Water resources in autumn 2004 (March to May 2004)
River flow
River flows for autumn were generally near normal. While parts of the Waikato produced higher flows than usual for the time of year, both Wellington/Wairarapa and Southland had much lower flows than usual, as a result of continuing low rainfalls. The average river flows for the season are a mix of generally low flows in March and April, and higher flows in May. Autumn 2004 was notable for the sustained dry weather over much of the country in March and April, after an extremely wet month of February. |
Lake levels
Most of the monitored lakes were at or above their normal levels for autumn. Lakes Taupo, Ohau, and Brunner were especially high. For many lakes, the levels are a reflection of recent weather. However, for lakes that are managed for hydro-electric power generation or irrigation, the levels also depend on how the lake is managed. For example, water can be stored when inflows are large, and released later, when demand is greatest. Exactly how this is done depends on the timing of the inflows, the patterns of demand for water, and the operating rules for managed lakes. |
|
Water clarity
Stream water clarity in autumn was normal or slightly above normal in many parts of New Zealand, but there were some significant regional variations. Streams in the Gisborne, Hawke’s Bay and Tasman regions were significantly clearer than usual for this time of year, while some streams in Waikato, Canterbury and Otago had rather lower clarity than usual. |
Slime index
The slime index records the cover of the bed by 'nuisance' slimes (thick algal mats or filamentous growths) that reduce the recreational and aesthetic value of the river if cover exceeds 30–60%. Maximum values over autumn were typically no more than 20% over much of the country, which is about normal for the time of year. However, several sites in the central North Island reported the highest values ever recorded at this time of year, because of the prolonged stable flows in March and April. |
|
Water temperatures
Stream temperatures were typically 1 °C cooler than normal in Northland, Waikato, Manawatu, Wellington, Buller, Otago, and Southland. Temperatures in most other places were near normal. |
Groundwater
Groundwater levels in all regions except eastern South Island are similar to, or higher than, levels in the historical record. Eastern South Island groundwater levels are generally below the seasonal average, but some aquifers have levels that are average, or high, for the time of year. High groundwater levels in western North Island reflect the high rainfall in February. |