A small stream in a predominantly dairying catchment in the Waikato region of New Zealand was monitored for 2 years at three sites. Total nitrogen (TN) concentrations were up to 7.09 g m -3in winter, with the bulk comprising nitrate nitrogen (NO -3 -N). During summer NO -3 -N was near zero and TN mostly comprised organic nitrogen. Maximum concentrations of total phosphorus (TP) and dissolved reactive phosphorus (DRP) were 1.64 and 0.555 g m -3 , respectively, and peaks coincided with spring and autumn applications of phosphorus fertiliser. Ammoniacal nitrogen concentrations exceeded 1 g m -3 on several occasions and mean concentrations at the three sites were 0.165-0.272 g m -3 . Faecal coliform and enterococci bacteria concentrations were 64-26000 and 7-23000 cfuper 100 Received 23 March 1999; accepted 23 June 1999 ml, respectively. Specific yields of TN and NO -3 -N (35.3 and 30.7 kg ha yr -1 , respectively) were much greater than any previously reported for New Zealand pasture catchments, whereas TP and DRP yields (1.16 and 0.54 kg ha yr -1 , respectively) were more in accord with other studies. Greater use of land treatment of liquid wastes will reduce stream inputs of faecal organisms, NH 4 -N and P. M99015

The potential impacts of climate change and socio-economic change on flow and water quality in rivers worldwide is a key area of interest.

A flood risk model was developed for the Czech Republic to calculate the probability of insured losses from flood events. The model was GIS based, making use of a 100 m horizontal resolution DTM and a network of the major rivers in the country. A review of historical flooding was undertaken to define the worst and most widespread flood events. Synthetic flood events were generated based on a study of the spatial variation in magnitude of river flows from selected historical flood events going back to 1935. A total of 30 synthetic events were generated each providing peak flows at 25 gauging stations throughout the country. The flows were converted into flood levels using rating equations based on information provided by the Czech Hydrological and Meteorological Institute. The extent of and depth of flooding was mapped on a cell by cell basis by applying an automated procedure developed using the grid option within the Arc/Info GIS. The flood depths were combined with maps of the postal codes to define an average flood depth per post code. The model was calibrated using maps of the observed flood extents from 1997 and 2002.

Abstract. The problem of soil erosion is particularly evident in New Zealand, given the combination of coarse‐textured soils, steep relief, high rainfall, and intensification of agriculture. A study was undertaken to assess the effects of land use change on soil erosion and sediment transport for the Ngongotaha catchment in New Zealand's North Island, using a GIS based decision support and modelling system. Model simulations considered the effect of increased catchment area under deer farming and forestry on the amount of sediment delivered to the catchment outlet, averaged over a period of six years. The simulations predicted that sediment loss from land under deer farming was considerably greater than from land under other livestock or forestry. Further model simulations testing best management practices demonstrated that sediment yield could be halved if deer farming was restricted to slopes under 20%.

No abstract