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ArticleTitle Pitfalls in application of the conventional chloride mass balance (CMB) in karst aquifers and use of thegeneralised CMB method
Article Sub-Title
Article CopyRight Springer-Verlag Berlin Heidelberg(This will be the copyright line in the final PDF)
Journal Name Environmental Earth Sciences
Corresponding Author Family Name SomaratneParticle
Given Name NaraSuffix
Division
Organization South Australian Water Corporation
Address 250 Victoria Square, Adelaide, SA, 5000, Australia
Email [email protected]
Schedule
Received 29 April 2014
Revised
Accepted 8 January 2015
Abstract There is unanimity in the literature that chloride mass flux crossing the piezometric surface requires asteady-state for the saturated or unsaturated version of the conventional chloride mass balance (CMB)method to apply. Data indicate that chloride concentration in point recharge fluxes crossing the piezometricsurface can remain at or near surface runoff chloride concentrations, rather than finding equilibrium withgroundwater chloride. Preferential groundwater flows were observed through an interconnected network ofhighly permeable zones with groundwater mixing along flow paths. Measurements of salinity and chlorideindicated that fresher water pockets exist at point recharge locations. A stable and measurable fresh waterplume develops only when a large quantity of surface water enters the aquifer as a point recharge. In suchcircumstances, assumptions and boundary conditions of the conventional CMB method are not met, andthe method requires modification to include both point and diffuse recharge mechanisms. This paperdescribes a generalised CMB that is applicable to groundwater basins with point recharge. In three casestudies, point recharge flux is estimated to contribute 63, 85, and 98 % of total recharge. However, long-term average annual point recharge volumes are much smaller than the aquifer storage, at 1.5, 1.95, and0.75 % and distributed across the basins at discrete locations. In the study basins, conventional CMB-estimated recharges are 46, 20, and 11 % of the recharge estimated using the generalised CMB, indicatingthe importance of accommodating point recharge into the CMB method. The generalised CMB methodprovides an alternative long-term net recharge estimation method for groundwater basins characterised byboth point and diffuse recharge.
Keywords (separated by '-') Sinkholes - Point recharge - Generalised CMB - Conventional CMBFootnote Information
UNCORRECTEDPROOF
ORIGINAL ARTICLE1
2 Pitfalls in application of the conventional chloride mass balance
3 (CMB) in karst aquifers and use of the generalised CMB method
4 Nara Somaratne
5 Received: 29 April 2014 / Accepted: 8 January 20156 � Springer-Verlag Berlin Heidelberg 2015
7 Abstract There is unanimity in the literature that chloride
8 mass flux crossing the piezometric surface requires a
9 steady-state for the saturated or unsaturated version of the
10 conventional chloride mass balance (CMB) method to
11 apply. Data indicate that chloride concentration in point
12 recharge fluxes crossing the piezometric surface can remain
13 at or near surface runoff chloride concentrations, rather than
14 finding equilibrium with groundwater chloride. Preferential
15 groundwater flows were observed through an intercon-
16 nected network of highly permeable zones with ground-
17 water mixing along flow paths. Measurements of salinity
18 and chloride indicated that fresher water pockets exist at
19 point recharge locations. A stable and measurable fresh
20 water plume develops only when a large quantity of surface
21 water enters the aquifer as a point recharge. In such cir-
22 cumstances, assumptions and boundary conditions of the
23 conventional CMB method are not met, and the method
24 requires modification to include both point and diffuse
25 recharge mechanisms. This paper describes a generalised
26 CMB that is applicable to groundwater basins with point
27 recharge. In three case studies, point recharge flux is esti-
28 mated to contribute 63, 85, and 98 % of total recharge.
29 However, long-term average annual point recharge volumes
30 are much smaller than the aquifer storage, at 1.5, 1.95, and
31 0.75 % and distributed across the basins at discrete loca-
32 tions. In the study basins, conventional CMB-estimated
33 recharges are 46, 20, and 11 % of the recharge estimated
34 using the generalised CMB, indicating the importance of
35 accommodating point recharge into the CMB method. The
36 generalised CMB method provides an alternative long-term
37net recharge estimation method for groundwater basins
38characterised by both point and diffuse recharge. 39
40Keywords Sinkholes � Point recharge �
41Generalised CMB � Conventional CMB
42Introduction
43Background
44Chloride mass balance (CMB) is one of the most frequently
45used recharge estimation methods; it was originally
46developed by Eriksson and Khunakasem (1969) to estimate
47groundwater recharge. The method is based on the fact that
48evapotranspiration removes water but not chloride, leaving
49chloride concentrated in groundwater, allowing application
50of simple mass conservation of chloride between rainfall
51and groundwater. Knowledge of chloride deposition by
52rainfall and concentration of chloride in groundwater
53enables an estimate of net recharge using CMB, expressed
54as (after Eriksson and Khunakasem 1969):
R ¼PcpþD
cRð1Þ
5656where R is recharge (LT-1), cp?D (ML-3) is the repre-
57sentative mean chloride concentration in rainwater
58including contributions from dry deposition, and cR is
59chloride concentration in recharge (ML-3). Following
60Eriksson and Khunakasem (1969), numerous studies show
61that this method provides reliable long-term estimates of
62net recharge if the essential boundary conditions and
63assumptions underpinning the method are met. Allison and
64Hughes (1978) extend Eq. (1) to estimate recharge using
65chloride concentration from soil water obtained from the
A1 N. Somaratne (&)
A2 South Australian Water Corporation, 250 Victoria Square,
A3 Adelaide, SA 5000, Australia
A4 e-mail: [email protected]
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66 lower part of the unsaturated zone (cu), which replaces cR67 in Eq. (1). Since the fundamental concept of the CMB
68 method is that atmospheric input of chloride in precipita-
69 tion and dry deposition concentrates in residual soil water
70 via evapotranspiration processes (Allison and Hughes
71 1978; Allison 1988; Guan et al. 2010), the method essen-
72 tially estimates diffuse recharge through the soil profile.
73 Ginn and Murphy (1996) describe Eq. (1) as the ‘con-
74 ventional CMB’ and summarise the implicit assumptions:
75 the precipitation and the accumulation rates of atmospheric
76 chloride can be averaged over the relevant period; chloride
77 is an inert tracer; flow is one-dimensional, vertical down-
78 ward, piston type; and water and tracer mass fluxes are
79 steady. Gee et al. (2005) confirm the above assumptions
80 and stipulate that no soil sources or sinks for chloride be
81 present. Further, point measurement of chloride concen-
82 trations can be used to represent a true spatial average of
83 the soil chloride flux. In unsaturated zone application,
84 chloride equilibrium at both the ground surface and in the
85 unsaturated zone is required for application of the con-
86 ventional CMB (Guan et al. 2010). As pointed out in
87 Scanlon et al. (2002), these assumptions are usually taken
88 to imply a constant chloride profile below the root zone.
89 Wood (1999) consider three potential problems with the
90 unsaturated version of the conventional CMB method: it is
91 difficult to quantitatively evaluate the chloride input to the
92 profile due to run-on and runoff processes; the method does
93 not account for macro-pore recharge that bypasses the soil
94 matrix; and there is difficulty in assessing the steady-state
95 chloride flux. In saturated zone application, cR of Eq. (1) is
96 replaced with groundwater chloride concentration (cg), and
97 recharge mass flux crossing the piezometric surface can be
98 calculated if (Wood 1999):
99 • chloride in the groundwater originates from precipita-
100 tion directly on the aquifer, and no unmeasured
101 chloride mass is recharged from overlying, underlying,
102 or adjacent aquifers, and no unmeasured runoff occurs,
103 • the chloride is conservative in the system,
104 • the chloride mass flux has not changed over time, and
105 • there is no recycling or concentration of chloride within
106 the aquifer.
107 Allison and Hughes (1978) note that where the ratio of
108 annual recharge to total volume of the aquifer is small, the
109 land use pattern needs to have remained unchanged for a
110 considerable period for a steady state to be assumed. Zhu
111 et al. (2003) highlight that for the saturated version of
112 CMB to be applicable, groundwater movement in both
113 unsaturated and saturated zones should be approximated as
114 one-dimensional piston flow. This essentially means that
115 chloride concentration of the mass flux crossing the pie-
116 zometric surface (cR) is at equilibrium with groundwater
117 chloride (cg).
118Subayani and Sen (2006) describe Eq. (1) as the ‘clas-
119sical CMB’ approach, which employs only arithmetic and
120weighted averages of input parameters for recharge esti-
121mation. These authors show that long-term average rainfall
122and chloride concentration estimation in groundwater are
123more accurate for less variable systems and, therefore, the
124equation is most valid under steady-state conditions;
125otherwise, the equation must be viewed as a gross
126simplification.
127When chloride concentrations of groundwater samples
128(cg) are used as cR values in Eq. (1) for saturated zone
129application, the recharge rates determined from the con-
130ventional CMB apply to locations in the catchment where
131the samples are recharged, not where the samples are
132collected. This requires that the hydrodynamic dispersion
133of chloride between recharge point and sampling location
134be small, which essentially requires the piston flow
135requirement in the unsaturated and saturated zones of Zhu
136et al. (2003) and the necessity of minimal mixing for less
137variability within the aquifer as indicated by Subayani and
138Sen (2006).
139Problems arise in maintaining the above assumptions in
140karst aquifers, because different recharge processes may
141operate simultaneously. Surface water may directly infil-
142trate into aquifers, bypassing the soil zone and diffuse
143recharge through the soil profile. Under these conditions, it
144appears that the basic premise of the conventional CMB
145method is questionable (Somaratne 2014). This paper
146critically examines the validity of the conventional CMB
147method for recharge estimation in three carbonate karst
148groundwater basins, with particular reference to chloride
149distribution in point and diffuse recharge zones. The paper
150introduces the generalised CMB method, which accounts
151for both diffuse and point recharge, and then compares
152results to recharge estimated using conventional CMB.
153Why the conventional CMB fails in karst aquifers?
154Carbonate karst aquifers are characterised by three types of
155porosity: granular matrix, small aperture conduits and
156fractures, and large cavernous conduit porosity (Martin and
157Dean 2001). The presence of these porosities in their rel-
158ative proportions within a karst aquifer can cause perme-
159ability to span many orders of magnitude resulting in
160laminar flow in matrix porosity to turbulent flow in frac-
161tures and conduits (Martin and Dean 2001). Conduit
162porosity can be connected to the surface through cavernous
163openings such as sinkholes. The presence of sinkholes
164gives a distinct recharge feature to karst systems via the
165duality of flow regimes (Gunn 1983; Taylor and Greene
1662001), which can be separated into point (shaft and conduit
167dominated), and diffuse (matrix, meso-pore, and macro-
168pore dominated) infiltration and recharge. Hydrologic
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169 characteristics of karst aquifers are largely determined by
170 the structures and organisation of the conduits (White
171 2003). Since karst aquifers are highly heterogeneous and
172 anisotropic (White 2003; Bakalowicz 2005), identification
173 of groundwater flow paths is problematic (Tihansky 1999).
174 White (2003), Taylor and Greene (2001), Lerch et al.
175 (2005), and Bakalowicz (2005) also recognise the complex
176 nature of flows resulting from the presence of karstic fea-
177 tures. Taylor and Greene (2001) and Bakalowicz (2005)
178 hold that conventional study methods used in classical
179 hydrogeology are generally invalid and unsuccessful in
180 karst aquifers, because the results cannot be extended to the
181 whole aquifer nor to particular parts, as is often possible in
182 non-karst aquifers.
183 Sinkholes and other karst features supply a significant
184 amount of recharge to many carbonate aquifers in tem-
185 perate and humid regions throughout the world (Herczeg
186 et al. 1997), yet applicability of the conventional CMB to
187 karstic systems has not been studied. Despite its impor-
188 tance, groundwater recharge remains difficult to quantify in
189 karstic settings due to the number of recharge mechanisms
190 operating simultaneously on variable temporal and spatial
191 scales (Leaney and Herczeg 1995). One inherent problem
192 from the presence of karstic features such as sinkholes is
193 that recharge estimation using the conventional CMB
194 method does not accurately account for the complex
195 hydrological processes in the system (Somaratne 2014).
196 For example, Fig. 1a shows surface runoff concentrates
197 to a sinkhole and directly recharges the aquifer, bypassing
198 the unsaturated zone. Point recharge (at sinkholes) feeds
199 karst conduits with very rapid groundwater flow (Fig. 1b).
200 It is important to realise that inflows to sinkholes always
201 depend on the capacity of the conduits, as most ground-
202 water flow is through conduits that are fed by the sinkholes.
203 Some of the recharge around sinkholes (Fig. 1a) will also
204 seep slowly into the granular porosity around the recharge
205 point. However, most of the recharge to the granular
206 porosity of the aquifer is through surface recharge across
207 the entire land surface of the aquifer, and recharge to the
208granular porosity from the point recharge areas would be a
209relatively minor contribution.
210The main features of point recharge are: it occurs
211through a relatively small cross-sectional area compared to
212the extent of diffuse recharge across the surrounding
213catchment area with diffuse recharge through matrix
214porosity; point recharge has a chloride concentration that is
215more reflective of surface runoff; and comprises mostly
216transient flow from runoff to sinkholes, rather than to the
217piezometric surface. This is because recharge via karst
218features occurs only after abundant rainfall over a certain
219threshold and once the soil profile is saturated (Herczeg
220et al. 1997). Clearly, the necessary conditions for unsatu-
221rated or saturated versions of the conventional CMB are
222not met.
223When point recharge crosses the piezometric surface
224and enters the saturated zone, it is expected to mix with
225ambient groundwater, as sinkholes are connected to con-
226duit porosity. Martin and Screaton (2001) recognise that
227karst aquifer systems comprise two components, in which a
228majority of the storage occurs within the matrix porosity of
229the diffuse system, while the majority of transport occurs in
230fractures and dissolution conduits. This clearly indicates
231that chloride distribution from point recharge sources is
232influenced by laminar flow within the matrix and turbulent
233flow within conduits. Depending on their relative propor-
234tions, fresher water pockets or lenses occur near point
235recharge sources with a broad spectrum of chloride con-
236centrations in groundwater.
237If an extensive monitoring network is established in the
238hope of obtaining representative chloride values for fresh
239water lenses or conduits carrying recharged water from
240point sources, the tendency is to monitor long-term resident
241chloride concentration of matrix porosity. This is because
242recharge through point-source features is only detectable
243on a local scale (Herczeg et al. 1997). Even if several
244monitoring wells intercepted mixing zones, recharge cal-
245culation using simple average, weighted average, or har-
246monic mean reflects neither actual recharge at the sampling
Fig. 1 Scowns sinkhole,
Tatiara catchment, southeast of
South Australia (Department of
Water, Environment, and
Natural Resources, unpublished
data). a Recharging through
Scowns sinkhole. b Measured
flow rate
AQ1
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247 point nor at the point sources. This is due to groundwater
248 chloride in the mixing zone not equilibrating with recharge
249 water chloride (cR) that actually crosses the piezometric
250 surface. Hence, increasing the number of sampling points
251 does not solve the problem of point recharge using the
252 conventional CMB method.
253 If it were possible to account for the mass of chloride in
254 the system, the mode of transport of chloride from the land
255 surface to groundwater would become irrelevant. Three-
256 dimensional numerical solute transport models are a suit-
257 able tool for mass balance calculations when extreme
258 concentration occurs in fresh water pockets or lenses due to
259 point recharge. The conventional CMB, being one of the
260 simplest forms of mass balance calculation method in
261 hydrology, may be inappropriate for accounting for mass
262 balance in karst systems. Obviously, if the aquifers were
263 continuously well mixed between matrix porosity and
264 conduit porosity, then the saturated zone conventional
265 CMB principles could be applied. Unfortunately, most
266 aquifers, particularly in karst, are not so obliging, and at
267 best lower chloride ‘lenses’ are evidence of bimodal
268 recharge processes. Hence, the only way to account for this
269 transient sinkhole recharge is to modify the conventional
270 CMB method to account for bimodal recharge (Somaratne
271 2014).
272 Generalised CMB method
273 Duality of recharge is considered in the development of the
274 generalised CMB equation (Somaratne 2012), which can
275 be applied to both diffuse and point recharge dominant
276 groundwater basins. The method integrates chloride mass
277 balance from the ground surface to the water table. In this
278 model, sinkholes connected to the water table bypass the
279 soil zone, directly recharging the aquifer as point recharge.
280 The unconnected sinkholes add runoff deeper into the
281 unsaturated zone, which then rapidly drains into the water
282 table by mechanisms described by Gunn (1983). It is
283 assumed that no chloride sources and sinks present within
284 sinkholes and, therefore, chloride mass flux entering the
285 sinkhole reaches the piezometric surface unchanged.
286 When long-term average rainfall P (LT-1) reaches land
287 surface with chloride concentration of rainfall cp (ML-3), it
288 mixes with chloride due to dry deposition D (MT-1L-2) to
289 form cP?D, representative mean chloride concentration of
290 rainwater including contribution from dry deposition
291 (ML-3). If the surface water undergoes evaporation, cP?D
292 is further enriched and, therefore, the chloride concentra-
293 tion of surface water, cs (ML-3), may be cP?D B cs. Fol-
294 lowing Nyagawambo (2006), chloride mass balance at the
295 soil surface can be written:
DðsscsÞ
Dt¼ PcpþD � Qp þ Qo þ F
� �
cs ð2Þ
297297where ss is surface storage (L), Qp and Qo are runoff to
298sinkholes and runoff out from the catchment expressed as
299depths of the catchment (LT-1), F is infiltration into soil
300profile (LT-1), and Dt is time (T). The following
301assumptions are made to simplify Eq. (2): the storage
302fluctuation term may be assumed to be negligible relative
303to inflows and outflows, if the time of integration is suffi-
304ciently long to cover several hydrological years (no salt
305accumulation or loss from the surface); water is assumed to
306evaporate in its pure form and, therefore, no chloride is lost
307through evaporative fluxes; the chloride concentration in
308surface flows at the point of runoff generation and the point
309of infiltration remains the same as in surface water. For a
310negligible change in chloride concentration at the soil
311surface, Eq. (2) reduces to:
Fcs ¼ PcpþD � Qp þ Qo
� �
cs ð3Þ
313313Similarly, application of chloride mass balance to matrix
314porosity in the unsaturated zone with the upper boundary is
315taken to be the ground surface with an infiltration, and the
316lower boundary is taken as the piezometric surface with
317recharge. It is assumed that point recharge and diffuse
318recharge from the catchment reach the piezometric surface
319unmixed. Thus,
DðsucusÞ
Dt¼ Fcs � Rucu ð4Þ
321321where su is unsaturated zone storage (L), cus is average
322concentration of chloride in the profile (ML-3), Ru is
323unsaturated zone diffuse recharge (LT-1), and cu is chlo-
324ride concentration of recharge water from the unsaturated
325zone (ML-3), which is equal to the chloride concentration
326below the root zone. If the time of integration is selected to
327be long enough to cover several hydrological years, the
328unsaturated zone storage fluctuation term may then be
329assumed to be negligible. The above assumptions reduce
330Eq. (4) to:
F cs � Rucu ¼ 0 ð5Þ
332332Combining Eqs. (3) and (5) and rearranging them gives:
Ru ¼PcpþD
� �
� Qp þ Qo
� �
cs
cuð6Þ
334334For long-term chloride equilibrium, cu is equal to diffuse
335recharge groundwater chloride concentration (Walker et al.
3361991; Cook et al. 1992; Scanlon et al. 2002), which is
337expressed as (cgd). Total net recharge (R) is R = Ru ? Qp;
338hence, for closed basins where QO = 0, the generalised
339CMB equation is:
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R ¼PcpþD
� �
þ Qp cgd � cs� �
cgdð7Þ
341341 When 100 % diffuse recharge takes place (Qp = 0) and
342 cgd = cg (groundwater chloride), Eq. (7) becomes the sat-
343 urated zone conventional CMB equation given in Eqs. (1)
344 and (8a). Similarly, when 100 % point recharge takes
345 place, diffuse recharge goes to zero and then cgd = cs,
346 Eq. (7) becomes point recharge, Qp, given in Eq. (8b).
R ¼PcpþD
cgð8aÞ
348348 R ¼PcpþD
cs¼ Qp ð8bÞ
350350 A special case occurs where ambient groundwater chloride
351 concentration is much higher than the chloride concentra-
352 tion of surface runoff, cgd � cs, and then (cgd - cs)/
353 cgd & 1, thus Eq. (7) yields:
R ¼PcpþD
cgdþ Qp ð8cÞ
355355 An attractive feature of the generalised CMB method is
356 that it is not necessary to measure groundwater chloride
357 (cg), as it is not required in the equation. Therefore,
358 uncertainty associated with extreme variability of ground-
359 water chloride concentrations due to point recharge is not
360 affected on calculated recharge.
361 Description of study basins
362 Three groundwater basins in South Australia characterised
363 by point and diffuse recharge are examined in this study. A
364 summary of the study basins are provided below with more
365 detail found in (Somaratne 2014).
366 Uley South basin
367 Uley South basin, approximately 113 km2 in area, is
368 located on the Southern Eyre Peninsula of South Australia
369 (Fig. 2). Average annual rainfall is 550 mm and average
370 annual pan evaporation is 1,550 mm. The basin has been
371 used for reticulated town water supply since 1976, and
372 currently about 6.8 9 106 m3 year-1 of groundwater is
373 extracted from the Quaternary limestone aquifer.
374 The hydrogeology of Uley South basin comprises
375 Quaternary limestone of an average thickness of 15 m,
376 followed by a Tertiary clay unit of 5–25 m thickness, and a
377 Tertiary sand aquifer (Evans 1997). As one might have
378 expected in karstic systems, the hydraulic parameters
379 obtained from a pumping test indicate high heterogeneity,
380 transmissivity ranged from 3,000 to 13,000 m2 day-1, and
381with specific yields from 0.03 to 0.72 (Evans 1997). The
382Tertiary clay forms an aquitard between the Tertiary sand
383and the Quaternary limestone aquifer systems, except
384where Tertiary clay is absent. Groundwater flow direction
385is from northeast to southwest (Somaratne et al. 2014a).
386The basin is topographically closed and bound by coastline
387and sand dunes to the west and inland to the north and east
388by topographic rises of dry limestone (allogenic zone),
389except along the north eastern edge (Fig. 2). During intense
390rainfall events, excess water from the dry limestone and
391basement high areas run-on to the basin from the landward
392boundary.
393The low-lying central part of the basin contains
394numerous sinkholes (autogenic zone). Runoff is highly
395ephemeral, occurring only after moderate- to high-intensity
396rainfall and persisting tens to hundreds of metres before
397entering a sinkhole (Evans 1997; Harrington et al. 2006;
398Ordens et al. 2012). A survey of a 4 km2 area found a
399density of about one sinkhole per 0.07 km2, with size
400ranging from 0.4 m to 2.5 m diameter (Somaratne et al.
4012014a). Somaratne and Frizenschaf (2013) show that the
402Uley South Quaternary limestone aquifer is hydraulically
403connected to the Tertiary sand aquifer through the Tertiary
404clay absence areas on the landward boundary. This has
405resulted in complex hydrochemical make-up of the Qua-
406ternary limestone aquifer due to mixing of different
407groundwater systems with different ages and different
408salinity and ion concentrations.
409Mount Gambier Blue Lake capture zone
410Blue Lake is located southeast of South Australia (Fig. 2).
411It is a volcanic crater complex and is the water supply
412reservoir for the city of Mount Gambier (Allison and
413Harvey 1983). The lake is groundwater fed through an
414extensive karst aquifer (Waterhouse 1977; Turner et al.
4151983). Currently 3.6 9 106 m3 is extracted annually for
416town water supply. The main source of recharge to Blue
417Lake is groundwater from the unconfined, karst Gambier
418Limestone aquifer underlying the urban area. Average
419saturated thickness of the Gambier Limestone aquifer is
420about 60 m. In the Blue Lake capture zone, transmissivity
421is in the range of 450–24,000 m2 day-1 and specific yield
422is 0.1–0.4 for the Gambier Limestone aquifer (Mustafa and
423Lawson 2002). Storm water derived from the central
42416.8 km2 of the city area (26.5 km2) is discharged to the
425unconfined aquifer through three sinkholes and about 400
426storm water drainage wells (Somaratne et al. 2014b).
427Average annual rainfall in Mount Gambier is 750 mm and
428average annual pan evaporation is 1,400 mm. The Blue
429Lake capture zone is located about 20 km from the coast-
430line. The regional groundwater flow direction is from north
431to south; however, Blue Lake receives groundwater flow
AQ2
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432 from the northwest to northeast direction of the capture
433 zone; and from the southern side due to the water level of
434 the Lake being lower than the surrounding aquifer in the
435 vicinity of the Lake.
436 Poocher Swamp freshwater lens
437 The Tatiara catchment area extends across the South
438 Australian border into western Victoria, and features
439 average annual rainfall ranging from 400 to 500 mm and
440 pan evaporation of 2,000 mm. The catchment area is
441 approximately 500 km2 (Herczeg et al. 1997). The
442 unconfined aquifer is Murray Group Limestone and con-
443 tains brackish water with average TDS (total dissolved
444 solids)[1,400 mg L-1, with a chloride concentration of
445 [500 mg L-1 (MacKenzie 2013; Fig. 2). Saturated
446 thickness of the limestone unconfined aquifer is approxi-
447 mately 50–60 m. Freshwater with TDS \1,000 mg L-1
448 occurs at locations where point recharge takes place
449through sinkholes, locally known as runaway holes. There
450are a number of sinkholes in the catchment that potentially
451impact surface water yield. Poocher Swamp’s freshwater
452lens, which is the largest of these freshwater plumes that
453float on brackish water, is a result of flows from Tatiara
454Creek which enter Poocher Swamp. The major recharge is
455through two sinkholes located in the northwest section of
456the swamp (Herczeg et al. 1997). The area encompassed by
457the 1,000 mg L-1 salinity contour comprises approxi-
458mately 20 km2. This catchment generates irregular annual
459volumes of freshwater (0.05–2) 9 106 m3 year-1, but on
460rare occasions up to 19 9 106 m3 year-1. Poocher Swamp
461is located some 200 km north of Mount Gambier and
462100 km from the nearest coastline to the west. Ground-
463water flow direction is from east to west. Currently, an
464annual volume of 0.6 9 106 m3 of groundwater is extrac-
465ted from the freshwater lens for town water supply, with
466average salinity 490 mg L-1 and chloride concentration of
467115 mg L-1.
Fig. 2 Locations of study basin
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468 Methods
469 Field measurements
470 Groundwater chloride for the Uley South basin is from
471 Evans (1997), with further groundwater samples collected
472 in 2008 and 2012. Data gaps were filled by linear regres-
473 sion of TDS to chloride (R2= 0.98) for monitoring wells
474 where TDS are available but no chloride measurements
475 have been undertaken. Selected monitoring wells are away
476 from brackish water, upward leakage areas from Tertiary
477 sand aquifer, and salinity stratified wells (Somaratne and
478 Frizenschaf 2013), the swamp, and coastal monitoring
479 wells to avoid chloride contamination from other sources.
480 For the Blue Lake capture zone, existing groundwater
481 chloride data were supplemented with samples taken from
482 unconfined aquifer monitoring wells within and outside the
483 city. Selected sampling wells are away from historically
484 known contaminated sites (Fig. 2). In addition to the
485 monitoring wells, groundwater samples were taken from
486 drainage wells and surface runoff for major ion chemistry
487 analysis. Water samples were collected from Tatiara Creek,
488 Poocher Swamp, aquifer monitoring wells, and town water
489 supply wells in 2012.
490 Groundwater samples were collected using micro-purge
491 (low-flow) sampling procedure (Vail 2011) and grab
492 sampling technique. The micro-sampling is employed to
493 gain representative groundwater samples within the open
494 hole of monitoring and drainage wells. Low-flow purging
495 is considered (Vail 2011) superior to bailing and high-rate
496 pumping and results in a more representative sample than
497 the typical well purge methodology. The assumption in the
498 grab sampling is that the hydrostratigraphy in the well is in
499 hydraulic equilibrium prior to sampling. To collect the
500 sample by this method, an electronic depth sampler con-
501 nected to a geophysical logging line is advanced to the
502 target sampling depth, and the unit is electronically opened,
503 allowing groundwater to enter the sampler. Salinity profiles
504 of monitoring and drainage wells were obtained using
505 Hydrolab sonde (Eco Environmental 2013) connected to a
506 logging truck cable and lowered down the well from sur-
507 face to the well base, recording electrical conductivity data
508 along the way (Somaratne 2014).
509 Point recharge estimates
510 In Uley South basin, Ward et al. (2009) use LEACHM
511 (Hutson 2003), a variably saturated model of the soil pro-
512 file that uses the curve number approach described by
513 Williams (1991) to estimate surface runoff. The Uley South
514 model considers four surface cover scenarios from flat
515 slope to steep sites with a slope of 0.15. The surface cover
516 includes: deep-rooted vegetation with high cover and steep
517slope; deep-rooted vegetation with high cover on flat sur-
518faces; shallow rooted vegetation cover with steep slope;
519and shallow rooted vegetation cover on flat ground sur-
520faces. Potential evapotranspiration was calculated using the
521methods of Linacre (1977), and four different soil and sub-
522soil profiles were considered to include the significance of
523the soil and the presence of calcrete at near-surface depths
524of up to 2 m. Unsaturated zone properties are assumed,
525based on prior knowledge of similar soil and sub-soil types.
526In Uley South, about 90 % of the basin features are flat
527ground surface. The LEACHM modelling result is criti-
528cally dependent on the assumption that all runoff becomes
529recharge via sinkholes. The simulations were not sensitive
530to the four soil and sub-soil profiles. The only profile that
531showed a slight difference was one with 300 mm of soil on
532calcrete (Ward et al. 2009).
533As part of the recharge estimation for Blue Lake in
534Mount Gambier, Nguyen (2013) used the urban storm
535water model MUSIC (2009) to quantify storm water runoff
536to drainage wells. In the Nguyen study, rainfall and runoff
537process were modelled for the period 2007–2012 using a
538daily time step with daily rainfall and evaporation data. For
539sub-catchments with drainage wells, the average percent-
540age of impervious (51 %) and pervious (49 %) areas was
541determined using digital maps of the city using geographic
542information system tools. A rainfall threshold of 1 mm
543(initial loss) was used for impervious areas. Uniform soil
544storage capacity and field capacity values of 120 and
54580 mm, respectively, were used for pervious areas. Initial
546soil storage capacity was set at 30 %. Average annual
547runoff volume from both pervious and impervious areas
548was calculated as point recharge to drainage wells and
549three sinkholes. A sensitivity analysis indicated field
550capacity of the soil had the greatest effect on runoff from
551the pervious area (Nguyen 2013).
552Chloride concentrations of groundwater near the Po-
553ocher Swamp sinkhole (20–40 mg L-1) are similar to the
554low chloride in the swamp and Tatiara Creek water (28 mg
555L-1), indicating direct recharge into the groundwater sys-
556tem (Herczeg et al. 1997). Therefore, average annual flow
557calculated from daily flow data of Tatiara Creek measured
558at Bordertown, about 6 km upstream, is taken as the annual
559recharge, the majority of which is through two sinkholes
560(Somaratne 2014).
561Results and discussion
562Characteristics of basins with respect to limitation of
563applying conventional CMB method for recharge
564estimation.
565Groundwater in the Uley South limestone aquifer is
566derived from three main sources: diffuse recharge through
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567 granular porosity; point recharge through sinkholes, and
568 Tertiary sand water entering the limestone aquifer where
569 the two aquifers coincide in the Tertiary clay absent areas
570 on the landward boundary. Somaratne and Frizenschaf
571 (2013) show that the high-salinity plume of groundwater in
572 the Tertiary sand aquifer originates from Big Swamp,
573 located 14 km northeast from the basin. The plume moves
574 down-gradient, where it enters Uley South. As the plume
575 moves along its main flow path, it is diluted from
576 5,380 mg L-1 salinity at Big Swamp to 662 mg L-1 at the
577 Uley South boundary. As a result of the higher salinity
578 Tertiary sand water entering the Quaternary limestone,
579 pronounced salinity stratification is found in the Quater-
580 nary limestone aquifer monitoring wells down-gradient to
581 the Tertiary clay absent area (Somaratne and Frizenschaf
582 2013). The presence of sinkholes that may directly
583 recharge the aquifer, along with mixing of Quaternary
584 limestone water and Tertiary sand water with different
585 chloride concentrations (Fig. 3), results in unmet boundary
586 conditions and assumptions required for application of
587 conventional CMB. Groundwater chloride in the central
588 basin is not representative of recharge water chloride that
589 crosses the piezometric surface, as it is a mixture of three
590 sources. Thus, application of the conventional CMB
591 method to Uley South basin is frustrated.
592The main source of recharge to the unconfined, karst
593Gambier Limestone aquifer, below the city of Mount
594Gambier, is storm water derived from the central
59516.8 km2 of the city area (26.5 km2). Since sinkholes can
596be inaccessible for water sampling and, to illustrate the
597concept of small freshwater pockets around sinkholes in
598small sub-catchments (0.03–0.12 km2), Somaratne (2011)
599investigated storm water drainage wells in the city of
600Mount Gambier. The drainage wells represent discrete
601recharge points and are used to measure chloride con-
602centration in the aquifer. These small pockets of fresher
603water around point recharge sources result from surface
604water entering the aquifer while bypassing the soil matrix.
605Comparisons of chloride concentration in the aquifer at
606drainage wells and at monitoring wells are given in
607Fig. 4. Accordingly, chloride concentration in recharge
608water prior to crossing the piezometric surface remains at
609surface water concentration (chloride concentration of
61012 mg L-1), but in drainage wells slight mixing with
611ambient groundwater is seen, since the groundwater
612chloride in drainage wells is higher than the recharge
613water (average 21 mg L-1).
614The ambient groundwater chloride concentration of
615samples taken away from historical contaminated sites is
61663 mg L-1, which equates to the average groundwater
Fig. 3 Uley South recharge
conceptual model
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617 chloride concentration of the diffuse recharge zone
618 (Figs. 2, 4) and comparable to chloride values (70 mg L-1)
619 reported by Waterhouse (1977) in greater Mount Gambier
620 area, excluding contaminated sites but including irrigation
621 areas. This highlights the fact that groundwater samples
622 obtained from the monitoring network in point recharge
623 zones reflect long-term resident chloride concentration.
624 Salinity profiles obtained from monitoring wells and
625 drainage wells in the vicinity of primary fracture pathway
626 (Fig. 2) indicate low salinity zones deeper in the aquifer
627 (Somaratne 2014). The lower salinity zone of the profiles is
628 due to point recharge water moving along the primary
629 fracture pathway to Blue Lake (Lawson 2013). This indi-
630 cates that preferential pathways exist in the groundwater
631 systems, as described by Waterhouse (1977).
632 In this case study, the basic assumption that recharge
633 flux crossing the piezometric surface is in equilibrium with
634 groundwater chloride is found to be invalid, and the steady-
635 state or piston flow criteria is not satisfied. Therefore,
636 groundwater chloride, cR in Eq. (1), cannot be replaced
637 with cg, as chloride measurements within fresh water
638 pockets are neither representative of the recharged point
639 nor at the sampled points. Thus, application of the
640conventional CMB method is questionable in the Mount
641Gambier capture zone.
642In the Poocher Swamp freshwater lens (Fig. 2), the
643entire lens was formed due to point recharge of Tatiara
644Creek flow (Fig. 5) through two sinkholes. A wide range of
645chloride values obtained from the lens, from 40 mg L-1 at
646the WRG 32 monitoring well to 550 mg L-1 at the WRG
647110 well, result from freshwater mixing with ambient
648groundwater chloride in the lens.
649Vertical recharge (2.5 mm year-1) that crosses the pie-
650zometric surface corresponds to a diffuse zone average
651groundwater chloride concentration of 712 mg L-1 (So-
652maratne 2014). The freshwater lens recharge water is
653generated largely outside the lens area. Low salinity and
654chloride concentrations found in the lens result from a
655lateral flux moving from the sinkhole down-gradient.
656Taking chloride measurements from a lateral flux to esti-
657mate vertical recharge essentially estimates ‘apparent
658recharge’ (Somaratne 2014), which does not represent
659actual point recharge at the sinkhole or diffuse recharge
660within the lens where chloride samples were taken. Thus,
661application of the conventional CMB method to a fresh-
662water plume is invalid.
Fig. 4 a Schematic diagram
showing an example of differing
chloride concentrations in
drainage and aquifer monitoring
wells away from contaminated
sites. b Recharging through
Cave Garden sinkhole.
c Recharging through a storm
water drainage well
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663 Recharge estimation using the generalised CMB
664 method
665 Chloride is regarded as a conservative tracer. In diffuse
666 recharge zones, chloride in recharging water is in equilib-
667 rium with groundwater chloride. In point recharge domi-
668 nant zones, both point and diffuse recharge processes
669 contribute to the concentration of groundwater chloride. In
670 the Uley South basin, diffuse zone chloride samples were
671 taken from monitoring wells located within 2 km of the
672 basin boundary. In the Mount Gambier Blue Lake capture
673 zone, monitoring wells outside the city were used. For the
674 Poocher Swamp freshwater lens, chloride concentrations
675 from monitoring wells outside the lens were taken (Fig. 2).
676 Sinkhole areas in the Uley South basin where groundwater
677 chloride is derived from both diffuse and point recharge
678 (137 mg L-1) are, on average, 12 mg L-1 lower compared
679 to chloride concentration in areas where diffuse recharge is
680 the only contributor (Table 1). This is despite the fact that
681 higher salinity Tertiary sand water mixes with the lime-
682 stone aquifer in the central basin, where most of the
683 sinkholes are located. In the Mount Gambier capture zone
684 (63 mg L-1), such difference could not be confirmed.
685 With regard to point recharge in Uley South, for the
686 average annual rainfall of 550 mm, Ward et al. (2009)
687 obtained an average annual runoff volume of
688 8.5 9 106 m3, or basin equivalent depth of about 75 mm,
689 which flows through sinkholes to the water table. For
690 Mount Gambier with an average annual rainfall of
691 750 mm, Nguyen (2013) estimated 6.6 9 106 m3 of runoff
692 volume flows through drainage wells to groundwater from
693 a catchment area of 16.8 km2. Of this, 5.1 9 106 m3 of
694runoff volume is generated from the impervious areas of
695the catchment. Based on the annual flow of Tatiara Creek
696for the period 1980–2010, average annual recharge to
697groundwater in Poocher Swamp is taken as 2.5 9 106 m3
698through the two sinkholes. A similar estimate of
6992.3 9 106 m3 was made by Stadter and Love (1987) in
7001987.
701In the absence of direct measurement, cp?D can be
702estimated from Hutton (1976) using:
cpþD ¼ 35:45�0:99
d0:25� 0:23
� �
ð9Þ
704704where ‘d’ is distance in km from the ocean in the prevailing
705wind direction. For the Uley South basin, cs = cp?D was
706taken, as no surface water chloride measurements were
707undertaken.
708The average annual volume of point recharge is much
709smaller than typical aquifer storage volume. For example,
710when volumes are expressed by depths, the ratio of point
711recharge to water depth in the saturated thickness of the
712aquifer ratio (taking uniform aquifer porosity of 0.3) for
713Uley South is 1.5 %, for Mount Gambier Blue Lake cap-
714ture zone it is 1.95 %, and for the Poocher Swamp fresh
715water lens, it is 0.75 %.
716Much of the point recharge water found in conduit
717porosity is carried away at a faster flow rate than diffuse
718recharge water in granular porosity. Even though point
719recharge Qp is expressed by depth in generalised CMB, it
720occurs through hundreds of sinkholes in Uley South, and
721about 400 drainage wells and three sinkholes in Mount
722Gambier. Therefore, the low volume of surface runoff with
723low concentrations of chloride reaching groundwater is
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Flow (x1000 cubic meter) 2 2 2 3 34 432 330 926 508 297 8 26
Salinity (mg/L) 241 447 100 168 117 133 136 119 150 137 179 189
0
100
200
300
400
500
600
700
800
900
1000Fig. 5 Tatiara Creek average
monthly flow (average
1980–2010) and salinity data
(average 2006–2007) with
photographs of Poocher Swamp
at full capacity and empty with
exposed sinkhole
Table 1 Input parameters for recharge estimation using generalised CMB
Groundwater basin Average annual
rainfall (mm year-1)
Chloride in
rainfall (mg L-1)
Chloride in surface
runoff (mg L-1)
Chloride in diffuse
recharge zone (mg L-1)
Point recharge
(mm year-1)
Uley South 550 14.2 14.2 149 75
Blue Lake capture zone 750 8.5 12.7 63 390
Poocher Swamp fresh water lens 450 3.1 28 712 125
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724 insufficient to cause detectable changes in chloride con-
725 centrations due to mixing. This is in contrast to the large
726 volume of recharge that takes place at a single location as
727 in the Poocher Swamp freshwater lens.
728 For estimation of recharge using the generalised CMB
729 method, recharge to Uley South basin and Mount Gambier
730 in the Blue Lake capture zone is estimated using Eq. (7),
731 and for the Poocher Swamp fresh water lens, where cs -
732 cgd, Eq. (8c) is used. A comparison of generalised CMB-
733 estimated recharge with conventional CMB-estimated
734 recharge is provided in Table 2.
735 In the three case studies, the point recharge flux is
736 estimated to contribute 63, 85, and 98 % of total recharge
737 for Uley South, Blue Lake capture zone, and Poocher
738 Swamp freshwater lens, respectively. Similar observations
739 are made by Wood et al. (1997) on macro-pore recharge in
740 playa basins. Wood et al. (1997) report macro-pore
741 recharge flux ranges between 60 and 80 % of total
742 recharge. Conventional CMB-estimated recharge is 46, 20,
743 and 11 % of the recharge estimated using the generalised
744 CMB for Uley South, Mount Gambier, and Poocher
745 Swamp fresh water lens, respectively, indicating the
746 importance of accommodating point recharge into the
747 CMB method.
748 There is a degree of uncertainty in estimating point
749 recharge (Qp) at the large-basin scale, since total estimated
750 runoff does not flow to sinkholes, but rather to surface
751 storage in large depressions. Amoah et al. (2012) use
752 digital elevation models to estimate depressional storage
753 capacity in the catchment. There are many surface water
754 models available to calculate runoff volumes, both event-
755 based and continuous rainfall runoff processes. Their
756 choice is a matter of time and cost of data collection. In the
757 macro-pore recharge study, Wood et al. (1997) use a runoff
758 model to quantify total recharge. Another area of uncer-
759 tainty is whether the two flow types (point recharge and
760 diffuse recharge) mix well before arriving at the water table
761 or mix well in the water table. If this happens, no distin-
762 guishable point or diffuse recharge crosses the piezometric
763 surface. Therefore, the recharge flux arriving at the pie-
764 zometric surface may have a chloride concentration like
765that in a saturated zone (at least approximately), and the
766saturated zone conventional CMB is still applicable. This
767may apply to point recharge through root channels, bur-
768rows, cracks, and minor fissures or in large regional aqui-
769fers, such as the case reported by Herczeg et al. (1997), in
770which point recharge is 10 % of total recharge in the
771regional Tatiara catchment ([500 km2).
772Using the three criteria reliability assessments of
773recharge (Somaratne et al. 2014a) returns reliable recharge
774estimates for Mount Gambier and Poocher Swamp fresh-
775water lens using the generalised CMB method. However,
776estimated recharge for Uley South (120 mm year-1) is
777moderately reliable even though reliable recharge is
778125–129 mm per year using the water table fluctuation
779method (Somaratne et al. 2014a). The moderate reliability
780is due to moderate data quality on point recharge estimates
781of Ward et al. (2009) and sparsely distributed diffuse zone
782chloride in the basin. Improving or verifying data quality
783would improve reliability of the estimate. Improved data
784and conceptual models would also assist reliability of
785recharge calculations using other applicable methods. For
786example, the average annual recharge of 146 mm obtained
787from transient calibration of a groundwater model (Werner
7882010) based on MODFLOW (McDonald and Harbough
7891988) and PEST (Watermark Numerical Computing 2004),
790and 157 mm long-term average recharge value of the Eyre
791Region Water Resources Planning Committee (2000) is
792based on Darcy flow and water balance calculations of
793Evans (1997). However, generalised CMB-estimated
794recharge is significantly higher than conventional CMB-
795estimated average annual recharge of 52–63 mm (Ordens
796et al. 2012), 52–71 mm (SA Water, unpublished data) and
79771 mm (Evans 1997) for the basin. Average annual
798pumping from the Uley South basin over the years,
7992000–2014, is equivalent to 60 mm year-1 or about the
800same as the conventional CMB-estimated recharge.
801According to this estimation groundwater levels should be
802falling, however, the trend observed in the basin since 1999
803is characterised as either steady or rising water levels,
804indicating conventional CMB-estimated recharge is unre-
805alistically low (Somaratne et al. 2014a). This highlights the
806fact that application of the conventional CMB method to
807estimate total recharge in groundwater basins characterised
808by point and diffuse recharge is unsuccessful, using either
809unsaturated or saturated zone chloride as inputs. Thus,
810generalised CMB provides an alternative method for
811recharge estimation in karstic settings.
812Conclusions
813This paper critically examines the conditions in three
814karstic groundwater basins, under which the assumptions
Table 2 Comparison of generalised and conventional CMB-esti-
mated recharge
Groundwater basin Recharge using
generalised CMB
(mm year-1)
Recharge using
conventional CMB
(mm year-1)
Uley South 120 (13.6 9 106) 56 (6.3 9 106)
Blue Lake capture zone 491 (7.4 9 106) 101 (0.83 9 106)
Poocher Swamp
freshwater lens
127 (2.55 9 106) Apparent 14
(0.28 9 106)
Recharge volume in m3 is given within brackets
AQ3
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815 underpinning the conventional CMB equation do not hold,
816 and which subsequently lead to underestimation of
817 recharge. It presents case studies showing that karst sys-
818 tems have a distinct hydrologic function resulting from a
819 duality of flow regimes in infiltration and recharge, and in
820 preferential groundwater flow paths. In the three case
821 studies, estimated recharge using the conventional CMB
822 method is less than the point recharge estimates for the
823 study basins. The paper shows that simplified assumptions
824 in the conventional CMB make application of the method
825 to point recharge dominant groundwater basins unsuc-
826 cessful. For application of the generalised CMB equation,
827 obtaining diffuse recharge groundwater chloride and runoff
828 volume to sinkholes is critical to accuracy. Groundwater
829 chloride measurements should be obtained away from
830 freshwater pockets or plumes created by point recharge, or
831 soil–water chloride should be extracted from the unsatu-
832 rated zone above the water table to obtain diffuse zone
833 chloride. Quantification of runoff at the catchment or sub-
834 catchment levels is required for accurate assessment of
835 point recharge and to apply the generalised CMB equation
836 for total recharge estimation. For this purpose, many
837 available watershed models provide runoff estimates as
838 part of an overall water balance. A comparison of the
839 generalised CMB results with the long-term recharge
840 estimates obtained using the water table fluctuation (WTF)
841 method, groundwater flow modelling, and Darcy flow
842 calculations shows slightly lower but comparable results.
843 Hence, the generalised CMB method augments the con-
844 ventional CMB method by accounting for point recharge
845 that bypasses the unsaturated zone. It thus provides an
846 alternative, reliable, long-term recharge estimation method
847 for groundwater basins with point and diffuse recharge
848 mechanisms.
849 Acknowledgments The editor and anonymous reviewers are850 thanked for their useful comments. Much help was received from the851 following, who are gratefully acknowledged: Prof. Keith Smettem for852 contribution to an earlier version of the manuscript and reviews, Prof.853 Wolfgang Kinzelbach for reviewing the generalised CMB method-854 ology, Glyn Ashman and Jacqueline Frizenschaf for review of the855 manuscript, Jeff Lawson for assistance with groundwater sampling in856 Mount Gambier, George MacKenzie for providing Scowns sinkhole857 and Tatiara Creek flow data.
858 References
859 Allison GB (1988) A review of some physical, chemical and isotopic860 techniques available for estimating groundwater recharge. In:861 Simmers I (ed) Estimation of natural groundwater recharge.862 D. Reidel Publishing Co., Dardrecht, pp 49–72863 Allison GB, Harvey PD (1983) Freshwater lakes. In: Tyler MJ,864 Twidale CRT, Ling JK, Holmes JW (eds) Natural History of the865 South East. Royal Society of South Australia, South Australia,866 pp 61–74
867Allison GB, Hughes MW (1978) The use of environmental chloride868and tritium to estimate total recharge to an unconfined aquifer.869Aust J Soil Res 16:181–195870Amoah JK, Amatiya DM, Nnaji S (2012) Quantifying watershed871surface depression storage: determination and application in a872hydrologic model. Hydrol Processes 27(17):2401–2413. doi:10.8731002/hyp.9364874Bakalowicz M (2005) Karst groundwater: a challenge for new875resources. Hydrogeol J 13:148–160. doi:10.1007/s10040-004-8760402-9877Cook PG, Edmunds WM, Gaye CB (1992) Estimating paleo-recharge878and paleo-climate from unsaturated zone profiles. Water Resour879Res 28:2721–2731880Eco Environmental (2013) Salinity sonde, Environmental monitoring881and sampling equipment. http://ecoenvironmental.com.au882(accessed 08 October 2013)883Eriksson E, Khunakasem V (1969) Chloride concentration in884groundwater, recharge rate and rate of deposition of chloride885in the Israel Coastal Plain. J Hydrol 7:178–197886Evans SL (1997) Estimating long-term recharge in unconfined887carbonate aquifers using conventional and environmental isotope888techniques-Eyre Peninsula, South Australia, Masters Thesis,889Flinders University of South Australia, unpublished890Eyre Region Water Resources Planning Committee (2000) Water891allocation plan southern basins prescribed wells area. Govern-892ment of South Australia, through Department of Water893Resources, South Australia894Gee GW, Zhang ZF, Tyler SW, Albright WH, Singleton MJ (2005)895Chloride mass balance: cautions in predicting increased recharge896rates. Vadoze Zone J 4:72–78897Ginn TR, Murphy EM (1996) Generalized chloride mass balance:898Forward and inverse solutions for one dimensional tracer899convection under transient flux, Pacific Northwest Laboratory,900Prepared for the US. Department of Energy under contract DE-901AC06-76RLO 1830902Guan H, Love AJ, Simmons CT, Hutson J, Ding Z (2010) Catchment903conceptualisation for examining applicability of chloride mass904balance method in an area with historical forest clearance.905Hydrol Earth Syst Sci 14:1233–1245. doi:10.5194/hess-14-1233-9062010907Gunn J (1983) Point-recharge of limestone aquifers—a model from908New Zealand karst. J Hydrol 61:19–29909Harrington N, Zulfic D, Wohling D (2006) Uley basin groundwater910modelling project, Vol. 1, Project overview and conceptual911model development, DWLBC Report 2006/01, Government of912South Australia913Herczeg AL, Leaney FW, Stadter MF, Allan GL, Fifield LK (1997)914Chemical and isotope indicators of point-source recharge to a915karst aquifer, South Australia. J Hydrol 192:271–299916Hutson JL (2003) LEACHM—A process-based model of water and917solute movement, transformations, plant uptake and chemical918reactions in the unsaturated zone, version 4. Research Series No.919R03-1, Department of Crop and Soil Sciences, Cornell Univer-920sity, Ithaca, New York921Hutton JT (1976) Chloride in rainwater in relation to distance from922the ocean. Search 7:207–208923Lawson J (2013) Water quality and movement of the unconfined and924confined aquifers in the capture zone of the Blue Lake, Mount925Gambier, South Australia and implications for their manage-926ment, Masters thesis, University of South Australia, unpublished927Leaney FW, Herczeg AL (1995) Regional recharge to a karst aquifer928estimated from chemical and isotopic composition of diffuse and929localised recharge, South Australia. J Hydrol 164:363–387930Lerch RN, Wicks CM, Moss PL (2005) Hydrologic characterization931of two karst recharge areas in Boone County, Missouri. J Cave932Karst Studies 67(3):158–173
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r P
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UNCORRECTEDPROOF
933 Linacre ET (1977) A simple formula for estimating evaporation rates934 in various climates, using temperature data alone. Agric935 Meteorol 18:409–424936 MacKenzie G (2013) Hydrochemical data of the Tatiara catchment,937 Department of Environment, Water and Natural Resources,938 Naracoorte, unpublished939 Martin JB, Dean RW (2001) Exchange of water between conduits and940 matrix in the Floridan aquifer. Chem Geol 179:145–165941 Martin JB, Screaton EJ (2001) Exchange of matrix and conduit water942 with examples from the Floridan aquifer. In: Kuniansky (Ed), US943 Geological Survey Karst Interest Group Proceedings, Water944 Resources Investigation Report 01-4011, 99.38–44945 McDonald MG, Harbough BR (1988) A modular three-dimensional946 finite difference groundwater flow model, Techniques of Water947 Resources Investigations of the U.S. Geological Survey, Book 6,948 Geological Survey Open File Report 91-536, USGS949 MUSIC (2009) Model for urban storm water improvement concep-950 tualisation (MUSIC). MUSIC Development Team, eWaterCRC,951 Australia952 Mustafa S, Lawson JS (2002) Review of Tertiary aquifer properties,953 Gambier Limestone, Lower South-East, South Australia, Depart-954 ment of Water, Land and Biodiversity Conservation, Report955 DWLBC 2002/24, unpublished956 Nguyen K (2013) Estimating the annual storm water yield in the Blue957 Lake capture zone, South Australia, M. Eng thesis, University of958 South Australia, unpublished959 Nyagawambo NL (2006) Groundwater recharge estimation and water960 resources assessment in a crystalline basement aquifer, PhD961 thesis, Delft University of Technology, Delft, The Netherlands,962 A. A. Balkema Publishers, ISBN 0 415 41692 2963 Ordens CM, Werner AD, Post VEA, Hutson JL, Simmons CT, Irvine964 BM (2012) Groundwater recharge to a sedimentary aquifer in the965 topographically closed Uley South basin, South Australia.966 Hydrogeol J 20:61–72. doi:10.007/s10040-011-0794-2967 Scanlon BR, Healy RW, Cook PG (2002) Choosing appropriate968 techniques for quantifying groundwater recharge. Hydrogeol J969 10:18–39. doi:10.1007/s10040-001-0176-2970 Somaratne N (2011) Salinity profiling and chloride measurement in971 storm water discharge drainage wells in Blue lake capture zone,972 Internal Project Briefing Report, South Australian Water973 Corporation, South Australia, unpublished974 Somaratne N (2012) Pitfalls in the application of the chloride mass975 balance method to groundwater basins dominated by point976 recharge, SA Water Hydrogeological Research Report, SA977 Water 2012/1, unpublished978 Somaratne N (2014) Characteristics of point recharge in karst979 aquifers. Water 6:2782–2807. doi:10.3390/w6092782980 Somaratne N, Frizenschaf J (2013) Geological control upon ground-981 water flow and major ion chemistry with influence on basin982 management in a coastal aquifer, South Australia, J Water Res983 Prot, 5, 1170–1177. http://dx.doi.org/10.4236/jwarp.2013.984 512124985 Somaratne N, Smettem K, Frizenschaf J (2014a) Three criteria986 reliability analyses for groundwater recharge estimations. Envi-987 ron Earth Sci. doi:10.1007/s12665-014-3121-0988 Somaratne N, Lawson J, Ashman G, Nguyen K (2014b) Recharge to989 Blue Lake and strategies for water security planning, Mount990 Gambier, South Australia, J Water Res Prot, 6, 772–783, doi:10.991 4236/jwrp.2014.68073
992Stadter F, Love AJ (1987) Tatiara proclaimed region groundwater993assessment, South Australian Department of Mines and Energy,994Report Book 87/87, unpublished995Subayani A, Sen Z (2006) Refined chloride mass-balance method and996its application in Saudi Arabia. Hydrol Processes 20:4373–4380.997doi:10.1002/hyp.6172998Taylor CJ, Greene EA (2001) Quantitative approaches in character-999izing karst aquifers. US Geol Surv Karst Interest Group Proc,1000Water Resour Invest Rep 01–4011:164–1661001Tihansky AB (1999) Sinkholes, West Central Florida. In: Land1002Subsidence in the United States: US Geological Survey Circular,1003vol 1182, pp 121–1401004Turner JV, Allison GB, Holmes, JW (1983) Environmental isotope1005methods for determination of Lake-Groundwater relation: Appli-1006cation to determine the effect of Man’s Activities. International1007Conference on Groundwater and Man, Sydney, Australia1008Vail J (2011) Groundwater sampling, US. Environmental Protection1009Agency, Science and Ecosystem Support Division, Athens,1010Georgia, SESDRPROC-301-R21011Walker GR, Jolly ID, Cook PG (1991) A new chloride leaching1012approach to the estimation of diffuse recharge following a1013change in landuse. J Hydrol 128:49–671014Ward JD, Hutson J, Howe B, Fildes S, Werner AD, Ewenz C (2009)1015A modelling framework for the assessment of recharge processes1016and climate change, Report developed through the Eyre Penin-1017sula Groundwater allocation and Planning Project, Eyre Penin-1018sula Natural Resources Management Board, Government of1019South Australia1020Waterhouse JD (1977) The hydrogeology of the Mount Gambier area,1021Report of Investigations 48, Geological Survey of South1022Australia, p 611023Watermark Numerical Computing (2004) PEST-Model independent1024parameter estimation, User’s manual: 5th edition, available at:1025http://www2.epa.gov/sites/production/files/documents/PEST1026MAN.PDF (accessed 9 January 2014)1027Werner AD (2010) A groundwater model of Uley South Basin, South1028Australia, Flinders University of South Australia, unpublished1029White WB (2003) Conceptual model for karstic aquifers, Speleogen-1030esis and Evolution of Karst Aquifers, The Virtual Scientific1031Journal, 1(1), p 2, http://www.speleogenesis.info (accessed 151032January 2013)1033Williams JR (1991) Chapter 18—Runoff and water erosion. In: Hanks1034J, Ritchie JT (Eds) Modelling Plant and Soil Systems, Agronomy1035Monograph 31, American Society of Agronomy, Madison,1036Wisconsin, chap. 18, pp 439–4551037Wood WW (1999) Use and misuse of the chloride mass balance1038method in estimating groundwater recharge, Technical Com-1039mentary, Groundwater, vol 37, pp 2–31040Wood WW, Rainwater KR, Thompson DB (1997) Quantifying1041macropore recharge: examples from a semi-arid area. Gr Water104235:1097–11061043Zhu C, Winterle JR, Love EI (2003) Late Pleistocene and Holocene1044groundwater recharge from the chloride mass balance method1045and chlorine-36 data. Water Resour Res 39(7):1182. doi:10.10461029/2003WR001987
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