Thesis Proposal, revision 3
From GeoMod
Contents |
Introduction
This study will attempt to identify patterns in river systems where exchange with groundwater systems has altered the geomorphic form of the river. A multi-method approach will be used to study the effect of groundwater/river water exchange to ensure accuracy and integrity of the study. Field observations will be the primary source of data, utilizing temperature probes, seep tanks, aerial photography, and stream gauging. In the field, areas of high groundwater discharge will be identified by using temperature probes to detect bed locations in which a temperature gradient moving towards the groundwater standard temperature exists. Bed forms and larger scale features will be statistically analyzed and compared to [low Lurbano) exchange river sections. A channelized meandering river system [the Loosahatchie river, Lurbano] will be used for the study area for ease of comparison of large scale features, such as reinitiated meander bends, and for ease of sampling in lower velocity waters. [Previous research has shown substantial changes in ground-surface water exchange along reaches of this river Lurbano] Field data will then be correlated to observed features obtained by sand box modeling to ensure accuracy of scale. The goal is to form a better understanding of the processes [and feedbacks governing fluid exchange Lurbano] between the surface and subsurface environment.
Literature Review
Previous work has shown that a correlation can be made between river geomorphology and groundwater movements. A Texas study by Larkin and Sharp (1992) found that streams with a significant base flow tended to have a sinuosity greater than 1.5 when compared to other streams. Lower gradients where also associated with base flow dominated systems. The reason for this behavior was not investigated. Previous studies done on the exchange of groundwater and surface water have mainly studied fluid transport. Although the geomorphic effect of this exchange is often overlooked, the methods used to determine amount of exchange are very useful. Becker (2004) describes the following three approaches to estimating the amount of groundwater flux and the problems involved with each approach.
- Traditional stream gauging is done by determining river flow volume at various locations along the river. Any discrepancy in the flow volume is perceived as groundwater discharge or recharge. The traditional method does not account for other possible sources of added river water, such as runoff, and are made inaccurate by any kind of precipitation.
- A second method uses macroscopic surveying of river water for temperature change. River water that is closer to the groundwater temperature is presumed to have a groundwater influence. This method can determine location of groundwater exchange but does not determine rate.
- Another point temperature based method of acquiring discharge rate is said to be accurate, independent of precipitation, but only measures rate at a single location. This is done by burying temperature data loggers at various depths and determining the temperature gradient with depth over time (Becker et al, 2004).
- [You must mention seepage tanks and their relative benefits and disadvantages since they are one of the oldest and most commonly used methods Lurbano]
Since the goal of this study is to determine [the geomorphic influence of ground-surface water exchange Lurbano], it is necessary to determine precise areas of groundwater exchange. The macroscopic temperature methods [confirmed by seepage tanks Lurbano] will be utilized for its ability to locate these finite locations. The traditional method will be used to determine general volume of discharge. The point temperature method will not be used due to the suspect accuracy encountered by Becker (2004) and the long time needed to obtain data. [Get this following sentence in your list. This should make it clear to read Lurbano] Seepage meters offer another means of measuring point discharge. A tank inserted into the riverbed, effectively cutting off a small section of river bed from the river water. A bag is then slowly filled by the groundwater that seeps into the tank from below. An overall seepage rate for the river is then extrapolated. Meters of this sort have a claimed error of less than 20%. Seepage rates in close proximity should be similar provided that the geology is not highly heterogeneous (Belanger and Montgomery, 1992).
A study by Wells(2002) in Western New York compared the accuracy of the stream gauging method with the temperature gradient discharge method. Sediment of various sizes was subjected to simulated solar heat and subsequent cooling to model the diurnal effects of the sun on river water. It was found that a temperature change educed by simulated solar heating existed in cobble sized sediment to a depth of 0.5 meters while in bedrock substrate, the temperature change was only present to a depth of 0.1 meters. Deeper sediment should have less change in temperature. The discharge rates found from stream gauging were an order of magnitude higher than those found by temperature gradient in Wells’ study. It is possible that the temperature sample location was not in a peak discharge area. This kind of non-uniform discharge may create unique bedfroms or channel pathways.
[You may want to consider sub headings. The above discussion would cover groundwater discharge and the section below would cover geomorphology Lurbano] Bank erosion processes have been the focus of several studies and may be an important factor in meander propagation. Toth (1999) found that positive pore pressure had the effect of loosening the grain matrix in sediment while negative pre pressure had the effect of increasing the cohesiveness of sediment. A later study found that increased pore pressure created by effluent groundwater reduced the overall bed friction and may therefore increase erosive ability of the river (Simon et al., 2000).
Description of Study Area:
Loosahatchie River, Shelby County, Tennessee
The purpose of this study is to qualitatively analyze the effects of groundwater exchange on meandering river systems. The Mississippi Embayment offers an ideal location due to the abundance of meandering rivers in contact with aquifer outcrops. The embayment itself is shaped like a south plunging syncline composed of alternating layers of sand and clay shallowly dipping towards the axis of the syncline. This axis line trends approximately below the Mississippi River.
(Consider also adding the map of the embayment Image:MEmbay 06.jpg Lurbano)
The embayment itself was formed by transgressive and regressive sequences of coastal facies formed by the recurrent flooding the embayment. In Shelby County, Tennessee, continuous sand and shale outcrops trending in a north/south direction outcrop across the width of the county. The sand layers are well known for their excellent groundwater transport ability(USGS, HA 730-F). The shale/clay layers in the region are also known to be of varying thickness with thin spots and windows throughout. The rivers in Shelby County tend to cross these outcrops perpendicular to strike direction, flowing from East to West towards the Mississippi River. The Loosahatchie River was chosen primarily for its East/West orientation and relative straightness along its length in Shelby County. In 1968, the Loosahatchie River was channelized by the Shelby County Drainage District to reduce flooding and increase drainage potential. Prior to channelization, the Loosahatchie River was highly sinuous with a general East/West orientation. Channelization of the Loosahatchie has resulted in substantial downcutting with steeply sided banks which restricts meandering. (You need to mention the Urbano et al., 2006 paper that indicates the large systematic changes in groundwater/surface water exchange. It's these changes that make this river good for this study Lurbano)
The Wolf River, a river in Shelby County similar to the Loosahatchie River, was channelized and straightened in the early 1960’s by the Corp of Engineers. Flow velocity subsequently doubled and the river channel incised to varying degrees along the length of the river (Van Arsdale, et al., 2003). Similar effects can be expected to have occurred along the Loosahatchie River. (You should move this paragraph into the discussion or conclusion section to indicate where there can be further work done to confirm your research Lurbano)
Problem Description:
(this section should be under the literature review or the introduction Lurbano)
The Corp of Engineers and area drainage districts channelized many meandering rivers across Tennessee in the 1950’s and 60’s. Since then, these river channels have begun to revert back to a meandering state. Along with increased sediment load, destruction of habitat, loss of organic carbon sources for aquatic life, and loss of floodplain soil renewal, channelizing rivers costs money. Periodic maintenance is required to maintain the form desired by planning engineers. By removing natural streambeds and exposing aquifer recharge sediment directly to free flowing runoff sources, the potential for groundwater contamination has also increased. A better understanding of the relationship between the geomorphology of channelized rivers and the underlying aquifer systems may aid in determining the potential for increased contamination. Several models exist to explain the propagation and migration of river meanders. Einstein and Shen (1964) proposed a method by which twin, periodically reversing, surface convergent helical cells scour alternating pools, leading to stable meanders. Thompson (1986) devised a model were surface convergent flow interacts with a mobile bed, subsequently creating riffle and pool sections mimicking the stage 1 meander initiation predicted in Keller’s 1972 model of the 4 stages that a channel undergoes in reverting to a meandering state. The macroturbulant flow model predicts velocity bursts at various locations along the river. These bursts create deeper pool sections and may initiate meanders (Yalin, 1971). None of these models are able to account for the existence of seemingly regular meander patterns in tandem with very irregular meander patterns (Fergasun, 1979). The symmetry encountered in many meandering systems seems to imply that an external factor to the river system is at work. Irregularity can be accounted for by consideration of variant riverbed geology or sediment deposition, but why regular bends and irregular bends occur in similar geologic settings comes into question. Nor can any model convincingly describe the process of meander belt initiation. The traditional view analyzes single reaches or bends and analyzes finite properties of the bend (Marham and Thorne, 1992). An alternative view analyzes the meanders in a collective sense, taking into account general trends and property change throughout the series of meanders (Fergason, 1984, Howard, 1992). Fergason (1979) uses this approach to analyze three main components of stream geometry; a scale variable, sinuosity, and degree of irregularity. The benefit of this approach becomes apparent when analyzing property change at various locations along the river length. The traditional approach still retains value when analyzing finite properties of an individual reach.
Proposed Solution:
The effect of groundwater exchange on the geomorphology of river systems has the potential to answer the question of meander initiation as well as meander regularity or irregularity. (While the following two sentences are important they distract from current discussion. They would probably be better placed in the literature review or in the discussion/conclusion sections. Lurbano) It is important to first note that the confining layers in the Mississippi embayment are not of uniform thickness, nor are they always continuous. The possibility exists for thin locations and windows throughout the confining clay layers(USGS, HA-730-F). Several possibilities exist for potential impact.
- 1. Discharge to the river form the groundwater system is not uniform along the riverbed. Locations of peak discharge may exist with a decreasing gradient of discharge radiating out around them, or possibly windows in the riverbed may exist allowing groundwater discharge solely through these windows.
- 2.The up-flow of groundwater in gaining streams may aid in destabilizing streambed grains, aiding in entrainment and resisting deposition. The minimum energy needed to entrain sediment is found by means of calculating the critical shear stress of bed material (Knighton, 1998).
Ï„c = k(Ï?s – Ï?)g D - or approximately - Ï„c = 0.73D
where: Ï„c = critical shear stress D = Particle size
- This potentially creates deeper sections, or pools, at areas of higher groundwater discharge. River water volume and velocity increases at these pools and the traditional meander propagation model developed by Einstein and Poole(1964) then applies.
- 3. Groundwater discharge through riverbeds may create a reduced surface or bed friction. This resistance factor can be found using Manning’s equation (Knighton, 1998):
n = k(R2/3*s1/2)/v
where: n = resistance factor k = 1(SI units) R = hydraulic radius s = slope of energy gradient v = mean velocity
- River water flowing through these areas increases in velocity. The velocity increase then promotes increased bank erosion in these sections.
Methodology
The problem will be approached by means of two methods. The primary method will involve direct measurement and observation of field conditions along the Loosahatchie River. The direct results of channelization and meander initiation can be studied and documented. A sand box model will act as a secondary method of investigation. This a priori approach will allow a controlled physical environment in which contributing factors to meander propagation and migration can be tested.
Field Observation Methodology:
Since the thickness of the confining units that outcrop throughout Shelby County have variable thickness and outcrop location, it becomes necessary to first locate areas of groundwater discharge. The primary method that will be used utilizes the temperature difference in groundwater and surface waters. Since subsurface water equilibrates with the 58° F surrounding lithology, groundwater maintains a constant ground temperature. During summer months, surface waters in lakes and rivers averages well above this, and during winter months surface water temperature can be well below the 58° F ground water temperature. Gaining streams receive water from groundwater sources, therefore areas in the river that deviate in temperature from the surface water average towards the ground water average can be inferred as areas of groundwater discharge. For the purposes of this study, this deviation in temperature will be used as a proxy for groundwater discharge location. To locate discharge zones, a (?panel? Lurbano) of temperatures at varying locations, depths, and cross sectional distances will be analyzed.
- A 10 cm long ground penetrating grounded K-type thermocouple will then be attached to the end of the sampling pole. Grounded K-type thermocouples have an accuracy of +/- .5 degrees Celsius at the temperature range in question and a response time of 0.5 seconds. A skid plate will be attached directly above the probe to prevent penetration of more than the 10 cm probe length.
- River bed temperature will be measured at several locations at varying depths for an extended period to determine the diurnal variation in temperature. Temperature will be measured at 0 cm, 5 cm, 10 cm, and 15 cm depth. This diurnal variation will be used to calibrate further temperature readings.
- A general temperature and depth profile will be made of the study area. A temperature data logger will be attached to the end of a one meter pole and set to sample at 5 second intervals. A GPS unit will also be set to take continuous special readings at the same 5 second interval. A boat will then travel downstream towing the pole with data logger at a 0.2 meter depth along the entire study area. The temperature data from the data logger will then be correlated to the position data from the GPS unit to from a temperature profile of the study area. This will give a general idea of areas of groundwater discharge and allow for the testing and accuracy of the data logger/GPS setup. Depth will be correlated with GPS location as well to generate a rough depth profile.
- From the temperature profile, an area containing a discharging location will be selected, as well as a non discharging location. Using a ground penetrating thermocouple probe, sub-riverbed temperatures will be measured at a depth of 5 cm below bed surface along a cross sectional profile running perpendicular to river bank. These sub-bed temperatures will be taken at a one meter interval across the cross section. This cross sectional measurement method will be applied at a one meter interval for a 50 meters. A river water temperature profile will also be created. At the same one meter interval across the same cross sections, water temperature and depth will also be measured at 10 cm above river bed, mid river depth, and at 10 cm below water surface. This will generate a river water temperature cross section that will be compared to sub-riverbed temperatures. Areas of high discrepancy between river water and sub-bed temperature will be treated as high groundwater discharge areas. A down stream line can then be created by correlating all cross section profiles to find the downstream path of highest groundwater discharge.
To test for solution 1: (change to "Reach-Scale Discharge measurements" Lurbano)
A section of river will be chosen that has been determined to be gaining. A one meter spaced grid will be overlaid above the river. Temperature and depth measurements will be recorded for each node. Temperature will be recorded for 10 cm below bed, bed surface, and mid water. A fixed data logger located mid water will be set to record the river temperature while data is being collected along the grid. This will allow for subsequent adjustments of measurements to compensate for diurnal increase and decrease in temperature. Temperature and depth will be recorded on a weekly basis to determine if groundwater consistently discharges in isolated locations or in a more diffusive pattern.
Seep tanks will also be installed at various locations in the study area. Variable filling rates of seep tanks will also show that discharge is not uniform along the river bed. It will also show that seep tanks are inaccurate when used to extrapolate total groundwater discharge rates for the aquifer.
To test for solution 2: (change to "Bedform evolution" Lurbano)
The area used for solution 1 will also be used for solution 2. The bed elevation data will be correlated to groundwater discharge locations on a weekly basis. This should determine if deeper pool areas consistently occur in discharge locations. If bed forms are observed to move while discharge pools are seen to remain stationary, it can be concluded that the discharge points have a control on pool locations.
Aerial photographs taken on a regular basis will also be taken for a defined stretch of river. Bar and pool locations will be analyzed for location and correlated to discharge volumes found by flow gauging. If pool locations remain constant while bar locations migrate around them, it may be assumed that an external force from normal river flow dynamics is influencing pool location. It may also be possible to determine relative rate of discharge by interpreting frequency of bars and pools.
To test for solution 3: (change to something else, maybe "Friction reduction" Lurbano)
Flow rate will be measured at an even interval along the study area. Rates will be obtained using an acoustic Doppler probe as well as a handheld flow meter. Using Manning’s equation, the resistance of stream bed will be calculated for the study area. The sets of data will then be processed statistically using F-test and t-test methods. This will reveal any statistical correlation that may exist. If the data sets are statistically similar, the possibility of friction reduction in discharging areas can be eliminated. (To test this you will also need to have some surface sediment samples to show that this does or does not affect things Lurbano)
Scientific Importance of Study
The straightening of rivers has caused a host of problems, many of which we may not be aware of yet. The ability to predict a rivers future path would allow planning engineers to produce a more environmentally sound, cost effective, and structurally stable solution. Knowledge of the dynamic processes at work in such exchange systems would also aid in contaminant transport prediction in groundwater systems. The possibility also exists for measuring river flow volume by satellite if a true temperature gradient in peak discharge locations can be identified. Geomorphic surface forms may allow interpretations of subsurface geology. Applications of this would have an impact on hydrology, the petroleum industry, and even extra-planetary exploration.
Work Schedule
Field Data Acquisition
May 13 Scout the river • Find suitable boat landing points • Locate apparent meander cut banks and point bars • Locate suitable study area • Record depths at various distances downstream to get an idea of general depth range • Create a mid-water downstream temperature profile o Purpose is to test equipment o Generates a “general� idea of the effectiveness of the equipment o Identify unforeseen needs for taking temperature samples o Is the stream temperature significantly different than the groundwater Temp?
May 20 Measurement • From up stream end of study area, measure flow volume at beginning, middle, and end of study area • Create a sub-streambed temperature cross sectional profile along bend, riffle zone, and the up and downstream transition zones from bend to riffle • Create an in stream temperature profile. Record temperature and depth just above streambed, mid-depth, and at surface across the river in 1 meter intervals
May 27 Downstream Profile • Record sub-streambed temperature at 2 second intervals along the highest discharge line found on day 2 • Record river temperature 10 cm above streambed at 2 second intervals along the highest discharge line found on day 2
Budget
Item means of acquisition Source of Funding Amount needed GPS Unit use GWI owned unit (3) waterproof temperature data loggers use GWI units Boat use DES or other 100 ft of polybraided rope purchase personal purchase $15 15 ft, 1 in diameter PVC pipe purchase ? $5 thermocouple data logger purchase ? $100 data logger interface dock purchase ? $30 J type thermocouple, 10 cm shielded purchase ? $30 30 feet, type J thermocouple wire, vinyl coated purchase ? $10 Type J thermocouple coupling purchase ? $5 Sand Box supplies 8 X 10 foot plywood purchase grant $30 water pump purchase grant $35 tubing purchase grant $15 fiberglass resin purchase grant $25 plumbing fittings purchase grant $20 screws purchase grant $5 reservoir bucket purchase grant $10 Total $335 (optional) Infrared Camera Rental rental ? $400 Total $735
Sources:
• Becker, M. W., Georgian, T., Ambrose, H., Siniscalchi, J., Fredrick, K., 2004. Estimating flow and flux of ground water discharge using water temperature and velocity, Journal of Hydrology 296, 221 – 233. • Cleland, Carol E., 2001. Historical science, experimental science, and the scientific method, Geology 29, 987 – 990. • Hudson, Paul F., Kesel, Richard H., 2000. Channel Migration and meander bend curvature in the lower Mississippi River prior to human modification, Geology 28, 531 – 534. • Jackson II, Roscoe G., 1975. Velocity-bed-form-texture patterns of meander bends in the lower Wabash River of Illinois and Indiana, Geologic Society of America Bulletin 86, 1511 – 1522. • Knighton, David, 1998. Fluvial Forms and Processes, Oxford University Press, New York. • LaFleur, Robert G., 1999. Geomorphic aspects of groundwater flow, Hydrology Journal 7, 78 – 93. • Larkin, Randell G., Sharp, John M., 1992. On the relationship between river-basin geomorphology, aquifer hydraulics, and ground water flow direction in alluvial aquifers, Geologic Society of America Bulletin 104, 1608 – 1620. • Lewin, John, 1976. Initiation of bed forms and meanders in coarse-grained sediment, Geologic Society of America Bulletin 87, 281 – 285. • Malin, Micheal C., Carr, Micheal H., 1999. Groundwater formation of martian valleys, Nature 397, 589 – 591. • Pederson, Darryll T., 2001. Stream Piracy Revisited: A Ground water Sapping Solution, GSA Today September 2001, 4 – 10. • Scott A. Wells, Robert L. Annear, Report for 2002OR2B: Temperature Effects of Streambed Heating, Water Resources Research institute Annual Technical Report, 2002, pgs 3 – 10. • Scott A. Wells, Robert L. Annear,2002. Report for 2002OR2B: Temperature Effects of Streambed Heating, Water Resources Research institute Annual Technical Report 2002, pgs 3 – 10. • Simon, Andrew, Curini, Andrea, Darby, Stephen E., Langendoen, Eddy J., 2000. Bank and near-bank processes in and incised channel, Geomophology 35, 193-217. • Smith, Charles E, 1998. Modeling High sinuosity meanders in a small flume, Geomoprphology 25, 19 - 30. • Torgersen, Christian E., Faux, Russel N., McIntosh, Bruce A., Poage, Nathan J., Norton, Douglas J., 2001. Airborne thermal remote sensing for water temperature assessment in rivers and streams, Remote Sensing of Environment 76, 386 – 398. • Toth, Jozsef, 1999. Groundwater as a geologic agent: An overview of the causes, processes, and manifestations, Hydrogeology Journal 7, 1 – 14. • Van Arsdale, Roy, Waldron, Brian, Ramsey, Natasha, Parrish, Shane, Yates, Rhonda, 2003. Impact of River Chennelization on Siesmic Risk: Shelby County, Tennessee, Natural Hazards Review, February 2003, 2 – 11.
