Objectives

DAMOCLES will develop and apply advanced modelling technologies to assess hazards posed by rapid slope failures in mountain areas and will disseminate these technologies to local end-users for application in land use planning. In order to accomplish these goals, the proposed work integrates research-based model development with the direct involvement of local planning and civil protection authorities as data suppliers, advisors, and recipients of the project results.

The Problem

Hazard resulting from rapid slope failure (defined here as debris flows and rockfalls) is a continual threat. In the Province of Lecco in the Lombardy Region of Italy, debris flows and rockfalls account for 80-90% of recorded landslides. Both phenomena are a familiar hazard in European mountain environments and regularly cause considerable loss of life, livelihood, and property (e.g. Simons, 1988; Cancelli and Crosta, 1993; Aulitzky, 1994a; White et al., 1997; Versace et al., 1998). Direct costs such as deaths, personal injuries and financial loss, destruction of infrastructure and agricultural assets can be high even for moderate events. Severe events result in deaths of over 100 men, women, and children. Monetary damage is in the tens of millions of euros. Indirect impacts such as temporary closure of roads and siltation of river courses and reservoirs with debris are less easily defined monetarily but are still clearly significant. For example, just one provincial authority in northeast Italy reports an annual budget of 20 million euros for debris flow management alone.

Hazard posed by rapid slope failures is dynamic. As European mountain areas are increasingly developed, the potential costs of rapid slope failures also increase. Insurance claims as a result of this threat are steadily rising in mountain areas. In addition, the result of development increases the incidence of debris flows by changing their topographic, soil, and vegetation controls. Consequently, there is increasing concern that the spread of roads along with development of leisure and recreational areas, together with changes in agricultural practices and forest management, is having an adverse effect (e.g. Simons, 1988; Garcia-Ruiz and Valero, 1998; Wasowski, 1998). Additionally, changes in climate (including more extreme rainfall events or an altered balance between rainfall and snowfall) and loss of tree cover (due to atmospheric pollution or fire) can similarly change the incidence of slope failure.

It is now increasingly recognized that hazard assessment forms an important part of land use planning in mountain environments. Those authorities with the responsibility for protecting populations, settlements, and infrastructure from the threat of rapid slope failures are particularly concerned with three critical aspects: 1) The spatial distribution of the phenomenon; 2) Predicting their occurrence and impact; and 3) Minimising the impact.

Objectives

This project will develop technologies for assessing the distribution of rapid slope failures and their hazard, for determining the physical impact of debris flows and, hence, for assessing the mitigating effects of torrent control works and land management, with these technologies being transferred to relevant end-users. To achieve these aims, the specific project objectives are to:

1. Develop and apply advanced models for hazard assessment, impact prediction and mitigation studies, relevant at a range of scales including: 1) A Geographical Information System (GIS) model for assessing the debris flow and rockfall hazard; 2) A debris flow model for predicting the local on-site impact in basins up to 10 km²; and 3) A landslide sediment yield model for predicting debris flow occurrence and sediment yield impact in basins up to 500 km². Models (2) and (3) will be integrated with (1).

2. Conduct field surveys and assemble databases in support of model development and refinement. The surveys will include the spatial distribution and characteristics of rapid slope failures and information on meteorological and geomorphological controls. Field data collection and data analysis will identify process relationships for insertion into the models.

3. Transfer the technologies to end-users and make outcomes accessible through the public domain. Model applications will include assessment of possible future land use and climate change impacts.

Innovation

Debris flow and rockfall hazard is the potential for adverse impacts caused by existing and future debris flows and rockfalls. It refers to the probability of occurrence of a particular magnitude of event within a specified area over a given period of time. The term risk is introduced to account for the combination of likelihood and significance of event, involving the expected degree of loss due to a particular magnitude of rapid slope failure. Hazard assessment refers to the procedures and techniques used to identify and delimit the potential for loss-inducing rapid slope failures in terms of magnitude, frequency and type. However, hazard assessments can only effectively be undertaken where some appreciation of, and concern about, the possible adverse effects of impact (ie risk) has been acquired by the relevant land managers and decision makers, together with an understanding that slope failures are scientifically explicable events, not random occurrences. Education is therefore a pre-requisite for assessment (Jones, 1995).

Hazard assessment involves both prediction and forecasting (Jones, 1995). Prediction concerns the establishment of the general likelihood and character of slope failure within specified areas; it is a spatially extensive exercise concerned with establishing zones of different levels of threat. Forecasting concerns the identification of the location, timing, magnitude and character of individual future events and is more closely linked with simulation models. An example of forecasting is the identification of conditions likely to result in the generation of debris flows within an area over a limited period of time.

A number of techniques have been developed and applied to identify and map natural hazards, e.g. combining information on past events with geomorphological surveys (Aulitzky, 1994b). However, there is no uniformity of approach in Europe and available techniques are approximate (because of lack of data) and give only qualitative or relative estimates of hazard. They do not allow, for example, the contribution of critical channel features (bends, obstacles, etc) to debris flow impact to be assessed or conversely appropriate control structures to be designed. In addition these approaches may not always provide a sound basis for determining the effects of change in the local environment (e.g. removal of forest cover), especially if the area has not previously been considered hazardous.

The search for quantitative techniques has made use of recent developments in computer power and Geographical Information System (GIS) techniques (e.g. Kienholz et al., 1984; Kienholz & Mani, 1994; Carrara et al., 1991, 1995). Incorporation of geotechnical stability models and data layers in a GIS framework (Van Westen, 1994) provides a promising approach and offers the potential for both prediction and forecasting. However, the combination of factors which triggers debris flows and rockfalls is not always fully understood and there remains uncertainty in the application of the technique.

There is a considerable literature on debris flows (e.g. Johnson, 1984; Takahashi, 1991; Iverson, 1997), including modelling developments (e.g. Chen, 1987; O’Brien, 1993; Hungr, 1995). A number of recent EC projects (e.g. EC, 1998) have investigated debris flow behaviour (e.g. EROSLOPE I, DEBRIS-FLOW-RISK and RUNOUT), producing models for debris flow transport and deposition in the fan area. However, the research nature of available models and the difficulties of applying their constitutive rheological laws reduce their user-friendliness. Poor data availability has also hindered their validation.

Despite considerable research on debris flow trigger mechanisms (e.g. Sidle et al., 1985; Crozier et al., 1986; Guzzetti, 1998), improvements in process modelling are needed to meet the needs of end-users (EC, 1998). This requires both improved databases and model developments. To be of use for forecasting, the databases must be able to indicate the effects of land use change and rainfall return period on debris flow occurrence. Similarly, physically based models are required for simulating the impacts of possible future conditions. Following improvements in computer power and the development of GIS and Digital Terrain Models, factor of safety geotechnical models have been combined with hydrological models as a basis for simulating spatial and temporal occurrence of landslides in river basins. Mostly these are limited to scales of a few square kilometres (e.g. Montgomery and Dietrich, 1994; Wu and Sidle, 1995). However, through the use of an innovative technique for modelling hydrological and debris flow responses at dual resolutions, the SHETRAN model is able to simulate both debris flow occurrence and the resulting sediment yield at scales up to about 500 km² (Burton & Bathurst, 1998).

There has been considerable research into rockfall processes (e.g. Cancelli & Crosta) but there has been no incorporation of this into DTM methodologies and very little work on statistical modelling through GIS, mainly because of difficulties in identifying source and runout areas.

DAMOCLES will advance end-use capability in debris flow and rockfall hazard assessment, while at the same time advancing scientific understanding of the problem, as follows:

1. Provision of new databases at scales from individual debris flows to river basins, according to the project’s model requirements.

2. Development of quantitative relationships on debris flow occurrence (including land use and rainfall return period effects) and characteristics (e.g. volumes of material mobilized, runout distance.)

3. Development of a quantitative GIS model for debris flow and rockfall hazard assessment, incorporating both statistical and physically based approaches.

4. Development of a user-friendly debris flow impact model for basins up to 10km² , capable of representing the effects of stream control works and land use change in the fan area.

5. Application of the advanced SHETRAN model to simulate debris flow occurrence and the resulting basin sediment yield as a function of possible future land use and climate scenarios.

6. Application of (4) and (5) to enhance the prediction and forecasting capabilities of (3).

7. Education of end-users through their direct involvement in the project.

8. Development of a proposal for a standard approach to hazard assessment and zonation based on the project deliverables.