scholarly journals Calibration of a transient transport model to tritium measurements in rivers and streams in the Western Lake Taupo catchment, New Zealand

2012 ◽  
Vol 9 (8) ◽  
pp. 9743-9765
Author(s):  
M. A. Gusyev ◽  
M. Toews ◽  
U. Morgenstern ◽  
M. Stewart ◽  
C. Daughney ◽  
...  
Keyword(s):  
New Zealand ◽  
Transport Model ◽  
Groundwater Age ◽  
Uniform Grid ◽  
Groundwater Levels ◽  
River Waters ◽  
Transient Transport ◽  
Western Lake ◽  
Small Streams ◽  
River Catchments

Abstract. Here we present a general approach of calibrating transient transport models to tritium concentrations in river waters developed for the MT3DMS/MODFLOW model of the Western Lake Taupo catchment, New Zealand. Tritium is a time-dependent tracer with radioactive half-life of 12.32 yr. In the transport model, the tritium input (measured in rain) passes through the groundwater system, and the modelled tritium concentrations are compared to the measured tritium concentrations in the river outlets for the Waihaha, Whanganui, Whareroa, Kuratau and Omori river catchments from 2000–2007. For the Kuratau River, tritium was also measured between 1960 and 1970, which allowed us to fine-tune the transport model. In order to incorporate all surface flows from rivers to small streams, an 80 m uniform grid cell size was selected in the steady-state MODFLOW model for the model area of 1072 km2. The groundwater flow model was first calibrated to groundwater levels and stream flow observations. Then, the transport model was calibrated to the measured tritium concentrations in the river waters. The MT3DMS model results show good agreement with the measured tritium values in all five river catchments. Finally, the calibrated MT3DMS model is applied to simulate groundwater ages that are used to construct groundwater age distributions for the river catchments.

scholarly journals Calibration of a transient transport model to tritium data in streams and simulation of groundwater ages in the western Lake Taupo catchment, New Zealand

2013 ◽  
Vol 17 (3) ◽  
pp. 1217-1227 ◽  
Author(s):  
M. A. Gusyev ◽  
M. Toews ◽  
U. Morgenstern ◽  
M. Stewart ◽  
P. White ◽  
...  
Keyword(s):  
New Zealand ◽  
Transport Model ◽  
Groundwater Age ◽  
Uniform Grid ◽  
Groundwater System ◽  
Small Surface ◽  
Streams And Rivers ◽  
Groundwater Levels ◽  
Transient Transport ◽  
Western Lake

Abstract. Here we present a general approach of calibrating transient transport models to tritium concentrations in river waters developed for the MT3DMS/MODFLOW model of the western Lake Taupo catchment, New Zealand. Tritium has a known pulse-shaped input to groundwater systems due to the bomb tritium in the early 1960s and, with its radioactive half-life of 12.32 yr, allows for the determination of the groundwater age. In the transport model, the tritium input (measured in rainfall) passes through the groundwater system, and the simulated tritium concentrations are matched to the measured tritium concentrations in the river and stream outlets for the Waihaha, Whanganui, Whareroa, Kuratau and Omori catchments from 2000–2007. For the Kuratau River, tritium was also measured between 1960 and 1970, which allowed us to fine-tune the transport model for the simulated bomb-peak tritium concentrations. In order to incorporate small surface water features in detail, an 80 m uniform grid cell size was selected in the steady-state MODFLOW model for the model area of 1072 km2. The groundwater flow model was first calibrated to groundwater levels and stream baseflow observations. Then, the transient tritium transport MT3DMS model was matched to the measured tritium concentrations in streams and rivers, which are the natural discharge of the groundwater system. The tritium concentrations in the rivers and streams correspond to the residence time of the water in the groundwater system (groundwater age) and mixing of water with different age. The transport model output showed a good agreement with the measured tritium values. Finally, the tritium-calibrated MT3DMS model is applied to simulate groundwater ages, which are used to obtain groundwater age distributions with mean residence times (MRTs) in streams and rivers for the five catchments. The effect of regional and local hydrogeology on the simulated groundwater ages is investigated by demonstrating groundwater ages at five model cross-sections to better understand MRTs simulated with tritium-calibrated MT3DMS and lumped parameter models.

scholarly journals Simulated tritium concentrations in river waters of the western Lake Taupo catchment, New Zealand with MODPATH particle tracking

2014 ◽  
Vol 11 (3) ◽  
pp. 3083-3109 ◽  
Author(s):  
M. A. Gusyev ◽  
D. Abrams ◽  
M. W. Toews ◽  
U. Morgenstern ◽  
M. K. Stewart
Keyword(s):  
Particle Tracking ◽  
Tritium Concentration ◽  
Convolution Integral ◽  
River Waters ◽  
Western Lake ◽  
Transit Times ◽  
Concentration Time Series ◽  
Actual Shape ◽  
River Catchments ◽  
Probability Density Function Pdf

Abstract. We simulated in a previous study tritium concentrations in the river waters of the western Lake Taupo catchment (WLTC) using MODFLOW/MT3DMS model (Gusyev et al., 2013). The model was calibrated to match simulated tritium to measured tritium in river waters at baseflows of the Waihaha, Whanganui, Whareroa, Kuratau and Omori river catchments of the WLTC. Following from this work we now utilized the same MODFLOW model for the WLTC to calculate the pathways of groundwater particles (and their corresponding tritium concentrations) using steady-state particle tracking with MODPATH. In order to simulate baseflow tritium concentrations with MODPATH, transit time distributions (TTDs) such as cumulative frequency distribution (CFD) and probability density function (PDF) are generated with particle tracking for the river networks of the five WLTC catchment outflows. Then, PDFs are used in the convolution integral with tritium concentration time series obtained in the precipitation. The resulting MODPATH tritium concentrations yield a very good match to measured tritium concentrations and are similar to the MT3DMS simulated tritium concentrations, with the greatest variation occurring around the bomb peak. MODPATH and MT3DMS also yield similar Mean Transit Times (MTT) of groundwater contribution to river baseflows, but the actual shape of the TTDs is strikingly different. While both distributions provide valuable information, the methodologies used to derive the TTDs are fundamentally different and hence must be interpreted differently. With the current models setting, only the methodology used with MODPATH provides the true TTD for use with the convolution integral.

scholarly journals Simulation of past variability in seasonal snow in the Southern Alps, New Zealand

1995 ◽  
Vol 21 ◽  
pp. 377-382 ◽  
Author(s):  
B.B. Fitzharris ◽  
C.E. Garr
Keyword(s):  
New Zealand ◽  
Southern Alps ◽  
Model Output ◽  
Total Water ◽  
Seasonal Snow ◽  
Temperature And Precipitation ◽  
Major River ◽  
River Catchments ◽  
Snow Deposition

There are no systematic measurements of seasonal snow in the Southern Alps, New Zealand, so little information is available as to its past variability. To rectify this, a conceptual model is developed that calculates seasonal snow deposition, ablation and accumulation. The model is based on daily temperature and precipitation data from long-established climate stations about the Southern Alps. Output is given as daily specific net balance of snow at five elevation bands from 1000 to 2200 m and as total water stored as seasonal snow over several major river catchments. Model output is in general agreement when tested against the few historical observations of snow and is tuned to the long-term water balance. A chronology of seasonal snow is reconstructed from 1931 to 1993. Area-averaged annual maxima average 366 mm. They show no trend, but large inter-annual variability from less than 200 to over 650 mm w.e. Seasonal snow can peak at any time between September and January.

The Ecology and Management of Wood in World Rivers

2003 ◽  
Keyword(s):  
Land Use ◽  
Land Use Changes ◽  
Livestock Grazing ◽  
Wood Structures ◽  
Groundwater Levels ◽  
Stream Discharge ◽  
Small Streams ◽  
World Rivers ◽  
Beaver Dams ◽  
Stream Systems

<em>Abstract.</em>—Beaver dams alter the hydrology and geomorphology of stream systems and affect habitat for fishes. Beaver dams measurably affect the rates of groundwater recharge and stream discharge, retain enough sediment to cause measurable changes in valley floor morphology, and generally enhance stream habitat quality for many fishes. Historically, beaver dams were numerous in small streams throughout most of the Northern Hemisphere. The cumulative loss of millions of beaver dams has dramatically affected the hydrology and sediment dynamics of stream systems. Assessing the cumulative hydrologic and geomorphic effects of depleting these millions of wood structures from small and medium-sized streams is urgently needed. This is particularly important in semiarid climates, where the widespread removal of beaver dams may have exacerbated effects of other land use changes, such as livestock grazing, to accelerate incision and the subsequent lowering of groundwater levels and drying of streams.

Numerical simulation of transient groundwater age distributions assisting land and water management in the Middle Wairarapa Valley, New Zealand

2016 ◽  
Vol 52 (12) ◽  
pp. 9430-9451 ◽  
Author(s):  
Michael W. Toews ◽  
Christopher J. Daughney ◽  
Fabien J. Cornaton ◽  
Uwe Morgenstern ◽  
Ryan D. Evison ◽  
...  
Keyword(s):  
Water Management ◽  
Numerical Simulation ◽  
New Zealand ◽  
Groundwater Age ◽  
Land And Water Management

scholarly journals Simulation of past variability in seasonal snow in the Southern Alps, New Zealand

1995 ◽  
Vol 21 ◽  
pp. 377-382 ◽  
Author(s):  
B.B. Fitzharris ◽  
C.E. Garr
Keyword(s):  
New Zealand ◽  
Southern Alps ◽  
Model Output ◽  
Total Water ◽  
Seasonal Snow ◽  
Temperature And Precipitation ◽  
Major River ◽  
River Catchments ◽  
Snow Deposition

There are no systematic measurements of seasonal snow in the Southern Alps, New Zealand, so little information is available as to its past variability. To rectify this, a conceptual model is developed that calculates seasonal snow deposition, ablation and accumulation. The model is based on daily temperature and precipitation data from long-established climate stations about the Southern Alps. Output is given as daily specific net balance of snow at five elevation bands from 1000 to 2200 m and as total water stored as seasonal snow over several major river catchments. Model output is in general agreement when tested against the few historical observations of snow and is tuned to the long-term water balance. A chronology of seasonal snow is reconstructed from 1931 to 1993. Area-averaged annual maxima average 366 mm. They show no trend, but large inter-annual variability from less than 200 to over 650 mm w.e. Seasonal snow can peak at any time between September and January.

Geochemical processes affecting the major ion composition of rivers in the South Island, New Zealand

1999 ◽  
Vol 50 (7) ◽  
pp. 699 ◽  
Author(s):  
Jonathan P. Kim ◽  
Keith A. Hunter ◽  
Malcolm R. Reid
Keyword(s):  
New Zealand ◽  
River Water ◽  
Major Ions ◽  
Geochemical Processes ◽  
Ion Composition ◽  
The South ◽  
Atmospheric Input ◽  
Geochemical Model ◽  
River Waters ◽  
Major Ion

The major ion (Na+ , K+ , Mg2+ , Ca2+ , Cl− , SO42− and reactive SiO2 ) compositions of seven rivers in the South Island, New Zealand (Manuherikia, Clutha, Takaka–Cobb, Haast, Grey, Aorere and Rakaia rivers) are reported. All the rivers were pristine in comparison with global average river waters, and the concentrations of most major ions were close to the 1% percentile levels for global river water compositions. A geochemical model that attributes ion compositions to both rain input and to the weathering of various simple mineral types in the catchment was applied to these data, and to data already published. This model, although simplistic, accounts for the main features of major ion composition in the rivers studied. The dominant sources of major ions were the weathering of limestones and feldspars. Atmospheric input was relatively small except for Na+ and Cl− .

scholarly journals Halon-1301 – further evidence of its performance as an age tracer in New Zealand groundwater

2017 ◽  
Vol 21 (8) ◽  
pp. 4213-4231 ◽  
Author(s):  
Monique Beyer ◽  
Uwe Morgenstern ◽  
Rob van der Raaij ◽  
Heather Martindale
Keyword(s):  
New Zealand ◽  
Groundwater Age ◽  
Contaminated Sites ◽  
Mixing Models ◽  
Residence Times ◽  
Halon 1301 ◽  
Groundwater Environment ◽  
Groundwater Samples ◽  
Mean Residence Times ◽  
Insight Into

Abstract. We recently discovered a new groundwater age tracer, Halon-1301, which can be used to date groundwater recharged after the 1970s. In a previous study, we showed that Halon-1301 reliably inferred groundwater age at the majority of groundwater sites studied. At those sites, ages inferred from Halon-1301 agreed with those inferred from SF6 and tritium, two reliable widely applied groundwater age tracers. A few samples, however, showed reduced concentrations of Halon-1301, preventing meaningful age interpretation from its concentration. These reduced concentrations were likely a result of degradation or retardation of Halon-1301 in the aquifer. However, we could not provide full evidence for this due to the limited number of groundwater samples analysed (18 in total). In this study, we assess the potential of Halon-1301 as a groundwater age tracer for a larger dataset of groundwater samples under specific groundwater conditions, including highly anoxic young groundwater which can significantly degrade Halon-1301, to gain more information on the magnitude of occurrence and the causes of reduced Halon-1301 concentrations. In this study, we analysed 302 groundwater samples for Halon-1301, SF6, tritium and the CFCs CFC-11, CFC-12 and CFC-113. Comparison of age information inferred from the concentrations of these tracers allows assessment of the performance of Halon-1301 compared to other well established and widely used age tracers. The samples are taken from different groundwater environments in New Zealand and include anoxic and oxic waters with mean residence times ranging from < 2 years to over 150 years (tritium-free). The majority of assessed samples have reduced or elevated concentrations of CFCs, which makes it impossible to infer a reliable age using the CFCs for these samples. Halon-1301, however, reliably infers ages for CFC-contaminated waters. Three other groundwater samples were found to have elevated SF6 concentrations (contaminated). Again, at these SF6-contaminated sites, ages inferred from Halon-1301 agree with ages inferred from tritium. A few samples (14 sites) exhibit reduced concentrations of Halon-1301, which result in elevated inferred Halon-1301 ages in comparison to those inferred from SF6, tritium and/or CFC-113. Assessment of the groundwater environment at these sites gives further insight into the potential causes of Halon-1301 reduction in groundwater. Overall, Halon-1301 gives age information that matches ages inferred from SF6 and/or tritium for the majority (97 %) of the assessed groundwater sites. These findings suggest that Halon-1301 is a reasonably reliable groundwater age tracer, and is in particular significantly more reliable than the CFCs, which may have contamination and degradation problems. Halon-1301 thus has potential to become a useful groundwater age tracer where SF6 and the CFCs are compromised, and where additional independent tracers are needed to constrain complex mixing models.

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