Ood Events Research Articles

An Analysis of Changes in Climate Variability and the Persisting Flood Events in Kinondoni District, Dar es Salaam, Tanzania

Th is paper off ers an analytical view on climate variability and fl ood events in the City of Dar es Salaam. Th is is a response to a central question whether there is relationship between substantial changes in climate variability especially rainfall and temperature to the persistence of fl ood events. Th e study gathered climatology data from two weather stations provided by Tanzania Meteorological Agency (TMA) and employed mixed methods approach in data collection, analysis and presentation of fi ndings. Th e study revealed that temperature has shown a signifi cant increasing trend to about 2.45 0C in the last 31 years, while rainfall data indicated the decline in annual rainfall especially during short-rainy seasons. Furthermore, there was a relative increase in rains in March and April unlike in May where there is a decline in rainfall. Despite all these changes, correlation value between rainfall intensities and fl ood events was found to be 0.5 indicating a weak to moderate positive relationship. It is under this regards where poor planning in infrastructure and poor waste disposal plays a critical amplifying role in persistence fl oods. Th erefore this paper recommends that, since temperature has shown an increasing trend then future scenarios of climate change in region should not be underestimated or exaggerated at all levels of decision making, planning and development.

ACCESSIBILITY AND FLOOD RISK SPATIAL INDICATORS AS MEASURES OF VULNERABILITY

Based on the recent literature relating transport service level and social exclusion, as well as perceptions about the capacity of the population to cope with the occurrence of fl ood events, this paper identifi ed the spatial pattern related to fl ood risk and accessibility to urban facilities. For that, composite spatial indicator is developed and compared with socioeconomic data. The analysis shows the outskirts of the city with the most vulnerable places, with high levels of fl ood risk and low levels of accessibility. Those regions with low level of accessibility and close to fl ood prone areas are characterized by low income level as well as the low percentage of residents with sewage system.

Overview of June 2013 Flood and Landslides with focus on Darchula Disaster

In mid June 2013 there was a cloud outburst in northern Uttarakhanda, India and far western region of Nepal, due to simultaneous activation of monsoon arms one from Bay of Bengal in the east and other from the southwest. There was 322mm of rainfall in Uttarakhanda during the week 13-19 of June 2013 (847% of the nor-mal rainfall of Uttrakhanda for this period). The extreme ?ood event caused thousands of human lives lost and several billions of property damages in India and extensive damages in Nepal. The Mahakali River a border river between India and Nepal caused very heavy damages in several places in Nepal's Darchula and also in Dodhara and Chandhani, the Nepali settlements in west side Mahakali River. Contribution of Dhualiganga a tributary of the Mahakali River where a 280 MW hydro plant with 6.2 million cubic meters of storage reservoir capacity is constructed by India for the severity of flash flood in the region cannot be overlooked. The sudden spillway gate opening from this reservoir added the already very heavy floods in Mahakali that devastated Darchula the district HQ of Darchula. More than 100 houses in Darchula were washed away by the big flood event. However, India was quick to refute the charge of sluice-gate-opening of the Dam and stated that the disaster in Darchula was not caused by the dam opening. Detailed Investigation is yet to be done. This papers analyses the events surrounding the 17-18 June catastrophic flood causing wide spread damages in Darchula District Head Quarter. Both the countries need to work honestly for mutual benefit especially for minimising the effects of any disasters in the future.DOI: http://dx.doi.org/10.3126/hn.v13i0.10043HYDRO NEPA LJournal of Water, Energy and EnvironmentIssue No. 13, July 2013Page: 57-63Uploaded date: 3/13/2014

Estimation of repair costs of individual non-domestic buildings damaged by floods

It is evident that there is no established fl ood damage prediction tool for individual non-domestic buildings that can account in any detail for their different types of construction. Unlike domestic buildings, non-domestic buildings often feature several different types of construction within the same premises. This absence makes it diffi cult for building owners and designers to calculate what appropriate measures should be taken to enhance resilience against fl oods. This paper, developed in the context of the European Community FP7 project FloodProBE, and presented at the Sustainable City 2012 Conference, discusses the current estimation methods used in the UK, Germany, USA and Australia, and suggests a way to improve on these by devising a tool capable of estimating damage to individual non-domestic buildings. Standard damage and repair parameters are investigated and the major variables are considered ‐ those related to the fl ood event such as overfl oor depth, velocity, rate of rise, debris, contaminants, frequency and duration of inundation and timing, and those relate to the building characteristics, such as structure, construction, materials and their vulnerability to water and drying characteristics, services and their locations. The aims and functions of a prototype fl ood damage estimation tool are described, including the type of users aimed at, and the method of calculation, input data required and types of output delivered. The model is demonstrated on one case study of an actual building damaged by fl ooding and the predicted cost compared with the actual cost of reinstatement. A sensitivity analysis is made on the fl ood characteristic inputs. The conclusions contend that that the prototype tool is worth developing to produce a useful way of predicting the costs of fldamage to individual buildings which will enable calculations to be made for assessing the cost‐benefi t analysis of installing fl ood mitigation/resilience measures to the building in order to protect it and its contents.

Outlet work optimization in flood control reservoirs

An examination of the general and hydrological planning criteria for artifi cial reservoirs clarifi es the importance of choosing the correct type of outlet works both for stored volume management and for fl ooding events control. This choice becomes even more important, if we consider the effects of the climate change we have seen in recent years on extreme events. In this paper, the hydraulic operation of an extremely functional outlet work is studied using a physical model. The work is composed of an uncontrolled spillway and a mid-level outlet unifi ed into a single structure. In particular, it proves of extreme interest both in the lamination of fl ood events and also in reducing the global costs of outlet works. The tests have highlighted the outstanding hydraulic operation of the works under any condition and, in particular, when the spillway fl ow and the mid-level outlet fl ow converge into a single duct.

Spatiotemporal analysis of channel wall erosion in ephemeral torrents using tree roots—An example from the Patagonian Andes

This paper presents absolute ages for fl ash fl oods and related sediment entrainment in headwater catchments to construct a spatiotemporal framework of process dynamics and locations of major areas of channel wall erosion. The most reliable method for dating erosion is through dendrogeomorphic studies of exposed tree roots. Based on the analysis of erosion signals in root-ring records we documented a time series of channel wall erosion and successfully dated 21 erosive fl ash fl ood events since A.D. 1870 in an ephemeral gully in the Patagonian Andes. The study was performed with roots from Austrocedrus chilensis, Nothofagus dombeyi, and Pseudotsuga menziesii. Results demonstrate the potential of root analyses for the determination of major areas of sediment entrainment. In addition, we show that the position of damage within individual root rings allows inferences about the seasonal timing of fl ash fl ood effects and thus an assessment of possible meteorological triggers of erosive events, short intense storms occurring primarily in austral fall and late winter in this case. The approach presented adds signifi cantly to the documentation of sediment entrainment and facilitates identifi cation of areas of rapid erosion in small, remote headwater catchments with ephemeral fl ash fl ood activity.

The threat of alluviation of lakes resulting from torrents (case study: lake volvi, north greece)

Lakes or natural reservoirs are usually formed by the water supplied by torrents runoff. Furthermore, runoff, according to the torrential environment that forms the watershed (climate, geology, vegetation and relief) is usually associated with debris fl ow. As a result, many lakes and reservoirs are undergoing an alluviation process which leads to an important reduction of their total capacity. In fact, long-term process of torrents may threaten their existence. Lakes and reservoirs have an important role since the impounding water is used for multi purposes such as municipal supply, irrigation and recreation. Often, lakes form wetlands that are really important and are protected by national or international treaties. In this paper, the methodology we use involve the analysis of torrential environment (potential) of the lake Volvi watershed. Moreover, the mean annual sediment yield calculated according to Gavrilovic method so as to assess the risk of alluviation. Also, Kronfellner‐Kraus method used in order to take under consideration the sediment that can fl ow into the lake after an extraordinary fl ood event. Finally, fl ood control works proposed so as minimize the threat of alluviation. The present study shows that the torrential environment (potential) is rather moderate, although during intense rainfalls great volume of water and

Overbank sediments along the middle Wieprza as a record of flood phenomena

Today’s fl ood events along the River Wieprza assume a quite characteristic course entailing calm spillovers of water from the bed in places of riverbank lowering and in sections above and below bridges, where a narrowing of the channel is present. The identity of the land inundated relates to morphology, the near-channel part of a fl oodplain may be affected or those parts in depressions that serve as fl ood basins. Riverbank exposures on both sides of the present river channel plus pits reveal the construction of the Wieprza fl oodplain. The sediments that build the fl oodplain represent channel and overbank facies with subfacies of palaeomeander fi lls. Analysed exposures are located along the valley section between Slawsko and Staniewice, mostly in close proximity to the Early Mediaeval fortifi ed site of Wrześnica. The content of the exposures indicates that the uniform cover of overbank sediments across the fl oodplain emerged during the last 1000 years. It is now impossible to say when exactly, so it is unknown what the rank of the extreme fl oods which took place at the end of 19th century was, and what their role in forming the present fl oodplain.

Riesgo por inundaciones en asentamientos precarios del periurbano. Morelia, una ciudad media mexicana: ¿El desastre nace o se hace?

During the past decades, cities at risk have considerably increased in number, particularly in developing countries, stimulated by demographic growth and constant urban remodeling. Such parameters are expressed in urban expansion, creating marginal and precarious peri-urban sectors that when impacted by fl ooding events magnify their vulnerable condition. During the past ten years the city of Morelia has repeatedly shown such problematic due to the increase in precarious populations, which is in turn, is a reflection of the peripheral socio-residential characteristics. Therefore, the consequences of fltend to be accompanied by different decisions and human conditions. The present work branches off from the correlation of physical and social variables, as well as from the use of a number of methods and tools in order to obtain the needed parameters for the recognition of precarious areas and their relationship with risk of disaster due to fl

Impact of rainfall pattern on the occurrence of flash floods in Hungary

ash fl ood hazard mapping as part of the FFG system, in the present study we considered and included both passive environmental factors (PFB model), and randomly occurring active environmental factors (precipitation). Currently, we determined the (i) spatial and (ii) the temporal patterns and behavior of rainfall events in Hungary and prepared a hazard map that is based on both passive and active environmental factors (APFB model). Extreme rainfall pattern was analyzed both in time and space using data provided by the National Oceanic and Atmospheric Administration (NOAA) and the Hungarian Meteorological Services (HMS). Th e hazard map was then validated using HEC-HMS simulations and calculated threshold discharge values. Th e spatial pattern of extreme events indicates a strong orographic eff ect. Th e frequency of extreme precipitation is always higher on the watersheds of the PFB model with highest hazard, than in both the zone of the PFB model with the lowest hazard and the national average. Consequently, the vulnerability of the passive factor-based most endangered areas will be further enhanced by the higher frequency of extreme events. Temporal changes are ambiguous based on the long term observed data of extreme rainfall. Model indicated increase of extreme rainfall events is not clearly shown based on the employed HMS and NOAA data. However, a flcyclic pattern is clearly identifi able. Th e majority of the observed years was characterized with a lower-than-average number of extreme events. However, these long periods are interrupted with short spells (usually lasting a year or two) when the number of extreme events signifi cantly exceeded the mean value. Th e temporal frequency of fl ash fl ood events is lower than expected based on model validation processes. Th is discrepancy is likely to be explained by (i) the duration diff erence between the simulated rainfall period and the observed rainfall period, (ii) the overestimation of total runoff

Supply and dispersal of flood sediment from a steep, tropical watershed: Hanalei Bay, Kaua’i, Hawai’i, USA

In contrast to many small, mountainous watersheds in temperate coastal regions, where fl uvial discharge and wave energy commonly coincide, deposition and reworking of tropical fl ood sediment can be seasonally decoupled, and this has important implications for coral-reef ecosystems. An understanding of the interaction between tropical fl ood sedimentation and wave climate is essential to identifying and mitigating effects of watershed changes on coral reefs as urbanization and climate change proceed. Sedimentary facies and isotopic properties of sediment in Hanalei Bay, on the island of Kaua’i, Hawai’i, USA, were used to assess deposition and reworking of fldeposits from the Hanalei River in a case study demonstrating the potential ecosystem effects of runoff from a steep, tropical watershed. In Hanalei Bay, the youngest and thickest terrigenous sediment was consistently present near the river mouth and in a bathymetric depression that acted as at least a temporary sediment sink. During this 2 yr study, the largest fl ood events occurred in late winter and spring 2006; substantial terrestrial sediment delivered by those fl oods still remained in the bay as of June 2006 because oceanic conditions were not suffi ciently energetic to transport all of the sediment offshore. Additional sediment was deposited in the bay by a summer 2006 fl ood that coincided with seasonal low wave energy. In most years, fl ood sediment accumulating in the bay and on its fringing reefs would be remobilized and advected out of the bay during winter, when the wave climate is energetic. Turbidity and sedimentation on corals resulting from late spring and summer fl oods during low wave energy could have a greater impact on coral-reef ecosystems than fl oods in other seasons, an effect that could be exacerbated if the incidence and sediment load of tropical summer fl oods increase due to urbanization and climate change.

Hazard and Risk Assessment from Hurricane Ivan (2004) in Grenada using Geographical Information Systems and Remote Sensing

Please click here to download the map associated with this article. Hurricanes are destructive storms with strong winds, intense storm surges, and heavy rainfall. The resulting impact from a hurricane can include structural damage to buildings and infrastructure, ooding, and ultimately loss of human life. This paper seeks to identify the impact of Hurricane Ivan on the affected population of Grenada, one of the Caribbean islands. Hurricane Ivan made landfall on 7th September 2004 and resulted in 80% of the population being adversely affected. The methods that were used to model these impacts involved performing hazard and risk assessments using GIS and remote sensing techniques. Spatial analyses were used to create a hazard and a risk map. Hazards were identified initially as those caused by storm surges, severe winds speeds, and ooding events related to Hurricane Ivan. These estimated hazards were then used to create a risk map. An innovative approach was adopted, including the use of hillshading to assess the damage caused by high wind speeds. This paper explains in detail the methodology used and the results produced.