..•••.•••••.••••..•.•..•...... •...... ••..•..•••..... ••...... ••••...... ""'8'0 870 ...... 650 850 ...... !DO 8.10 ...... 810 ·····-······················································································· 610 ·••·•····•···••·•·············•··•··•····•··•••····•··•·····•··••··••······•···••···•········ 0 SOX) JCXOJ JSIXI) 200X) 2500J 5000 1sroo 2sroo HORIZONTAL DISTANCE (Fl) HORIZONTAL DISTANCE (Fl) MJLE4 MILE6 1190 1110""' 1170 1150 1150 mo mo 1110 1110 1o;o 1090 1oro 1070 l "" 10000 15000 "" 10000 HORIZOTAL DISTANCE(Ff) HORIZONTAL DISTANCE (FT) MILE7 MILE9 1190 1190 1170 1170 1150 1150 11!10 mo 1110 1110 1090 1090 1070 t; i:: l Di'O U:60 e l(l;O z uno 1030 0 z c: 1010 0 1010 990 f:: 990 < 970 >< 970 ..J 950 UJ 950 L:J ..J 930 u.: 930 910 910 890 890 8:70 870 650 S50 830 830 810 810 790 790 lllXXl lllXXl IS HORIZONTAL DISTANCE (F1) HORIZONTAL DISTANCE (FT) MILE 10 MILE12 1190 1170 11711 1150 1150 :::!::::::::::i: :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 1130 1130 1110 1110 ::gjj:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 1090 ····:E-0!····················································································· 1090 1070 1070 g l (l;O l(l;() 1(00 1030 15 1010 1010 f:: < 990 990 970 ""' ····························································································· ..J 950 950 ·•••••··••·••·••••••••••·••••••••··•••··••••••··••····••••••••••••···••···•·••···••·•·•·•···· L:J 930 930 ... ··•·•••••••••• •••••••••••••·••·••·····•····•·••••·•·••••·••••••··••···········•·········· 910 890 690 ·····································································-······················· 870 870 850 650 ·································-·····················································-····· 830 830 610 ·- ...... 810 ·············-····································· ·········································· 10000 HORIZONTAL DISTANCE (F1) HORIZONTAL DISTANCE (FT) MILE14 MILE!6 1170 1170 1150 1150 1130 1110 _:_:_:_:_:_:_:_:_:_:_:_:!:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_ 1110 ::J::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 1090 1090 ····fl-·································································-···········-······ 1070 1(770 1050 _·_:_·_:_:_·;_:_:_·_:4 :::_·_·_:_:_._._:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_:_ E ,a;o Ul30 1010 z 1010""° 990 g 990 9i'O --·························································------·············--·.- < 970 950 iii 950 9311 •••••••••••••·•••••••••••• ••••••••••••••••••• ••• ••••••••••••••• •• ••••• ••••••••••••••••••••••• ..J 'XJO l.1J 910 910 ···········------········································································· 890 890 8i'O ------810 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-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-::-:-:-:-:-:-:-:-:-:-:-:-:-:-.-:-:-:-:-:-:-:-:-:-:-:-:-:-: < m 950 ·················-··------·--·-········-······································· 960 930 Gi_, 930 UJ 910 ····Ail---·········-···········-······························································ 910 !ISO : s;u 850 850 830 ...... 830 810 ·-········· ·························-················································· ······· 610 ...... 0 500J lllXll 2500J "" 0 5000 10000 15000 2SOOO HORIZONTAL D!SfANC E (FT) HORIZONTAL DISTA NCE (Fl) MILE28 MILE JO 1110 1liU 1150 1150 mo llJO 1110 1110 :::r::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ::.-E.·.·.·.·.·.·.·.·.·.·.·.·.·.·_·_·_·_·_·_·_-_-_·_·_-_-_-_-_-_-_-_-_-_-_-_·_·_-_·_·_·_·_·_·_·_·_-_-_-_-_·_-_·_·_-_-_-_·_-_-_·_·_·_·_·_·_·_·_·_-_-_·_-_-_·_·_·_·_·:_·_·_-_-_-_·_·_· rnro 1070 llW llW llllO IOJO 1010 1010 990 990 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··············································································-·············· 890 ···-··-·············-·--··---··-·········-·---········-······································ 870 •••••••••••••••••••• • ••• •• •••••••••••••••••u•••• ••••••••••••• •••••••• ••••••••••••••••••••••• ""'8i'O •••••·•••··•• •••··• ••••••••····•••·•••···••·•·•••·•• ·•·••··••••·••••••••···••••••••·•··•••••• sso 850 830 ·················································-·····························-·····-·····-· 830 ······································•··············•······································· 810 ··-··········-················································-·············-·············-·· SlO ------···----··················-········-·······-··············------······-·--·-·-··-·-- .... 0 5000 10000 15000 20000 25000 0 5000 10000 15000 20000 25000 HORIZONTAL DISTANCE (Ff) HORIZONTAL DISTANCE (Fl) MILE 34 MILE36 1190 lliU 1170 1150 1150 mo 11-'0 1110 1110 1070 "'·························································································· !; :: p lt50 IOJO s UDO z z 1010 0 1010 0 8::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: [::: 990 ··--····· ------·------······------[::: 990 < HORIZONTAL DISTANCE (Ff) HORIZONTAL DISTANCE(Fl) MILE 36 MILE:57 1190,------1170 nro llSO 1150 1130 mo UJO 1110 llro ltro ) (170 1070 1050 1050 g lCllO !; 1000 z z 1010 0 0 i: 990 < 970 950 ...J Ul 930 iii...J Ul 910 ------.•..• ------· ------··········------·------. 690 ··········-·-·-·····-······················· ··········································· 8?0 ················----··-----··························-··································· 850 830 810 ••·•••••••·••·•••••··•·•·•••••••• ••••••·•••· •••·••••··•··••••••••···••·· ...•...•.••. ....•.. 5000 lllllO 15000 2llll0 lllllO 15000 25000 HORIZONTAL DISTANCE (FT) HORIZONTAL DISTANCE (FT) MILE38 MILE39 1100,------1110 1170 1150 1150 mo 1130 JttO ! 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