HYDROLOGY AND FLOOD MANAGEMENT

Transcription

1 HYDROLOGY AND FLOOD MANAGEMENT B. C. K. Mishra 1 JK UPADHYAY 2 1 Executive Director, UJVN Limited, Dehradun 2 Exeuctive Engineer, UJVN Limited, Dehradun ABSTRACT Hydrology, flood estimation and flood management ever remained the domain of the hydrologists, water resources engineers and statisticians. The floods are created and influenced by characteristics of the catchment, such as meteorology, topography and geology. Hydrological Model Studies have been the component of flood hazard management, which are the actions to be taken to avert flood disasters. It is a cyclical process initiated by occurrence of an excessive flood. It leads through the reconstruction and rehabilitation phase to hazard assessment and project planning and implementation, and finally to operation and preparedness for a next intense flood again. The tasks of flood management can be divided into two consecutive parts i.e. planning and operation. These parts basically require different kinds of hydrological models. For planning, real time runoff is not desirable, one works with design scenarios. For this task, models should be used suitable to the tasks at hand, which reflect characteristics of land area as well as of hydrological scale. For operation, hydrological forecast models are required which have to meet different set of situations. INTRODUCTION For centuries, men have been investigating where water comes from and where it goes, why some water is salty and some is fresh, why sometimes there is shortage and sometimes there is excess. All questions and answers related to water have been kept together into a discipline Hydrology. The name hydrology is formed by two Greek words i.e. "hydro" and "logos" meaning "water" and "science. It indicates that Hydrology means the science of water. The science of water deals with the occurrence, circulation and distribution of water of the earth and its atmosphere. It is related with the water in streams and lakes, snowfall and rainfall, the quantum of snow and ice on the land and water existing below the earth s surface in the pores of the soil and rocks. The understanding of the hydrologic processes is important for the assessment of the water resources, their management and conservation on global as well as regional scales. Generally engineering hydrology deals with Estimation of water resources, the study of processes such as evapotranspiration, precipitation, run off and study of problems such as floods and droughts and strategies to come out from them. A flood is a surprisingly high stage in a River normally the level at which the River overflows its banks and inundates the adjoining area. The damages caused by floods in terms of loss of life, property and economic loss due to disruption of economic activity are all well known. Flood control is normally used to denote all the measures adopted to minimize the damages to life and property by floods. There is always a possibility, however remote it may be, of an extremely large flood happening in River. The complete control of the flood to a level of zero loss is neither physically possible nor economically feasible. Floods are natural phenomena, which is water linked disaster. Floods cannot be totally controlled but can only be managed and flood losses can be reduced.

2 ICHPSD-2015 FLOOD Of all the disasters that regularly hammer India, floods are possibly the most repeated and they impact large areas. India is also one of the most flood prone countries of the world, with 23 out of the 35 states and Union Territories vulnerable to floods (Source: MHA). In terms of geographical area, about one eighth (1/8) or 40 million hectares of land are prone to flooding. All Indian Rivers basins are vulnerable to floods. The main causes of devastating floods are attributed to heavy rainfall and topography of catchment area, insufficient drainage, failure in flood control structures like embankments and levees etc. Poor permeability of soil causes flash floods. Human interferences like constructions in riverbeds, poor planning and implementation, poor drainage and sewerage system are main causes of urban floods. Floods are among the most frequent natural disasters. Conditions that cause floods include heavy or steady rains for several hours or days that saturate the land. Flash floods happen suddenly due to quickly rising water along a stream/river or low lying area. A flood is an excess of water or water with mud on land that is normally dry and is a situation wherein the inundation is caused by high flow, or overflow of water in an established watercourse, such as a river or stream, or drainage channel; or ponding of water at or near the point where the rain is falling. This is a duration type incident. A flood can hit anywhere without warning. It occurs when a large volume of rain falls within a short time. Almost, all Indian Rivers carry heavy floods during the monsoons when their catchment receives intense and heavy rainfall. In the upper reaches of Rivers, where it flows through mountainous terrain or undulating area, there is generally no overflow of the banks during high flows or flood. In low lying areas, especially where the area is comparatively flatter, the rivers flow over their banks and cause inundation, submerge crops & property and also disrupt communications. In order to know the availability of surface water in a country and its related flood problems, it is always necessary to recognize the river stream of that country. TYPES OF FLOODS Flash Floods Floods occurring within six hours mainly due to heavy rainfall coupled with towering cumulus clouds, thunderstorms, tropical cyclones or during passage of cold weather fronts, or by failure of dam or other river obstructions. River Floods Floods caused by heavy precipitation over a large catchment area, melting of snow or both, built up slowly or on a regular basis. These floods may prolong for days or weeks. The key factors of these floods are moisture, vegetation cover, thickness of snow, area of the catchment basin etc.

3 Coastal Floods Floods associated with cyclonic activities like Hurricanes, Tropical cyclones etc generating a disastrous flood from rainwater which often aggravate wind induced storm and water surges along the coast. Urban Flood The land converted from agricultural fields or woodlands to roads and parking etc loses its ability to absorb rainfall. Urbanization decreases the capability to absorb the water 2 to 6 times over what occurs on natural terrain. During periods of urban flooding, the streets become swift moving rivers while basements become pond or death traps as they fill with water. Ice Jam Floating ice accumulates at natural or human made obstruction and stop the flow of water thereby caused floods. Flooding may also occur when the snow melts at a very fast rate. Glacial Lake Outbursts Flood (GLOF) Many of the big glaciers melt rapidly and form origin to a large number of glacier lakes. Due to snow and ice melting at a faster rate caused by the global warming or what soever, the accumulation of water in these lakes increase rapidly and result in sudden discharge of large volume of water and debris and cause flooding in the downstream. CAUSES OF FLOOD Inadequate capacity of the rivers to contain water within their banks, the extensive flows brought down from the upper catchment areas following heavy rainfall, leads to flooding. The tendency to occupy the floodplains has been a serious concern over the years. Because of the changeable rainfall distribution, many a times the areas which are not usually prone to flood, also experience severe inundation. Areas with poor drainage system get flooded by accumulation of water from heavy rainfall. Excess irrigation water applied to command areas and an increase in ground water levels due to seepage from canals and irrigated fields also are factors that bring out the problem of water logging. The problem is aggravated by factors such as silting in the riverbed, reduction in the carrying capacity of river channels, erosion of banks and beds lead to changes in river courses, obstructions in flow due to landslides, synchronisation of floods in the main and tributaries and retardation due to tidal effects. Rainfall in Catchment area Whenever there is heavy precipitation in the catchment area in terms of intensity, duration and spread, the river will carry high discharge and thus this is the main reason of rivers to be in flood. The high intensity of rainfall in the catchment area is the main cause of flood. If the precipitation is normal and the storm duration is short, the surface run off will flow easily through the tributaries and rivers will not create any problem to the downstream area. But if the precipitation is very heavy and the storm duration is longer, then the surface run-off will be increased and it may exceed the normal carrying capacity of the river and hence

4 ICHPSD-2015 overtopping of the river banks may occur and the surrounding area may get flooded. It is evident that larger the catchment area more will be the flood. The catchment area having steep slopes increases the runoff and sediment inflow due to the high velocity of flow. The shape of the basin also affects floods. For a fan shaped catchment, the time of concentration will be less and therefore the storm hydrograph base period will be less and the peak flow will be more. In case of an elongated shaped catchment of equal area and the same storm, the time of concentration will be more. Hence, the storm hydrograph base period will be more and the peak flow will be comparatively less. Therefore it is established that the size, slope and shape of the catchment area directly affects the flow of the river. Sedimentation in Rivers and Reservoirs Reduction in flood control capacity of reservoir due to heavy silting will affect the flow of the river. If the tributaries of a river bring heavy sediment load, the river bed goes on silting up slowly every year. It will influence the carrying capacity of the river. Ultimately the cross section of the river will be reduced and it will not be able to bear the high flood flow. Thus sedimentation of rivers and reservoirs are also responsible for the flood. Obstruction in the River flow Whenever there is a heavy landslide in the river, it may cause flood in the upstream due to arrest of flow and subsequent rise in water level. Due to heavy precipitation, when the water pressure reaches at maximum value, then suddenly obstruction may be removed and a high column of water may charge downstream area. The river also changes its course due to obstruction and causes in flooding the area. Contraction of River Section Inadequate waterways at the crossings of rail and road also affect river flow. During construction of road or railway bridges across the river, the approach works are done on both banks, which decrease the cross section of river. The flow carrying capacity of the river also reduce due to construction of piers in waterways and causes risen the flood level. In this case, the water rises in the upstream due to inadequate passage and thus the upstream area may get flooded. Inadequate C ross D rainage Wor ksconstruction of cross drainage works also reduces the depth of flow for the high flood flow. In cross drainage works such as aqueduct, the river passes below the canal. In such a case the structure which is constructed for the smooth running of the river flow may be insufficient for the high flood flow and water level may rise in the upstream side, which may inundate the surrounding area. Other Causes Floods may be caused due to heavy melting of glacier and ice. In Case there is breach of a dam, the reservoir water may charge towards the downstream side causing heavy flood for a short period. Sometimes river bed may be raised due to earthquake. This may also cause flood in the upstream due to the arrest of flow as well as on the downstream, for some distance for a small period.

5 Flood due to failure of a dam. Global warming. FLOOD CONTROL Floodplain is a pleasing location for man and his activities, it is important that floods be controlled so that the damage does not go beyond an acceptable limit. The damage caused by floods in terms of loss of life, property and economic loss due to disruption of economic activities are well known. It is not possible to stop floods but it is possible to reduce the damage due to floods by controlling the floods. Thus flood control or flood management is defined as the prevention or reduction of the flood damage. Though the complete control of flood up to the extent of zero loss is neither physically possible nor economically feasible but its effect can be moderated for reducing losses to life and property. Traditionally flood control measures can be classified as hereunder: i. Structural method a. Storage and detention reservoirs, b. Levees (flood embankments), c. Floodways d. Channel improvement and, e. Soil conservation ii. Non-structural method a. Flood warning and evacuation. i. Structural method a. Storage and detention reservoirs Storage reservoirs are one of the most reliable and efficient methods of the flood control. In this method a part of reservoir is reserved to absorb the incoming flood. The stored water is released in a controlled way over an extended time so that downstream channels / river do not get flooded. To attain complete flood control in the entire length of river, a large numbers of reservoirs at planned locations in the catchment shall be required. A detention reservoir consists of an obstruction to a river with an unrestrained outlet. These are basically small structures and operate to reduce the flood peak by providing temporary storage and by restriction of the flow rate. b. Levees (Flood embankments) Levees are also known as dikes or flood embankments which are earthen banks constructed parallel to the course of the river to confine it to a fixed course by limiting cross sectional width. The height of levees is kept well above the design flood level with free board. Levees are one of the oldest common techniques of flood protection work adopted in the world. It is the most economical structural flood measure.

6 ICHPSD-2015 c. Floodways Floodways are natural channels into which a part of the flood is diverted during high threat. A flood way may be a natural or constructed channel and its location is controlled by the topography of the area. Whenever it is possible, floodway is alternative to other structural flood control remedies. To trim down the level of Jhelum River at Srinagar (Jammu & Kashmir), a flood way canal with a capacity of 300 cumecs has been constructed. This canal is located 5 km upstream of Srinagar city and it terminates in Wullar Lake. d. Channel Improvement In this technique, existing channels or canals in the catchment require continued maintenance such as widening or digging of the channel to enlarge the cross sectional area of the channel and reduction of the channel roughness etc. e. Soil conservation Soil conservation actions in the catchment when properly planned and effected lead to all round improvement in the catchment characteristics affecting abstractions. Increased infiltration, greater evatranspiration and reduce soil erosion are some of its easily identifiable results. ii. Non-structural method a. Flood Plain Zoning Areas near the river are the most susceptible for the flood hazards provided the areas are not a highland. Therefore, public should not be allowed to those flood prone areas for construction houses. Places lying below the high flood level should be restricted for inhabitation. These areas should be retained for parks, recreation ground, etc so that inundation of such areas may result in saving life and properties. b. Flood Forecasting The emergency evacuation of the endangered area is one of the most effective means of reducing damage due to flood under certain circumstances. Once the flood happens, the normal activities of the people are badly disrupted with huge losses. Therefore, flood forecasting is a real requirement to minimize the immense losses. Temporary evacuation of people and shifting the important assets to safer paces could be done before the flood arrives. c. Flood Proofing In cases where certain isolated high value properties are threatened by flooding, they may be individually flood proofed. It consists of a combination of structural change and emergency action. Structural change includes construction of the building wall with some water proofing chemical and material, closure of low level windows and providing some techniques of watertight enclosure for the doors. Thus, even when the building may be surrounded by water, the property kept in it is protected from harm and many normal functions can be carried on. In

7 such a way, the industrial plant having buildings, storage yards, roads, etc. may be protected by construction a ring levee or flood wall. d. Mathematical Modelling In the flood tragedy mitigation measures, pre defined mathematical model by computer can predict flood intensity and area of inundation whether it is flood in river or a flash flood due to dam break or dike failure or what soever. When natural flood in upstream of a river is recognized, mathematical model of flood routing can predict the flood amount at some downstream locations of the river. Thus mathematical modelling techniques can alleviate the flood disaster in the river valley in case of both natural or dam break flood situation. LOSSES DUE TO FLOOD There are two types of losses due to Flood Disaster. Tangible Losses The tangible losses are those, which can be estimated in terms of some currency value. (i) (ii) (iii) (iv) (v) Damage of properties like buildings, public facilities & utilities, roadways, bridges, canals, embankments, telephone lines and electric lines etc suffer considerable part of flood damages. These damages are assessed on the basis of estimated cost of repairs and restoration. Damage to the crops occurs more than 60% of the total damages in India and hence greater care is necessitated for its assessment. Thus the correct technique of estimating the damage of flood to the crop is the preliminary estimate prepared just after the flood less the return obtained from replacing after the flood. Loss due to disruption of trade etc. Loss due to disruption of road and railway infrastructure. Cost of remedial measures. Intangible Losses The Intangible losses are those which cannot be estimated in term of currency. The Intangible Losses are: (i) (ii) (iii) (iv) (v) Loss of Human life and Cattle; Loss of health due to sickness caused by flood; Loss Caused by social pain; Loss due to interruption in development works of towns or cities; Snake bites and other physical ailments. HYDROLOGICAL TASKS FOR FLOOD HAZARD MANAGEMENT Recent large floods in many regions of the world have created new awareness for the need of systematic movement to flood disaster prevention. In response to this requirement, flood hazard management has developed as a method, which scientifically covers all actions for obtaining and managing feasible and financially affordable safety measures against floods. It

8 ICHPSD-2015 includes not only measures for safeguard of people and goods at risk, but also for prevention of environment. Modern design techniques include the requirement of non technical measures as well as temporary protection wherever possible. This technique has been promoted worldwide by the International Decade of Natural Disaster Reduction of the United Nations (UN/ISDR, 2004). Hydrological tools for these techniques are flood forecast models and models to calculate design floods for flood protection measures. Prerequisite for many other provisional flood protection measures is a good forecast of anticipated flood levels, while design for permanent measures requires flood levels for different exceedance probabilities. FLOOD PROTECTION AND ITS HAZARD MANAGEMENT Hazard or risk management is a cyclic activity, which is shown in Fig. 1. This figure depicts the fact that there are two parts to risk management. The lower half cycle includes the planning phase, design and project implementation. The upper half includes the operational phase including maintenance, preparedness, response and recovery after an intense event. Although planning and operation phase are affected by different factors, it is essentially required that they are considered together as a part of comprehensive flood hazard management for each flood prone location. After a phase of relief, remedial measure and reconstruction as immediate response to a flood disaster, the flooding situation is reassessed, which often leads to demands for an improved protection system. A planning phase is started, in which options for meeting these demands are identified and their effects appraised. In particular, for areas, that experience floods occasionally, it is necessary to also develop potential damage scenarios for floods larger than design floods, or for situations created by breaking of dikes or dams. Damage assessment methods for dam breaks should also be used for dikes, although consequences of dike breaks generally are less severe than those from breaking of dams that confiscate large reservoirs. Fig. 1 MODELS FOR OPERATION Vs MODELS FOR PLANNING Models for flood protection should be application based. For the planning phase one requires models for developing flood inundation and flood risk maps, or models for determining water levels or discharges for the design of flood protection measures. Furthermore, in preparation

9 for the operational phase, models are needed to determine operation rules, for operation of dam & reservoirs. Most reservoir operation rules are based on scenario calculations with chronological floods. Nevertheless, today system operators want dynamic operational models which can be used in real time for taking decision for releases in anticipation of future floods, or for controlling series of barrages for effective lively storage of flood waters, as required. Flood forecasting and warning models have to be developed, tested on past events of flood, and set into service in the planning and implementation phase. Such models are also required for decisions on setting up temporary protection walls and for evacuating endangered population. Development of all plans require for response to cases of extreme floods, which exceed the capacity of the protection system and are part of the planning and implementation phase of flood hazard management. Flood forecasting and warning systems function in both phases of the flood risk management cycle, during planning and during operation. The forecast model is designed and calibrated for its successful operation and it is prerequisite for effective early warnings. Since an effective flood forecast and early warning system is generally cheap compared to other technical measures, it is often the most economical flood protection system in particular for many developing countries. This is the ideal condition for some of the large rivers of Asia or Africa, where floods are normal and lead to large losses of lives such as in 1998 on the Limpopo in Mozambique and in 2000 on the Mekong where more than 3000 people were drowned. Flood forecasting is the preferable technique for preventing or reducing such losses of lives in the future. It follows from these descriptions that there are two important categories of models to be used in flood risk management forecast models and planning models. PRECIPITATION RUNOFF (PR) MODELS FOR FLOOD MANAGEMENT Two types of precipitation Runoff (PR) models for determination of floods of given frequencies can be established. One type uses precipitation runoff modelling of the scale of runoff in a river. Historical time series of precipitation (suitably area averaged) are used and the resulting calculated runoff time series is compared with the observed runoff time series. Differences between values from observed time series and from PR model can be interpreted as realizations of a random process. Their average value is a measure of model bias to be corrected by parameter adjustment and their variance is a measure of uncertainty. Because different sets of parameters may yield the same difference, this system may yield good results on the average for the observed time series, but it may not pass when extrapolated, as is observed when the probability distribution of great values of the observed time series of runoff at some gauge is compared with a distribution of extreme values of the calculated series. The second type of PR model is event based. It is not planned to be used for the whole time series. Its exclusive purpose is to predict extreme values of runoff i.e. peaks, volumes and shapes of flood effect. When used for planning purposes in flood risk management these models use hypothetical precipitation fields. All PR models have in common that they have to describe the physical transformation of precipitation into runoff. This needs a common structure for all PR models.

10 ICHPSD-2015 COMPARISON OF FLOOD MODELS FOR PLANNING AND FORECASTING Advantages and disadvantages of flood models for planning The principal statistical technique for planning flood protection works is extreme value analysis. Extremes of runoff are calculated by two independent methods. The first and more established method uses directly extreme values of time series for discharges for calculation of design floods with a return period of 100 years. There are numerous disadvantages to this approach. It relies on measured time series of water discharges at a point; therefore it requires gauging of the river near the location for which one wants to determine the design flood. For statistical calculations it requires observations of long time series for a reasonable fit.. The second method uses PR models, which also depend on statistical data. Uncertainty of runoff prediction from PR models primarily stems from prediction of the extreme precipitation event for the catchment. Additional uncertainties are caused by the time variability of soil moisture and other dynamic catchment parameters necessitated converting precipitation into runoff. Advantages of PR models are noticeable. Precipitation data inputs are less dependent on local conditions and thus precipitation statistics can be generalized for larger areas. The actual return interval for design floods is never accurately known because of numerous potential errors due to model complexity (model error), insufficient information on parameters or incomplete or inaccurate data (data and sampling errors). The true return interval of an observed flood peak can never really be ascertained. Advantages and disadvantages of forecast models The major difference between forecasting and planning models is its correctness. Flood forecast models essentially require higher accuracy than planning models. Flood forecast models require that an exact peak value forecast in contrast to results from planning models. It will never be possible to identify accurately the return interval of an extreme event that has actually happened. It could have been frequent or a less recurrent event. The case of flood forecasting is quite different, after a flood, one can know that the forecast has been true or accurate enough. On the other side, a forecast model does not have to correctly model the physical basis of the rainfall runoff process, therefore any technique which is practical and yields acceptable results may be used, for example those from regression analysis which have been trained on previous chronological records. The principal concern is to include the error band in the discussion of the results, i.e. to use the probability distribution of potential outcomes as basis for a purpose based forecast, for example take the collective average as best estimate and give error bands based on exceedance probabilities. FLOOD IN UTTARAKHAND (15 17 JUNE 2013) The recent floods in Uttarakhand are a classic example of flash floods in the River that devastated the Uttarakhand by killing thousands of people besides livestock. Though the duration of the event was too small as compared to other flood disasters in the country, it resulted in severe damages to property and life. The river banks were eroded completely along the river course due to the flash floods and many new channels were created. The extreme erosion took place in the upstream of Kedarnath, besides the breach of Chorabari

11 Lake and deposition of debris/sediments in the valley. Hydrological study was carried out by National Remote Sensing Centre, Indian Space Research Organisation, Hyderabad in the Mandakini River using space - based inputs to quantify the causes of the flash floods and their impact. As the slopes are very steep in the upstream catchment area, lag-time of the peak flood was found to be less and washed off the Kedarnath valley without any alert. The study shows quantitative parameters of the disaster which was due to an integrated effect of high rainfall concentration, sudden breach of Chorabari Lake and very steep topography. During June 2013, excessive rainfall occurred in Uttarakhand and caused devastating floods and landslides in the country s worst natural disaster since the 2004 tsunami. Experts say that it is an warning alarm regarding the impact of rapid climate change/global warming effect on the environment. The massive landslides occurred in the upstream of the Kedarnath valley due to high intensity of rainfall. The disaster was due to a cumulative effect of heavy rainfall intensity, sudden outburst of a lake (Chorabari), and very steep topographic conditions. Unprecedented rainfall between 10 to 18 June 2013 in the Alaknanda and Bhagirathi catchments was the main cause of the disaster in Uttarakhand. Mandakini River which is a tributary of the Alaknanda, generally receives normal rainfall during June. The historical average rainfall in June at Kedarnath during was less than 200 mm. According to the India Meteorological Department, cumulative rainfall during June 2013 at Tehri, Uttarkashi, Tharali and Jakoli was 381, 359, 326 and 390 mm respectively. Various sources quoted that heavy rainfall occurred during the flood event, but data of very few stations are available as many rain gauge stations were washed- off. FLOOD FORCASTING As earlier said that flood cannot be absolutely controlled but its danger can be reduced. The accurate flood forecasting system can reduce the damages. One solution is, of course, alerting and warning people before the catastrophe actually strike them. This means, an efficient and accurate flood forecasting and early warning systems is essential in the country. Many people consider these services as one of the most cost effective measures available today. They help to alert people in the flood prone area, give time to the disaster management agencies to move in action and prepare for the impending disaster and thus reduce the damages. In India, Central Water Commission (CWC) of Government of India is responsible for issuing flood forecasts warning at 172 stations, 145 for water level forecast and 27 for inflow forecast. These stations are situated in 14 flood prone States, in Union Territories and in Delhi. The process of forecasting system is as follows: i. The Indian Meteorological Department monitors the catchment area of various rivers and streams vulnerable to flood like circumstances and informs the flood forecasting centres. ii. The centres provide the daily water level and flood forecast bulletins to concerned civil and engineering authorities. iii. The warnings are then sent to the central control room of state and district headquarters of the in danger State Government. iv. From there, the warning is sent to the affected areas. Rescue and relief operations are also organised. v. National broadcasting agencies like All India Radio and Doordarshan are informed for wider publicity.

12 ICHPSD-2015 vi. Revised forecasts are sent as new information comes in. The effectiveness of forecasts depends on two aspects accuracy and timeliness. These make sure that there is enough time to publicize the forecast, and warn people. The following measures are also required to be taken to minimize the damages due to flood: A system of early warning, forecasting and dissemination for all kinds of disasters, particularly those related to rainfall and landslides is essentially required. It is technologically feasible to predict even cloud bursts at least 3 hours in advance. Doppler radar system would have enabled this forecasting. However, communities and local governments have to be at the centre of all such warning and forecasting systems. The coordination between NDMA, IMD and State Government are essentially required to exchange the information. Put in place a clearly defined monitoring system in place which will give prompt reports of actual rainfall events even as they start so that people and administration in the downstream can be warned. Protection and conservation of rivers, riverbeds and flood plains, including aquatic biodiversity. Restrict encroachment of riverbeds and floodplains. Prepare clearly defined space for rivers, have river regulation zone in place and remove all illegal encroachments in river beds and flood plains in a time bound manner urgently through legislation, followed by executive action. CONCLUSION Beside the flood control measures and flood modelling, the present study highlights the urgent need to develop flash flood forecast models to help in improved preparedness for flood damage mitigation in hilly terrains. As the flood forecast lead time in steep terrains is short, there is a need to improve spatial and temporal resolution precipitation forecast data in such flood forecast models. In modern times, under climate change scenario, glacier lakes are an escalating threat in the hilly regions. Outbursts of such lakes individually or in combination with rainfall runoff will cause severe damage to the downstream environment. Development of flood forecast models in conjunction with the flood inundation simulation models can provide flood alarms in the floodplains,which is an effective non structural method of flood damage mitigation. REFERENCES 1. Plate, E. J. Skalen in der Hydrologie, Zur Definition von Begrif- fen, Regionalisierung hydrologischer Parameter, Beitragssamm- lung Deutsche Forschungsgemeinschaft, Bonn, Germany, 33 44, Plate, E. J. and Zehe, E. (Eds.): Wasser- und Stofftransport aus kleinen la ndlichen Einzugsgebieten, 365 pp., Schweizerbart, Stuttgart, Germany, Zehe, E., Maurer, T., Ihringer, J., and Plate, E. J.: Modelling wa- ter flow and mass transport in a Loess catchment, Phys. Chem. Earth, Part B, 26, , Refsgaard, J. C. and Storm, B.: MIKE SHE, in: Computer Mod- els of Watershed Hydrology, edited by: Singh, V. P., Water Re- sources Publications, , Plate, E. J.: Early warning and flood forecasting for large rivers with the lower Mekong as example, Journal of Hydro-Environment Research, 1,

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