Snelder T.H.,LWP Ltd |
McDowell R.W.,Agresearch Ltd. |
Fraser C.E.,Aqualinc Research Ltd
Journal of the American Water Resources Association | Year: 2017
Causes of variation between loads estimated using alternative calculation methods and their repeatability were investigated using 20 years of daily flow and monthly concentration samples for 77 rivers in New Zealand. Loads of dissolved and total nitrogen and phosphorus were calculated using the Ratio, L5, and L7 methods. Estimates of loads and their precision associated with short-term records of 5, 10, and 15 years were simulated by subsampling. The representativeness of the short-term loads was quantified as the standard deviation of the 20 realizations. The L7 method generally produced more realistic loads with the highest precision and representativeness. Differences between load estimates were shown to be associated with poor agreement between the data and the underlying model. The best method was shown to depend on the match between the model and functional and distributional characteristics of the data, rather than on the contaminant. Short-term load estimates poorly represented the long-term load estimate, and deviations frequently exceeded estimated imprecision. The results highlight there is no single preferred load calculation method, the inadvisability of “unsupervised” load estimation and the importance of inspecting concentration-flow, unit load-flow plots and regression residuals. Regulatory authorities should be aware that the precision of loads estimated from monthly data are likely to be “optimistic” with respect to the actual repeatability of load estimates. © 2016 American Water Resources Association
Booker D.J.,NIWA - National Institute of Water and Atmospheric Research |
Snelder T.H.,Aqualinc Research Ltd |
Greenwood M.J.,NIWA - National Institute of Water and Atmospheric Research |
Crow S.K.,NIWA - National Institute of Water and Atmospheric Research
Ecohydrology | Year: 2015
Robust relationships between biological characteristics and hydrological indices are required to provide a quantitative basis for environmental flows. Data from 1075 river sites distributed across New Zealand were used to investigate relationships between invertebrate communities and flow regimes, whilst also including the influence of additional environmental factors. Variance decomposition analysis was used to investigate the proportion of variance explained by hydrological, geomorphological, land cover, and catchment characteristics for the community matrix and each of three biotic indices representing taxon richness, Macroinvertebrate Community Index, and percentage of species in the Ephemeroptera, Plecoptera, and Trichoptera orders. Results showed that hydrological regime contributes a unique component to the explainable variation in the community, but this contribution is overestimated if other explanatory factors are not considered. A gradient forest model comprised of 93 random forest models, each predicting the probability of occurrence of a taxon, indicated the importance of high flows and also other dimensions of hydrological variation for predicting invertebrate taxa and biotic indices. Although many freshwater invertebrates in New Zealand are well adapted to a range of flow conditions through resistance traits and/or rapid colonization, this study suggests that several aspects of the flow regime influence invertebrate communities. These results suggest that environmental flows may be designed to sustain or even optimize specific ecological attributes or taxa, but changes along several dimensions of hydrological variability are likely to disadvantage other taxa and change invertebrate community composition. © 2014 John Wiley & Sons, Ltd.
The role of science in setting water resource use limits: Case studies from New Zealand [Le rôle de la science dans létablissement de limites dutilisation des ressources en eau: Une étude de cas en Nouvelle-Zélande]
Snelder T.H.,NIWA - National Institute of Water and Atmospheric Research |
Snelder T.H.,Aqualinc Research Ltd |
Rouse H.L.,NIWA - National Institute of Water and Atmospheric Research |
Franklin P.A.,NIWA - National Institute of Water and Atmospheric Research |
And 3 more authors.
Hydrological Sciences Journal | Year: 2014
Water resource use limits ensure protection of environmental values and define the availability and reliability of water supply for out-of-channel use. We examined how three types of scientific tools (environmental flow setting methods, hydrological analyses for setting total allocations and spatial frameworks) have been used to define limits across jurisdictional regions comprising multiple catchments in New Zealand. We found that recently developed minimum flow and total allocation setting tools are widely used. Spatial frameworks are increasingly used to discriminate and account for variation in environmental characteristics, thereby increasing the specificity of water resource use limits. The uptake of scientific tools has enabled improvements in the clarity of water management objectives and the transparency of limits defined by regional water management plans. We argue that more integrated use of scientific tools could improve the clarity and transparency of regional limits by explicitly demonstrating the trade-off between out-of-channel use and protection of environmental values. Editor D. Koutsoyiannis; Guest editor M. AcremanCitation Snelder, T.H., Rouse, H.L., Franklin, P.A., Booker, D.J., Norton, N., and Diettrich, J., 2014. The role of science in setting water resource use limits: case studies from New Zealand. Hydrological Sciences Journal, 59 (3-4), 844-859. © 2014 © 2014 IAHS Press.
Penas F.J.,University of Cantabria |
Barquin J.,University of Cantabria |
Snelder T.H.,Aqualinc Research Ltd |
Booker D.J.,NIWA - National Institute of Water and Atmospheric Research |
Alvarez C.,University of Cantabria
Hydrology and Earth System Sciences | Year: 2014
Hydrological classification has emerged as a suitable procedure to disentangle the inherent hydrological complexity of river networks. This practice has contributed to determining key biophysical relations in fluvial ecosystems and the effects of flow modification. Thus, a plethora of classification approaches, which agreed in general concepts and methods but differed largely in specific procedures, have emerged in the last decades. However, few studies have compared the implication of applying contrasting approaches and specifications over the same hydrological data. In this work, using cluster analysis and modelling approaches, we classify the entire river network covering the northern third of the Iberian Peninsula. Specifically, we developed classifications of increasing level of detail, ranging from 2 to 20 class levels, either based on raw and normalized daily flow series and using two contrasting approaches to determine class membership: classify-then-predict (ClasF) and predict-then-classify (PredF). Classifications were compared in terms of their statistical strength, the hydrological interpretation, the ability to reduce the bias associated with underrepresented parts of the hydrological space and their spatial correspondnece. The results highlighted that both the data processing and the classification strategy largely influenced the classification outcomes and properties, although differences among procedures were not always statistically significant. The normalization of flow data removed the influence of flow magnitude and generated more complex classifications in which a wider range of hydrologic characteristics were considered. The application of the PredF strategy produced, in most of the cases, classifications with higher discrimination ability and presented greater ability to deal with the presence of distinctive gauges in the data set than using the ClasF strategy. © Author(s) 2014.
Fraser C.E.,Aqualinc Research Ltd. |
Mcintyre N.,Imperial College London |
Mcintyre N.,University of Queensland |
Jackson B.M.,Victoria University of Wellington |
And 2 more authors.
Water Resources Research | Year: 2013
Metamodeling uses computationally efficient models to emulate the outputs of complex models, trading off computational time against prediction accuracy and/or precision. Although potentially powerful, there is limited understanding of the uncertainty introduced by the metamodeling procedure. In particular, the errors associated with transformations of the predictions, such as aggregations during upscaling or differences between results used for impacts analysis, have not been explored in the metamodeling literature. We present an application of metamodeling that upscales physics-based model predictions to make catchment scale predictions of land management change impacts on peak flows. Two parallel sets of simulations are conducted, one with the original physics-based models and the other with metamodels. Despite good performance in emulating the local scale physics-based model simulations, once incorporated into a catchment scale model and especially once impacts of change are calculated, errors associated with the metamodeling procedure alone become significant, accounting for almost half of the prediction uncertainty in peak flows. The additional (metamodel-contributed) uncertainty is introduced both through biases in peak flows and through increases in peak flow variance. In the context of land management impacts, the results demonstrate the importance of tracking propagation of errors during upscaling, and of evaluating a model's ability to predict change, as well as independent observations. Despite these errors, the predictions of land management impacts from both physics-based models and metamodels are broadly consistent between each other, and in accordance with expectations from the literature. Key Points Metamodelling used to predict impacts of land use change Metamodelling significantly reduces computational time Metamodel errors increase when transformations on the predictions are performed ©2013. American Geophysical Union. All Rights Reserved.
Burbery L.F.,Institute of Environmental Science and Research |
Burbery L.F.,Y Ventures |
Flintoft M.J.,Institute of Environmental Science and Research |
Flintoft M.J.,Aqualinc Research Ltd |
Close M.E.,Institute of Environmental Science and Research
Journal of Contaminant Hydrology | Year: 2013
Five re-circulating tracer well tests (RCTWTs) have been conducted in a variety of aquifer settings, at four sites across New Zealand. The tests constitute the first practical assessment of the two-well RCTWT methodology described by Burbery and Wang (Journal of Hydrology, 2010; 382:163-173) and were aimed at evaluating nitrate reaction rates in situ. The performance of the RCTWTs differed significantly at the different sites. The RCTWT method performed well when it was applied to determine potential nitrate reaction rates in anoxic, electro-chemically reductive, nitrate-free aquifers of volcanic lithology, on the North Island, New Zealand. Regional groundwater flow was not fast-flowing in this setting. An effective first-order nitrate reaction rate in the region of 0.09 d- 1 to 0.26 d- 1 was determined from two RCTWTs applied at one site where a reaction rate of 0.37 d- 1 had previously been estimated from a push-pull test. The RCTWT method performed poorly, however, in a fast-flowing, nitrate-impacted fluvio-glacial gravel aquifer that was examined on the South Island, New Zealand. This setting was more akin to the hypothetical physiochemical problem described by Burbery and Wang (2010). Although aerobic conditions were identified as the primary reason for failure to measure any nitrate reaction in the gravel aquifer, failure to establish significant interflow in the re-circulation cell due to the heterogeneous nature of the aquifer structure, and natural variability exhibited in nitrate contaminant levels of the ambient groundwater further contributed to the poor performance of the test. Our findings suggest that in practice, environmental conditions are more complex than assumed by the RCTWT methodology, which compromises the practicability of the method as one for determining attenuation rates in groundwater based on tracing ambient contaminant levels. Although limited, there appears to be a scope for RCTWTs to provide useful information on potential attenuation rates when reactants are supplemented to the aquifer system under examination. © 2012 Elsevier B.V. All rights reserved.
Ballard C.E.,Imperial College London |
Ballard C.E.,Aqualinc Research Ltd |
McIntyre N.,Imperial College London |
Wheater H.S.,Imperial College London |
Wheater H.S.,University of Saskatchewan
Hydrology and Earth System Sciences | Year: 2012
Open ditch drainage has historically been a common land management practice in upland blanket peats, particularly in the UK. However, peatland drainage is now generally considered to have adverse effects on the upland environment, including increased peak flows. As a result, drain blocking has become a common management strategy in the UK over recent years, although there is only anecdotal evidence to suggest that this might decrease peak flows. The change in the hydrological regime associated with the drainage of blanket peat and the subsequent blocking of drains is poorly understood, therefore a new physics-based model has been developed that allows the exploration of the associated hydrological processes. A series of simulations is used to explore the response of intact, drained and blocked drain sites at field scales. While drainage is generally found to increase peak flows, the effect of drain blocking appears to be dependent on local conditions, sometimes decreasing and sometimes increasing peak flows. Based on insights from these simulations we identify steep smooth drains as those that would experience the greatest reduction in field-scale peak flows if blocked and recommend that future targeted field studies should be focused on examining surface runoff characteristics. © 2012 Author(s). CC Attribution 3.0 License.
Wohling T.,Lincoln Ventures Ltd. |
Wohling T.,University of Tübingen |
Bidwell V.J.,17 Brookside Road |
Barkle G.F.,Aqualinc Research Ltd.
Journal of Contaminant Hydrology | Year: 2012
A model is presented for simulating one-dimensional advective dispersive solute transport in the vadose zone. The finite-volume, mixing-cell model uses drainage flux intervals as the index variable, which are calculated by a soil water balance model. The modelling approach considers solute transport from two different regions as well as a slow and a fast transport domain in each region as parallel transport processes. The model is applied to breakthrough curves of Cl- and Br- measured at different locations and different depths in the volcanic vadose zone of the Tutaeuaua subcatchment of Lake Taupo, New Zealand, following a dual tracer application. Estimates of transport parameter and model predictive uncertainty were derived using the differential evolution adaptive metropolis, DREAMZS adaptive Markov chain Monte Carlo algorithm, a formal Bayesian likelihood function, observed leachate volumes, and Cl- breakthrough curves. The model was subsequently evaluated using Br- breakthrough curves from the dual tracer experiment and a previously conducted Br- tracer-only experiment. Uncertainty bounds derived by this MCMC method simultaneously capture the observed Br- and Cl- breakthrough curves and corresponding drainage volumes. Results suggest that the slow transport domain properties are relatively similar for different locations in the vadose zone and that the variability in contaminant fluxes is predominantly driven by structural variability of the vadose zone causing lateral flow. © 2012 Elsevier B.V.
Barkle G.F.,Aqualinc Research Ltd |
Wohling T.,Lincoln Ventures Ltd. |
Stenger R.,Lincoln Ventures Ltd. |
Mertens J.,LABORELEC |
And 3 more authors.
Vadose Zone Journal | Year: 2011
In this technical note we present the design, installation, and evaluation of a field monitoring system to directly measure water fluxes through a vadose zone. The system is based on use of relatively new measurement technology-automated equilibrium tension lysimeters (AETLs). An AETL uses a porous sintered stainless-steel plate to provide a comparatively large sampling area (0.20 m 2) with a continuously controlled vacuum applied under the plate. This vacuum is in "equilibrium" with the surrounding vadose zone tension to ensure measured fluxes represent those under undisturbed conditions. Fifteen of these AETLs have been installed at five depths through a layered volcanic vadose zone to study the impact of land use changes on water quality in Lake Taupo, New Zealand. We describe the development and testing of the AETLs, the methods used for installing these devices, a condensed data set of the measured physical properties of the vadose zone, and the initial results from the in situ operation of the AETLs, including the preliminary results from a bromide tracer test. For an AETL installed at the 0.4-m depth, where soil pressure heads are most dynamic, the average deviation between the target reference pressure head, as measured in the undisturbed vadose zone and the pressure head measured above the sampling plate was only 5.4 hPa over a 180-d period. The bromide recovered in an AETL at the same depth was equivalent to 96% of the bromide pulse applied onto the surface area directly above the AETL. We conclude that this measurement technique provides an accurate and robust method of measuring vadose zone fluxes. These measurements can ultimately contribute to bett er understanding of the water transport and contaminant transformation processes through vadose zones. © Soil Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved.
Brown P.D.,Aqualinc Research Ltd. |
Cochrane T.A.,University of Canterbury |
Krom T.D.,Touchwater Ltd.
Agricultural Water Management | Year: 2010
As water resources are limited and the demand for agricultural products increases, it becomes increasingly important to use irrigation water optimally. At a farm scale, farmer's have a particularly strong incentive to optimize their irrigation water use when the volume of water available over a season is production limiting. In this situation, a farmer's goal is to maximize farm profit, by adjusting when and where irrigation water is used. However, making the very best decisions about when and where to irrigate is not easy, since these daily decisions require consideration of the entire remaining irrigation season. Future rainfall uncertainty further complicates decisions on when and which crops should be subjected to water stress. This paper presents an innovative on-farm irrigation scheduling decision support method called the Canterbury irrigation scheduler (CIS) that is suitable when seasonal water availability is limited. Previous optimal scheduling methods generally use stochastic dynamic programming, which requires over-simplistic plant models, limiting their practical usefulness. The CIS method improves on previous methods because it accommodates realistic plant models. Future farm profit (the objective function) is calculated using a time-series simulation model of the farm. Different irrigation management strategies are tested using the farm simulation model. The irrigation strategies are defined by a set of decision variables, and the decision variables are optimized using simulated annealing. The result of this optimization is an irrigation strategy that maximizes the expected future farm profit. This process is repeated several times during the irrigation season using the CIS method, and the optimal irrigation strategy is modified and improved using updated climate and soil moisture information. The ability of the CIS method to produce near optimal decisions was demonstrated by a comparison to previous stochastic dynamic programming schedulers. A second case study shows the CIS method can incorporate more realistic farm models than is possible when using stochastic dynamic programming. This case study used the FarmWi$e/APSIM model developed by CSIRO, Australia. Results show that when seasonal water limit is the primary constraint on water availability, the CIS could increase pasture yield revenue in Canterbury (New Zealand) in the order of 10%, compared with scheduling irrigation using current state of the art scheduling practice. © 2010 Elsevier B.V. All rights reserved.