A STUDY OF SUBSURFACE WATER FLOW IN A SOUTHEASTERN MINNESOTA KARST DRAINAGE BASIN

Transcription

1 A STUDY OF SUBSURFACE WATER FLOW N A SOUTHEASTERN MNNESOTA KARST DRANAGE BASN A THESS SUBMTTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNVERSTY OF MNNESOTA BY ERC HERBERT MOHRNG N PARTAL FULFLLMENT OF THE REQUREMENTS FOR THE DEGREE OF MASTER OF SCENCE AUGUST 1983

2 By June our brook's run out of song and speed. Sought for much after that, it will be found Either to have gone groping underground Or flourished and come up in jewel-weed, Weak foliage that is blown upon and bent Even against the way its waters went. ts bed is left a faded paper sheet Of dead leaves stuck together by the heat A brook to none but who remember long. This as it will be seen is other far Than with brooks taken otherwhere in song. We love the things we love for what they are. - Robert Frost

3 ABSTRACT The Root River drainage basin in Fillmore county, southeastern Minnesota has well developed karst topography and karst groundwater flow in carbonate sedimentary rocks of upper Ordovician age. n the upper carbonate aquifer subsurface water flows rapidly through solutionenlarged fractures and conduits, and is intimately connected to surface water. As such it is very susceptible to pollution. An area was chosen in the drainage of the South Branch of the Root River, southeast of the town of Spring Valley, for detailed hydrologic study. The area has one of the highest densities of karst features in Minnesota. The first part of the study involved quantitative fluorometric tracing of subsurface water using the fluorescent dye Rhodamine WT and a field fluorometer. The tracing studies delineated subsurface flowpaths, revealed travel times and dispersion along the flowpaths, and permitted mass balance calculations of inflowing and outflowing water. The traces defined the recharge area of Moth and Grabau Springs at the head of Forestville Creek, an important trout stream. A gauging station was installed to measure the discharge of these springs, and so far has produced two years of continuous record. A network of rain gauges was installed to measure precipitation over the recharge area. Data from these installations describe the way the karst system responds to recharge events. Several sub-environments of flow exist within the aquifer. nitial estimates of transmissi vi ty and aquifer diffusivity can be derived from the data. -i-

4 ACKNOWLEDGMENTS This research was supported by grants from the Legislative Commission on Minnesota Resources to the Minnesota Geological Survey. Financial support was also provided by a University of Minnesota nstitute of Technology Corporate Associate Fellowship, and by a Lando Fellowship. First of all would like to thank Calvin Alexander for his unceasing support and guidance over the last few years, and for many productive and lively discussions during all phases of this project. This study would not have been possible without the previous mapping and subsurface water tracing work of Ron Spong, Ramesh Venkatakrishnan, and many others. am grateful to all those who assisted me in the field in various ways, including Bridget O'Brien, Warren Beck, Paul Book, Phil Hewitt, Dave Rogers, Stephen Mohring, Mike Mccrum, Kate Mader, Shiela Grow, and Barb Silverman. wish to thank the United States Geological Survey Water Resources Division in St. Paul, and especially Jerry Hicks, for loaning a water level recorder and assisting in the construction of the gauging station. would like to thank the residents of Fillmore county who helped in this project. Thanks to Niel Davie for giving me access to Mystery Cave. Thanks to Mike Hellerud for operating the recording rain gauge, and to other residents around Spring Valley for faithfully keeping daily precipitation records. Thanks to Ken Hadland for lodging and for the use of his house as a field base station. Finally, special thanks to the Root family for letting me tromp on their land at all hours of the day and night, for permitting me to construct the gauging station on -ii-

5 their land, and for all-around hospitality. -iii-

6 TABLE OF CONTENTS Page ABSTRACT i ACKOWLEDGMENTS ii TABLE OF CONTENTS iv LST OF FGURES vii NTRODUCTON 1. GEOLOGCAL SETTNG AND DESCRPTON OF STUDY AREA 6 Geology Physiography Karst Development g Description of Karst Features in the Study Area 11 South Branch of the Root River 13 Mystery Cave 13 Seven Springs Moth and Grabau Springs 16 Fairview Blind Valley 16 Other Karst Features 19. QUANTTATVE FLUOROMETRC DYE TRACNG 21 Methods 22 Data Analysis Results Disappearing River to Seven Springs, Oct. 1, Disappearing River to Seven Springs, Sept. 2, Formation Route Creek to Seven Springs 28 -iv-

7 Matheson Sink to Seven, Moth, and Grabau Springs 28 Fairview Blind Valley to Moth and Grabau Springs 32 High Flow Low Flow Natural Well to Moth and Grabau Springs 35 Red Tail Sink to Moth and Grabau Springs 38 Lefevre Blind Valley to Moth and Grabau Springs 38 Root River Dye Traces 38 August 1981 Root River Dye Trace 41 August 1982 Root River Dye Trace 43 nter-basin Connection 47 Summary and Conclusions V. STUDY OF MOTH AND GRABAU SPRNGS DRANAGE BASN 54 Gauging Station Construction Calibration 55 Rain Gauge Network Expected Results 58 Results Storm Responses Recession Curve Analysis 68 Summary and Conclusions 79 V. CONCLUSONS REFERENCES 83 APPENDX A 87 -v-

8 APPENDX B 97 APPENDX C 9 9 -vi-

9 LST OF FGURES Figure Page 1. Location of the study area 3 2. Two ways of investigating a karst aquifer 5 3. Generalized stratigraphic column 7 4. Geologic map of the study area 8 5. Karst features and dye trace connections in the study area Location of Mystery Cave Map of Seven Springs and area Map of Moth and Grabau Springs Map of Fairview Blind Valley Map and cross section of Natural Well Dye trace from Disappearing River to Seven Springs, Oct. 1, Dye trace from Disappearing River to Seven Springs, Sept. 2, Dye trace from Formation Route Creek to Seven Springs Dye trace from Matheson Sink to Seven Springs, Moth Spring, and Grabau Spring Dye trace from Fairview Blind Valley (Hellerud Sink A) to Moth and Grabau Springs Dye trace from Fairview Blind Valley (Poldervaard Sink A) to Moth and Grabau Springs Schematic cross section of the subsurface flowpath between Fairview Blind Valley and Moth and Grabau Springs 36 -vii-

10 18. Dye trace from Natural Well to Moth and Grabau Springs Dye trace from Red Tail Sink to Moth and Grabau Springs Dye trace from Lefevre Blind Valley to Moth and Grabau Springs Dye injection points for 1981 and 1982 Root River dye traces Seven Springs response curves for the 1981 Root River dye trace Moth and Grabau Springs response curves for the 1981 Root River dye trace Seven Springs response curves for the 1982 Root River dye trace Moth and Grabau springs response curves for the 1982 Root River dye trace Schematic flow chart interpretation of the dye trace data Recharge area for Moth and Grabau Springs Stage-discharge relation for Moth Spring, Grabau Spring, and combined flow Log-log plot of stage-discharge relation for Moth and Grabau Springs combined flow Expected hydrograph response for a karst aquifer Moth and Grabau Springs discharge from April to November, Response to May 3, 1982 storm Response to May 12, 1982 storm 64 -viii-

11 34. Response to July 12 and July 16, 1982 storms Response to October 19, 1982 storm Response to November 9-11, 1982 storms Composite recession curve for Moth and Grabau Springs Relationship between recession discharge and water volume remaining Estimated drawdown curve derived from recession data 77 -ix-

12 -1-. NTRODUCTON An extensive area of karst topography is developed in southeastern Minnesota including parts of Fillmore, Olmstead, Mower, Dodge, Winona, and Houston Counties, where early Paleozoic carbonate rocks are located very near the surface. Karst is formed by the dissolving action of groundwater on carbonate bedrock, resulting in such features as sinkholes, allogenic (sinking or disappearing) streams, solution-enlarged fissures and joints, caves, underground drainage, and resurgent springs. Karst topography and hydrology are particularly well developed in Fillmore County in the drainage basin of the Root River. Southeastern Minnesota contains substantial groundwater reserves, a large fraction in carbonate formations. There are many problems associated with karst groundwater flow. Complex localized flow in networks of fissures and solution cavities makes aquifer analysis difficult. Well yields and aquifer storage capacities are often unpredictable. Karst groundwater is highly susceptible to pollution due to the intimate connection between surface water and groundwater. Contaminants can enter the subsurface through discrete recharge points and travel very rapidly through the network of connected cavities and fractures. t is important to understand subsurface water movement in these terrains because of the importance of these and other carbonate aquifers, and because of their susceptibility to pollution. There is very little published work on the karst hydrology of southeastern Minnesota. Broussard et al. ( 1975) give a good general presentation of the water resources of the Root River watershed, and define the hydrolgeologic uni ts, but do not address the specifics of

13 -2- karst groundwater flow. Giammona (1973) gives a rather cryptic account of dye tracing work in the area. Alexander ( 198) and Alexander and Shaw ( 1979) describe karst features and some hydrologic work in the area. The Minnesota Speleological Survey (MSS) and its publication Minnesota Speleology Monthly have furthered the knowledge of caves and karst in the area. Singer et al... ( 1982) address the problem of groundwater quality in southeastern Minnesota. This thesis examines subsurface water flow in an area of Fillmore County where karst groundwater flow is particularly well developed and accessible (Fig. 1). The study area is in the drainage of the South Branch of the Root River southeast of the town of Spring Valley. The thesis is divided into two main parts corresponding to two different avenues of inquiry. The first describes detailed dye tracing of subsurface water flow in the study area. Tracers are very useful for delineating subsurface flowpaths in karst regions. This study used a quantitative fluorometric dye tracing technique which involved injecting dye into the aquifer and monitoring the concentration of dye as it emerged from springs. The second part of the study concentrates on the drainage basin of two karst resurgences, Moth and Grabau Springs. A gauging station was installed to provide a continuous record of the discharge of these springs. A recording rain gauge and a network of smaller rain gauges were installed in the recharge area to measure input into the system. Data from these installations describe the way the system responds to precipitation events, and the way water is withdrawn from storage in the absence of precipitation.

14 Figure 1. Location of the study area.

15 <( w a: <( > c ::::, t.) LL z j:: <(..J i.s (. ~,, / r' / / ' ' ( / /, ~- Q) ) "8,, c:... ~ ~ LL. <( w a: <( > c ::::, 1- u,

16 -4- These methods of inquiry are similar in that they attempt to derive information about the system by measuring how it responds to certain inputs or stresses. n a sense they are both "black-box" approaches (Fig. 2). n the first case the input is a slug of dye injected into the karst aquifer, and the measured output is a dye pulse as it emerges from a spring. n the second case, the input is precipitation and the output is spring discharge. Both techniques are valuable in deciphering the complex groundwater relationships in this and other karst areas.

17 Figure 2. Two methods used in this study to investigate karst groundwater flow. Top: a slug of fluorescent dye is injected into a sinkhole or sinking stream, and dye concentration is monitored at a spring. discharge are monitored. Bottom: precipitation and spring

18 -5- input: dye slug l output: +---n:=;;;--, karst aquifer l.._-,-_j!::::==,-==-=r=-=====,---~) u. u c time input: precipitation l l l output: karst 1--,,=~ ; aqu if e r--.-1 G> )... a,.c u l--:---l--4!:=:=!::::~~:::::>"'j=::::::::..., --)..,.! 'O hydro graph time

19 -6-. GEOLOGC SETTNG AND DESCRPTON OF STUDY AREA Geology Southeastern Minnesota is underlain by Lower and Middle Paleozoic sedimentary rocks. These were deposited in seas that occupied the Hollandale embayment, a shallow depression between the Wisconsin Dome to the northeast and the Transcontinental Arch to the northwest (Austin, 1972). The lowermost units are primarily sandstones with some carbonate and shale beds. These grade upward into carbonates containing subordinate sandstones and shales. The uppermost strata consist almost entirely of carbonate rocks (Sims and Morey, 1972). t is with the upper, primarily carbonate units that this study is concerned. n the study area, the rocks dip gently to the southwest, with an average dip of a few meters per kilometer, and are exposed on the northeastern limb of a broad syncline which plunges gently to the south. Non-marine Cretaceous sediments of the Windrow Formation are exposed in patches about the area on a post-devonian erosion surface (Figs. 3 and 4). The area did not receive till from the last (Wisconsinan) glaciation, and is generally mapped as 11 driftless 11 However there are scattered occurrences of older, perhaps Kansan, till (Wright, 1972) The area is mantled by loess presumably dating from the main Wisconsinan glaciation. The thickness of surficial materials increases westward from the study area, attaining many tens of meters in thickness within the margins of the Des Moines lobe drift area of Wisconsinan glaciation. The occurrence of karst decreases with increasing thickness of surficial

20 Figure 3. Generalized stratigraphic column for the study area. From Milske ( 1982).

21 u,... Cl) 7 -Cl) E 6 - w...j 5 <C CJ) 4...J <C 3 -a: w 2 > 1 WSCONSNAN LOESS PRE-WSCONSNAN DRFT WNDROW FM - clay, sand, sandy clay, and gravel overlying massive concretionary limonite CEDAR VALLEY FM - dolomite and dolomitic limestone MAQUOKETA FM - silty dolomite, shaley dolomite and dolomite limestone with thin calcareous shale DUBUQUE FM - limestone interbedded with calcareous shale GALENA FM - STEWARTVLLE MBR massive dolomite and dolomitic limestone PROSSER MBR silty dolomite limestone, limestone and sandy limestone CUMMNGSVLLE MBR limestone and shaley limestone with calcareous shale beds DECORAH FM - calcareous shale Q- QUATERNARY K - CRETACEOUS D - DEVONAN - ORDOVCAN

22 Figure 4. Geologic map of the study area. From unpublished field work by Ramesh Venkatakrishnan and Ron Spong, and from Sloan and Austin (1966). EXPLANATON WNDROW FORMATON CEDAR VALLEY FORMATON Omd MAQUOKETA AND DUBUQUE FORMATONS Og GALENA FORMATON Odpg DECORAH, PLATTEVLLE, AND GLENWOOD FORMATONS ST. PETER FORMATON

23 -8- 'O E... / r ; 'O E..-...r..,.. ]~i Q) iii U) ~ Q e )..., \ (......_.,.

24 materials. -9- Karst features are rare when the thickness of surficial deposits is greater than 15-2 m, and disappear almost entirely when the thickness of surficial deposits :reaches about 3 m. Physiography The Root River and its tributaries, as well as other tributaries of the Mississippi (the Zumbro, Cannon, Whitewater, and upper owa Rivers) are deeply entrenched into gently :rolling, loess-mantled uplands. This dissection becomes more pronounced east of the study area, towards the Mississippi River, where relief is as great as 15 m. The Root River has its headwaters in Mower county, within the pre-wisconsinan grey drift area (Hobbs and Goebel, 1982). As it flows eastward the gradient increases, and it starts to incise into bedrock. The maximum channel gradient occurs where the South Branch of the Root River crosses the Galena Formation (Milske, 1982). The uplands are intensively farmed, while the steep hill slopes are forested. The valley floors are flat, alluviated, and often cleared of forest for farming. There is an abrupt break in slope between the valley floors and the hill slopes. Karst Development Karst is formed in carbonate bedrock by the dissolving action of groundwater. Karstification begins as water becomes acidified in the upper layers of soil. As it infiltrates, it slowly dissolves the carbonate rock, enlarging pre-existing fissures and joints. As these openings become enlarged, groundwater flow becomes increasingly localized,

25 -1- and surface drainage becomes increasingly diverted to the underground conduit system. Water enters the system through discrete, localized input points such as sinkholes or sinking streams, and by diffuse percolation. Springs discharge water from the system. Karst is best developed in southeastern Minnesota between the easternmost edge of the pre-wisconsinan Gray Drift and the westernmost outcrop of the Decorah Shale in the carbonate formations overlying the Decorah Shale. These units, the Galena, Dubuque, Maquoketa, and Cedar Valley Formations, are hydrologically connected, and are collectively referred to as the "upper carbonate aquifer" (Broussard et al., 1975). Karstification has been greatly speeded up by the presence of a welldeveloped system of joints in the Galena and Dubuque Formations. n the study area, the development of joints can be readily seen in limestone quarries. There are two primary joint orientations, one trending roughly east-west and the other trending roughly northeast-southwest. A third orientation, roughly northwest-southeast, is less frequently present. The alignment of springs, sinkholes, and cave passageways along major joint trends shows the influence these joints have on karst development and groundwater flow. n the study area water enters the upper carbonate aquifer through sinkholes and blind valleys in the uplands, and through streamsinks (swallow holes) in the channel of the South Branch of the Root River. There is also diffuse recharge from infiltrating soil moisture. Springs in the stream valleys discharge water from the aquifer. The springs are either just above the contact with the Decorah Shale or at the base level established by local stream valley incision.

26 -11- The exact age of the karst is unknown. t is probably related to the incision of the Root and Upper owa Rivers into the upland plateaux, which is in turn related to the development and incision of the proto-mississippi River. The south-flowing Mississippi probably became established in early Pleistocene time. The major incision of the upper Mississippi Valley probably occurred prior to Kansan time in the early Pleistocene (Frye, 1973; Milske, 1982). The increased hydraulic gradient resulting from this entrenchment promoted the flushing and enlarging of solution channels, and the formation of caves in the Ordovician carbonate rocks, particularly within the Galena Formation. U/Th disequilibrium dating of speleothem deposits in one such cave, Mystery Cave, gives ages as great as 16 thousand years (Lively, 1983). When the speleothems were deposited, the cave was already well formed, so the actual age of cave formation is much greater (Lively and Alexander, 198). The initial network of solution-enlarged joints appears to have formed before the effects of river incision were felt, perhaps as early as Cretaceous time (Wopat, 1974). The karst is a "fluviokarst" in the classification of Sweeting ( 1973), as it resulted from the combined action of fluvial and karst processes. Description of Karst Features in the Study Area Figure 5 shows the major karst features in the study area, together with dye trace connections.

27 Figure 5. Map of the study area showing streams, major karst features including blind valleys and springs, and dye trace connections.

28 ,. \, ( i \ \, \ \.\ ( (' / -. \ \, \ _.. _ j!/...- r.,, /.r /,. \ ) / i /,., /!...,... ('.. ( i Red Tail,.,.,_,.._\ \ '' :,..., \ \,.., ' ,; \ \ \..,,. EXPLANATON e-v spring ~ streamsink ;. cave entrance ~ dye trace connection.i1. gaging station recording rain gage scale O.5 1mile.5 ~ 1 km / \,.{ r /- _,.<V r '- \ f-' N /' 1' /'/ ( j i ( ( /.i ( / / )... t \.., \..., },. s. \),.. )... \ i/ \,.._i ' \., Disappearing',, R 1ver. ' )..,., / ) j j //,>?'--" ~~)~ ~) ; /.i- _./ \... ' \ \., /...,... ) ~-... _,...,_.,, -~,., i, )._, \ //~.,,, ~, / \ ) [_ :'< N r

29 South Branch of the Root River -13- The South Branch of the Root River (hereafter referred to as the South Branch) flows eastward across the study area. Starting at Disappearing River, at the entrance to Mystery cave, it loses water to a series of streamsinks along the river channel. Under low flow conditions, the surface channel is completely dry from Matheson Sink downstream to the resurgence at Seven Springs. Under high flow conditions, water flows all the way along the surface channel. Mystery Cave Developed at or near the Dubuque/Galena contact, Mystery Cave acts as a subsurface meander cutoff for the South Branch (Fig. 6). The plan of Mystery Cave is almost totally controlled by joint orientations. The cave contains over 18 km of surveyed passageways, some of which are tens of square meters in cross section. Seven Springs At Seven Springs water resurges from several outlets along the base of a wall of Galena Limestone and flows into the South Branch channel (Fig. 7). The South Branch may or may not be flowing upstream from Seven Springs, depending on the flow conditions, but the springs flow year-round. There is another small outlet about 1 m northeast of outlet 111. The discharge at Seven Springs averages around 3 liters/sec (9 cfs).

30 Figure 6. Location of Mystery Cave in relation to surface topography. 11T 11 indicates the location of the First Triangle Room. From Milske (1982).

31 t NORTH SCALE Contour nterval: 5 feet 3 feet 1 meters Adapted from USGS 7.5 minute topographic maps: Wykoff, MN and Cherry Grove, MN.

32 Figure 7. Map of Seven Springs showing the different outlets. Adapted from an original map prepared by R.C. Spong.

33 ...,.15- / / / / / / / SEVEN SPRNGS i2a o~ & Fillmore County, Minnesota (Sec. 21,Tl2N.,R.12W.) Surveyed 2/ 8/8 by R.C. Spong Bose USGS 1 Cherry Grove 7-f, 1965 Contours ±5 feet 1 m - METERS Nji-c-.!: 5, 11 a g, ::;; "' (D

34 -16- Moth and Grabau Springs Moth and Grabau Springs are major resurgences forming the head of Forestville Creek (Fig. 8). the south side of the valley. Moth Spring is the larger of the two, on The flow from the spring issues from a cave opening in the base of a Galena cliff. Across the valley at Grabau Spring, water flows from a series of small outlets along the base of the hill slope. The flow from the two springs merges 75 m downstream from Grabau Spring. The combined flow ranges from 4 liters/sec (14 cfs) to over 8 liters/sec (28 cfs). Forestville Creek flows for 3 km before its confluence with the South Branch of the Root River. Forest ville Creek is an important trout stream. t is the only stream in the state of Minnesota supporting a naturally breeding trout population. Fairview Blind Valley Formerly known as Zimmer Blind Valley, Fairview Blind Valley is a major karst sink draining an area of several square kilometers. A perennial stream flows from the west and sinks into a number of stream sinks (Fig. 9). The location of the terminal sink depends on flow. Under low flow conditions the stream goes completely underground at the west end of the valley. Under higher flow conditions the stream flows to the east end of the valley before sinking. During extremely high flow the whole valley may fill up for a few hours. The valley floor is flat and alluviated. The valley is a window through the Dubuque Formation into the Stewartville Member of the Galena Formation. There is an extensive, recently discovered cave system beneath Fairview Blind Valley which has not been thoroughly explored (R.C. Spong, personal communication, 1981).

35 Figure 8. Map of Moth and Grabau Springs. Adapted from an original map prepared by R.C. Spong.

36 lf4o :-- l +-s MAG. l>ecuh. GRABAU SPRNG / / / / / ~ / A,,~/ / / / / ~1, -' --...] ,,so FORESTVLLE CREEK FLLMORE CO., MNNESOTA. 2 JULY 198 SURVEY a CARTO GRAPHY BY R. SPONG. BASE: USGS WYKOFF 7,5' QUAD 1965.

37 Figure 9. Map of Fairview Blind Valley, showing the various streamsinks including Hellerud Sink A and Poldervaard Sink A. Adapted from an original map prepared by R.C. Spong.

38 ~4.7 "' x , )\j 132 x t HELLERUD O ~ 5. D x : O.,_,, FARVEW BLND Fillmore County, Minnesota Sec. 6, T2N., R.12W.) Surveyed 12/31/79 by R.C. Spong Base: USGS, Wycoff 7~, 1965 VALLEY~' Air Photograph MHF , METERS f " 555.4: 3 ~..- :; t' w "' w "' x x- _ x ,.,_,,o..,, ij ,.,_,,o,,'2-o 4.9 D ~ ,-,_,'1-5.3,.,_,-,_,o "'

39 -19- Other Karst Features There are many sinkholes in the upland plain north of Fairview Blind Valley. One of the larger of these is Red Tail Sink, which accepts flow from surficial seeps to the west (Fig. 5). Another major feature is Lefevre Blind Valley, where an intermittent stream flowing from the southwest sinks (Fig. 5). Natural Well is a small cave in the Prosser Member of the Galena Formation (Fig. 1). There are many other karst features in the study area, but the ones described above are most relevant to the hydrologic studies of this paper.

40 Figure 1. Map and cross-section of Natural Well. Adapted from an original map prepared by R.C. Spong.

41 WELL HOUSE,r:: ENTRANC& (Apprex.el4evflt1on).tt!~ 12.i 5.. T. MSL... NATURAL WELL fllllll\ore CO., MNNESOTA SURVE.'< 21 Oct 1977 BY T.MARSHALL,R. VEN'<ATh KRSHNAN ( R.SPONG. CAlttOGRAPHV R.SPONG. BASE: USGS WVKOFF7!i. GAlENAFM PROSSER MOO (ls) N ± ~ ' ~ 19E,5 MA'1,. l)l!cln. SCALE ~ 5z -~, FT. o :J. 3 M.

42 -21-. QUANTTATVE FLUOROMETRC DYE TRACNG Tracers of various kinds have been used for many years in the study of karst groundwater flow. A tracer is introduced into a sinkhole or sinking stream and detected or recovered at one or several spring resurgences. Fluorescent dyes, minute biological materials such as Lycopodium spores or bacteria, soluble salts, and radioactive materials are examples of tracers used in various studies (Aley and Fletcher, 1976). An ideal tracer should have the following properties: 1) its introduction into the subsurface should be easy; 2) it should be easily detectable or recoverable at the resurgence points; 3) its flow velocity should approximate that of its host water; 4) its adsorption onto the aquifer material should be minimal; and 5) its potential for harmful environmental effects should be small. The fluorescent dye Rhodamine WT, used in this study in conjuction with a field fluorometer, adequately satisfies these requirements. The fluorometer (a Turner Designs model 1-5) is capable of accurately measuring dye concentrations down to a fraction of a part per billion. The advantage of the fluorometric technique is that the concentration of dye as it emerges from a spring resurgence can be monitored, yielding quantitative travel time and dispersion data. Rhodamine WT can also be used semi-quantitatively by placing a packet of activated charcoal in a spring resurgence. f dye emerges from the spring, it will adsorb onto the charcoal. The packet can then be collected and analyzed for dye.

43 -22- Methods The basic procedure used in this study was as follows: 1. An input point (sinkhole or sinking stream) and resurgence points (springs) were chosen. 2. Packets of activated charcoal were placed in all the suspected resurgences, since it was not possible to monitor every spring with the fluorometer. 3. A known quantity of Rhodamine WT was injected at the input point. 4. Discharge measurements of the spring(s) were taken. At first this was done by measuring the cross-sectional area of the stream and measuring the velocity of floating or suspended objects at intervals along this cross-sectional plane. After the first several traces, flow measurements were done using a dye dilution technique. Dye of known concentration C was injected in the spring at constant rate q, using a Mariette vessel constant head injector device (see Cobb, 1968). After equilibrium was established, the downstream concentration C was measured with the fluorometer. The discharge Q was then determined using the formula: Q = q ( 1) c 5. The concentration of the dye as it emerged from one spring or several springs was monitored for as long as possible. 6. The final step on leaving the field was to change the charcoal packets in all the springs in order to catch any dye that might not

44 -23- have been detected and to measure long-term washout. The charcoal packets were analyzed for Rhodamine using the technique of Aley and Fletcher (1976). Data Analysis The fluorometric data were plotted as concentration versus time curves. These pulse response curves contain information about the travel time and dispersion of the subsurface water. Also, the area under such a curve is proportional to the amount of dye discharged from the spring: (X) m = JQ(t)c(t)dt (2) where m = mass of dye recovered c(t) = dye concentration in spring Q(t) = spring discharge f spring discharge is constant over the period of the trace (a tenuous assumption), Q can be taken outside of the integral. Using this relationship it is possible to perform mass balance calculations, thereby determining what proportion of the water entering a given sink point emerges at a given resurgence. When several springs are being monitored, it is possible to determine how the water entering a given sink is partitioned among several resurgences. The concentration versus time curves were integrated numerically, using a simple trapezoidal formula. The tails of the curves were extrapolated using an exponential decay rule, and the areas under the extrapolated tails were determined analytically. The tails contained a

45 -24- significant proportion of the total area. The total area under each curve was multiplied by the measured spring discharge to determine the mass of dye recovered (equation 2). This was compared to the amount of dye injected to derive a percentage dye recovery. The greatest uncertainties in this analysis are in the discharge measurements. Results Figure 5 shows all the quantitative fluorometric dye traces accomplished in the study area. The traces will be discussed one by one, with most of the information appearing in figures. The data from the dye traces is in Appendix A. Disappearing River to Seven Springs, Oct.!.Q..z (Figure 11) This was the first of several traces to Seven Springs. Dye was introduced at the commercial entrance to Mystery Cave, where the South Branch first starts losing water to the subsurface. The flow conditions were relatively low, with the South Branch going completely underground. t is interesting that the various outlets at Seven Springs, which are only a few meters apart, responded differently from one another. The response at outlet /11 peaked at a lower concentration and was more dispersed than the responses of the other outlets. When the curves are averaged, the resulting curve represents an 89.5% dye recovery. Given the uncertainty of the flow measurements and the inaccuracies introduced by a simple averaging of the pulses, this represents essentially complete dye recovery.

46 Figure 11. Disappearing River to Seven Springs, Oct. 1, 1979 Time of dye drop: 3:13 a.m., October 1, 1979, at Mystery Cave entrance. Amount, type of dye: 914 g Rhodamine WT 2% solution Horizontal distance: 2.38 km (1.48 miles) Vertical drop: 18 m (6 ft) Arrival of leading edge of dye pulse: 7.75 hours Arrival of peak dye concentration: 1 hours Flow measurements: 259 liters/sec (measured with tape and stopwatch) Dye budget calculations: 89.5% of dye recovered Springs where dye did not emerge: Moth Spring, Grabau Spring, Cold Spring The numbering of the outlets is shown in Figure 7.

47 SEVEN SPRNGS ro - m a. a. -- -~ : ' c c i 2 ~ (.) t - 3:: \: -i 3 -i 25 \~ ~ 2 ; 15 - ~1 1' - 15 E c -.c :: 1 - / \...').,. - 1 N (.J1 5 5 L -~~-.L L l ~, ;---L -~ ~ :..._ ~ ;---'' o..., Hours After Dye njection n Disappearing River =1:1=,,2, """T-.-r-r... ~ * 9...., ~7,Blo

48 -26- Disappearing River to Seven Springs, Sept.!. 198 (Figure 12) The flow conditions were much higher during this trace than for the previous trace from Disappearing River to Seven Springs, with the South Branch flowing all the way along its surface channel. response differed markedly from that of the first trace. The spring The responses for the different outlets form a nestled family of curves, with the higher numbered outlets showing the highest concentrations. All curves show the same dispersion through time, and all have a second peak with a lag time of 3 hours after the first peak. The double-peaked response curves can be best explained by a divergence in the flowpath, followed by a later reconvergence, with different travel times associated with each pathway. The fact that the double peak occurs under high flow, but not under low flow conditions suggests that the alternate pathway is an overflow channel available only under high flow conditions. The nestled pattern of the response curves is best explained by varying degrees of dilution of essentially the same pulse by undyed water from another source. The diluting water could be sinking in streamsinks in the South Branch downstream from Disappearing River, such as those between Matheson Sink and Seven Springs (see Fig. 5), and preferentially travelling to the lower numbered (northernmost) outlets of Seven Springs. Under high flow conditions, when water is flowing all the way along the surface channel and sinking into these downstream sinks, the response curves show increasing dilution from high to low numbered outlets at Seven Springs. Under low flow conditions, there is little or no water infiltrating in these sinks, so the response curves

49 Figure 12. Disappearing River to Seven Springs, Sept. 2, 198 Time of dye drop: 6: a.m., September 2, 198, at Mystery Cave entrance Amount, type of dye: g Rhodamine WT 2% solution Horizontal distance: 2.38 km (1.48 miles) Vertical drop: 18 m (6 ft) Arrival of leading edge of dye pulse: 6.75 hours Arrival of peak dye concentration: 8.25 hours Flow measurements: Seven Springs - 39 liters/sec (measured by dye dilution) The numbering of the outlets is shown in Figure 7.

50 -27-!?... '... D Cit > a: D c:... Cl Q.,,, Q... c:.,, ~ Cl) Q. Q. ~ ~... Q Q: ~ ~ Q. Cl >- Q ~ c '4.a Cl)... ~ : % N CD

51 -28- do not show as pronounced a pattern of increasing dilution from high to low numbered outlets. Formation Route Creek to Seven Springs, Aug. E2l. 198 (Figure 13) Formation Route Creek flows through the northwestern portion of the Mystery Cave system, or "Mystery Cave". Dye was injected beneath a room known as the "First Triangle Room", where the creek is accessible (see Fig. 6). Water was flowing all the way along the surface channel of the South Branch at the time. The pulse response curves are nestled as in the second trace from Disappearing River to Seven Springs, except that there is no second peak. Again, the lower numbered (northernmost) outlets had the lowest concentration. This further supports the idea that the lower numbered outlets are preferentially fed by a source not associated with the Mystery Cave system, such as the sinks on the South Branch between Matheson Sink and Seven Springs. Matheson Sink to Seven, Moth, and Grabau Springs, Oct. 2-21, 1979 (Figure 14_)_ n this dye trace water was simultaneously traced from Matheson Sink on the South Branch to Seven Springs, Moth Spring, and Grabau Spring, and all three pulses were monitored. Under low flow conditions, Matheson Sink can act as the terminal sink of the South Branch before it resurges at Seven Springs. The dye pulse first arrived at Seven Springs. The response was similar to that of the first (low flow) trace from Disappearing River to Seven Springs. The pulse at outlet #1 had a slightly lower peak and was slightly more dispersed than at the other outlets.

52 Figure 13. Formation Route Creek {Mystery Cave) to Seven Springs, August 25, 198 Time of dye drop: 1:19 a.m., August 25, 198, under First Triangle Room in Mystery cave Amount, type of dye: 39.3 g Rhodamine WT 2% solution Horizontal distance: 1.63 km (1.2 miles) Vertical drop: 6 m (18 ft) Arrival of leading edge of dye pulse: 5. hours Arrival of peak dye concentration: 6.25 hours Flow measurements: Seven Springs - 22 liters/sec (measured by dye dilution) Springs where dye did not emerge: Moth and Grabau Springs The numbering of the outlets is shown in Figure 7.

53 -29- & SEVEN SPRNGS -.a - a. Q, Houn After Dye Dropped n Formation Route Creek 15

54 Figure 14. Matheson Sink to Seven Springs, Moth Spring and Grabau Spring, October 2-21, 1979 Time of dye drop: 6:35 a.m., October 2, 1979 Amount, type of dye: 1118 g Rhodamine WT 2% solution Horizontal distance: Seven Springs km (1.7 miles) Grabau Spring km (2.4 miles) Moth Spring km (2.37 miles) Vertical drop: Seven Springs - 12 m (4 ft) Grabau Spring - 26 m (85 ft) Moth Spring - 26 m (85 ft) Arrival of leading edge of dye pulse: Seven Springs - around 8.5 hours Grabau Spring hours Moth Spring hours Arrival of peak dye concentration: Seven Springs hours Grabau Spring hours Moth Spring hours Flow measurements: Seven Springs liters/sec Grabau Spring liters/sec Moth Spring liters/sec (measured with tape and stopwatch) Dye budget calculations: Seven Springs - 5.8% (4.5%) of dye Grabau Spring % (26.6%) of dye Moth Spring - 89.% (68.9%) of dye (numbers in parentheses have been scaled down to 1% dye recovery) Springs where dye did not emerge: Cold Spring The numbering of the outlets of Seven Springs is shown in Figure 7.

55 GRABAU SPRNG MOTH SPRNG 2 m t 15 - \, --l 15 ~ c:... c c: Q) c: u : \ j \ J \ \ - 1 ln Q) c: - E c "C.s:: a:: 5 - ;:)t:.vt:.n '\.. \ - 5 Y ~ --, f*, e, Hours After Dye njection At Matheson Sink

56 -31- Most of the dye emerged at Moth and Grabau Springs. The subsurface connection between the South Branch of the Root River and Forestville Creek was suggested in 1958 when souvenirs from the Mystery Cave concession stand, which had been washed away in a flood, were found below Moth Spring. t is surprising that the Moth Spring response curve lags behind that of Grabau Spring by almost six hours. Not only is Grabau Spring farther away from Matheson Sink than Moth Spring, but it is across the deeply incised stream valley of Forestville Creek (see Figs. 5 and 8). The discharge from Moth Spring is also much greater than that from Grabau Spring. A partial explanation for the surprising travel times lies in the nature of the spring openings. nside the Moth Spring cave entrance is a large pool which overflows to produce the spring outflow. The output from Grabau Spring comes from isolated small outlets. The mixing time for the large reservoir inside Moth Spring cave could account for some of the increased dispersion and travel time for the dye pulse. However the peak concentration of the Moth Spring response is greater than that of Grabau Spring, so there is more going on than simple lagging and routing through a reservoir. Whatever the mechanism, the connection to Grabau Spring is shorter and involves less dispersion than that to Moth Spring. The mass balance calculation for this trace produced a 129.1% dye recovery (Fig. 14). This is clearly impossible, and due no doubt to inaccurate flow measurements. Figure 14 also gives numbers wich have been scaled down to 1% recovery. t is interesting that over 9% of the water which infiltrates at Matheson Sink gets pirated off to another drainage.

57 -32- Fairview Blind Valley to Moth and Grabau Springs Two traces were done from Fairview Blind Valley, one under high flow and one under low flow conditions. As mentioned before, under high flow conditions the stream flows all the way to the end of the valley, finally disappearing in a collection of sinks known as the Hellerud Streamsinks (Fig. 9). Under low flow, the stream makes it only as far as the Poldervaard Streamsinks. High Flow Hellerud Sink 'A' to Moth and Grabau Springs, Nov , 1979 (Figure 1~ The terminal sink on November 17, 1979 was identified as Hellerud Sink 'A' to distinguish it from the other Hellerud Streamsinks (see Fig. 9). The response curves show several interesting features. Again, the Moth Spring response lags behind the Grabau Spring response, this time by two hours. Notice the similarity in shape of the two curves, and the pronounced double peak in both. Some of the water takes a faster path, producing the first peak, while most of the water takes a second, slower path, producing the main, larger peak. The similarity of the two curves indicates that the divergence and reconvergence occur before the final split between the flows of Moth Spring and Grabau Spring. Low Flow Poldervaard Sink 'A' to Moth and Grabau Springs, July 13-22, 198 (Figure 16) The terminal sink on July 13, 198, was one of the Poldervaard Streamsinks, and was identified as Poldervaard Sink 'A' (see Fig. 9). Note that the travel time is twice that from the downstream (Hellerud) sink of Fairview Blind Valley. The Moth Spring response lags by 6-9

58 Figure 15. Fairview Blind Valley (Hellerud Sink A) to Moth and Grabau Springs, November 17-21, 1979 Time of dye drop: 3:3 p.m., November 17, 1979 Amount, type of dye: 863 g Rhodamine WT 2% solution Horizontal distance: Moth Spring km (3.5 miles) Grabau Spring km (3.52 miles) Vertical drop: 47 m (155 ft) Arrival of leading edge of dye pulse: Grabau Spring hours Moth Spring hours Arrival of peak dye concentration: Grabau Spring hours Moth Spring hours Flow measurements: Grabau Spring liters/sec Moth Spring liters/sec (measured with tape and stopwatch) Dye budget calculations: Grabau Spring % (1.9%) of dye Moth Spring % (89.1%) of dye (numbers in parentheses have been scaled down to 1% dye recovery) Springs where dye did not emerge: Cold, Stagcoach, Freiheit, Barr, Narcissus, Mahood Springs

59 [ 2, ~ c... Cl... c G) () c u GRABAU SPRNG ~ \ MOTH ~ 2. SPRNG L / \\ J - 1. ~ r r \ \ -l 1. 3,: G) c E Cl "Cl.s:::. :: l:..n l:..n Hours After Dye njection At Fairview Blind Valley

60 Figure 16. Fairview Blind Valley (Poldervaard Sink A) to Moth and Grabau Springs, July 13-22, 198 Time of dye drop: 6.36 p.m., July 13, 198 Amount, type of dye: 123 g Rhodamine WT 2% solution Horizontal distance: Moth Spring km (3.7 miles) Grabau Spring km (3.71 miles) Vertical drop: 5 m (165 ft) Arrival of leading edge of dye pulse: Grabau Spring hours Moth Spring - 98 hours Arrival of peak dye concentration: Grabau Spring hours Moth Spring hours Flow measurements: Grabau Spring - 7 liters/sec Moth Spring liters/sec (measured by dye dilution) Dye budget calculations: Grabau Spring % of dye Moth Spring % of dye

61 7.---~~~~,-~~~~--,--~~~~-.-~~~~~..-~~~~-.-~~~~-.-~~~~-..~~~~----.~~~~~..-~~~~-.-~~~~-.-~~~~~ 6 GRABAU - 51 SPRNG..a c c a, u c u : \ \ (.N ~ G) c E c,:, _g 2 a: Hours After Dye Dropped at Poldervaard Sink (Fairview Blind Valley Upstream Sink)

62 -35- hours, and there is no pronounced double peak. The difference between the high flow and low flow response curves are best explained by the level of water in the aquifer. Under high flow conditions, the large conduits are more nearly full, and water is flowing at a higher velocity. There are alternate overflow channels available, which can produce double-peaked response curves as in Figure 15. n the case of Figure 15, most of the water travelled the slower of the alternate pathways, while a smaller amount took a short cut". Under low flow conditions, the main conduits are not full, so the flow is slower, and overflow passageways are not available. The same pattern shows up at Seven Springs: high flow conditions produce a double peak, while low flow conditions produce a single-peaked response. Figure 17 gives a simplified, schematic cross section of the flow between Fairview Blind Valley and Moth and Grabau Springs. The figure does not by any means represent all the complexities of the system. t simply shows the kind of conduit geometry which could produce the observed results. Moth Spring is shown as being farther away from Fairview Blind Valley than Grabau Spring. This is to show that the distance along the flowpath is longer, and does not reflect the areal geometry. Natural Well to Moth and Grabau Springs, May 12-17, 198 (Figure 18) Natural Well is a small cave in the Prosser Member of the Galena Formation (Fig. 1). A small stream of water sinks into the floor of the cave, and this is where dye was injected. As in other traces to Moth and Grabau Springs, the Moth Spring response lags behind the Grabau Spring response. There are some unusual

63 Figure 17. Schematic cross-section of the subsurface flowpath between Fairview Blind Valley and Moth and Grabau Springs, showing one kind of conduit geometry which would produce the observed dye trace response curves.

64 -36- -Q > "O c: >..

65 Figure 18. Natural Well to Moth and Grabau Springs, May 12-17, 198 Time of dye drop: 4: p.m., May 12, 198 Amount, type of dye: 44.8 g Rhodamine WT 2% solution Horizontal distance: 1.83 km (1.14 miles) Vertical drop: 17 m (55 ft) Arrival of leading edge of dye pulse: Moth Spring - 55 hours Grabau Spring hours Arrival of peak dye concentration: Moth Spring hours Grabau Spring hours Flow measurements: Moth Spring liters/sec Grabau Spring - 92 liters/sec (measured by dye dilution) Dye budget calculations: Moth Spring % of dye Grabau Spring - 9.9% of dye Springs where dye did not emerge: Root Spring

66 -37- N a... ::, z -a c,:, Q, Q,... Q ct

67 -38- oscillations near the peaks of both curves. The response curves cannot account for all of the dye, suggesting that some of the water infiltrating at Natural Well might be emerging elsewhere. Root Spring, located 1 km northeast of Moth Spring, showed no positive response. Red Tail Sink to Moth and Grabau Springs, June 28 - July 2.t_ 198 (Figure 1gy Red Tail Sink is a large sinkhole north of Fairview Blind Valley, which drains the outflow from several surficial seeps when they are flowing. The sink is near the topographic divide between the drainages of the Middle and South Branches of the Root River. The travel time to Moth and Grabau Springs is relatively long and the response curve is fairly dispersed. While the dye recovery is less than complete, dye was not detected at any neighboring springs. The characteristic lag of the Moth Spring response is present. Lefevre Blind Valley to Moth and Grabau Springs, October 7-1, 198 (Figure 2) Lefevre Blind Valley is a major sink draining an intermittent stream. When flowing, the stream drains into several streamsinks at the end of the valley, and this is where dye was injected. The response curves were fairly typical for Moth and Grabau Springs. Data from the initial rise of the curves is missing, and was approximated by an exponential rise for the dye budget calculations. Root River Dye Traces The Root River dye traces were large scale dye trace experiments performed in August of 1981 and August of n each case, a large pulse of dye was injected into the South Branch south of Spring Valley

68 Figure 19. Red Tail Sink to Moth and Grabau Springs, June 28-July 9, 198 Time of dye drop: 1:1 a.m., June 28, 198 Amount, type of dye: 1325 g Rhodamine WT 2% solution Horizontal distance: 6.69 km (4.16 miles) Vertical drop: 58 m (19 ft) Arrival of leading edge of dye pulse: Grabau Spring - around 77 hours Moth Spring - around 81 hours Arrival of peak dye concentration: Grabau Spring hours Moth Spring - 12 hours Flow measurements: Grabau Spring - 82 liters/sec Moth Spring liters/sec (measured by dye dilution) Dye budget calculations: Grabau Spring % of dye Moth Spring % of dye Springs where dye did not emerge: Mahood, Barr, Narcissus, Freiheit, Stagecoach, Root, Cold, Seven, Frost, and Bartsch Springs

69 ~~~~~~~~----,.--~~~~~~~~~...-~~~~~~~~--.g N.ac st c N - Cl) / / jf / / / / / / / /" / Cl...,:, it> - a:: -C(,:, N a. - :... :,,. = = -C(... :, - :::c en Cl) L-~~~~~~~--'-~L-~~~~~~~~~L-~~~~~~~~---g N ( qdd) UO!'DJJUG:>UO:).1.M 9U! WDpOU:l

70 Figure 2. Lefevre Blind Valley to Moth and Grabau Springs, October 7-1, 198 Time of dye drop: 5: p.m., October 7, 198 Amount, type of dye: g Rhodamine WT 2% solution Horizontal distance: Moth Spring km (2.89 miles) Grabau Spring km (2.91 miles) Vertical drop: 52 m (17 ft) Arrival of leading edge of dye pulse: missed exact arrival time Arrival of peak dye concentration: Grabau Spring hours Moth Spring hours Flow measurements: Grabau Spring - 9 liters/sec Moth Spring liters/sec (measured by dye dilution) Dye budget calculations: Grabau Spring - 8.% of dye Moth Spring % of dye

71 -.a a. a. 5 - ~ 4 GRABAU SPRNG -D... -c u ~ ~ c - 2 E D 'a.: : h MOTH \ \ SPRNG i..p Hours After Dye Dropped n Lefevre Blind Valley