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Napier, New Zealand

Baalousha H.M.,Hawkes Bay Regional Council
Journal of Hydrology | Year: 2012

This study derives two dimensional analytical solutions for drawdown and stream depletion resulting from a pumping well near a stream. The solutions were obtained for both line-width and finite-width streams in unconfined/confined aquifers, based on the principle of superposition. These solutions are general enough to be used for different hydrogeological settings within both unconfined and confined aquifers. Results of analytical solutions for both drawdown and stream depletion were checked against results obtained using numerical models for confined/unconfined aquifer. It has been found that both line-width and finite-width stream depletion results are close to numerical results, but the finite-width stream solution has less error. Drawdown results show that the line-width stream solution slightly over-estimates the drawdown, and the finite-width stream solution has a good match with the numerical drawdown results. The error in drawdown results is directly proportional to the increase in stream width, but is higher in the case of a line-width stream. © 2012 Elsevier B.V. Source

O'Driscoll M.,East Carolina University | Johnson P.,Hawkes Bay Regional Council | Mallinson D.,East Carolina University
Hydrogeology Journal | Year: 2010

Channel sediment and alluvial aquifer hydraulic properties exert a major control on river-groundwater interactions. Channels and floodplains are often asymmetrical, resulting in differences in sediment hydraulic properties across the river. Floodplain asymmetry is common along Coastal Plain rivers in South Carolina and North Carolina, USA. The Tar River, North Carolina, has an asymmetrical valley. The study objective was to characterize the effects of floodplain asymmetry and geological controls on river-groundwater interactions. Floodplain and river channel sediments adjacent to the river were characterized with split spoon cores and hand auger samples along a 22-km reach. Hydrogeology was characterized with 38 piezometers and water level recorders in and adjacent to the river. Ground penetrating radar was used to define the shallow stratigraphy. Channel sediments were significantly different between the north and south sides of the river. Hydraulic conductivity and groundwater inputs were greater on the side of the river (north) that contained more permeable fluvial deposits. Groundwater chemistry (δ18O, specific conductance) data also suggested greater exchange between surface water and groundwater on the north side of the river channel. A conceptual hydrogeological model illustrates that groundwater movement and contaminant transport to the river differs across the channel due to asymmetrical geology. © 2010 Springer-Verlag. Source

Morgenstern U.,Institute of Geological & Nuclear Sciences | Daughney C.J.,Institute of Geological & Nuclear Sciences | Leonard G.,Institute of Geological & Nuclear Sciences | Gordon D.,Hawkes Bay Regional Council | And 3 more authors.
Hydrology and Earth System Sciences | Year: 2015

The water quality of Lake Rotorua has steadily declined over the past 50 years despite mitigation efforts over recent decades. Delayed response of the groundwater discharges to historic land-use intensification 50 years ago was the reason suggested by early tritium measurements, which indicated large transit times through the groundwater system. We use the isotopic and chemistry signature of the groundwater for detailed understanding of the origin, fate, flow pathways, lag times and future loads of contaminants. A unique set of high-quality tritium data over more than four decades, encompassing the time when the tritium spike from nuclear weapons testing moved through the groundwater system, allows us to determine detailed age distribution parameters of the water discharging into Lake Rotorua.

The Rotorua volcanic groundwater system is complicated due to the highly complex geology that has evolved through volcanic activity. Vertical and steeply inclined geological contacts preclude a simple flow model. The extent of the Lake Rotorua groundwater catchment is difficult to establish due to the deep water table in large areas, combined with inhomogeneous groundwater flow patterns.

Hierarchical cluster analysis of the water chemistry parameters provided evidence of the recharge source of the large springs near the lake shore, with discharge from the Mamaku ignimbrite through lake sediment layers. Groundwater chemistry and age data show clearly the source of nutrients that cause lake eutrophication, nitrate from agricultural activities and phosphate from geologic sources. With a naturally high phosphate load reaching the lake continuously via all streams, the only effective way to limit algae blooms and improve lake water quality in such environments is by limiting the nitrate load.

The groundwater in the Rotorua catchment, once it has passed through the soil zone, shows no further decrease in dissolved oxygen, indicating an absence of bioavailable electron donors along flow paths that could facilitate microbial denitrification reactions. Nitrate from land-use activities that leaches out of the root zone of agricultural land into the deeper part of the groundwater system must be expected to travel with the groundwater to the lake.

The old age and the highly mixed nature of the water discharges imply a very slow and lagged response of the streams and the lake to anthropogenic contaminants in the catchment, such as nitrate. Using the age distribution as deduced from tritium time series data measured in the stream discharges into the lake allows prediction of future nutrient loads from historic land-use activities 50 years ago. For Hamurana Stream, the largest stream to Lake Rotorua, it takes more than a hundred years for the groundwater-dominated stream discharge to adjust to changes in land-use activities. About half of the currently discharging water is still pristine old water, and after this old water is completely displaced by water affected by land use, the nitrogen load of Hamurana Stream will approximately double. These timescales apply to activities that cause contamination, but also to remediation action. © Author(s) 2015. Source

Greer M.J.C.,Environment Canterbury | Crow S.K.,NIWA - National Institute of Water and Atmospheric Research | Hicks A.S.,Hawkes Bay Regional Council | Closs G.P.,University of Otago
New Zealand Journal of Marine and Freshwater Research | Year: 2015

Sediment resuspension during and after mechanical excavation of macrophytes may have a significant impact on resident fish populations. Unfortunately, little is known about the influence of this sediment on the respiratory performance and feeding abilities of fishes in New Zealand waterways. We examined the effects of suspended sediment (SS) concentrations previously observed after a large-scale macrophyte removal operation on oxygen consumption (MO2) and feeding rates of brown trout (Salmo trutta). MO2 at 0 mg L-1, 150 mg L-1, 300 mg L-1, 450 mg L-1 and 600 mg L-1 of SS was measured using semi-closed respirometry. Feeding rates at the same SS concentrations were also measured using laboratory tank experiments. Results suggest that SS concentrations up to 600 mg L-1 have no effect on MO2. Conversely, feeding rates were significantly reduced at 450 mg L-1 (22% reduction) and 600 mg L-1 (31% reduction), indicating that sediment concentrations above 450 mg L-1 may negatively affect brown trout populations. © 2015 The Royal Society of New Zealand. Source

Baalousha H.M.,Hawkes Bay Regional Council
Environmental Earth Sciences | Year: 2012

Modelling groundwater and surface water is important for integrated water resources management, especially when interaction between the river and the aquifer is high. A transient groundwater and surface water flow model was built for Ruataniwha basin, New Zealand. The model covers a long-time period; starting in 1990, when water resources development in the area started, to present date. For a better resolution, the simulation period was divided into 59 stress periods, and each stress period was divided to 10 time steps. The model uses data obtained from surface water, and groundwater collected over the last 20 years. Rivers and streams were divided into 28 segments and flow and streambed data at the beginning and end of each segment was used. Parameter estimation and optimisation 'PEST' was used for automatic calibration of hydraulic conductivity, groundwater recharge and storativity; whereas riverbed conductance was manually calibrated. Model results show that the rivers gain from the aquifer considerably more than the river losses. The cumulative groundwater abstraction over the last 20 years is approximately 210 million m 3. This amount is very low compared to other water budget components; however, the effect of groundwater abstraction on storage is significant. Based on the results of this study, it was found that the loss of storage over the last 20 years is more than 66 million m 3. Results also reveal that the effect of groundwater abstraction on rivers and springs flow is significant. The rivers gain from the groundwater system, and the springs flow have been decreasing. © 2011 Springer-Verlag. Source

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