The Use of Natural Heat as a Tracer to Quantify Surface Water and Groundwater Interactions: Maules Creek, New South Wales, Australia

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1 The Use o Natural Heat as a Tracer to Quantiy Surace Water and Groundwater Interactions: Maules Creek, New South Wales, Australia G. Rau, A. McCallum, M.S. Andersen and R.I. Acworth 1. Introduction Surace water and groundwater are intimately connected. Surace water includes rivers, streams, creeks, ponds, lakes, etc. Groundwater is water that ills the voids between sediment grains in the subsurace. Eective water management must consider surace water and groundwater as a single water resource. The Water Research Laboratory is currently undertaking a major research project within the Maules Creek Catchment o the Namoi River, unded by the Cotton Catchment Community CRC, to investigate the issue o how surace water and groundwater are connected (see Figure 1). Figure 1: Map o Australia, New South Wales and Maules Creek Catchment (enlarged). There are our possible scenarios o surace water and groundwater interaction as shown in Figure 2. UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

2 Figure 2: Schematic illustration o the interaction between surace water and groundwater: (a) neutral reach, (b) disconnected reach, (c) losing reach and (d) gaining reach (modiied rom Winter et al, 1998). The connectivity can be seen in records o river low through time (i.e. stream hydrographs). For example, as shown in Figures 3 and 4, more water passes the Namoi River at Boggabri than downstream at Turrawan. This is largely due to this section o the river being a losing reach (i.e. type c in Figure 2). Namoi River 11,000 10,000 9,000 8,000 7,000 Flow (ML/day) 6,000 5,000 4,000 3,000 2,000 1, May Aug Nov Feb Jun Sep Dec-07 Boggabri Turrawan Figure 3: Stream Hydrographs or Boggabri and Turrawan Gauging stations (see Figure 1). The graph shows three occasions o water release rom Lake Keepit dam between May 06 and Dec 06, and three low events generated by storm events rom Feb 07 to Sept 07, ollowed by the start o a ourth dam release in Dec 07. UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

3 Namoi River 70,000 60,000 50,000 Volume (ML) 40,000 30,000 20,000 10, May Aug Nov Feb Jun Sep Dec-07 A: Cummulative Flow at Boggabri B: Cummulative Flow at Turrawan A minus B Figure 4: Summation o water lowing through Boggabri and Turrawan. Blue line represents quantity o water removed rom river system between these two gauging stations, indicating a losing reach. As surace water and groundwater are a single resource, it is important to estimate the luxes between them. This is commonly carried out using the Darcy method. This method uses a water level gradient combined with a hydraulic conductivity o the subsurace to give an estimate o the lux. The hydraulic conductivity, however, is very sensitive to variations in grain size and sorting. Consequently, sparse knowledge o the distribution o the hydraulic conductivity may lead to erroneous or uncertain luxes. This research project investigates the use o natural heat as a tracer o water movement as an alternative method to the traditional Darcy method. 2. Theory In a porous medium, such as streambed sediments, heat is transported by both conduction and convection, as shown in Figure 5. Heat conduction occurs through the bulk medium while convection is caused by luid moving in the voids between sediment grains. Both processes can be superimposed. UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

4 Figure 5: Illustration o the travel path o heat by conduction (grey) and convection (black) in a porous medium. These processes can be mathematically described using the conduction-convection equation: T t = 2 T z κ e 2 nv ρ c ρc T z In this equation T is temperature which varies with time (t ) and depth ( z ), eective thermal diusivity, n is porosity, v is vertical luid velocity, ρ and κ e is c are bulk density and heat capacity o the luid, and ρ and c are density and heat capacity o the saturated sediment-luid system. The atmospheric temperature luctuates due to daily, seasonal and annual changes in solar radiation. These luctuations also aect the temperature o shallow surace waters which are then transerred into the subsurace by conduction and convection. The temperature luctuations can be used to derive luxes between surace water and groundwater using two dierent approaches. Approach One Forward Modelling I the temperature signal at the surace o the sediments is recorded, it is possible to predict the temperature signal at any depth within the sediments, using (Silliman et al, 1995): where: T n s n i, i 1 0 ( z) + Ts ( z, ) i= 1 ( z, t) = T τ with τ = t ti UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

5 T i, i 1 s ( z, τ ) = T i, i 1 w 2 z Cτ Cz erc + exp 2 Dτ D z + Cτ erc 2 Dτ where: ρ c C = nv and ρc κ e D = ρc, In the equations above T i i 1 s ( z, τ ) is the temperature at any depth ( z ) and time ( t ), T 0 is the temperature at depth z when t=0, T is the change in temperature at depth i, i 1 w z=0. The orward modelling approach involves comparing the predicted temperature signal against a recorded temperature signal at some depth, and adjusting the lux until both signals are the same, thereby deriving the lux. The ield setup used or this approach is shown in Figure 6. Figure 6: Cross section o stream-aquier showing the locations o thermistors or recording temperature variations. Approach Two Transient Modelling A second approach is to record one temperature signal at the surace o the sediments and another at some depth within the sediments. The temperature signal at depth will display an amplitude drop and phase shit, as shown in Figure 7. UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

6 Figure 7: Two hypothetical temperature signals showing how a signal at 0.3 m depth will have an amplitude drop and phase shit compared to a signal at 0 m depth (i.e. just above the sediments) (modiied rom Hatch et al, 2006). These phenomena can then be used to derive the lux using (Hatch et al, 2006): v = 2κ z e α i + ln( Ar ) + 2 v 2 and: v = φ4πκ e α i P z 2 where: α = i v πκ e P 2 where: v = v ρ c ρc In the equations above amplitude dierence between temperature signals, z is the spacing between temperature signals, temperature signals, P is the period o the temperature luctuation. A r is the φ is the phase dierence between UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

7 3. Field Application The ield site is located within the Maules Creek catchment (see Figure 1, above). The Maules Creek area is composed o Tertiary alluvial sediments with medium to heavy clays and lenses o sand and gravel overlain by sands, gravels and cobbles to a depth o approximately 10 m (see Figure 8). Recent investigations by Andersen and Acworth (2007) suggest that that groundwater is discharging slightly upstream o the conluence o Maules Creek and Horsearm Creek. The water then lows through a series o perennial pools and in a shallow unconined sand and gravel aquier o approximately 200 m width. Closer to the Namoi River, surace low in Maules Creek stops when it crosses a large subsurace paleochannel. Figure 8: Resistivity Image across Maules Creek (LHS is North, RHS is South). The high resistivity ( m) material overlying low resistivity material (2 70 m) probably corresponds to an upper zone o variably saturated sands, gravels and cobbles overlying more clayey lithology (ater Andersen and Acworth, 2007). Three sites were selected on Maules Creek or investigation. These locations are shown on the aerial photograph (Figure 9). UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

8 Figure 9: Location o investigation sites: at Elin crossing (EC), upstream on Horsearm Creek (HC) and downstream on Maules Creek (DEC). For each site a temperature array was designed, constructed and installed (see Figure 10). The array consisted o ive temperature probes separated by insulators. The arrays were installed in the streambed with the uppermost probe at the surace o the sediments. This allowed or the collection o temperature signals at ive dierent depths. The probes logged temperature data every 15 minutes. UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

9 Figure 10: A temperature array (let) and photos rom installation in the ield (right). 4. Results and Discussion One set o results are shown in Figure 11. The upper graph shows two temperature signals: one rom 0 m depth and the other rom 0.6 m depth. The lower graph shows the same data but transormed by a iltering process rom true temperatures to relative temperatures. This iltering process allows the daily luctuations in temperature to be more clearly observed and analysed. UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

10 Figure 11: Temperature data rom Elin Crossing (see Figure 9 or location). Using the data shown in the upper graph in Figure 11 it was possible to apply Approach One Forward Modelling to derive a lux (see Figure 12). For this location at Elin crossing the calculated velocity was approximately 0.6 m/day downwards into the streambed. Figure 12: Results o applying Approach One Forward Modelling to data rom Figure 11. Approach Two Transient Modelling was then applied to the data shown in the lower graph in Figure 11 to derive a lux (see Figure 13). This method showed that although the lux was approximately 0.6 m/day downwards, it varied over time. UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

11 Figure 13: Results o applying Approach Two Transient Modelling to data rom Figure 11. These results show clearly that during the time o the experiment, water was moving downward rom the pool into the aquier at Elin Crossing. To achieve a total volume lux, a number o measurements would need to be made at dierent locations in the pool and integrated. 5. Conclusion Surace water and groundwater interactions are important to understand rom the perspective o water resource management. One method to calculate the luxes is the Darcy method, but a lack o knowledge o the hydraulic conductivity distribution makes this diicult to use in practice with any accuracy. A complimentary method, that does not have the same limitations as the Darcy method, is to use natural heat as a tracer o water movement. This research project has investigated the use o two dierent mathematical approaches to derive values or the exchange luxes. The two approaches gave very similar results. At Elin Crossing (Figure 14) it appears that the water is percolating downwards rom the stream into the streambed, at a rate o approximately 0.6 m/day (Figure 14). UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

12 Figure 14: View o Elin Crossing where the initial results indicate that water is moving rom the pool into the aquier at a rate o 0.6m/day The results rom this study show that the use o natural heat as a tracer o water movement could become a reliable standard method or estimating luxes between surace water and groundwater. Signiicant scope exists or the method to be urther developed to account or unsaturated sediments and two or three dimensional water movement. Acknowledgements This article is a based on research undertaken by Gabriel Rau or a Master s Thesis, Universität Stuttgart, Department o Hydromechanics and Modeling o Hydrosystems, Germany. The research project was made possible through unding provided by the Cotton Catchment Community CRC (Project No ). Department o Water and Energy (Armidale) provided stream hydrograph data. UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March

13 Reerences Andersen, M.S. and Acworth, R.I., Surace water groundwater interactions in an ephemeral creek in the Namoi Valley, NSW, Australia Controls by geology and groundwater abstraction. In Ribeiro L., Chambel, A. and M.T. Condeso de Mel Eds. Groundwater and Ecosystems, International Association o Hydrogeologists Congress Lisbon. September. ISBN , Published by IAH Hatch, C.E., Fisher, A.T., Revenaugh, J.S., Constantz, J. and Ruehl, C., Quantiying surace water-groundwater interactions using time series analysis o streambed thermal records: Method development. Water Resources Research, 42(10). Silliman, S.E., Ramirez, J. and McCabe, R.L., Quantiying Downlow through Creek Sediments Using Temperature Time-Series - One-Dimensional Solution Incorporating Measured Surace-Temperature. Journal o Hydrology, 167(1-4): Winter, T.C., Harvey, J.W., Franke, O.L. and Alley, W.M., Ground Water and Surace Water: A Single Resource. Geological Survey (USGS). UNSW Connected Waters Initiative, Use o Natural Heat as a Tracer, March