INUNDATION MAPPING FOR FUTURE TSUNAMI DISASTERS CASE STUDY: HAMBANTOTA AREA

The 26 December 2004 earthquake off the west coast of Sumatra, Indonesia generated one of the deadliest Tsunami waves in history. It demolished the coastal areas of Indonesia, Sri Lanka, India, and Thailand, since they are located in the shadow zone of this tectonic belt. Thousands of people were killed and injured in addition to the loss of houses, properties and infrastructures worth millions of Dollars. Therefore it is necessary to step up tsunami awareness effects such as tsunami forecasting methods and inundation mapping of risk communities in the coastal belt. This paper briefly describes tsunami hazards assessment, education, warning, and mitigation in Hambantota coastal region by using COMunity Model Interface for Tsunami (COMIT), topographic data, near shore bathymetric data and Satellite images and preparing tsunami inundation maps integrated with a GIS environment.

Tsunami impact study has been undertaken along coastal region of Hambantota area. The study area was badly hit by tsunami waves and is currently devoted to larger development projects. Therefore it is important to prepare large scale action maps on tsunami inundation incorporating land use details using a GIS tool. Under tsunami inundation mapping along Hambantota coast an integrated approach was adopted to prepare thematic maps on land use/land cover and coastal topography using Multispectral remote sensing data. Accurate bathymetric data of shallow water with digital topographic data and LIDAR data were used to generate the tsunami wave by using COMIT simulations model. Accurate bathymetric data of shallow water and JEBCO (1 min.) bathymetry data with digital topographic data and LIDAR data were used for propagation and inundation modeling to study tsunami inundation, maximum wave height, wave speed, and reflection in the Hambantota costal area. The GIS environment has been used to incorporate and analyze the maximum wave run-up and thematic maps derived from remote sensing data with other social and economic factors. The amplitude of tsunami waves, which were generated by COMIT, was compared with tide gauge details of 26 December 2004 earthquake.

This study provides an important clue on variations in tsunami inundation along the Hambantota coast, which is mainly controlled by local geomorphologic set-up, coastal zone topography including natural barriers to protect coastal erosion and near shore bathymetry. This study focuses on the information of most vulnerable areas of tsunami and also provides indication to distinguish suitable locations for rehabilitation and standard and methodology for preparing inundation maps for coastal belt of the country

PGRNI Pussella1, RKA Ariyarathne2, RMKGSPB Koswatte1, YNR Nilupa Kumari2
1- Faculty of Geomatics, Sabaragamuwa University, Sri Lanka
2- National Aquatic Resources Research &Development Agency, Sri lanka

Optimization of wastewater treatment through Bio-Geo filter for hotels surrounding Bolgoda Lake

Wetland systems are playing a key role of keeping rich bio-diversity in favors of mainly aquatic lives of in and around inland waters. Bolgoda wetland is an important wetland system in Sri Lanka, which keeps number of endemic species and a bird sanctuary, compiled with striking natural beauty. This unique feature ultimately helps to increase the number of hotels, restaurants and residences in the vicinity. As a result improper waste disposal become a significant threat to the wetland system, causing nutrient enrichment followed by massive growth of water hyacinths at the lake.

Controlling measures of nutrient enrichment of Bolgoda Lake is an utmost need, and therefore a study was aimed to identify present wastewater disposal practices in order to develop an economical wastewater treatment system that can be adopted by hotels and dwelling units.  Hence, a questionnaire survey was carried out among hoteliers to identify the significant malfunctions of present wastewater disposal practices. The results showed that only 7% of hotels use proper wastewater treatment units and 20% use combined units of septic tanks and soakage pits, while 46% use only septic tanks. It has also revealed that septic tank effluents are directly discharged into the lake through subsurface soil and even available soakage pits are malfunctioning due to high ground water table. Hence this research was then focused to design a low-cost wastewater treatment unit to optimize nutrient    removal    efficiency.

The BGF is a subsurface flow constructed wetland cell, consisted with two key components of bio and geo materials which interrelate with each other offering a combined physical and biological treatment process, in removing pollutants from wastewater. Considering the nitrogen, phosphorous, BOD and suspended solids concentrations in wastewater and the level of treatment required, Bio-Geo filters were designed for three categories such as: a hotel with 10 rooms/ 05 rooms and for a dwelling unit, having wastewater flows of 14 m3/d, 9 m3/d and 1 m3/d respectively. The filter ditch was designed with a bottom layer of laterite (Kabook) of 0.6m deep and top layer of sand and coir dust mixture of 1:1 proportion of 0.2m deep. Washed laterite of effective diameter of 40mm was used as the main geo material, as it enhances phosphorous removal while marigold, colias and some aquatic plant were selected as bio materials concerning their performance within the system. The analysis revealed that average retention time requirement of any BGF is about 20 hrs and their treating capacity is about 80-85% removal of BOD, 78% removal of suspended solids, 59% removal of nitrogen and 65% removal    of    phosphorous.

The cost of BGF unit is estimated as approximately Rs 75,000-100,000 for 1m3/d wastewater flow, which is considerably low compared to the common wastewater treatment systems. Possible drawbacks of the system, such as clogging or flooding are also called-upon with suitable alterations.
Chandima Jayasekara, Bandunee Liyanage
Department of Civil Engineering, The Open University of Sri Lanka

River sand mining and management; Case study in Nilwala river basin – Sri Lanka

Sand is one of the key materials used in the construction industry in Sri Lanka. After the tsunami disaster the demand for sand increased significantly. The demand for sand for building construction within the country is approximately 7-7.5 million cubic meters per year. This high demanding market of sand led to mining the sand drastically in lots of areas; not only the sediment sand also river bed sand and river bank sand mining are increased. The river sand mining directly affect to the natural equilibrium. Nilwala river is the main river that suffering most of the illegal and rapid sand mining in Southern Sri Lanka. There are some other rivers in southern Sri Lanka also facing to this problem in various scales.  It is estimated that mining of sand in Nilwala River has increased by three times that of 1997 and 50km river length from sea badly affected due to heavy sand mining. Over-mining of Nilwala River causes many problems like salinization of Matara drinking water due to the intrusion of sea water into the river, collapse of river bank, loss of river land. Considering the importance of scientific assessment on the extent of environmental degradation consequent to indiscriminate sand mining, an attempt has been made in this research study to identify corrective and behavior of the environmental impacts in Nilwala river basin of Southern Sri Lanka due to river sand mining. River sand mining reduced significantly recent past years due to people’s participating and integrating research outputs, following the legal frameworks, Community Based Organizations networking. But now river sand mining completely controlled due to growth of the crocodile population.

Ranjana. U.K. Piyadasa1, Champa.M.Naverathna2, Kusum Athukorela3
1Department of Geography, University of Colombo, Sri Lanka
2Department of Agricultural Engineering, University of Ruhuna, Mapalana, Sri Lanka
3Network of Women Water Professionals, Sri Lanka

Trends in water quality parameters for river Maha Oya

Maha Oya, is one of the main rivers in Sri Lanka, much used for drinking water extraction. It flows through five important districts of Sri Lanka offering water through fourteen water supply intakes. Only three of the associated plants offer conventional treatment for water. Several small to medium urban centers are located on the main stem of the river and on tributaries. Hence, the river receives much organic waste from the upstream. Industrial discharges and harmful anthropogenic activities are common in the final 50 km stretch of the river. This study aims to find trends of water quality changes along the river and find out the reasons for them.

Records of water quality from Maha oya in years 2002 and 2003 during high and low flow rate conditions on six heavy metals (Cu, Cr, Pb, Mn, Cd, and Zn), COD and BOD along selected sampling locations were used to investigate the pattern of  water quality variation along the river.

These values were compared with the values obtained for the same parameters from same locations in year 2008 from January to December. The comparison shows that the heavy metal concentration of the river has decreased significantly the 2008. Values of BOD and COD show that there is only an insignificant reduction from past records.

Values obtained for heavy metals are significantly below the proposed standards of the Central Environmental Authority during the year. Furthermore values obtained for COD and BOD for the latter stretch of the river are comparatively higher than the standard value. There is a significant difference between the values obtained during the low and high flow rates of the year for heavy metals, COD and BOD.

C. D. K Pathirana, N. J G.J Bandara
Department of Forestry and Environmental science, University of Sri Jayewardenepura

Development of broiler offal silage with molasses

Objective of the present study was to determine the feasibility of ensiling broiler offal (BO) with molasses. Forty two-days old broiler chicks were slaughtered and processed manually. Offal without feathers were cut into small pieces and ensiled in airtight plastic containers for four weeks. The experiment followed a completely randomize design in 4*2 factorial arrangement. The treatment combinations were four molasses concentrations (5, 15, 25 and 35% w/w) and two inoculation levels (0 and 10%). Yoghurt was used as the innoculum. Each treatment combination had five replicates. pH was measured at time 0, 12hrs, 24 hrs, day 3, day 7, day 14, day 21 and day 28 of the ensiling process. pH was 4.8 at the beginning of the ensiling process. After 12 hrs, in all treatments pH dropped slightly to around 4.6. The pH at 5% molasses level dropped quickly within a day of ensiling, and was significantly lower than the pH values of other molasses levels. However, pH at 5% molasses rose thereafter, and reached to an undesirable level by day 3. By one week of ensiling, the pH at 15, 25 and 35% molasses levels were 4.1, 4.2 and 4.2, respectively. Those were the lowest pH values observed for the respective molasses concentration. At all of the above three molasses levels, there was a slight pH increase by day 14 of the ensiling. Thereafter pH maintained at a constant levels of 4.5, 4.2 and 4.4 at 15, 25 and 35% molasses levels, respectively. Except 5% molasses level, all other three levels of molasses gave typical odour of good silage. Liquefaction of the BO was poor and thus grinding of the offal before ensiling may be useful. Inoculation had no effect on pH until day 3 and, thereafter inoculation increased the pH and thus was detrimental for the ensiling process.. It was concluded that BO could successfully be ensiled with 25% molasses. Inoculation with yoghurt culture had no beneficial effect on ensiling process.

N S B M Atapattu and N D C Sirisena
Department of Animal Science, University of Ruhuna, Sri Lanka.

From Proceedings of the International Forestry and Environment Symposium 2006 of the Department of Forestry and Environment Science, University of Sri Jayewardenepura, Nugegoda, Sri Lanka (22-23 December, 2006, Wadduwa, Sri Lanka)

Aquatic Weeds in Sri Lanka

Darshani Samarakkody

Sri Lanka is an agricultural country with a population of 19 million people. Farmers and farming communities rely on a multitude of reservoirs for water as the country knows prolonged dry periods. There are some 50000 reservoirs in Sri Lanka ranging in size from 10Km2 to 1045 Km2, which have been constructed over the past 3000 years mainly for irrigati. The rural communities in Sri Lanka depend on inland water for rice and vegetable production, animal protein as well as fresh water supply. In recent years, moreover the country has seen a rapid increase in the number of dams, reservoirs and canals resulting from development of irrigation and hydroelectric projects. Recent observation and reports have demonstrated that both natural and artificial water bodies in Sri Lanka have become infected with the aquatic weeds.

In its native range water weeds is largely restricted to costal lowlands and along the margins of lagoons and slow moving waters. It occur low densities, only becoming a problem where the hydrological regime of a water body has been altered by human activities, or where the level of nutrients in the water has been increased. They provide a habitat for vectors of several diseases, increase the areas at risk as a result of flooding, and affect drinking water supply, inland fisheries and rural transport. The mosquito populations have increased at an alarming rate during the last five years due to the large mat of floating weed infestations in coastal districts.

Programms to control its growth have been initiated in most countries where it occurs. Chemical and mechanical control measures have been used to combat water weeds, but are expensive and ineffective on all but small infestation. Eradication of the weed has been rare because of its rapid growth rate and its ability to reinfest from seeds or isolated plants. Increasing concern about the financial and environmental costs associated with herbicidal control measures and their limited effectiveness has led to growing interested in the use of biological control. Biological control of water weeds offers sustainable, environmentally-friendly, long-term control and is the only feasible method to provide some level of control to those infestations which cover huge areas, are difficult to access and / or do not warrant the high cost of physical or chemical control.

The area colonized by this weeds appear to have increased in the recent years as the Government suffers from foreign exchange difficulties, lack of aquatic management knowledge, expertise and programms. Thus aquatic weeds have received very little attention in Sri Lanka so far.