Heavy Flash Floods Research Articles

Urban hydrological model (UHM) developed for an urban flash flood simulation and analysis of the flood intensity sensitivity to urbanization

An urban hydrological model (UHM) forced by radar-observed rainfalls was developed for producing rainstorm-related urban inundation maps for obtaining flash flood forecasts. The parameter sets of the land use and land cover (LULC) and urban drainage capacity derive from satellite multispectral images and high spatial resolution GIS datasets, relating to the urban hydrology and hydraulic properties. The hydrodynamics model was based on the simplified shallow water equation (SWE) neglecting the convective acceleration and pressure terms in the St. Venant equation. The intense convective rainstorm that induced heavy flash floods on 21 Jul. 2012 and the large-scale stratiform precipitation that occurred from 19 Jul. to 21 Jul. 2016 in Beijing were deliberately selected to perform flood-simulation and model-validation case studies. The simulation of severe flooding scenarios in the 2012 event was fairly reproduced and verified using media reports. In the case studies, the sensitivity tests verified that the flood intensity (1) would be enhanced slightly on pure impervious surfaces, (2) would be reduced significantly on pure pervious surfaces, and (3) would increase by 30%–60% without a drainage system. No false alarm could be perceived in the simulation of the 2016 event in a prolonging stratiform precipitation. The case studies confirmed the perspectives of using the hydrological model fed by QPEs/QPFs for flash flood forecasting and concluded that the hourly precipitation surpassing 30 mm/h would be indicative in impending flash floods in Beijing metropolis.

Effectiveness of the Submersible Embankment in Haor Area in Bangladesh

The north-eastern part of Bangladesh is very productive for agriculture and fishing, and the region involves several depressed (haor) areas. Flash floods during the pre-monsoon period bring devastating damage to agriculture in the haor region recurrently. To protect crops from flash floods, the Bangladesh Water Development Board constructed several ring-type submersible embankments. In this research, we have investigated the effectiveness of submersible embankments in controlling flash flooding in the Matian and Shanir haors in the Sunamganj district. A two-dimensional rainfall runoff inundation model was applied considering several scenarios for simulating heavy flash flood events in 2004, 2010, and 2016. Without an embankment, the river overflow would have entered the Matian haor 3 days, 22 days, and 9 days earlier in 2004, 2010, and 2016, respectively, whereas it would have been 7 days and 23 days earlier in 2004 and 2010 for the Shanir haor. The event in 2016 was successfully stopped by the Shanir haor embankment. To avoid river overflow entering into the Matian and Shanir haor completely, the embankment height must be elevated further by 1 m and 0.7 m, respectively. Providing proper drainage facilities for the accumulated rain water inside the hoar is still an important issue for protecting the crops effectively.

A Multidisciplinary Approach for Clarifying the Recharge Processes and Origin of Saline Water in the Semi-Arid Punata Alluvial fan in Bolivia

The analysis of stable isotopes assisted in identifying that groundwater in the Punata alluvial fan is mainly recharged by heavy flash floods, and the recharge from rainfall is of less importance. In addition, the hydrochemical analysis identified the Pucara River as the main source of recharge. Other streams in the north and northwest of the fan do not seem to contribute to the recharge. The hydrochemistry also shows that there is an increase of the Na+ and Cl− concentrations in the middle and distal part of the fan. The salinization of groundwater is most likely a result of the mixing of fresh water with residual saline pore water in the lacustrine deposits and/or ion exchange within these layers. Geophysical surveys assisted in describing the aquifer system layering, and indicated a fine-grained bottom layer where ion exchange might occur. This study demonstrates that the integration of several methods (e.g., hydrochemistry, hydrogeophysics, and stable isotopes) is valuable for clarifying ambiguities during the interpretation process and for characterizing hydrogeological processes in alluvial fans in general.

Flash Flood Prediction by Coupling KINEROS2 and HEC-RAS Models for Tropical Regions of Northern Vietnam

Northern Vietnam is a region prone to heavy flash flooding events. These often have devastating effects on the environment, cause economic damage and, in the worst case scenario, cost human lives. As their frequency and severity are likely to increase in the future, procedures have to be established to cope with this threat. As the prediction of potential flash floods represents one crucial element in this circumstance, we will present an approach that combines the two models KINEROS2 and HEC-RAS in order to accurately predict their occurrence. We used a documented event on 23 June 2011 in the Nam Khat and the larger adjacent Nam Kim watershed to calibrate the coupled model approach. Afterward, we evaluated the performance of the coupled models in predicting flow velocity (FV), water levels (WL), discharge (Q) and streamflow power (P) during the 3–5 days following the event, using two different precipitation datasets from the global spectral model (GSM) and the high resolution model (HRM). Our results show that the estimated Q and WL closely matched observed data with a Nash–Sutcliffe simulation efficiency coefficient (NSE) of around 0.93 and a coefficient of determination (R2) at above 0.96. The resulting analyses reveal strong relationships between river geometry and FV, WL and P. Although there were some minor errors in forecast results, the model-predicted Q and WL corresponded well to the gauged data.

Recruitment and decay rate of Acacia seedlings in the hyper-arid Arava Valley, Israel

Acacia trees, including Acacia pachyceras, Acacia raddiana, and Acacia tortilis, constitute some of the main keystone species throughout the hyper-arid Arava Valley of Israel. Several studies performed over the last several decades have revealed drastic changes in the acacia populations, with high mortality rates and low recruitment rates. The objective of this study was to examine the patterns of survivability – through measuring the decay rate – of acacia seedlings during the first year after germination. Following the 2012–2013 rainy season, we measured – over one entire year – the survivability of acacia seedlings in 12 ephemeral rivers (wadis). Data analysis revealed that the main impediment to the recruitment and survival of acacia seedlings is their desiccation, resulting in their mortality. This limiting factor was predominant despite the above-average and well-distributed precipitation during the year of the study. Another, secondary impediment is imposed by erosional and depositional processes under heavy flash floods, resulting in either the uprooting of the seedlings or their burial under deposited soil and fine pebble sediments. Therefore, the novelty of this study stems from the identification, quantification, and modeling of two different mechanisms that determine the decay of acacia seedlings: one with a constant mortality rate that is caused by drying, and the second with a mortality rate that grows with time, which is caused by fluvial processes. The mortality due to drying revealed high fitting to an exponential decay, while the mortality due to fluvial processes closely fits a Gaussian decay function.

(A289) Developing Damage Assessment Methodology with Community Participation — Case Study of the 2010 Leh Flash Flood

The frequency of catastrophic events has increased considerably in recent times. As a result, impacts of such catastrophes have multiplied exponentially. It is the responsibility of the government to revive and reconstruct the communities and economies affected by disasters. Domestic institutions should be resilient enough to absorb the shocks and mitigate the impacts. Too often, damage assessments rely on quantification in terms of monetary valuations of damage. This approach has created various distortions in valuation. Damage evaluation in developed countries is higher because of the monetary value of infrastructure and housing. On the contrary, in a poor, informal settlement, the value of the damage is less, but the impact is huge from a human development perspective. The government follows a standard procedure for items and means of assistance for initiating post-disaster recovery and response. All affected families are entitled to compensation based on the damage done to life and property, irrespective of socio-economic conditions. All items are listed beforehand, with their monetary values ascertained respectively. This paper examines Leh (Ladakh, India), which was struck by heavy flash flood in the month August 2010. It explores the methodology adopted for damage assessment in 42 affected villages of Leh. This case study demonstrates the inherent drawbacks of the standard procedure and methodology in assessing post-disaster damage and needs assessments, and analyzes the role of community participation in household and community damage assessment. The paper presents recommendations for a flexible and accommodating approach for conducting damage assessments on a contextual basis.

River Processes in Different Climates

The article contains a general discussion on river processes in different climates. It is stressed that a good knowledge of the natural river processes is of great importance, both for purely scientific reasons and in the interests of society. The prediction of future development and the forecasting of possible environmental risk factors are essential elements in the physical planning. Both the hydrological regime and the sediment production are controlled to a great extent by climate, but they are also affected by a multitude of different factors, mutually related and seldom independent. Vegetation, bedrock and soil conditions, topography and channel geometry are some of these factors.Some typical examples are given from different climatic regions. The influence of the perennially frozen ground on the fluvial processes in arctic regions is discussed and exemplified. In humid, mid-latitude climates, the influence of, among other things, the seasonality and the possible presence of snow and ice during the winter is discussed. The partial absence of vegetation in dry climates and the occurrence of heavy flash floods is discussed, and their significance for the processes is stressed. The close relationship in the dry zones between the fluvial processes, particularly the transport of bed load, and the general geomorphological evolution of the landscape is pointed out. In the tropics, the vegetation plays a very important role, bot other factors, for instance, the “lahar” activity in volcanic areas, may also be significant as regards the river characteristics.In a concluding section, some general concepts are presented. It is pointed out that the fundamental hydrodynamic and fluvial processes are the same, irrespective of climate and other external conditions (concept of similarity), and that the rate of most river processes and their morphological and sedimentological results are directly or indirectly controlled by climate, for instance, by permafrost, river ice, snow and vegetation (concept of climatic control). There is a balance or quasi-balance in all rivers between water discharge and sediment load, determining the general character of fluvial processes and morphological development (water-sediment relationship). As the processes in a river depend on conditions and processes also in other parts of the river basin, it is necessary to treat the whole river basin as a compound unit (the river basin as the fundamental unit). The importance of geomorphological events of different frequencies and magnitudes varies with climate. This is an important topic for further studies (frequency-magnitude relationship). Man's influence on river processes is becoming more and more important. It is necessary to develop satisfactory methods for the prediction of the effects of human activities (man's influence). Process geomorphology would be a useful term to utilize, covering both the influence of climate and other factors, for example man's influence, on the long-term geomorphological development.