FLOOD THREAT IN AN AREA TOPICAL NATURAL HAZARD. Milan Trizna

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1 Geographica 36, FLOOD THREAT IN AN AREA TOPICAL NATURAL HAZARD Milan Trizna Department of Physical Geography and Geoecology, Faculty of Natural Sciences, Comenius University Bratislava, Slovak Republic Head of the Department: Ass. Prof. Dr. Jozef Minár Received March 25; accepted July 10, 2000 KEY WORDS: Natural Hazard and Risk, Vulnerability, Flood Hazard ABSTRACT Based on last years experience we can say, that problem of flood threat in an area has already exceeded engineer-hydrological, respectively water economy frame. There are clear indicions, which indicate, that this phenomenon needs a complex view. It means particularly knowledge of run-off relations, which are connected with time and spacial wide spread of rainfalls, but also with land cover and land use. Methodics of identification and evaluation of natural hazards and risks allow such complex view. Problems of consideration of natural processes as factors, which limit or even threat interests of human society is very topical. Also extreme (maximum) basin run-off can be included among such processes. In the first part of presented study, there is a brief review of papers, which deal with such evaluation. An application of methodical advance in a concrete area is presented in the second part. 1. INTRODUCTION Interaction of human society and landscape can be on the first hand considered as a looking for a real or potentional sources for satisfaction of human needs. On the other hand, there appear mainly perception of natural processes, as factors, which limit or even threat some interests of human society. Both of the views are used in geography from the very beginning and it seems to be a question of concrete period, which one prevails. At present problems of human society vulnerabillity increase, especially in connection with intensive land use, where natural conditions have not been respected. Thus identification and evaluation of natural hazards and creation of possibilities of consequent formulation of relevant technical and organizational measures. The presented study brings review of projects about this theme and practical realization of methodical advance in the concrete area. 2. NATURAL HAZARD AND NATURAL RISK BASIC NOTIONS The term natural hazard means dangerousness of natural process, which can terribly influence landscape and also man earthquake, drought, flood, avalanche, cold, abrasion, volcano erruption, tropical storm, atmosphere dim (Monkhouse, Small, 1978). Natural risk expresses influence of hazard on society interests, which can be expressed in a social or economical categories life losts, economical losts in crowns etc. (Minár, Tremboš, 1994). Relationship between hazard and risk is unambiguous according to Panizza (1986 fig. 1) Fig. 1: Natural risk definition (Panizza, 1994) Risk hazard susceptibility vulnerability = EVALUATION OF SELECTED NATURAL HAZARDS Despite the knowledge level of natural process and man abilities, this processes can be controlled at the very high level, still thesis of I. R. Burton and G. F. White is in:...a man should not underestimate preparation for protection against snares of environment, which surrounds him. Most of natural processes, which come from the period of relative quiet to the period of sudden active impact by jump is a permanent danger for man and his activities or interests in landscape. For example seismic hazard, slope movement hazard (rock avalanche, slide, rock dashing), erosion hazard (wind, dip,...), increasing material accumulation hazard etc. The authors, who pay attention to the matter define impact of these natural processes as a hazard for man and his activities in landscape. Quite large is a list of projects, which deals with geomorphological hazard evaluation. Hrádek, Matejka, Švehlík (1994) in the term include seismic hazard, slope movement hazard, sudden lowering of soil hazard (caused by mining), erosion hazard but also flood hazard and so-called eolic hazard.

2 90 Acta Universitatis Palackianae Olomucensis Facultas Rerum Naturalium Fig. 2: Seismic risk of the United States (Costa, Baker, 1981) Panizza (1986) deals with evaluation of geomorphological hazard, resp. geomorphological risk. According to the scheme presented in the figure no.1 author pays attention to risk evaluation by natural hazard evaluation, susceptibility and vulnerability of environment. The author applies an analogical advance in the narrower specialized paper (Panizza, 1989) to evaluate seismic risk. The seismic risk map of the USA (fig. 2) was already finished (Costa, Baker, 1981) in The example of spatial spreading of seismic hazard in selected area is presented in papers Degg (1986, 1987). The results of earthquake hazard in California Hodgson, Palm (1992) are presented as a map outputs. The maps represent not only spatial wide spread of the hazard, but also evaluate changes of settling development, land use, prices of lands and other aspects based on a more years research, which are caused by existence of natural hazards. Volcanic hazard is also connected with tectonic lines, resp. neotectonic movement of earth crust (Cooke, Doornkamp, 1990). Hrnčiarová, Miklós (1991) have been interested in evaluation of morphometric indexes in interpretation of water and material movement dynamic downhill with the aim to propose protection against soil erosion. Juneja (1974) deals with potentional soil erosion as one of hazards. Cartographical illustration of many natural as well as anthropogeneous hazards is included in the work. Hreško (1998 a, b) deals with the soil erosion hazard (and avalanche hazard), too. In the last period, more of papers appear, which deal with evaluation of drought hazard. It is caused by global world tendention of increasing interest in problems of global climate changes, which are simplified and often called as global warming. Papers (Changnon, 1989, Lamb, 1992, Mathews et al., 1994) deal with consequences of such changes in the concrete regions. Papers (Hewitt, 1983, Cross, 1994 a, b) directly analyze relationship between climate changes and man activities in landscape, e.g. agriculture. Presented review of papers is not definite at all. It is compiled in a way to allow sufficient review about wide exploitation of methodics of topical natural hazard identification and evaluation. A cartographical illustration (area maps) of natural hazard, resp. risk connected with it is the most often practical output. 4. FLOOD HAZARD IN THE GEOGRAPHICAL LITERATURE In 1993 V. R. Baker attracts attention to the fact, that every previous flood situation seems to be a source of unvaluable experience to overcome the next one, which consequences might be moderate thankfully to this access. Seriousness of flood situation is dependable on the flow bigness, size of reached culminative discharge rate, rise conditions of the discharge rate (amount and intensity of rainfalls), period of advance, retention capacity of basin but also land cover and land use, especially in the very close surroundings of water flow (flood plain). Knowledge of these natural and anthropogeneous conditions is a further important step to cope with mini-

3 Geographica 36, Fig. 3: Flood hazard (Juneja, 1974) malization impact task during flood situation on man and landscape. Just methodics of flood hazard evaluation tries to integrate hydro-meteorological, engineerhydrological and geographical (geoecological) advances to evaluate flood situation. Practical utilization of the methodics can be find in papers from seventies. Study of Juneja (1974) (fig. 3) is an example. As an example of sensibility of natural environment evaluation considering Baker (1994) work is presented. The author is specialized on evaluation of geomorphological river-bed parameters of water flows and their changes during and after flood. The paper tells, that knowledge of sensibility of natural environment regarding to flood threat must lead to decrease in flood hazard. Dunne, Leopard (1978) deal with intention of environmental planning, which can be threat by flood hazard. Tremboš (1992) is interested in relation between natural hazard and environmental limits, their place in applied landscape research is analyzed in Minár, Tremboš, Machová (1994). Works Smith, Tobin (1979) and Petak, Atkinsson (1982) tell about how people can cope with this kind of situation in afflicted areas. Great floods in July 1997 caused arise of more papers, which deal with problems of flood hazard as a part of wider mosaic of solving flood hazard. Paper Lichý, Klačan, Styk (1997)

4 92 Acta Universitatis Palackianae Olomucensis Facultas Rerum Naturalium is presented as an example of flood area modelling at some discharge rate level using geographical information systems (GIS). Löw (1997) deals with analysis of urbanistic flood reflexion. We agree with the author s idea, that flood has showed the basic weakness of present philosophy in society protection against natural catastrophes, which is estimation of quantitative, normative protection level. This quantitative normativ has become also technologically human nature limit and if it is exceeded, nature fails and we just watch indignantly. The advance explicited in this paper is very close to vulnerability evaluation of socio-economical landscape structure, which is a part of flood risk evaluation. Markvart (1997) pays attention to analysis of area-planning documentation at the level of domiciles in connection to extreme (maximum) discharge rate. An object of the interest was determination of flooded area (element evaluated as a part of flood hazard methodics) in areaplanning documentation. The author says, that the data are missing in 43% of cases in area-planning documentation. In the end, we will pay attention to a paper of Gilard (1996). Not only because it is one of the newest papers of its kind, but also because of the fact, that the methodics is quite close to our methodics. The author considers term risk in two dimensions, in socio-economical vulnerability and hydrologicalhydraulic hazard (fig. 4). He presents a new strategy, based on experience with quite inefficient land use management in the flooded areas in France. The strategy should have three levels: 1. Prevention during land use management, 2. Forecasting to manage crisis and individual risk, 3. Culture to improve citizen reactions before flood risk. Fig. 4: Risk conceptualisation (Gilard, 1996) When speaking of the risk situation, some complex concepts appear. In fact, we intuitively make a difference between a camping localised near a river with slow flow of the same camping near a torrent, for instance, and we will say that the first situation is better than the second one. We also make the same intuitive difference between a house development near a river and an indudstrial area, and in this case, the first situation is worse. (Gilard, 1996). The author comes to the conclusions based on a quite simple as well as appropriate examples, that risk can be considered at two levels. One is based on the socioeconomic perception of risk and the other one is depending on the hydrologic and hydraulic knowledge of hydrological regime. The first factor will be called vulnerability and it represents susceptibility of land use to the flood phenomenon. The second factor is called hazard and depends only on the flow regime of river, independently from land use of flood plain. That is to say that the same flow will flood the same area with the same physical parameters, whatever should be a real land use. According to this basic factors, a real flood risk level requires a certain level of hazard and for the same location, a certain level of vulnerability. A further advance consists of construction of two map types, vulnerability map and hazard map. Vulnerability maps are in fact land use maps in the whole major bed of the river, which is supposed to be maximal extension of extreme flood. Each land use type will be affected with a need of protection expressed in term of hydrological variables such as frequency of the tolerable flood, its duration, its depth, and eventually its velocity. After elaboration of vulnerability map and flood hazard map (using the same unit) it is possible to compare them. A result is a synthetic map of flood hazard, which sumarize results connected with risk situations. In a concrete evaluated case, there are three types of flood risk illustrated in the map: 1. for the first case where plot are not flooded even from in the worst event, 2. in the second case when plots are overprotected, 3. in the third case where plots are underprotected, according to their expressed need. Based on achieved results, the author can say, that extreme floods in 90-ties in France caused, that we can not solve this kind of problem in traditional way, which is mainly based on hydraulic technical rules. The author sees a new way in a quantitative risk evaluation along a water flow. The evaluation should deals with unit definition of carrying capacity risk, changes in land use. Therefore such land use is supposed, which is less vulnerable etc. The author deals with problem of diversity mobilization and landscape potential (natural reclaimed summer land, woods,...) and avoiding mistakes in wrong land use management.

5 Geographica 36, APPLICATION OF FLOOD HAZARD IDENTIFICATION AND EVALUATION METHODICS In this part, we are trying to bind on works (e.g. Junea, 1974 or Gilard, 1996), in which evaluation of extreme run-off were included. We have already dealed with this idea in the past (Trizna, 1994, Trizna, Minár, 1996), now we can present quite complete conception. Methodical advance of flood risk identification and evaluation has been realized in a following steps: characteristics of initial natural process (extreme run-off), altitude calculation of water level (in cross profiles), natural environment sensibility estimation, flood hazard map construction. The methodical advance has been applied on the Žarnovica flow in Diviacka pahorkatina, which is a part of Turčianska kotlina. A close area to the flow (flood plain) in a section of Malý Čepčín Dolná Štubňa. While characterizing initial natural process (extreme run-off), values of so-called N-year discharge rates are the most important. In the case of analyzed flow, data from the SHMÚ station have been used. Discharge rate level, which appears on average in N-years does not give information about its spatial reach in landscape directly. It is necessary to identify on the basis of geodetical network in cross profiles, which are overlayed by hydraulic model of water flow in open river-bed. A result is information about water level altitude, relevant to value of N-year discharge rate in cross profile. To determine flooded areas between profiles, we exploit not only interpolation based on contour lines, but especially on detailed geomorphological map of the area. On the base of our experience can be said, that georelief form application allows determine flooded area more accurate, because also in scale 1: a difference between contour lines (2 m) in unsufficient. A proposal geomorphological map is a base, which is used in natural environment sensibility evaluation. Except georelief forms, there are some other elements illustrated, which are related to flood hazard evaluation. There are mainly places of potentional disturbance of levees with the lower bottom than a flow level during higher discharge rates, old branches etc. Natural environment sensibility evaluation is based on field works, knowledge of particular sections of water flow and it can be evaluated as a quite difficult part of flood hazard identification methodic. The areas of flooded area at the relevant value of discharge rate are constructed to pay attention to all mentioned matters. Areas of flooded area at the level relevant to 50- and 100-years discharge rate are illustrated in fig. 5 a, b. We want to call attention to the fact, that all cartographically illustratable areas connected to map scale are there. The presented areas express flood hazard for an analysed area. We built on suspection, that any principal changes in determinaiton of landscape elements in an area will not happen, e.g. earthwork slope slidings, area destruction of levees, etc. In the case of consideration of mentioned facts, other threated areas can be illustrated. These areas are marked as a potentionally threatened (3) in map legend. Even if its threatening suppose almost catastrophical destruction of earthwork roads (I/65), resp. relevant level to 1000-year discharge rate, experience from previous flood situations in last years at home but also abroad signalizes, that it is not possible. Flood hazard identification is the first step to better cope with land use management along a water flow. A further steps are socio-economical vulnerability analysis, which are localized close to a flow and can result in flood risk identification in the area (e.g. Trizna, 1998). 6. CONCLUSION Flood events of last years were moving impulse in a part of hydrology and hydrogeography, which deals with extreme (maximum) run-off. As follows from the paper review, but also graphical enclosures, suitability of selected natural processes for spatial illustration is different. It results from character of its process (hazard) as well as spatial connections in which appear. From this point of view seismic hazard illustration or soil erosion illustration is more simple than flood risk illustration. There is evidence, that papers evaluating other hazards prevail. Flood situations of last years, particularly in domiciles located on small flows, tells about one significant fact, lack of information about a real flood threat. There is information about rainfalls and run-off characteristics in an area, on which parameters of extreme run-off wave can be estimated, its spatial reach can be determined and area-planning intentions etc. built on it. We think, that it would be suitable to intensify scientific discussion on this theme how to protect areas against flood discharge rates and determine level of object protection in dependance on potentional damages, which could happen in an area. To determine it, evaluation of natural environment sensibility and vulnerability of social and technical structure of evaluated area is necessary. This advance is contained in flood hazard evaluation and subsequently flood risk evaluation (see fig. 1). Also, it is necessary to emphasize, that a lot of cases can be find, when localization of relevant anthropological object regarding to a measure of flood threat in the locality can be called like a commiting suicide. There is a space for legislatve changes, consistent control of land use in a close surrounding of water flow as well as in a wider space (basin), which is determining from the point of run-off creation.

6 94 Acta Universitatis Palackianae Olomucensis Facultas Rerum Naturalium Fig. 5a, b: Flood hazard of the Teplica basin (1 Q 100, 2 Q 50, 3 Potentionally threatened) ACKNOWLEDGEMENTS This research was supported by VEGA Grant Agency, No 1/7333/20. SUMMARY Problems of extreme (maximum) surface run-off are very topical at present. In the period of last years, there have appeared several significant flood situations, which attracted our scientific attention to this phenomenon. The paper deals with extreme run-off as a natural hazard, which threats interests of human society in landscape. Consideration of selected processes as hazards is very common in most of Anglo-American, but also in French environmental geographical literature. It is based on consideration of natural hazard as an danger of natural process, which can impact landscape and by this also man. Works presented in the first part deal with evaluation of selected natural hazards, their reasons and consequences. Works, where the natural harard is spatially fixed in a map output are emphasized. Spatial reach

7 Geographica 36, of the evaluated natural process is the main contribution to this consideration. Then our attention is paid to evaluation of extreme run-off as a natural hazard. We have built on the papers, which deal with the problem to create a methodical advance of flood hazard evaluation. Again, we are trying to emphasize illustration of spatial reach, but it is necessary to say, that there is less of this kind of papers. The reason is quite complicated way of flood reach illustration. An application of flood hazard identification and evaluation methodics in a selected area is in the second part of work. At present there is a minimum of such specialized papers in our scientific literature. We guess, that they will pay an important role in identification and evaluation of flood threat in our conditions, too. The practical output of this papers is the most often cartographical illustration (area map) of appurtenant natural hazard, resp. risk connected with it. This kind of output is explicit, understandable and is able to be read by scientists from the other fields and emploees of state administration. SÚHRN Problematika extrémneho (maximálneho) povrchového odtoku je v súčasnosti ve mi aktuálna. V období posledných rokov sa opä vyskytlo nieko ko významných povodňových situácií, ktoré upriamili pozornos odbornej verejnosti na tento fenomén. V predloženej práci sa zaoberáme poh adom na extrémny odtok ako na prírodnú hrozbu, ktorá ohrozuje záujmy udskej spoločnosti v krajine. Chápanie vybraných prírodných procesov ako hrozieb je v súčasnosti vlastný väčšine prác anglo-americkej ale i frankofónnej environmentálnej geografie. Vychádza z chápania prírodnej hrozby ako nebezpečenstva plynúceho z prírodného procesu, ktoré môže drasticky ovplyvni krajinu, a tým i človeka. V prvej časti uvádzame práce, ktoré sa zaoberajú hodnotením vybraných prírodných hrozieb, ich príčinami a dôsledkami. Dôraz kladieme na práce, ktoré danú prírodnú hrozbu priestorovo fixujú do podoby mapového výstupu. Práve znázornenie priestorového dosahu hodnoteného prírodného procesu je hlavným prínosom tohto chápania. Naša pozornos sa alej sústre uje na hodnotenie samotného extrémneho odtoku ako prírodnej hrozby. Vychádzame z prác, ktoré sa uvedeným problémom zaoberajú za účelom vytvorenia metodického postupu hodnotenia povodňovej hrozby. Opä sa snažíme klás dôraz na znázornenie priestorového dosahu, je však potrebné uvies, že prác tohto typu je všeobecne menej. Príčinou je pomerne komplikovaný spôsob znázornenia rozsahu zaplaveného územia. V druhej časti sa venujeme aplikácii metodiky identifikácie a hodnotenia povodňovej hrozby na vybranom území. V našej odbornej literatúre je v súčasnosti minimum takto zameraných prác. Domnievame sa však, že zohrajú dôležitú úlohu pri identifikácii a hodnotení povodňového ohrozenia aj v našich podmienkach. Praktickým výstupom týchto prác je najčastejšie kartografické znázornenie (areálová mapa) príslušnej prírodnej hrozby, resp. rizika s ňou súvisiaceho. Takýto kartografický výstup je jednoznačný, zrozumite ný a dokážu ho číta aj odborníci z iných oblastí, pracovníci štátnej správy a pod. REFERENCES Baker, V. R.: Flood hazards Learning from the past. Nature, vol. 361, 1993, p Baker, V. R.: Geomorphological understanding of floods. Geomorphology, 10, 1994, p Burton, I. R., White, G. F.: The Environment as Hazard. OUP Oxford, Cooke, R. U., Doornkamp, J. C.: Geomorphology in Environmental Management. A New Introduction. Clarendon Press, Oxford, 1990, 410 p. Costa, J. E., Baker, V. R.: Surficial Geology, Building with the Earth. Viley, New York, Cross, J. A.: Agroclimatic Hazards and Wisconsin Dairy Farming. The Geographical Review, 84, 1994, p Cross, J. A.: Natural Hazards and Agriculture: Observation from the Midwestern United States. Abstract, IGU Praha, Degg, M.: The 1985 Mexican Earthquake. Reinsurance Offices Association, London, Degg, M.: History of natural hazards. Reactions, 1987, pp Dunne, T., Leopold, L. B.: Water in Environmental Planning. Freeman, San Francisko, Gilard, O.: Flood Risk Management: Risk Cartography for Objective Negotiations. Third IHP/IAHS George Kovacs Colloquium, UNESCO, Paris, sept Manuscript. Hewitt, K.: Climatic hazards and agricultural development: some aspects of the problem in the Indo-Pakistan subcontinent. In: K. Hewitt (ed.): Interpretation of Calamity. Allen & Unwin, London, 1983, p Hodgson, M. E., Palm, R.: Attitude toward disaster: A GIS design for analyzing human response to earthquake hazards. GeoInfo Systems, 2(7), 1992, p Hrádek, M., Matejka, J., Švehlík, R.: Náhlá ohrožení geomorfologickými katastrofami v České republice. Sborník České geografické společnosti, číslo 3, svazek, 99, 1994, p Hreško, J.: Lavínová ohrozenos vysokohorskej krajiny v oblasti Tatier. AFSHENUP, Prírodné vedy, Folia geographica 2, ročník XXX, 1998 a, p Hreško, J.: Erózna ohrozenos územia Toryskej pahorkatiny. AFSHE- NUP, Prírodné vedy, Folia geographica 2, ročník XXX, 1998 b, p Hrnčiarová, T., Miklós, L.: Morphometric indices in the interpretation of water and material motion dynamics illustrated on the example Dolná Malanta. Ekológia (ČSFR), Vol. 10, No.2, 1991, p Changnon, S. A.: Midwestern drought conditions Drought and Climate Change: Miscellaneous papers on the 1988 Drought and the issue of future climate change Research Report Midwestern Climate Center Staff, Champaign: Illinois State Water Survey, Juneja, N.: Performance Requirements for the Maintenance of Social Values Represented by the Natural Environment of Medford Township, N. J. Center for Ecological Research in Palnning and

8 96 Acta Universitatis Palackianae Olomucensis Facultas Rerum Naturalium Design, Department of Landscape Architecture and Regional Planning, Univerity of Pennsylvania, Philadelphia, Lamb, P. J. (ed.): The Drought in Illinois: Causes, Dimensions and Impacts (Research Report 121). Champaign: Illinois State Water Survey, Lichý, J., Klačan, J., Styk, J.: Modelovanie neustáleho prúdenia vôd. Zborník Geoinfo Slovakia 97. Bratislava, 1997, p Löw, J.: Urbanistická reflexe povodní. Zborník z konferencie Povodně a krajina 97, Brno, 1997, p. 8/9 8/13. Markvart, J.: Problematika regulativú ÚPD, vyplývajících z vymezení zátopových území. Zborník z konferencie Povodně a krajina 97, Brno, 1997, pp. 8/19 8/20. Matthews, K. B., et all.: Climatic soil moisture deficit climate and soil data integration in a GIS. Climatic Change 28, 1994, p Minár, J., Tremboš, P.: Prírodné hazardy hrozby, niektoré postupy ich hodnotenia. AFRNUC Geographica Nr. 35, 1994, p Monkhouse, F. J., Small, J.: A Dictionary of the Natural Environment. Edward Arnold, London, 1978, 320 pp. Oancea, V., Stanescu, A. V., Mic, R.: Application of the QDF models in regional analysis of rare floods. Annual report n O 4, FRIEND AMHY Group, UNESCO, Paris, Panniza, M.: The geomorphological hazard assessment and the analysis of geomorphological risk. In: V. Gardiner (ed.): International Geomorphology, Wiley, Chichester, 1986, p Panizza, M.: Geomorphological Contributions to seismic risk assessment. Supplementi di Geografia Fisica e Dinamica Quaternaria, Supplemento II, 1989, p Petak, W. J., Atkinson, A. A.: Natural hazard risk assessment and public policy: anticipating the unexpected. New York, Springer Verlag, XVI, 1982, 489 p. Smith, K., Tobin, G.: Human Adjustment to the Flood Hazard. Longman, London, Tremboš, P.: Environmental limits their forms and importance in the process of ecological landscape carrying capacity evaluation. AFRNUC, Geographica Nr. 33, 1992, p Tremboš, P., Minár, J., Machová, Z.: Identification of Selected Natural Hazards from Viewpoint of the Evaluation of Environmental Limits. AFRNUC Geographica Nr. 34, 1994, p Trizna, M.: Hydrologické aspekty hodnotenia povodňovej hrozby. AFRNUC Geographica Nr.35, 1994, p Trizna, M., Minár, J.: Niektoré nové metodické aspekty hodnotenia povodňovej hrozby. AFRNUC Geographica Nr. 39, 1996, p Trizna, M.: Hodnotenie zranite nosti územia pri identifikácii povodňového rizika. AFRNUC Geographica Nr. 41, 1998, pp RNDr. Milan Trizna, PhD. Department of Physical Geography and Geoecology Faculty of Natural Sciences Comenius University Mlynská dolina, Bratislava 4 Slovak Republic Trizna@fns.uniba.sk Reviewed: doc. RNDr. Juraj Hreško, CSc. Acta Univ. Palacki. Olomuc. Fac. Rer. Nat. (2000), Geographica