Monday,
February 9, 2009
6:00 - 7:30 pm
Pellissippi
State Technical Community College
10915 Hardin
Valley Road, Knoxville
J.L. Goins Administration Building, Cafeteria Annex
FEBRUARY
PRESENTATION
Karst
Hydrogeology of the Ten Mile Creek Watershed, West Knoxville,
Tennessee
by
Tom Zondlo
Shaw Environment & Infrastructure, Inc.
Knoxville, Tennessee
The objective of this presentation is to introduce the Ten Mile Creek Watershed in preparation for the upcoming field trip. Although an overview of the hydrogeology of the entire watershed will be attempted, the principal focus of the field trip is the hydrogeology of the Ebenezer sinks area in the downgradient portion of the watershed. In this area the entire discharge from the roughly 16 square mile watershed goes underground in a complex series of under- and overflow swallets, conducted through the Ebenezer-Ten Mile-Fox Bones-Three Holes cave system for nearly 1.5 miles to emerge from a cave and series of springs at the base of a bluff at Sinking Creek (Tennessee River). The cave system is a multi-storied network of vadose and phreatic conduits formed within the Holston and Lenoir formations along a reverse fault that extends through the swallet and resurgence points. The caves host an active cave stream which links accessible/enterable segments of the flowpath(s) comprising the cave network. The capacity of the swallet complex to facilitate drainage to the subsurface and the conduit network to convey the water to the resurgence point is controlled by a number of factors, including seasonal and storm related pool stage conditions at the resurgence point, antecedent rainfall, and loading from the remainder of the watershed. It has been estimated that when streamflow in Ten Mile Creek exceeds ~ 440 cfs that the swallet capacity is exceeded and flooding commences. Modeled peak streamflow discharge for the 100- and 500-year flood events are on the order of 6,670 and 8,730 cfs, respectively. For reference the modeled peak discharge for a 2-yr storm event is on the order of 1,520 cfs. Consequently, once the capacity of the drain is exceeded flooding prevails, with flood levels rising nearly 18 to 30 ft above normal creek stage associated with the 100- and 500-year flood events, inundating large areas along the creek for miles upstream of the sinks.
Ten Mile Creek is the principal stream that drains the basin, originating at Presley Lake on the flanks of Black Oak Ridge and ultimately discharging to the Tennessee River (Fort Loudon at Sinking Creek Embayment). Along the way, additional streamflow volume is contributed by three tributary streams (Sinking Creek, the West Hills tributary, Ebenezer Branch and the Echo Valley tributary), and, via groundwater discharge via discrete springs and diffuse gaining reaches. All of these streams transect a number of thrust faults and flow across a terrane underlain predominantly by carbonate bedrock that hosts a well developed karst. Gaining and losing reaches occur along the streams and for much of the year, the streams in the upper reaches of the watershed are dry, such that all recharge follows subsurface flow routes in the well developed karst. In fact, a significant proportion of the watershed lacks surface drainage features and is internally drained via the subsurface karst network. Surface drains where present function only to convey runoff into sinkholes and karst windows, terminating at these features. Flow in the surface channels is largely ephemeral.
Ten Mile Creek is also an (increasingly) urbanized watershed, with considerable stormwater runoff and management issues that factor into flooding in the sinks area as well as locally within other parts of the watershed. While natural drainage to the karst affords stormwater control, runoff is also focused or injected into the underlying karst currently at 36 permitted Class V injection points (and probably many others that are not) within the watershed. The &ldquoinjection wells&rdquo comprise a full spectrum ranging from facilitated drainage to cave openings to sinkhole improvements of varying design, and injection wells.
The hydrogeologic and hydraulic aspects of this watershed are both complex and fascinating, and provide an opportunity to observe both unique and classic components of karst hydrogeology, all in our &ldquobackyard&rdquo.
ETGS NEWS:
Winter/Spring Field Trip: Tom Zondlo is preparing a day-long field trip in the Ten Mile Creek karst watershed of west Knoxville. Be sure to attend the February 9 meeting for an introductory presentation and more information about the trip. Potential dates include February 28 and March 7, and it is anticipated that the trip will last from 7:30 a.m. until approximately 5:00 p.m. This trip is for adults or older kids only because field conditions will include difficult access routes and a possible cave entry.
Field Trip Overview
The field trip as planned will &ldquofollow the water&rdquo from the headwaters on Black Oak Ridge to the resurgence point at Sinking Creek embayment. A number of brief stops in the upper part of the watershed are intended to document the ephemeral nature of streamflow and predominance of subsurface flow in that portion. A key stop within the central portion of the watershed will show examples of natural and various induced (injection) infiltration in an area lacking surface streams. Parking the vehicles in a central point, a number of these features can be observed with minimal/limited walking involved. Additionally, this stop will highlight the difference between surface and groundwater divides and will introduce the hydrogeology and flooding issues in the Dutchtown-Cedar Bluff area.
Early lunch (fast food - Cedar Bluff area or brownbag)
Following lunch, we&rsquoll proceed through the downstream portion of the watershed, making three brief stops at key groundwater discharge sites, and an interesting epikarst example (and a good look at the Lenoir Ls). At that point, we&rsquoll leave the vehicles for about 2 hours and walk into the sinks area, following the railroad tracks. This affords the opportunity to observe the stratigraphic section moving toward the sinks and Ebenezer Cave. Be advised that this part can be strenuous as there is some relief, trains, and vegetation to contend with. In the sinks area, it can be fairly slick and in places muddy - dress accordingly.
From the sinks area we&rsquoll make a few quick &ldquowindshield&rdquo stops along the course of the cave system within the Gettysvue community.
The trip will culminate at the resurgence point where there is an opportunity to observe the fault, the cave mouth, and the relationship to the river level. The property also hosts an old quarry and there is also the opportunity for those suitable for going underground to do so. This is private property which contains the Mud Flats cave. The cave is not extensive, does intersect the stream (seasonally) and can be muddy. The entrance is a drop down a steep, clay embankment. However, the owner has a rigged handline to aid ingress/egress. If considering going underground be sure to bring gloves, a helmet and a headlight (I can provide up to 4 headlights, but no helmets). (Depending on group interest and time, it may be more appropriate to arrange for a later visit to the cave).
January Presentation: Thanks to Dr. Barry Beck for an excellent presentation on the karst setting of a pair of diamond-bearing kimberlites in Ontario. Although interesting in its own right, his talk was a nice follow-up to the November 2008 presentation by Dr. Kula Misra and field trip lead by Travis Paris, both of which addressed kimberlites. The following animation (approximately 25 minutes long) summarizes the formation of the Ontario kimberlites, as well as plans for mining, processing, and reclamation at the Victor Mine: www.discoverabitibi.com/animation/Geology.swf.
Page updated May 26, 2018 |