Nat Hazards (2011) 56:509–527 DOI 10.1007/s11069-010-9507-8 ORIGINAL PAPER
IFKIS-Hydro: an early warning and information system for floods and debris flows Hans Romang • Massimiliano Zappa • Nadine Hilker • Matthias Gerber Franc¸ois Dufour • Vale´rie Frede • Dominique Be´rod • Matthias Oplatka Christoph Hegg • Jakob Rhyner
• •
Received: 3 December 2008 / Accepted: 30 January 2010 / Published online: 7 March 2010 Springer Science+Business Media B.V. 2010
Abstract IFKIS-Hydro is an information and warning system for hydrological hazards in small- and medium-scale catchments. The system collects data such as weather forecasts, precipitation measurements, water level gauges, discharge simulations and local observations of event-specific phenomena. In addition, IFKIS-Hydro incorporates a web-based information platform, which serves as a central hub for the submission and overview of data. Special emphasis is given to local information. This is accomplished particularly by human observers. In medium-scale catchments, discharge forecast models have an increasing importance in providing valuable information. IFKIS-Hydro was developed in several test regions in Switzerland and the first results of its application are available now. The system is constantly extended to additional regions and may become the standard for warning systems in smaller catchments in Switzerland. Keywords Flood warning Early warning Monitoring Information system Debris flows Risk management H. Romang (&) Federal Office of Meteorology and Climatology MeteoSwiss, Kraehbuehlstrasse 58, 8044 Zurich, Switzerland e-mail:
[email protected] M. Gerber F. Dufour J. Rhyner WSL Institute for Snow and Avalanche Research SLF, Fluelastrasse 11, 7260 Davos, Switzerland M. Zappa N. Hilker C. Hegg Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zuercherstrasse 111, 8903 Birmensdorf, Switzerland V. Frede Axpo AG, 5401 Baden, Switzerland D. Be´rod Federal Office for the Environment FOEN, 3003 Berne, Switzerland M. Oplatka Department for Wastes, Water, Energy and Air of Canton Zurich, 8090 Zurich, Switzerland
123
510
Nat Hazards (2011) 56:509–527
1 Introduction Natural hazards regularly cause fatalities and property damage all over the world. Over recent decades, the number of events as well as the economic losses has increased, with a more pronounced increase in the number of weather-related events such as floods and hurricanes than in geological catastrophes such as earthquakes or tsunamis (Munich Re Group 2007). Given the evidence that flood risks are rising and the fact that the risks cannot be reduced by technical, biological and planning measures alone, the importance of organisational measures and effective emergency management becomes even more evident in an integrated approach to risk management. However, emergency management and rescue operations are major challenges. To be fully effective, emergency measures have to be prepared before an event actually happens. In determining when best to take the appropriate action and, at the same time, to minimise false alarms, emergency managers need the best information possible. The crucial point in this regard is lead time. In the case of small catchments having short response times, good emergency management poses a genuine challenge. This challenge may be met largely by a site-specific early warning system which provides information about the evolution of possibly hazardous situations. Such systems are increasingly being developed and used throughout the world (Markar et al. 2005; Rabuffetti and Barbero 2005; Butts et al. 2006; Clark et al. 2007; Loster 2008). More and more of these systems do not simply focus on flood forecasting often supported by hydrological models, but, rather, integrate additional information such as the assets at risk and the possible mitigation measures which affect decision support systems (Ahmad and Simonovic 2006). However, there seem to be more systems available for and successfully applied to larger rivers than for smaller and generally steeper catchments. Here, only a few examples exist. In the 1980s in California, first steps toward an early warning system for flash floods and debris flows were made (Wilson et al. 1993). Based on this progress, in 2005, a far-sighted initiative for a debris flow warning system was started (NOAA-USGS Debris Flow Task Force 2005). In other regions of the world too, some early warning systems for smaller catchments, debris flows and landslides have been studied (Georgakakos 1986; Chan et al. 2003; Aleotti 2004). Also, in Switzerland, flood warning focuses on the larger rivers (Buergi et al. 2007), whereas small rivers and torrents, up to now, were not treated similarly. Today, the smallest operationally modelled catchments are 124 km2 in area, though the results are only used in forecaster teams and not yet communicated to end-users (Zappa and Vogt 2007). Particularly for smaller catchments, early warning systems cannot be solely based on modelling results. Additional information such as the general weather forecast, nowcasting systems (e.g. rainfall radar) or local know-how and experience about the hazards could be helpful; otherwise, the knowledge about the relevant processes such as runoff generation or debris flow initiation is incomplete. Therefore, to provide useful information for emergency management even in small catchments, a project was initiated in 2004 aimed at developing an information and warning system for hydrological hazards in small- and medium-scale catchments in the range of 1 to 1,000 km2 in Switzerland. The system was based on significant experience and infrastructure of the avalanche warning system IFKIS and was, therefore, named IFKIS-Hydro.
123
Nat Hazards (2011) 56:509–527
511
2 Design and functionality of IFKIS-Hydro 2.1 Avalanche warning system IFKIS IFKIS is the Intercantonal Early Warning and Crisis Information System (Interkantonales Fu¨hwarn- und Kriseninfomationssystem) for snow avalanches (Bruendl et al. 2004). Today, the avalanche-prone cantons in Switzerland use this system to collect and distribute relevant information such as weather and snow conditions, hazard forecasts and avalanche activity. In addition, the organisation of the safety services, as well as the unification of avalanche education and training, is handled within the framework of IFKIS. The Federal Office for the Environment (FOEN) supervises the whole process. The WSL Institute for Snow and Avalanche Research SLF plays a key role as the official Swiss avalanche warning centre. The IFKIS system is well established for avalanche warning in Switzerland. The IFKISHydro initiative is an effort to use infrastructure and concepts from avalanche warning for hydrological hazards. People and authorities in charge of avalanche risk management are often responsible for other natural hazard risks, such as floods, too. Moreover, there are several similarities between snow- and water-driven processes, e.g. concerning the type of information needed or the crisis management methods used. In both cases, one needs meteorological data such as measured and predicted precipitation, local information such as the observed process activity, and the results from simulation models such as snow cover modelling and discharge forecasts. Therefore, the principle of IFKIS can be used for flood hazards without ignoring well-known differences to avalanches, such as faster reactions to precipitation, especially in smaller catchments, or possibly greater variation in the initial conditions in different catchments. 2.2 Structure of IFKIS-Hydro To fulfil the function of a decision support system (DSS) for the local emergency response officials, IFKIS-Hydro is based on three pillars: • Monitoring: changes in the catchments are gathered periodically (at least once a year) and after each event. The monitoring helps to be better informed about pre-existing conditions in the areas of concern and, thus, to evaluate emergencies appropriate to the actual situation. • Real-time information: in emergencies, IFKIS-Hydro provides fast access to information such as weather forecasts, discharge predictions, measurement data and local observations. Such information can be qualitative as well as quantitative. • Event documentation: information on former events is very helpful for the effective management of current and future events on a long-term basis; however, this information is mostly missing at present. Therefore, an important function of IFKISHydro is to collect and store such information on past events for future application. This is of particular interest for local observations, which are stored nowhere else. The processes of data collection, data processing, interpretation and dissemination have been standardised within the IFKIS system. The design (Fig. 1) is mainly dedicated to the operation of the system in emergency situations. However, it also supports the long-term use of the system for monitoring purposes and for data storage.
123
512
Nat Hazards (2011) 56:509–527
Fig. 1 The design of IFKIS
2.3 Main elements of IFKIS-Hydro When applied to a specific region, the elements of the system have to be adapted to the respective situation, especially to the data available. In general, the main elements of IFKIS-Hydro can be characterised as follows: • Meteo: meteorological information such as weather forecasts, satellite or radar images, or quantitative precipitation forecasts is essential for flood warning systems. Generally, IFKIS-Hydro uses the information offered by official weather services, research institutions and specialised private companies. • Gauging stations: measured data such as precipitation intensity or discharge level give precise information on the current situation in a specific location and may be approximately representative of a larger area. As far as possible, existing gauge networks such as official networks at the national or regional level, as well as private networks, i.e. from hydropower plants, are integrated in IFKIS-Hydro. To fit the needs of the system and to deliver accurate data, the stations have to meet a given standard, e.g. concerning gauging accuracy and intervals, as well as data storage, transmission and maintenance. When applied to rather small areas, IFKIS-Hydro needs to rely on a dense network and, often, new stations have to be installed. Up to now, the evaluation of the number and the best position of these stations and how many of them are really needed has been evaluated pragmatically based on a local analysis and on local experience, e.g. for the test area Evole`ne (210 km2), we recommended six rain gauges to represent accurately the rainfall pattern in that alpine topography. However, the optimal density of gauging networks for a forecast and warning system must still be considered an open question. • Models: process models help in understanding the formation, initiation and propagation of physical processes. In particular, they transfer the meteorological data into processrelevant information such as discharge. Up to now, only rainfall–runoff simulation models were used within IFKIS-Hydro, but the framework is open to other models (e.g. prediction of debris flows initiation) that are useful in handling the respective situation. The runoff models used help to increase the time available for the emergency preparation. The main limits to application are the size of the modelled area, the available data, the model accuracy, its calibration and the resulting uncertainties (Pappenberger and Beven 2006).
123
Nat Hazards (2011) 56:509–527
513
• Observers: people working in the field are often very effective and efficient providers of event-related information. Observers can be flexibly deployed and even barely measurable factors such as slope instabilities, debris flow activity, floating wood or bed load can be gathered and later interpreted. Moreover, the integration of specialised local personnel is a must, as they have a large responsibility, both for the interpretation of the data and the realisation of the intervention. • A Java-based web platform called InfoManager serves as a central hub for the submission and visualisation of the data, as well as for its entry by the observers (Fig. 2). All of the information is stored in a central database (Oracle). It is not limited to current data, but allows the inclusion of available information from former events. Especially in small catchments with few records up to now, the systematic collection of data and its storage should improve the overall understanding of the respective catchment, and, thus, should support decisions in future emergency situations. Up to now, IFKIS-Hydro does not have a national warning mandate as is the case for the IFKIS avalanche warning system and, therefore, does not provide bulletins for public information. This is due to the pilot nature of the project. However, a clear indication for the probable need for an extension of the system in the future exists.
Fig. 2 Entry of observed data in the InfoManager, the web platform of IFKIS-Hydro
123
514
Nat Hazards (2011) 56:509–527
2.4 Areas of application in Switzerland IFKIS-Hydro has been developed and used as a pilot project in different regions of Switzerland (Fig. 3). The first applications were based in alpine settings, but subsequently expanded into the lowland regions of Switzerland.
3 Test area Valais 3.1 Focussing on small catchments Canton Valais in the south-west of Switzerland is dominated by the Rhone river valley and numerous mountainous side valleys with mountains of up to 4,600 m in altitude, some of them famous, such as the Matterhorn. IFKIS-Hydro focuses on the small and generally steep catchments in the side valleys. For the Rhone river, the forecast system MINERVE has already been developed and implemented by Jordan et al. (2006) and Jordan (2007). In the six test regions of IFKIS-Hydro in Canton Valais, the hazard and risk situations were first evaluated. The hot spots for emergency management were then identified. Together with local responsible officials, possibilities to improve local information by observation or via higher density gauging networks were evaluated. Considering the rather small size of the investigated areas, the availability of local information is of pivotal importance. As for the gauging stations, some new stations were suggested, but, in particular, IFKIS-Hydro aimed at a better coordination of existing networks, e.g. belonging to hydro-electric power plants or to other administrative services. The project is being realised step by step. The first two test areas of IFKIS-Hydro became operational in autumn 2005. For the other regions, the concepts were completed in 2007 and the implementation is pending. Last but not least, the Illgraben catchment, a wellknown debris flow prone catchment, has also been integrated into IFKIS-Hydro (Badoux et al. 2009). Illgraben is a major threat to roadways, residences and, additionally, to people enjoying the outdoors.
Fig. 3 Pilot regions of IFKIS-Hydro (1 Glarus, 2 Valais; 2a Evole`ne, 2b Illgraben, 3 Zurich)
123
Nat Hazards (2011) 56:509–527
515
3.2 Local observations To understand and possibly predict hydrological events in smaller catchments, local information is of pivotal significance. Precipitation as well as the properties of individual catchments may vary greatly over rather small distances, as well as over short time periods (and a spatial averaging facilitating the forecast for extended catchments is not occurring). Such local information can be collected by people working in the field. They can be flexibly deployed and can gather even barely measurable factors such as slope instabilities, debris flow activity, floating wood or bed load transport. On the one hand, such observations can be carried out specifically during potentially critical situations and provide information for individual events. On the other hand, observations are also made regularly in order to monitor the areas of interest. Typical sites for regular observations are active slope movements, important bed-load or wood deposits, and structural countermeasures such as retention basins. Annual or more frequent observations at these sites should help to identify changing conditions that could lead to an increase in danger, for example, regarding the reaction of the catchment to heavy precipitation (Fig. 4). Observations in this sense have been described by Badoux et al. (2009) for one of the IFKIS-Hydro sites in the Valais. Moreover, this information should not only support the assessment of a single event, but should also contribute to a more proactive management of the watershed, i.e. by preventively initiating maintenance work or additional mitigation measures. During events, the observations can be continued for at least some of these critical sites (e.g. unstable slopes) but, in general, they will focus more on specific sections of the channel in order to gather event-relevant information, such as the water level or the erosional activity. The observations made during events should provide information which will improve the understanding of the reaction of the catchment to precipitation and, at the same time, they should directly support emergency management activities, for example, by alerting rescue services in case of abrupt changes, such as in the case of a sudden debris flow. The selected channel sections for observations should be stable and not significantly influenced by local erosion and accumulation of material. In addition, they have to be safely accessible to avoid serious danger for the observers themselves. When developing
Fig. 4 Changes in an unstable slope between October 2003 (left) and June 2005 (right). Frequent debris flows originating from this torrent section endanger a main road downstream
123
516
Nat Hazards (2011) 56:509–527
IFKIS-Hydro in the test areas in Canton Valais, the locations for observations as well as the data to be gathered there were defined in accordance with these principles (Fig. 5). 3.3 Interpretation of observed and measured data To take proactive emergency measures requires an accurate interpretation of the observed and measured data at an early stage, and also consideration of weather forecasts and similar information. This is a challenging task given the fact that the knowledge about hydrological processes, particularly in small catchments, is still limited and assessments of the local conditions are crucial. Moreover, although local officials often have some experience with such phenomena and are used to drawing conclusions pragmatically, the interpretation of the data demands specific knowledge that has to be provided once a system like IFKISHydro is installed. One possibility to improve the understanding of the hazard potential of a specific situation is to compare data, for example, the observed precipitation and threshold values. Such thresholds have been defined for several regions in the world and may play an important role in early warning systems (Wieczorek 1987; Cannon 1988; Crozier 1999; Carpenter et al. 1999; Guzzetti et al. 2008). In Switzerland, thresholds were developed for one of the IFKIS-Hydro sites, the intensely studied debris flow Illgraben catchment (McArdell and Badoux 2007). However, in most implementations of IFKIS-Hydro, as well as of similar early warning systems, the knowledge and the data to establish such precise thresholds still are missing. Moreover, due to the high dependency of these values on the local conditions, they are, in general, not transferable from one region to another. Thresholds can, in general, be defined only on the basis of a data series of sufficient length. IFKIS-Hydro also aims to build up such long-term series. However, to support the initial phase of the system, we have made a rather simple analysis described in the following for the test site Evole`ne in Canton Valais (Table 1), a high alpine valley with steep and, only in the lowest parts, afforested slopes ranging from 1,300 to 4,300 m asl. In this analysis, we compared precipitation data and information on previous floods and debris flow events in the area of concern for the time period of 1987 to 2003. The rainfall
Fig. 5 Human-readable water level control point in the test area Simplon South, Canton Valais (photo: M. Jeisy)
123
Nat Hazards (2011) 56:509–527
517
Table 1 Example of event analysis for the initial phase of operation of IFKIS-Hydro. Precipitation data related to five flood and debris flow events in Evole`ne Date of the event
Max. precipitation in 1 h (mm/h)
Max precipitation in 24 h (mm/24 h)
Total amount of precipitation (mm)
Duration of the event (h)
Sum of precipitation in the previous 5 days (mm) 10
24.–25.08.1987
5.9
35.0
48.9
61.7
24.–25.09.1993
7.9
41.8
95.2
85.2
49
15.1
24.5
24.5
1.7
15
24.–25.09.1994
2.2
12.0
20.1
88.0
42
13.–15.10.2000
7.6
82.5
127.6
67.5
66
23.07.1994
data were taken from an automatic gauging station which is situated in the lower part of the test site Evole`ne (210 km2) and is operated by the national weather service MeteoSwiss. The information on former events comes from documents related to the previously existing hazard map and from a national database of natural hazard events (Hilker et al. 2009). We identified five major events which led to floods and debris flows in the main river of the valley, as well as in the numerous tributaries. The according rainfall amounts occur rather frequently, i.e. the return periods mostly lie in the range of only a few years. The biggest event in October 2002 comes with a return period of about 30 years for the daily sum of precipitation. The comparison of measured and observed data aimed at revealing threshold values (if they exist) which are valid for this region. The analysis of precipitation data showed that: • Hazardous events in this area were mostly initiated by longer duration precipitation (four events had durations of at least 60 h, and one brief thunderstorm). • The 24-h total of such events generally exceeded 30 mm (September 1994 was only partially accurate, as the centre of the precipitation was in the back of the valley and, therefore, the measurement at the station was not representative). • The maximal hourly total rainfall was mostly more than 6 mm (again, with the exception of September 1994). Increasing intensities also seem to play a pivotal role in the final triggering of events. This can be seen in the 2000 event, where the intensities constantly rose to about 7 mm/h before the debris flows and the flooding finally occurred (Fig. 6).
Fig. 6 Timeline of precipitation in Evole`ne, October 13th–16th 2000 (source: MeteoSwiss)
123
518
Nat Hazards (2011) 56:509–527
Based on the data, we arrived at primary approximate threshold values: a daily total of 30 mm/24 h and an intensity of 7 mm/h. Both thresholds were exceeded by three of the five events, but not identically. The combination of the two values in the sense that either the threshold for 24 h or the threshold for 1 h has to be exceeded was found in four of five events. As explained above, the site of the gauging station was probably not representative for the event, which would not have met these thresholds (September 1994). Although these thresholds were fixed at a rather low level, it would not have been possible to detect all of the events. Moreover, we would have had a high number of non-events. Looking at the data from 1987 to 2003, the threshold values were exceeded three to four times per year. The simple analysis of the existing data in Evole`ne provides some hints for evaluating the hazard potential of future events. However, the derived thresholds only give a rough approximation and are not highly reliable. At this stage, they only can serve as supplementary information. We recommended that Evole`ne uses the value of 30 mm/24 h as a wake-up call and continuing to observe the development of intensity carefully (reference value 7 mm/h). In addition, other gauging stations should be integrated into IFKIS-Hydro to better cover the entire region. This is easily feasible because the stations already exist and have only to be adapted for automated communication and be connected to the system. Last but not least, additional observations of the weather situation will still play a crucial role because they can reveal small-scale and shorter-duration phenomena, such as the development of thunderstorms or the locally varying distribution of precipitation.
4 Test area Glarus 4.1 Background and general setting of the system The river Linth is an alpine river in Canton Glarus in the eastern part of Switzerland. The catchment area of about 600 km2 is mainly covered by forests (20%), grassland (31%) and rocky areas (34%). The runoff is influenced by three hydropower storage lakes with a total storage capacity of 144 Mio. m3; due to hydroelectric power production, the discharge fluctuates considerably over the course of a day. Additionally, during flood events, the reservoirs can serve as retention basins to significantly reduce the peak discharge as well as the total volume of discharge. Along the river Linth, several residential and industrial areas are threatened by floods, though the potential damage may be reduced by mobile protection measures. To decide when to initiate these measures, quick and reliable access to the relevant information is needed. Although the Linth catchment was already covered by many gauging stations, they either belonged to different networks or were not integrated in any network at all. This made the access and collection of data very time consuming previously. Therefore, IFKISHydro in this region was initially installed to simplify the data collection. The collected information was not only helpful for event management but it also enabled the development of a discharge model (Zappa et al. 2006). Today, IFKIS-Hydro Glarus brings together the data from precipitation (6) and discharge gauging stations (4), as well as the results from the discharge simulation, and allows for easy access via the web-based InfoManager. The system has been operational since 2006 and has already been applied successfully in some real events.
123
Nat Hazards (2011) 56:509–527
519
4.2 Discharge simulation and forecast In larger catchments, discharge forecast models play a pivotal role. Based on precipitation forecast and rainfall data, they can predict the possible peak discharge and the hydrograph, as well as the routing of the flood wave along the river. One of the objectives of IFKIS-Hydro Glarus was to apply numerical discharge modelling to a smaller catchment such as the Linth river (600 km2). The implemented model here is a further development of the semi-distributed hydrological model PREVAH (Precipitation–Runoff–Evapotranspiration–HRU related Model) (Gurtz et al. 2003; Viviroli et al. 2009). In addition, the application of PREVAH for the Linth river was the first time that measured data from the Federal Office for the Environment (FOEN), the national weather service MeteoSwiss and the IMIS monitoring network (operated by the WSL Institute for Snow and Avalanche Research SLF) were jointly used for a runoff forecast. Every hour, the rainfall data from the automatic gauging stations of MeteoSwiss and IMIS/SLF, as well as the discharge data from FOEN and Canton Glarus, are assimilated and processed by PREVAH. The most recent data are then spatially interpolated for the catchment area. Finally, the model simulates the last 12 days prior to the current measured values. If required, the model can be recalibrated. Selected simulation results (discharge, area precipitation, snow melt, evaporation and the average saturation level of the ground) are available 4 min after a model run in the IFKIS-Hydro InfoManager. After an assessment of the situation, the responsible parties can initiate further steps as needed, e.g. alerting of the emergency task force. The forecast version of PREVAH is driven locally and interactively. Based on the weather forecast, the responsible person can run different scenarios and get an overview of possible developments of the river discharge (Fig. 7). As for today, meteorological forecasts are entered manually—an automatic connection with probabilistic weather forecast is under development (see section titled Test area Zurich) and has already been tested in the framework of the MAP D-PHASE project (Zappa et al. 2008).
Fig. 7 Example of a discharge simulation for the Linth river in Mollis in August 2007 (initiation of the model run at 2 am on August 7th). The measured peak discharge on August 8th was about 220 m3 s-1. The graph represents a ‘‘best-fit’’ option modelled after the event
123
520
Nat Hazards (2011) 56:509–527
4.3 Organisation of emergency management The success of IFKIS-Hydro in the test area of Glarus is not only a result of the technical realisation of the system with the forecast model and the web platform, but also of the accompanying organisational and personal implementation by local administrations and the rescue services. All local participants are aware of their role and their responsibilities, and are organised in a way such that they can jointly act according to the information of the system. Since the system was set in operation, several smaller events have occurred, and every event provided further input to the development of IFKIS-Hydro. The most important event in the last 2 years was a flood event of August 2007. Its chronological sequence offers details as to how the system works: • Based on the weather forecast, several discharge scenarios were calculated (Fig. 4). In general, these forecast scenarios indicated a critical discharge level for the night of August 8th. • At 5 pm on August 8th, officials from the cantonal administration and from the municipal fire brigades met to analyse the situation. They decided to take precautionary measures. • The fire brigades were mobilised. They installed mobile protection measures such as sandbags and the Beaver flexible tube system at known vulnerable points. In addition, the residents were informed of the danger. • The water level of the Linth river rose remarkably faster than was estimated by the forecast. Nonetheless, most of the intervention measures were finished by 11 pm when the discharge finally hit its peak. • The development of the situation was continuously followed and supported by the InfoManager and the simulations. • On August 9th, the all-clear was given and, in the following days, the protective measures were removed. Additionally, the experiences of the event allowed for a further development of the discharge model PREVAH on the one hand and of the organisational measures of the cantonal and local emergency managers on the other hand. Based on Romang and Wilhelm (2009), so-called intervention plans have been elaborated (Fig. 8). This plan is dedicated mainly to support fire brigades, i.e. the people who are on the front lines in an emergency. The plan provides relief unit officers and safety managers with the information needed to plan and organise operations and to give priority to important objects at risk. They know where, how and when they have to act, e.g. to make optimal use of mobile levees. Based on the plan, the intervention can be prepared and practised before a real emergency situation occurs, and the needed materials such as mobile flood protection devices can be acquired in advance.
5 Test area Zurich 5.1 Background and target area The Sihl basin (336 km2) is a very challenging and flood-prone river basin and constitutes a serious threat for the surrounding of the Central Railway Station in Zurich (ZRS from now on), the most populated city of Switzerland. The potential for damage at ZRS as well as for the surroundings is much larger than one billion Euros. An analysis of worst-case
123
Nat Hazards (2011) 56:509–527
521
Fig. 8 Extract from the intervention plan Landquart River, Klosters, Switzerland (Romang and Wilhelm 2009)
flood scenarios by Schwanbeck et al. (2007) showed that flood events which lead to the inundation of ZRS and its environs are possible. A flood from the Sihl causing the inundation of ZRS should, therefore, be avoided at any cost and this is the reason why a realtime flood warning system is needed. The river Sihl is flowing in a channel underneath ZRS (Fig. 9). In the time frame 2008 to 2011, the potential hazards at ZRS will be additionally increased by the realisation of a new underground railway station underneath the river Sihl itself. For completing the excavation of the underground station, the capacity of the channel below ZRS has to be reduced by 40% for a duration of 3 years. Tide gates have been installed to seal two-fifths
Fig. 9 Situation map of the ensemble flood forecasting system IFKIS-Hydro for the Sihl basin and Central Railway Station in Zurich (ZRS). The river Sihl (c) is channelled underneath the surface rails (a) and will later flow above the new rails that are currently under construction (b). The discharge of the Sihlsee basin is collected in the Sihlsee Lake. Turbinated water is then diverged into the Lake of Zurich
123
522
Nat Hazards (2011) 56:509–527
of the cross-section of the river. This leads to a temporary increase of potential damage also for floods with small return periods. In the upstream part of the basin, a concrete dam is collecting waters from a headwater sub-basin of about 155 km2 in area. The dam forms the Sihlsee Lake. The waters of that lake are exploited by a private hydropower company. After exploitation, the water is diverged into the Lake of Zurich (Fig. 9). 5.2 Hydrological modelling and real-time data assimilation Similarly to the test area of Glarus, the hydrological ensemble prediction system implemented is a further developed and tailored operational version of PREVAH. Real-time data to force the model is obtained from an operational database collecting and integrating information from different observation networks on the national, as well as on the regional, level (operated by Canton Zurich and the hydropower company of the Sihlsee basin). The setup adopted for processing information from deterministic and probabilistic numerical weather prediction models (NWPs) is the same as that presented by Jaun et al. (2008) and Zappa et al. (2008) and is not further discussed here. For obtaining forecasts for different lead times, the NWP systems are made available by MeteoSwiss. Two deterministic models provide high-resolution forecasts for lead times ranging from 24 h up to 72 h. Such information is updated several times per day. An atmospheric ensemble prediction system provides once-per-day ensemble forecasts with 16 members and a lead time of up to 132 h (Molteni et al. 2001). These ensemble flood forecasts represent the uncertainties in atmospheric and hydrological prediction systems. Finally, PREVAH is coupled to a hydraulic model to route the discharge along the riverbed and to take into account the management of the Sihlsee Lake (Schwanbeck et al. 2007). 5.3 Operation of the system In the operational mode, a nowcasting run starting with the interpolation of meteorological data and ending with the computation of the discharge routing with the hydraulic model FLORIS is performed every hour over the last 5 days and chained with the forcing from different NWPs adopted. This generates runoff forecast with lead times varying between 24 h and 120 h (Fig. 10). After processing all of the data, warning levels and figures are created automatically and uploaded into a dedicated visualisation platform that will be integrated into the InfoManager of IFKIS-Hydro. The visualisation platform can be accessed by all members of the emergency task force responsible for taking decisions on flood control in the Sihl river basin. For flood control and the protection of ZRS, several options are then opened and routinely evaluated by experts. According to the latest flood forecast, a controlled drawdown of the lake can be ordered and completed. Decisions are taken by a panel of persons composed of stakeholders (local administrations, Swiss Federal Railways, insurance companies, members of the hydropower company and those responsible for the realisation of the new railway), meteorologists and hydrologists. An eventual decision on a controlled drawdown has to be taken up to 2 to 3 days before a potentially serious event occurs. On the one hand, an increase of retention volume in the Sihlsee Lake contributes to a reduction of the flood peak in Zurich considerably (Schwanbeck et al. 2007). On the other hand, the losses caused by reduced power production have to be compensated. A second option for flood mitigation, which applies only during the most critical temporary phase when the new rails are realised, is the controlled flooding of the two
123
Nat Hazards (2011) 56:509–527
523
Fig. 10 Ensemble hydrological forecast, starting from September 12th 2007 for the Sihl basin up to ZRS. The 16 ensemble members (red) are shown with corresponding interquartile range (Q25–Q75). The observed runoff is shown in blue and an initialisation forced by interpolated pluviometer data is shown in green. The thin horizontal lines display warning levels defined by the emergency task force responsible for flood control in the Sihl basin
sections closed by the tide gates. The opening of the gates can be employed to guarantee the full capacity of the channel below ZRS. In this case, the building contractor could lose up to 2 weeks of work, which would also cause important costs. Both options for flood control are connected with important financial consequences and, therefore, false alarms should be avoided. After first experiences with the operation of the forecast and warning system, a detailed risk-based definition of alarm thresholds should be carried out (Roulin 2007).
6 Discussion The test regions for IFKIS-Hydro represent a broad range of potential areas for the implementation of customised warning solutions in small and medium alpine catchments. The system is based on a concept proven in avalanche warning and, so, offers a generally applicable framework; nonetheless, it allows for adaptation to the situation at hand (e.g. available data, applicable models and local capabilities). It is an open system designed to integrate new technological and research developments such as enhanced models for probabilistic river flow forecasting. Moreover, improved access to information via a standardised web platform facilitates the work of safety officials and the exchange of data and experience. The most notable potential limitations are related to the small size of some catchments, to the lack of practical experience with a variety of events to thoroughly test the system and to the difficulties related to the transfer of warning information in emergency situations. Within the system, forecast models play an important role. The discharge model PREVAH was installed in two of the test areas. In Glarus, this model has already proven to be very helpful in proactively managing a potential flood emergency. Its installation in the test area of Zurich included additional ensemble forecasts. This is likely to be a promising approach. It can be assumed that the importance of such models in early warning systems like IFKIS-Hydro will certainly increase in the future. However, for smaller catchments up
123
524
Nat Hazards (2011) 56:509–527
to some 10 km2 in size and for areas in which data is scarce, the application of forecast models is more difficult and, so, the level of uncertainty increases. For this reason, until now, no models have been implemented for small catchments in IFKIS-Hydro. Besides the modelling aspect, operating a system like IFKIS-Hydro in smaller catchments, such as those in the test areas of Valais, is very challenging in general. A typical region for IFKIS-Hydro in Valais includes several torrents and rivers. On the one hand, the overall situation is characterised by the high spatial and temporal variability of weather phenomena, as well as the reaction of affected watersheds, and on the other hand by potentially very short lead times. The present experience shows that the operation of the system reaches its limits when these characteristics become extreme, e.g. in the case of a severe local thunderstorm. In other cases, especially when more time was available, IFKISHydro proved helpful and allowed users to stay informed, even in rather complex terrain. It is not yet possible to state exactly how effective IFKIS-Hydro would be in all circumstances. If there is as much information as in the case of the Illgraben catchment (provided by gauging stations, observations and automatic warning systems; see Badoux et al. 2009), it would definitely be possible to give valuable support to emergency management personnel, even in small catchments. Time will reveal to what extent similar information can be gathered and interpreted by low-tech procedures such as observations. Without question, observations seem to be an appropriate way to collect local information, in particular, under complex conditions such as in small mountainous watersheds, with a reasonable input of time and money. Independent of catchment size of the IFKIS-Hydro regions, the link to emergency measures is crucial—the test area at Glarus illustrates a feasible way to do this. Although the interventional aspect of emergency management is not covered by IFKIS-Hydro, its further development should also focus on this interface. Research is needed for the development of improved data interpretation, better decision processes in situations of higher uncertainty and increased effectiveness of emergency measures. In particular, social and behavioural science should also be included, as this will serve to strengthen communication between actors, e.g. with respect to uncertainty evaluation, dissemination of forecasts and warnings, and warning response behaviours (O’Connor et al. 2005; Drobot and Parker 2007). However, by explicitly including local officials and recognising their crucial responsibility in the emergency management and rescue chain, IFKIS-Hydro has already set the stage for better connecting warning and intervention. Warning and intervention should not only be linked technically, but should also be supported by an effective framework at the administrative and organisational level. If the responsible people do not have the skills and the resources to act appropriately, or if there are not sufficiently qualified and motivated people doing the job, IFKIS-Hydro cannot successfully improve emergency management at these locations. The pilot sites were, among other aspects, selected with respect to the competencies and the motivation of the people involved—their level of commitment was high. However, for additional installations of the system in other regions, more importance should be attributed to the education of and support for the users and also on the integration of IFKIS-Hydro into the administrative and organisational processes in emergency management. Last but not least, systems like IFKIS-Hydro must, of course, be highly reliable. Interruptions to service should not occur, and if there are interruptions, they should last no more than a few minutes. Thus, highly reliable communication networks and IT infrastructure, as well as 24/7 support services, are required. Due to the pilot nature of the projects, such services could only be partially provided. There is a strong need for the future establishment of appropriate operational systems and processes; nonetheless, as
123
Nat Hazards (2011) 56:509–527
525
interruptions still may occur, the local ability to react is crucial, even under very challenging conditions.
7 Outlook Today, IFKIS-Hydro is operational in six regions of Switzerland, covering a size range between 1 km2 and 600 km2. A series of requests to extend the system to other regions of the country demonstrate the positive evaluation of the users. There is a keen interest among the stakeholders involved to further advance IFKIS-Hydro and related tools for warning and intervention. Further progress should focus on the following aspects: • Advancement in weather forecasting focussing on small-scale and short-term predictions (e.g. thunderstorms), including the evaluation of new technologies such as smaller mobile radar stations (NOAA-USGS Debris Flow Task Force 2005; Couach et al. 2008) and the definition of an optimal density for gauging networks. • Better knowledge of hydrological processes (e.g. discharge formation, debris flow initiation) and the development of operational models for flood warning and decisionmaking, taking into account both physical-based models (Lehning et al. 2006) and alternatives such as those suggested by Martina et al. (2006) and McDonnell et al. (2007). • Combination of 1-D discharge models with 2-D inundation models to provide real-time flood forecasts, which allows for the preparation of mitigation measures at an earlier stage. • Further development of decision support schemes for the security officials guaranteeing an optimal use of the available data and information. A real challenge in this respect is decision-making based on probabilistic information such as ensemble forecasts, as well as public relations. • Increased local competency by creating optimal administrative conditions for emergency management (e.g. delegation of responsibilities and resources) and by providing advanced training courses for safety managers. • Uniting all of the players in the field of emergency management (e.g. at the local, regional and national level) and to establish networks to exchange and to share information. Combining resources and collaboration between actors at each level in order to fight against natural hazards is a central issue, and IFKIS-Hydro is an important milestone in this extent. As a consequence of the experiences gained during the large August 2005 flood event, an important initiative in Switzerland to strengthen the collaboration between the actors and to harmonise information at the national level, as well as to accelerate its dissemination, is GIN, the Common Information Platform on Natural Hazards (Gemeinsame Informationsplattform Naturgefahren). Based on IFKIS and IFKIS-Hydro, this platform is currently under development in a joint project between MeteoSwiss, FOEN and WSL/SLF. Boosted by GIN, some of the issues mentioned above will be tackled during the coming years. However, the scientific challenge particularly will still need great efforts to advance warning systems and emergency management, especially in small catchments, to contribute to an optimal and sustainable management of flood risks.
123
526
Nat Hazards (2011) 56:509–527
Acknowledgements We would like to thank the cantons of Glarus, Valais and Zurich, as well as the Prevention Foundation of the Cantonal Public Building Insurance Companies for initiating and supporting the IFKIS-Hydro project. The work on ensemble flood forecasting profited from research contracts in the framework of COST731 through the Swiss State Secretariat for Education and Research (SBF C05.0105). Simon Jaun (ETH and WSL) is acknowledged for his effort in developing the operational flood forecast system. Thanks go to MeteoSwiss and to the Federal Office for the Environment for the collaboration and valuable discussions. The simulations are based on the data and model results of MeteoSwiss.
References Ahmad S, Simonovic SP (2006) An intelligent decision support system for management of floods. Water Resour Manage 20(3):391–410 Aleotti P (2004) A warning system for rainfall-induced shallow failures. Eng Geol 73:247–265 Badoux A, Graf C, Rhyner J, Kuntner R, McArdell B (2009) A debris-flow alarm system for the Alpine Illgraben catchment: design and performance. Nat Hazards 49:517–539 Bruendl M, Etter HJ, Steiniger M, Klinger C, Rhyner J, Ammann WJ (2004) IFKIS—a basis for managing avalanche risk in settlements and on roads in Switzerland. Nat Hazards Earth Syst Sci 4:257–262 Buergi T, Sigrist B, Streit D (2007) Hydrologische Produkte des Bundesamtes fu¨r Umwelt—BAFU—bei Hochwasser. Forum fu¨r Wissen, Birmensdorf, WSL, pp 69–73 Butts MB, Klinting A, Ivan M, Larsen JK, Brandt J, Price D (2006) Flood forecasting system: integrating web, GIS and modelling. In: Proceedings of the 2006 ESRI International User Conference, San Diego, California, August 7–11, 2006 Cannon SH (1988) Regional rainfall-threshold conditions for abundant debris-flow activity. In: Ellen SD, Wieczorek GF (eds) Landslides, floods, and marine effects of the storm of January 3–5, 1982, in the San Francisco Bay region, California, pp 133–162. U.S. Geological Survey, Professional Paper 1434 Carpenter TM, Sperfslage JA, Georgakakos KP, Sweeney T, Fread DL (1999) National threshold runoff estimation utilizing GIS in support of operational flash flood warning systems. J Hydrol 224(1–2): 21–44 Chan RKS, Pang PLR, Pun WK (2003) Recent developments in the landslip warning system in Hong Kong. In: Proceedings of the 14th Southeast Asian Geotechnical Conference, Hong Kong, China, December 2001 Clark M, Woods R, Ibbitt R (2007) Flood forecasts for New Zealand communities. Water Atmos 15(3): 14–15 Couach O, Barrenetxea G, Luyet V, Le Bocey B, Krichane M, Bertholet T, Varidel T, Bystranowski M, Aberer K, Medico J, Parlange M, Vetterli M (2008) SensorScope: a new environmental monitoring system. Example of application in an Alpine environment. In: Proceedings of the International Congress on Environmental Modelling and Software (iEMSs 2008), Catalonia, Barcelona, Spain, 6–10 July 2008 Crozier MJ (1999) Prediction of rainfall-triggered landslides: a test of the antecedent water status model. Earth Surf Process Landforms 24:825–833 Drobot S, Parker DJ (2007) Advances and challenges in flash flood warnings. Environ Hazards 7:173–178 Georgakakos KP (1986) On the design of national, real-time warning systems with capability for sitespecific, flash-flood forecasts. Bullet Am Meteorol Soc 67(10):1233–1239 Gurtz J, Zappa M, Jasper K, Lang H, Verbunt M, Badoux A, Vitvar T (2003) A comparative study in modelling runoff and its components in two mountainous catchments. Hydrol Process 17:297–311 Guzzetti F, Peruccacci S, Rossi M, Stark CP (2008) The rainfall intensity–duration control of shallow landslides and debris flows: an update. Landslides 5(1):3–17 Hilker N, Badoux A, Hegg C (2009) The Swiss flood and landslide damage database 1972–2007. Nat Hazards Earth Syst Sci 9:913–925 Jaun S, Ahrens B, Walser A, Ewen T, Schaer C (2008) A probabilistic view on the August 2005 floods in the upper Rhine catchment. Nat Hazards Earth Syst Sci 8:281–291 Jordan F (2007) Mode`le de pre´vision et de gestion des crues—optimisation des ope´rations des ame´nagements hydroe´lectriques a` accumulation pour la re´duction des de´bits de crue. The`se de doctorat no. 3711, Ecole Polytechnique Fe´de´rale Lausanne Jordan F, Dubois J, Boillat JL, Schleiss A (2006) Pre´vision et gestion des crues par ope´rations pre´ventives sur les retenues alpines. In: Proceedings of the 22nd ICOLD Congress on Large Dams, CIGB-ICOLD, Barcelona, Spain, Q. 87–R. 34, pp 497–510
123
Nat Hazards (2011) 56:509–527
527
Lehning M, Voelksch I, Gustafsson D, Nguyen TA, Staehli M, Zappa M (2006) ALPINE3D: a detailed model of mountain surface processes and its application to snow hydrology. Hydrol Process 20(10):2111–2118 Loster TR (2008) Early warning: people-centered systems are the key. The Mozambique flood warning system SIDPABB. In: Proceedings of the 2008 International Disaster and Risk Conference (IDRC 2008), Davos, Switzerland, 25–29 August 2008 Markar MS, Clark SQ, Malone T, Gooda M, Chen Y, Min Y (2005) A new flood forecasting system for the Yangtze River in China. In: Proceedings of the 3rd International Symposium on Flood Defence (ISFD3), Nijmegen, The Netherlands, 25–27 May 2005 Martina MLV, Todini E, Libralon A (2006) A Bayesian decision approach to rainfall thresholds based flood warning. Hydrol Earth Syst Sci 10:413–426 McArdell BW, Badoux A (2007) Influence of rainfall on the initiation of debris flows at the Illgraben catchment, canton of Valais, Switzerland. In: Proceedings of the EGU General Assembly, Vienna, Austria, April 2007 McDonnell JJ, Sivapalan M, Vache K, Dunn S, Grant G, Haggerty R, Hinz C, Hooper R, Kirchner J, Roderick ML, Selker J, Weiler M (2007) Moving beyond heterogeneity and process complexity: a new vision for watershed hydrology. Water Resour Res 43:W07301 Molteni F, Buizza R, Marsigli C, Montani A, Nerozzi F, Paccagnella T (2001) A strategy for high-resolution ensemble prediction. I: definition of representative members and global-model experiments. Q J R Meteorol Soc 127:2069–2094 Munich Re Group (2007) Topics geo. Natural catastrophes 2006. Munich: Munich Reinsurance Company. Available online at: http://www.munichre.com/publications/302-05217_en.pdf, accessed 08/05/24 NOAA-USGS Debris Flow Task Force (2005) Debris-flow warning system—final report. U.S. Geological Survey, Circular 1283. Available online at: http://pubs.usgs.gov/circ/2005/1283/, accessed December 28, 2009 O’Connor RE, Yarnal B, Dow K, Jocoy CL, Carbone GJ (2005) Feeling at risk matters: water managers and the decision to use forecasts. Risk Anal 25(5):1265–1275 Pappenberger F, Beven KJ (2006) Ignorance is bliss: or seven reasons not to use uncertainty analysis. Water Resour Res 42:W05302 Rabuffetti D, Barbero S (2005) Operational hydro-meteorological warning and real-time flood forecasting: the Piemonte Region case study. Hydrol Earth Syst Sci 9(4):457–466 Romang H, Wilhelm C (2009) Emergency management of flood events in Alpine catchments. In: Samuels P, Huntington S, Allsop W, Harrop J (eds) Flood risk management: research and practice. Taylor & Francis, London, pp 1193–1197 Roulin E (2007) Skill and relative economic value of medium-range hydrological ensemble predictions. Hydrol Earth Syst Sci 11(2):725–737 Schwanbeck J, Viviroli D, Weingartner R, Ro¨ser I, Tro¨sch J (2007) Prozessbasierte Abscha¨tzung von Extremhochwassern im Einzugsgebiet der Sihl. Projektschlussbericht zum Auftrag des Amtes fu¨r Abfall, Wasser, Energie und Luft des Kantons Zu¨rich (AWEL). Bern und Zu¨rich: Geographisches Institut der Universita¨t Bern und TK Consult AG Viviroli D, Zappa M, Gurtz J, Weingartner R (2009) An introduction to the hydrological modelling system PREVAH and its pre- and post-processing-tools. Environ Model Softw 24(10):1209–1222 Wieczorek GF (1987) Effect of rainfall intensity and duration on debris flows in central Santa Cruz Mountains, California. In: Costa JE, Wieczorek GF (eds) Debris flows/avalanches: process, recognition, and mitigation: reviews in engineering geology. Geological Society of America, Boulder, CO Wilson RC, Mark RK, Barbato G (1993) Operation of a real-time warning system for debris flows in the San Francisco Bay area, California. In: Shen HW, Su ST, Wen F (eds) Hydraulic Engineering ‘93: Proceedings of the 1993 Conference, San Francisco, California, July 25–30, 1993, pp 1908–1913, American Society of Civil Engineers Zappa M, Vogt S (2007) Hochwasservorhersagesysteme der neusten Generation im Praxis-Test. WSL Forum fu¨r Wissen 2007, Tagungsband Zappa M, Rhyner J, Gerber M, Egli L, Sto¨ckli U, Hegg C (2006) IFKIS-Hydro MountainFloodWatch—Eine endbenutzer-orientierte Plattform fu¨r Hochwasserwarnung. In: Risikomanagement extremer hydrologischer Ereignisse, Beitra¨ge zum Tag der Hydrologie 2006, 22–23 Ma¨rz 2006. Forum fu¨r Hydrologie und Wasserbewirtschaftung 15(2):189–200 Zappa M, Rotach MW, Arpagaus M, Dorninger M, Hegg C, Montani A, Ranzi R, Ament F, Germann U, Grossi G, Jaun S, Rossa A, Vogt S, Walser A, Wehrhan J, Wunram C (2008) MAP D-PHASE: realtime demonstration of hydrological ensemble prediction systems. Atmos Sci Lett 9(2):80–87
123
