The impacts of climate change and land subsidence on inundation potential

Chen Ching-Nuo, Tfwala Samkele S. and Wang Yu Min

Flooding is a common catastrophe for Taiwan. Its location, geography and population density makes the impacts severe. Climate change combined with land subsidence further aggravates flooding within the Island. Hence, the study is aimed at modelling flooding under climate change without and with subsidence in Taichung city, central Taiwan. To accomplish the objective, we use a physiographic inundation model (PHI) to simulate inundation of 24-hour and 48-hour design rainfall for baseline and climate change scenario A1B for 25, 50, 100 and 200 year return periods. Before simulation, we validated the model using field investigations and simulated inundation from typhoon Morakot and 10-year historical typhoon events. The model agreed with the actual observations in terms of location and areas of inundation. The PHI showed inundation depths greater than 0.3m will increase under climate change, especially those between 1 and 1.5m which increased by 80% under the 24-hour design rainfall. Land subsidence worsened the impacts of climate change as areas with inundation depths greater than 1m increased by up to 11%. We concluded that Taichung city was at great risk under climate change; hence, government agencies and stakeholders should implement mitigation measures to counteract climate change and land subsidence effects on inundation.

Full Text

Remote Sensing and GIS based Approach for Identification of Artificial Recharge Sites in Vaniyar Sub-Basin, Ponnaiar River, Tamil Nadu, India

Kalphana K. R., Velkennedy R. and Senthil Velmurugan J.

The main aim of this paper is to demonstrate the capabilities of Remote Sensing (RS) and Geographic Information System (GIS) techniques for the demarcation of suitable sites for artificial recharge of groundwater aquifers in the Vaniyar sub-basin, Ponniar River basin, Tamil Nadu, India. Geographical Information System (GIS) with its capability of integration and analysis of spatial, multi-layered information obtained in a wide variety of formats both from remote sensing and other conventional sources has proved to be an effective tool in planning for watershed development. In this study, area and locale specific watershed development plans were generated for Vaniyar sub-basin, Ponniar River basin, Tamil Nadu, India using remote sensing and GIS techniques. Using the overlay and decision tree concepts water resource development plan was generated. The average annual rainfall spatial distribution map and satellite images LAND SAT Path-Row 096-055 Satellite data were acquired. Satellite data along with other field and collateral data on Geology Geomorphology, land use/land cover, slope, drainage density, lineament density and drainage of the study area which are essential pre-requisites for water resources planning and development, were acquired. Spatial data integration and analyses are carried out in GIS environment.

Full Text

An integrated approach to understand the lake water-groundwater interaction in coastal part of Arani - Koratalaiyar River basin, Tamil Nadu, India

Raicy Mani Christy and Elango Lakshmanan

Lakes are natural water harvesting structures which store water and recharge the aquifer. In the context of sustainable aquifer management it is crucial to understand and quantify the exchange processes between groundwater and surface water in lakes. The present study aims to investigate the role of a lake in enhancing the groundwater potential and groundwater quality in the Arani -Koratalaiyar River basin, north of Chennai, Tamil Nadu. The spatial variation of groundwater level and groundwater quality was studied by groundwater level and electrical conductivity measurements in the field. Resistivity Vertical Electrical Sounding (VES) surveys were carried out to characterize the subsurface lithology of the area. Groundwater table lies between 3 and 4m depth below the surface. The electrical conductivity of groundwater on the western side of the lake is less as compared to that on the eastern side of the lake. The groundwater table rose due to the water storing in the lake. The movement of groundwater on the eastern side of the lake is controlled by the clay layer present beneath in the study area. Thus the seepage rates in the land surface depressions in the area can be enhanced by the local fresh water mount formed by focused recharge and can push the seawater towards sea on the eastern side of the lake.

Full Text

Provisions of cross drainages in Ghat road alignment to prevent slope instability - A study in Palamalai Hills, South India using GIS

Arulmozhi R. and Subramani T.

Performance of hill road drainage systems physically relies upon the locations of cross drainage structures, size of vents and type of bed material and slope. In usual course such cross drainage structures are provided based on site condition and the experience of the investigator by leaving off hydraulic calculations of discharge from the catchments in due to the complexity. However, the sufficiency of the cross drainages can be confirmed by studying the linear waterway required to discharge the runoff resulted from the catchment area of all cross drainage structures in total. In view of this, a study has been undertaken to evaluate the adequacy of the cross drainage structures of a hill road in Palamalai Hills, Tamil Nadu, India. Established formulae of empirical method and rational method were used to calculate the total discharge of the catchment area. The catchment area that drains along the entire length of a proposed road was calculated using contour maps and referring satellite images. The GIS techniques were applied to calculate the catchment area, length and slope of the catchment. The linear waterways of all the drainage structures along the proposed hill road are added together and compared with a single linear waterway required to discharge the whole catchment area to check discrepancies in the provisions. The study indicates that the total catchment area demarcated from the digital map using GIS is 1.68 sq. km. The critical discharge of the catchment area is estimated as 57.65 cum./sec. The total number of sites identified for the provision of cross drainages to discharge the rainfall runoff is 14. The linear waterway required for cross drainage works to safely pass the discharge has been worked out as 47.83 m.

Full Text

Landslide hazard assessment based on geographic factors in the Thompson River Valley, British Columbia, Canada

Weiming Cheng and Min Zhao

The objective of this study was to develop a methodology for producing a landslide hazard map, to assess slope failure hazards with regard to railway infrastructure and traffic of the Thompson River Valley (TRV), in southern British Columbia, Canada. This area is a vital national transportation corridor with both major Canadian railways following the TRV to the port of Vancouver. Landslide-related parameters from multiple sources including topographical, geological, land cover and hydrological data were used to assess the level of hazard to railway traffic using a two-step analysis. First, a multi-parameter characterization model, based on the method of the estimation of the geometric mean, was used to classify slope failure into regional-scale landslide hazard categories. Second, correlation statistics and field measurements were conducted based on distance buffering from railway traffic. The results show that high and very high landslide hazard categories are distributed mainly within a 5-km-wide corridor along the Thompson River which accounts for 73% and 89% respectively of their occurrence with the entire study area. The large landslides that have occurred to the south of Ashcroft have been well documented and they demonstrate the very high slope failure hazard.

Full Text

Zonkizizwe Extension Six Settlers’ dolomite sinkhole risk awareness

Belle Johanes A. and Sikhakhane Mzwandile Mabutho

Dolomite sinkholes threaten many communities in Ekurhuleni Metropolitan Municipality, South Africa. This study focused on the area of Zonkizizwe Extension Six which is susceptible to dolomite sinkholes. The community’s awareness regarding dolomite sinkholes, information dissemination channels available to the community, and level of sinkhole risk understanding was assessed. The study adopted the mixed-methods approach, using questionnaires, interviews and field observation. A sample of 100 households was selected through random sampling and analysed descriptively. There is a need to increase the awareness of the community regarding dolomite sinkholes in order for the community to adopt risk reduction measures. There is also a need to consider the most relevant and accessible communication channels for dolomite sinkhole information dissemination. The study high- lights the need for municipal systems to work cooperatively in the management of sinkholes risks.

Full Text

Earthquake catalogue for estimating seismic hazard at Greater Mumbai, India

Desai Sarika S. and Choudhury Deepankar

An evaluation of seismic hazard of a region necessitates compilation of earthquake catalogue for the study area. An earthquake catalogue for a circular area around Greater Mumbai, India for a period of AD 1594 to 2012 of historical and instrumental earthquake events of Mw ≥ 3.5 is compiled from various sources. The catalogue is processed to remove clustered events and then subjected to conversion of earthquake magnitude in different scales to earthquake moment magnitude for homogenization. The Cumulative Visual Inspection Method (CUVI) is utilized to know the time period of completeness of different earthquake magnitude classes. Two significant seismicity parameters (‘a’ and ‘b’ value) obtained by application of Gutenberg-Richter recurrence law to these data set turn out to be 3.668 and 0.834 respectively that are typically indicative of small to moderately active seismic zone. The homogenized earthquake catalogue prepared in this study is used for the probabilistic seismic hazard evaluation of Greater Mumbai region.

Full Text