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Where the potential for future debris-flow occurrence is unrecognised, developments can be unknowingly exposed to debris-flow impact, with corresponding risks to lives. Debris-flow modelling is unsuited to routine local office use, so a simple screening procedure is proposed to enable local officials to identify locations where debris flow risk-to-life may be unacceptable, and prioritise where expert modelling and risk analysis are most urgently required for risk-management decision-making . This procedure calculates catchment Melton ratio R from topographic data, uses a linear upper bound of field data relating R to the annual probability of debris-flow occurrence, and matches a model-based debris-flow risk-to-life analysis for Matata, New Zealand. Our data suggest that any development exposed to debris flows will require a detailed risk assessment to ensure that risk-to-life does not exceed acceptable levels.

Debris flows are hazardous yet often unrecognised and poorly understood by the public and natural hazards community. Some catchments generate debris flows with average recurrence intervals (ARIs) <10 years, but most debris flow catchments have ARIs ranging from decades to millennia. Consequently, many debris flow catchments pose an underappreciated hazard, especially where there are dwellings on debris flow fans and other depositional areas. Here, we describe how to use simple and well-accepted methods to: Make a preliminary identification of catchments that are susceptible to debris flows. Estimate the threshold ARI for debris flows in a catchment below which there is an unacceptable annual risk to life for the occupiers of any dwellings. Identify the 'window of non-recognition' where debris flows are sufficiently infrequent within a catchment that it is not recognised as susceptible, yet frequent enough that the risk to life exceeds the accepted threshold. Explore the influence of the important parameters driving the annual risk to life from debris flows. We show that, given precautionary but realistic assumptions about debris flow hazards and the vulnerability of dwellings and their occupants, catchments with no history of debris flow activity can pose an unrecognised and unacceptable risk to life. [ABSTRACT FROM AUTHOR]

The Fundamental Soil Layers (FSL) serve historically as New Zealand's primary source of soil information. They contain a range of New Zealand's soil attribute information held in a spatial database. Despite their wide use in a range of applications, few direct assessments of the accuracy of FSL attribute information have been undertaken to date. This study aims to provide an assessment of the accuracy of the FSL by comparing observed data for Profile Available Water (PAW) and Potential Rooting Depth (PRD) with FSL estimates for these two attributes. Two datasets were used to conduct the tests. The first dataset (n = 35) contained measured observations for PAW and PRD. A second dataset (n=173) contained measured observations for PRD only. A regression model found a weak relationship between measured values and FSL estimates for PAW and PRD (correlations ranged from -0.08 to 0.17). Additional FSL estimates provided in the form of class intervals were tested by calculating the proportion of observed values within the specified FSL class interval. The effect of estimate lineage (underlying data and estimation method) on the accuracy of the class intervals was assessed using a logistic regression. Overall the FSL estimates for PRD and PAW were inaccurate, and allowance for data lineage did not improve the accuracy of the FSL estimates. Additional keywords: digital soil mapping, modelling, soil databases, soil physical properties, soil water, Received 15 January 2014, accepted 20 April 2015, published online 27 October 2015, Introduction The Fundamental Soil Layers (FSL) contain a range of New Zealand's soil attribute information within a Geographic Information System (GIS) accessible spatial database. The development of the FSL relied [...]

In New Zealand, a commonly sown pasture combination is perennial ryegrass with white clover. The hydrothermal time model (HTT) was used to quantify germination under different temperature (T) and water potential (WP) conditions for white clover 'Nomad' and perennial ryegrass 'Stellar AR1'. Seeds were germinated in vitro under a range of T × WP combinations, and HTT models were fitted to germination time course data. Rapid germination of white clover under optimum T and WP was reflected by a much lower value for its HTT constant compared with perennial ryegrass (10.8 vs 80.7 MPa °C d). However, the lower base water potential for perennial ryegrass (−1.29 vs −0.495 MPa) and a higher threshold temperature for thermoinhibition (21.8 vs 18.3°C), meant that predicted perennial ryegrass germination was more resilient in warm dry conditions. HTT models can be used to assist decisions about the timing of perennial ryegrass and white clover sowing. [ABSTRACT FROM AUTHOR]