Review of Flood Situation 1998/2001 and Recommendations on Flood Management | |
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Review of Flood Situation 1998/2001 and Recommendations on Flood Management for Tisa Basin, Zakarpattia Oblast. Contents 1. Overview of Tisa River Basin 1.1 Discharge Area 1.3 Agriculture 1.4 Status of engineering facilities in river basins 1.7 National system of forecasting, monitoring and response to disaster situations 2. The 1998 Flood Profile (based on expert conclusions of the government commission) 2.3 Status of flood engineering construction 3. 2001 Flood Background (as based on data presented by the ministries and other government agencies) 3.1 Hydrometeorologic status and forest impact 3.2 Disastrous environmental processes 3.3 State of construction of flood protection facilities 3.4 Flood Causes 5. Actions to be taken to prepare for future floods 5.1 Construction of anti-flood facilities 5.2 Improve silvicultural and agricultural practices 5.3 Hydrometereological support 6. Sources of background information
1. Overview of Tisa River Basin The Ukrainian part of the Tisa Basin encompasses Zakarpattia Oblast, which belongs to a high elevation region of the Ukrainian Carpathian mountains, stretching 250 kilometers from the northwest to the southeast, from the Upper San River to the riverhead of Seret. The larger part of the Tisa Basin is shared between Romania, Hungary, the Slovak Republic, and Poland. The area of the Tisa Basin, one of the largest tributaries of the Danube River, is 154,400 square kilometers, of which 12,700 square kilometers, or 8.1%, is within Ukraine, 46% - in Romania, 26.9% - in Hungary, 9.9% in the Slovak Republic, and 6.4% in Yugoslavia. The water discharge of the Tisa is formed primarily within the territories of the three countries of Romania (50.9%), Ukraine (25.6%), and the Slovak Republic (13.4%). The annual discharge median for the Tisa is 9.44 billion cubic meters, with discharges of the Latorytsia and Uzh Rivers as its main tributaries, totaling 7.3 billion and 5.07 billion cubic meters, respectively. Compared to other bordering states, the discharge and precipitation levels are estimated to be two- to threefold higher in Ukraine, increasing the risk of local disaster floods. A group of Carpathian ridges on the routes of humid air moving from Atlantic Ocean serve as a barrier, leading to intensified rainfalls that cover the territories as vast as 10,000 - 30,000 square meters. In this case, daily precipitation may reach 150-250 mm or two to three monthly medians. Zakarpattia Oblast is located within the two orographic zones. It mainly includes the area of the Carpathian Mountains and foothills, with the Hungarian plain encompassing an area of 2,500 square kilometers, or 25 percent of Zakarpattia Oblast . These orographic attributes have impact on river dynamics when flood situations arise. Steep mountain hills cause high flood velocities, with river stages raising 1.5 to 2.5 meters higher within three to four hours. The concurrent runoffs flow from the mountains to submontane Tisa and lower tributaries that are unified by numerous irrigation channels. As the banks of lowland rivers are not high, floodwaters cover vast territories leaving virtually no time to redirect flood flows. Natural factors were the primary causes behind the disaster floods in the years 1700, 1730, 1805, 1864, 1887, 1900, 1911, 1926, 1933, and 1941. However, over the last 50 years, anthropogenic factors played a determining role in disaster floods. It should be noted that in the first half of the twentieth century, anthropogenic impact on Carpathian landscapes was insignificant, and that the periods of low water became more rare, whereas the periods of high water reoccur with higher frequencies. The Hydrologic Meteorological Service revealed that in the 1990s, the period of high water succeeded the period of low water of 1982-1990. That period was characterized by high water encompassing not only Zakarpattia, but also other regions within Ukraine and Western Europe: 1992 (Zakarpattia), 1993 (Zakarpattia/Polisia), 1994 (Germany), 1995 (Zakarpattia), 1996 (Dniester-Basin), 1997 (Poland, Czech and Slovakia Republics, Germany), 1998 (Zakarpattia, Dniester, Slovak Republic, Germany). For Zakarpattia, relevantly high precipitation levels are common in November and December. There is a high probability that the period of high water will last through 2005 - 2008. Therefore, it should not be excluded that in the next few years, western Ukraine may face a reoccurrence of high floods. The precipitation-monitoring network showed that the period of excessive water content is characterized by high precipitation. In this case, the precipitation exceeds the annual precipitation median by two- to threefold. For instance, the most disastrous years for Zakarpattia were as follows: 1882, 1887, 1902, 1912, 1925, 1941, 1970, 1978, 1980, when the annual precipitation ranged between 1,600 and 2,400 mm (up from the normal level of 1,000 - 1,100 mm), and between 250 - 400 mm in specific months (up from the norm of 70-120 mm). According to the State Forestry Committee of Ukraine, intensive deforestation practices in the Carpathian forests commenced in the middle of the eighteenth century, with man-made deforestation beginning from the upper mountainside for the expansion of pastures and arable land, which led to a 1.5 fold decrease in forestland area . From the middle of the nineteenth century, industrial deforestation began and the age structure of the trees changed. Following World War II, the Carpathian forests substantially suffered from clear-cuts when their scopes exceeded scientifically admissible standards. In addition, in from 1957 -to 1960, windfalls hit more than 500,000 hectares of forests. Since the 1970s, industrial deforestation in Zakarpattia has been based on scientifically-sound standards with planned reforestation in the areas of the clear-cuts. The share of logging operations per hectare (38%) is substantially lower in Ukraine than in neighboring Hungary, Czech Republic, or Austria. The analysis of forestland area in Zakarpattia Oblast and the current level of silvicultural operation showed a positive trend. According to recent national forestland analysis, over the last ten years, forestland area increased by 7,000 hectares, to total 42 million cubic meters. The age structure is currently close to the optimum levels. Mature and over mature forests make up 23.2 percent of all forestland area. The age of all forest plantations in state forestry enterprises increased from an average of 56 years in 1973 up to the current age of 81. Of the total land area in Zakarpattia, the share of forestland area is currently rated at 50.8 percent, up from 42.6 percent as of 1946. However, certain gaps in silvicultural practices still exist. The Zakarpattia Scientific Commission presented data stating that the upper levels of forestland area are now 200 - 300 meters lower and that the age structure and composition of trees have dramatically changed. The under wood and middle-aged trees, which constitute up to 60 percent in some areas, have much lower water regulation capacities than mature and ripened woods. It should be noted that for Tisa tributaries, the share of forestland area should stand between 75 and 80 percent, up from the current levels of 50 - 60 percent. The 1995 decision of regional authorities, authorizing nearly 400 small and medium businesses to undertake logging activities in the region, had a harmful effect. The logging businesses were staffed with low-skilled specialists and outdated machinery, making impracticable the application of environmentally-sound logging techniques. Meanwhile, a Commission of the National Academy of Sciences concluded that under the extreme flood circumstances of November 1998 and March 2001, precipitation exceeded forest water regulation capacities by seven- to tenfold. Therefore, the forest cover should not be viewed as a key factor in the 1998 and 2001 flood trends. However, the above factors could have a negative effect on resistance of slopes to landslide and debris flows. To date, agricultural area forms up to one-third of Zakarpattia. It mainly consists of high elevation pastures, forest pastures, and small plots of arable land within forest belts,, orchards, wine grapes, hayfields, and pastures in Peredhirya (foothills), and Prytysk Lowland. According to the National of Sciences Commission, the pattern of agricultural practices has the highest influence on the formation of surface discharge and initial phases of debris flows. Unregulated overgrazing, primarily herds of sheep, led to the erosion of soils and turf, and drastic decrease in water regulation of high elevation pastures and water resistance of soils. That area became the place where intensified snow avalanches, surface drainage, soil and turf erosion and landslides now form. Unsatisfied division of agricultural and silvicultural practices and cattle grazing in forestland areas resulted in a decrease in soil protective and water regulatory functions, extra water discharge and erosion. 1.4 Status of engineering facilities in river basins Since 1863, a total of 685 kilometers of levees and nine water reservoirs, primarily for hydropower purposes, have been built in Zakarpattia. Because of the low total capacity of reservoirs and the lack of anti-flood component, they produced virtually no effect on the gauge heights and velocities of flood flows. It should be noted, however, that the levees have been constructed episodically by various countries, and have a diverse level of resistance and height. According to the State Water Management Committee, the levees constructed in the past are far from forming a unified anti-flood network and do not meet the technical criteria. Hydro-engineering facilities run by Hungary, the Slovak Republic, Romania, and Yugoslavia, as the countries within the Tisa Basin, where the conditions of heavy floods are quite identical to Ukraine, are not united into a single anti-flood network with Ukraine. Currently, seven railroad and nine motor bridges constructed in the Ukrainian part of Zakarpattia restrict the water floods in critical periods, causing follow-up pressure on close constructions and heavy floods in neighboring areas. The results of the regional survey of the geological service revealed nearly 1,600 sites of landslide hazards in Zakarpattia located within the areas of diverse geo-structural and basin pattern. The survey also revealed more than 120 debris flows, and multi-kilometer plots of eroded soils. According to preliminary information, in the past 30 - 35 years, the number of landslide sites doubled with the number of intensive landslides reaching 50 percent of the total landslides (up from a 15 - 20% critical level). Debris flows are mainly observed in high elevation areas and formed during intensive summer rainfalls. Debris flows can also happen in Zakarpattia in winter, when snowmelt is complemented by rare or mixed precipitation. Based on genetic classification, a landslide hazardous area was detected along the right bank of the Tisa tributaries in southwestern Zakarpattia. Extensive debris flows hit Ukraine three times: 1948, 1969, and 1998. The removal of debris flows of six to ten million cubic meters, which had practically no precedents in the twentieth century, are striking examples of threats that such occurrences may pose. The stream gauging and precipitation monitoring network in the Tisa Basin consists of ten precipitation gauging stations, 38 streamflow gauges, 30 precipitation gauging posts, four soil moisture gauging posts and 30 land plots where water content in snow is measured. Regretfully, there is only one automatic streamflow gauging post on the Tisa River, located in Tyachiv), and one more automatic precipitation gauging station in Khust. The data is transmitted via telephone and telegraph. In ordinary circumstances, a precipitation gauge measures the data every four hours, with streamflow gauges taking measurements every 12 hours. During floods, the stream flow gauge measurements become more frequent (every four hours). In the Tisa Basin, the introduction of an informational and forecasting system is underway. This system includes the following:
1.7 National system of forecasting, monitoring and response to disaster situations To resolve the issues relevant to forecasting, monitoring and response to disaster situations, the Zakarpattia Oblast State Administration issued a resolution establishing a permanent commission on emergency situations with the Vice Governor serving as its chairman. The commission consists of heads of regional divisions of ministries and government agencies, including the Ministry of Emergency Situations and Chornobyl Affairs, the Ministry of Ecology and Natural Resources, geologists and representatives of the hydrometeorologic service, officials from the health, water, communal, fishery, forestry, agriculture, manufacturing and communications industries. Similar commissions are established within each raion state administration. The State Commission on Technogene and Environmental Protection and Emergency Situations was established under the Cabinet of Ministers. Given the high frequency of heavy floods in Zakarpattia and extremely expansive flood-related restoration works, the Department for Coordination of Restoration and Construction Works, the only one of its type formed in Ukraine, has been established under the Zakarpattia Oblast Administration. 2. The 1998 Flood Profile (based on expert conclusions of the government commission) The summer and autumn of 1998 saw heavy precipitation in Zakarpattia. All precipitation gauging stations registered that the mean precipitation in those months exceeded the regular monthly gauge median. Precipitation in August and October was 1.2 to 1.5 times higher than regular indices. Overall precipitation gauged by the precipitation gauging stations and stream flow gauging stations averaged 45 - 74 mm, reaching 90 - 120 mm in several areas of the Latorytsia, Borzhava, Teresva, and Tisa Rivers, and up to 207 mm in the Upper Tisa. The daily averages peaked the monthly precipitation rates, with excessive daily precipitation in November exceeding the monthly rates by 150 percent. The stream flow gauges registered a 1.7 - 3.6 meter increase from regular river stages near Tyachiv and Vylok, with a 4.1 - 6.1 meter rise registered in the area adjacent to Mukacheve. The 13 gauges registered that water stage exceeded historic gauge heights. Intensified ground failure processes (mainly landslides and debris flows) in November and December 1998 and in the spring of 1999 (the total number of disastrous landslides and debris flows peaked to 900 and 100, respectively) coincided with high solar activity, and moistening of mountain soils over the previous three years, which became especially excessive in 1998. The catastrophic rainfalls complemented by other meteorological factors, intensified landslide and debris flows of diverse genetic origin, volumes and intensity, coming practically concurrent with the floods. Several ground failures had disastrous impacts. To mention a mere few, a 40 million cubic meter debris flow destroyed the adjacent village of Vilkhivski Lazy, with a debris flow of 12,000 cubic meters taking its death toll in the village of Ruska Mokra. The phase of intensified debris flows continued through 1999. 2.3 Status of flood engineering construction The Flood Management Program for 1994 - 2000 provided for construction of 200 levees, and regulation of 162 kilometers of river profiles. However, due to extremely unstable and scarce funding since its initial phase, as of November 1, 1998, a mere of 33 kilometers of levees have been constructed, or 17 percent of the initial program plans, and additional 20 kilometers of river banks (39%) were reinforced, 41 kilometers of river channels were regulated, or 25 percent of the program targets. Natural causes:
Anthropogenic impact and inappropriate water, silvicultural and agricultural practices over the last 200 years have had a negative effect on the scope of flooding:
The break up of rules and requirements during the construction of populated localities can be also cited amongst other anthropogenic factors of disastrous events in Zakarpattia. Social and economic after-affects would have had much less impact had the requirements on the allotment of land plots for the residential and farm business construction, and construction norms, particularly in seismic hazardous and environmentally hazardous areas been met. 3.1 Hydrometeorologic status and forest impact The Ukrainian Hydrometeorological Center and Zakarpattia Department of Water Management Committee said that between the evening of March 3 and the morning of March 5, because of a rapidly moving active cyclone, Zakarpattia saw high precipitation of rain and snow. (The regular precipitation for March is 60 mm). The precipitation measured by the stream flow gauging stations based in Zakarpattia, was distributed by river basins, including the mountain areas, as follows:
These data prove that precipitation was high practically throughout the Tisa Basin. The precipitation was especially high in the Upper Tisa and basins of its major tributaries: Teresva, Terebli, Riky, and Borzhava. The precipitation was much higher than the precipitation behind the heavy flooding in November 1998 (1.8 cubic kilometers versus 1.1 cubic kilometers). During March 3 - 5, 2001 the precipitation in the rest of Zakarpattia (Latorytsia and Uzh basins) was close to the regular levels of 50 mm to 100 mm. Prior to the rainfalls, the snow cover was 3 - 18 cm high, and up to 44 cm in the mountain areas. In 1998, the snow cover in the mountain areas was insubstantial. The temperature rises from 5C to 13C, concurrent with heavy rainfalls, led to snow melting both in mountain areas and lowlands. According to estimates of hydrologic experts, the March 3 - 5 flooding was caused mainly by high rain precipitation (80%) and less by melted snow (20%). It should be noted, however, that the highest registered water discharge was of a mixed origin. During the March 2001 flood, the regulatory role of forests was much less than required. The trees and bushes could resist only three mm of the precipitation in beech forests and ten mm in pine forests. In the summer season, because of the trees covered with leaves, as well as transpiration, those indices would have been much higher. Regularly, the leaves remaining on the ground in forests could absorb five to seven mm of precipitation, and up to six mm in pine forests. During that flood, leaves on the ground had already been moistened. Soil can absorb moisture most when the ratio between the minimum and full moisture absorption ranges between 120 mm and 130 mm. However, the soil moisture prior to the rainfalls of March 4 and 6 was high, peaking at practically the highest admissible level. Therefore, the water absorption of the forest cover was enough only to sustain the precipitation of 30 - 45 mm. On March 5 - 9 the maximum gauge heights registered in the river basins of Tisa, Borzhava, Latorytsia, and Rika reached the November 1998 flood levels, exceeding previous flood levels in some areas. The Tisa-Khust stream flow gauge recorded that historic height was surpassed by 31 cm, at Tisa-Tyachiv gauges by 16 cm, in Tisa-Rakhiv by 75 cm, in Latorytsia - Chop by four cm, and Tisa-Chop by 19 cm. A new phase of floods that hit the area close to the Hungarian town of Tarpa on March 6, 2001, overtopped and ruined a right bank levee, flooding the neighboring territories, with waters billowing into Ukraine. The design of the above levee was enough to sustain the floods exceeding the historic heights only by one percent. According to recent updates, the breakthrough of the levee was up to 200 meters in length, whereas the flood stage exceeded a three-meter height, overtopping the levee's crest. The water volumes billowing into Hungary as a result of the breakthrough of the levee totaled 120 million cubic meters, with the water discharge reaching at times up to 600 cubic meters per second. According to preliminary data, the flood flows totaling 90 million cubic meters reached Ukrainian territory (Zakarpattia raions of Berehiv and Uzhhorod raions) when the major stage of domestic floods in Tisa, was about to end. 3.2 Disastrous environmental processes According to the NASU Commission, the intensified geologic processes in March 2001 were of different origin. In 2000 the total precipitation was lower than regular norms, and mountain soils within the landslide and debris flow areas have not suffered from excessive moistening. The majority of landslides and debris flows (i.e., 446 landslides and debris flows in 98 settlements), were the result of short-term excessive moistening of soils on the mountain hills on March 3, 4, and 5, 2001. This moistening was behind the intensified but not excessive landslides and debris flows. The runoff from small rivers that brought stones downstream played a key role in the occurrence of debris flows. 3.3 State of construction of flood protection facilities A mere of 60 kilometers out of 200 kilometers of levees have been constructed, or 30 percent of initial program targets under the Comprehensive Flood Management Program for 1994 - 2000. Only 68 percent of riverbank protection facilities (35 percent of 51 kilometers initially planned) have been erected, with 52 percent kilometers of river channels having been regulated (84 kilometers of 162 initially planned). Following the November 1998 flood a new (target) program was designed. It was entitled the 1999 - 2000 Flood Management Program in Zakarpattia Oblast. The Cabinet of Ministers approved the program in its resolution #488 as of March 31, 1999. The program envisioned the construction and restoration of 29 hydro engineering facilities, 101.7 kilometers of levees, 39.2 kilometers of bank protection facilities and adjustment of 88.63 kilometers of river profiles. According to the State Water Management Committee, during 1999 - 2000, a total of six hydro engineering facilities were constructed and restored (20.7%), 27.3 kilometers (26.9%) of bank protection structures were built; 14.3 kilometers of levees (36.6%) were erected, and 43.4 kilometers (49%) of river profiles were adjusted. All those actions have made 70 settlements flood-protected, down from 119 settlements as initially defined in the program. The causes of the 2001 flood are identical to the causes behind the 1998 flood events but are higher in scope of disastrous events. The precipitation levels during the similar flood peak were 40 times higher than in 1998, complemented by frozen ground. The precipitation was complemented by melted snow (20%) and lowered transpiration from forests in the winter period; budget constraints and limited time in mitigating the 1998 flood after-affects, as well as gaps in silvicultural practices. During those flood events 40,793 residential houses were underwater, of which 2,695 houses collapsed and 2,877 damaged. Twelve bridges and 48.6 kilometers of highways suffered damage. Eighteen water inlets, 28 sewage-pumping stations, 20 purification plants, and 45 boiler units were out of service. A 3.1-kilometer railroad track was damaged, and 2.4 kilometers of railroad track were ruined. The November rainfalls and follow-up floods caused 810 million UAH (149.7 million) in damages to Zakarpattia Oblast, including 12.08 million UAH in damages to hydro-engineering facilities. According to the Zakarpattia Oblast Administration, as of May 27, 2001, the flood events ruined 1,924 residential houses, forcing displacement of 4,948 residents. As a result of the flood events, six bridges were ruined, 17 bridges collapsedand 52.7 kilometers of highways were damaged. Additionally, 1.4 kilometers of railroad track were out of service, with an additional 9.15 kilometers of railroad track damaged. A Zakarpattia oblast) geological survey group detected an additional 539 active landslides encompassing an area of 6.4 square kilometers with the total volumes of 18.5 million cubic meters, as well as 88 debris flows in a total area of 0.5 square kilometers, and in the volumes of 0.6 cubic meters, 143 plots of the 26 - kilometer bank erosion areas. Those ground failure processes damaged 231 houses and ruined 17 houses. The survey group recommended monitoring of 749 houses located within the zones of highest activity of landslides and debris flows. The flood had a death toll of nine (five fatalities in Vynohradiv raion, and four in Khustk raion). According to preliminary data, the March 2001 flood, resulting from high precipitation and melted snow, brought 317 million UAH (58.6 million) in damages to Zakarpattia. 5.1 Construction of anti-flood facilities (based on data from the State Water Management Committee)
The budget of all flood preparedness actions totals 1.26- billion UAH (232.9 million) and is practically concurrent with the damage incurred by the nation from the latest two disastrous floods.
5.2 Improve silvicultural and agricultural practices (based on the recommendations presented by the Zakarpattia Oblast Administration, NASU Commission, and State Forestry Committee)
5.3 Hydrometereological support (Source: Department of Hydrometeorology and Monitoring within the Ministry of Ecology and Natural Resources)
6. Sources of background information ULRMC expresses its appreciation to the Ministry of Emergency Situations and Chornobyl Affairs of Ukraine, the Ministry of Environment and Natural Resources, the State Water Management Committee of Ukraine, the State Forestry Committee of Ukraine, the National Academy of Sciences of Ukraine, Zakarpattia State Oblast Administration, the Hydrometeorologic Institute for providing the organizational and informational support in conducting the research on the causes and implications of flooding in Zakarpattia. The following materials have been used in preparation of this document:
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[ Last updated : 22-Jun-2001 18:34 ] |
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