Regional Council, New Zealand
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Mohssen M.,Lincoln University at Christchurch | Goldsmith M.,Otago Regional Council
International Journal of Safety and Security Engineering | Year: 2011

A new concept for fl ood modelling of lake levels has been introduced, analysed, and tested for Lake Wakatipu in the South Island of New Zealand. Lake level response to signifi cant rainfall events is substantially different from rivers. Lakes usually have enormous storage to absorb the peak of the fl ood event, and their outfl ows are dependent on their level rather than the infl ows. The new concept is based on carrying out a lagged correlation analysis between hourly data for the cumulative rainfall and the total rise of the lake level in order to determine the lagged time series of total lake rise which will provide the best projection for its forecast onto the cumulative rainfall. The focus has been to carry out this analysis on hourly data during signifi cant rainfall events which resulted in signifi cant lake rise. In return, the time frame for such analysis is usually several hours or few days, as is the case for Lake Wakatipu. Thus, some variables which are usually considered for lake analysis, such as evapotranspiration, can be negligible compared with the huge amount of rain causing the fl ood event. Based on the best lagged correlation, three models have been derived to forecast fl ood levels of Lake Wakatipu. Correlation analysis of lagged correlations showed that a lag of 11 hours results in the highest correlation between cumulative rainfall and total rise of Lake Wakatipu level, while 14 hours produced the highest correlation between cumulative rainfall and total lake infl ows. All three models utilised these optimum lagged hours for the best projection of total lake rise/infl ow. The fi rst model is a lag-11 non-linear regression model, while the second model is a lag-11 linear regression model, and the third one is a lag-14 comprehensive hourly mass balance model. The results of model testing showed that the simple linear regression model produced the best forecasts, while the more sophisticated complete mass balance model, in general, was not as good, and the non-linear regression model (while having the highest determination coeffi cient) was the least performing. © 2011 WIT Press.

David B.O.,Environment Waikato | Hamer M.P.,Environment Waikato | Collier K.J.,Environment Waikato | Collier K.J.,University of Waikato | And 5 more authors.
New Zealand Journal of Marine and Freshwater Research | Year: 2010

The New Zealand fish fauna contains species that are affected not only by river system connectivity, but also by catchment and local-scale changes in landcover, water quality and habitat quality. Consequently, native fish have potential as multi-scale bioindicators of human pressure on stream ecosystems, yet no standardised, repeatable and scientifically defensible methods currently exist for effectively quantifying their abundance or diversity in New Zealand stream reaches. Here we report on the testing of a back-pack electrofishing method, modified from that used by the United States Environmental Protection Agency, on a wide variety of wadeable stream reaches throughout New Zealand. Seventy-three first- to third-order stream reaches were fished with a single pass over 150-345m length. Time taken to sample a reach using single-pass electrofishing ranged from 1-8 h. Species accumulation curves indicated that, irrespective of location, continuous sampling of 150 stream metres is required to accurately describe reach-scale fish species richness using this approach. Additional species detection beyond 150m was rare (<10%) with a single additional species detected at only two out of the 17 reaches sampled beyond this distance. Apositive relationship was also evident between species detection and area fished, although stream length rather than area appeared to be the better predictor. The method tested provides a standardised and repeatable approach for regional and/or national reporting on the state of New Zealand's freshwater fish communities and trends in richness and abundance over time.

McDowell R.W.,Agresearch Ltd. | Kitto J.A.,Otago Regional Council | Kitto J.A.,Canterbury Agriculture and Science Center
New Zealand Journal of Agricultural Research | Year: 2013

An average of 16 years' data at sites in the upper Taireri River catchment was used to determine if water quality had changed commensurate with an increase in the irrigated area and land-use change. To help remediate perceived gaps in the nutrient modelling software Overseer®, data was also collected from a low-intensity border dyke and high-intensity spray-irrigated property. Filterable reactive phosphorus concentrations increased over time and were attributed to the irrigation of poor anion storage capacity (ASC) soils and irrigation-return flows. Differences were noted between measured nitrogen and phosphorus loads and those predicted by Overseer®, which were attributed to a combination of low ASC soils, spray irrigation and artificially drained soils receiving effluent. These data will be used to calibrate future versions of Overseer®. However, with an increase in spray irrigation and land-use change forecast for the catchment, strategies should be employed to mitigate further water quality deterioration. © 2013 The Royal Society of New Zealand.

Shearer K.A.,Cawthron Institute | Hayes J.W.,Cawthron Institute | Jowett I.G.,Jowett Consulting Ltd | Olsen D.A.,Otago Regional Council
New Zealand Journal of Marine and Freshwater Research | Year: 2015

We developed habitat suitability curves (HSC) using generalised additive models (GAMs) for nine benthic macroinvertebrate taxa from a small New Zealand river for hydraulic-habitat modelling assessments of instream flow requirements. We included interaction terms between the primary variables (water depth, velocity, substrate) when significant, to address a longstanding criticism of univariate HSC. To date, only large-river univariate HSC have been available and these have been used in hydraulic-habitat applications on small rivers, despite doubt over the transferability of HSC between rivers of different size and type. We tested the outcome on the predicted abundance-flow relationship of applying the small-river habitat suitability GAMs versus large-river GAMs for two taxa on the same small river. We found the effects of flow allocation were overestimated by the large-river GAMs relative to the small-river GAMs. Further research to develop general HSC for categories of river size and type is needed to better inform hydraulic-habitat modelling applications. © 2015 The Royal Society of New Zealand.

McDowell R.W.,Agresearch Ltd. | Snelder T.,NIWA - National Institute of Water and Atmospheric Research | Littlejohn R.,Agresearch Ltd. | Hickey M.,Otago Regional Council | And 2 more authors.
Agriculture, Ecosystems and Environment | Year: 2011

Land use change and the expansion of dairying are perceived as the cause of poor water quality in the 1881km 2 Pomahaka catchment in Otago, New Zealand. A study was conducted to determine the longterm trend at four sites, and current state in 13 sub-catchments, of water quality. Drains in 2 dairy-farmed sub-catchments were also sampled to determine their potential as a point source of stream contamination. Data highlighted an overall increase in the concentration of phosphorus (P) fractions at long-term sites. Loads of contaminants (nitrogen (N) and P fractions, sediment and Escherichia coli) were greatest in those sub-catchments with the most dairying. Baseline (without human influence) contaminant concentrations suggested that there was considerable scope for decreasing losses. At most sites, baseline concentrations were <20% of current median concentrations. Contaminant losses via drainage were recorded despite there being no rainfall that day and attributed to applying too much effluent onto wet soil. Modelling of P concentrations in one dairy-farmed sub-catchment suggested that up to 58% of P losses came from point sources, like bad effluent practice and stock access to streams. A statistical test to detect "contaminated" drainage was developed from historical data. If this test had been applied to remove contaminated drainage from samples of the two dairy-farmed sub-catchments, median contaminant concentrations and loads would have decreased by up to 58% (greater decreases were found for E. coli, ammoniacal-N and total P than other contaminants). This suggests that better uptake of strategies to mitigate contamination, such as deferred effluent irrigation (and low rate application), could decrease drainage losses from dairy-farmed land and thereby improve water quality in the Pomahaka catchment. © 2011 Elsevier B.V.

Hannah P.,Otago Regional Council
Journal of Hydrology | Year: 2014

Acoustic Doppler Current Profilers (ADCPs) differ from traditional propeller current meters largely in the flexibility of the way they can be deployed in the field during flood events. Otago Regional Council (ORC) now uses four methods to deploy ADCPs for flood flow measurements, including mounted on the side of a jet boat, towed from a bridge by hand, towed from a fixed or portable cableway and, more recently, towed by a helicopter. The helicopter tow method was developed and trialed by ORC in April 2012. For flood flow measurement ORC uses an ADCP mounted inside a modified white water kayak hull. Of the four deployment methods, the heli-gauging method has proven to be the most beneficial during large flood events in the Otago Region. Since then the heli-gauging method has been utilized by ORC to conduct flow gaugings during two large flood events with a high level of success. A case study of a two day heli-gauging run is used to outline why the heli-gauging method has proven to be a cost effective, highly efficient and accurate method of collecting flow information which is not affected by poor access and flooded access roads. © New Zealand Hydrological Society.

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