H.A.H. Jayasena

Holocene Indian Ocean tsunami history in Sri Lanka

Sediment cores from Karagan Lagoon in southeastern Sri Lanka retrieved deposits from the A.D. 2004 Indian Ocean tsunami and older similar deposits that provide evidence for a tsunami 2417 ± 152 cal. (calendar) yr B.P. to 2925 ± 98 cal. yr B.P., and for six tsunamis between 4064 ± 128 cal. yr B.P. and 6665 ± 110 cal. yr B.P., a period for which the sediment record appears continuous. Radiocarbon dating indicates that the recurrence interval is variable, ranging from 181–517 yr to 1045 ± 334 yr, with a mean recurrence interval of 434 ± 40 yr during the ca. 4000–7000 cal. yr B.P. continuous interval. Assuming that these tsunamis were generated by giant earthquakes along the Sumatra-Andaman subduction zone, a reasonable assumption for this far-field transoceanic location, this record extends the giant-earthquake history for the Indian Ocean region. The longest recurrence interval of more than 1000 yr implies that earthquakes along the subduction zone may reach twice the size of the 2004 earthquake.

General geology and petrology of some Precambrian crystalline rocks from the Vijayan Complex of Sri Lanka

Abstract Detailed field studies of the Precambrian Vijayan Complex terrain, Sri Lanka, reveal the occurrence of granites, gneisses and migmatites in association with calc-silicate gneisses, quartzites and dolerites. Microcline-rich granites and gneisses show both sharp and gradational contacts with the adjacent migmatites. Petrological observations favor a magmatic origin for the granites and gneisses. These bodies seem to have intruded into pre-existing metasedimentary rocks which were subsequently subjected to retrograde metamorphism under amphibolite facies conditions.

A permo-triassic(?) plant microfossil assemblage from Sri Lanka

Abstract Palynological observations on peaty and sandy clay beds of some sedimentary sequences from the Kurunegala district of Sri Lanka reveal the occurrence of plant microfossils of probable Permo-Triassic age. The microfossils are found in sediments considered to be of glacial origin deposited on the Sri Lankan fragment of the Gondwanaland.

Origin of geothermal systems of Sri Lanka

Abstract Along the Highland Group—eastern Vijayan tectonic boundary of Sri Lanka there is a 350 km long thermal spring line indicating a large geothermal system beneath. Chemical geothermometers yield temperatures of about 150°C at depth for some of the thermal springs with higher surface temperatures. Tectonic movements as indicated by microseismic activity along the geothermal zone, the presence of a line of serpentine bodies, granites and anomalous uranium-bearing regions all indicate probable sources of heat. Serpentinization provides exothermic reactions that contribute significantly to heat production. The length of the geothermal zone and its location in a tectonically active zone indicate a deeper-lying thermal source that needs to be investigated in detail as a potential energy source of Sri Lanka.

Geochemical characteristics of sediments from a reservoir (tank) ecosystem in Sri Lanka

Major, trace and selected high field strength element geochemistry of fresh-water sediments from the Malagane tank, Deduru Oya basin, Sri Lanka, has been investigated in this study. Sediment samples were collected from 13 locations and analyzed for their elemental distribution using the X-ray fluorescence technique. The sediments were characterized by relatively low organic matter, ranging from 4.8 to 16.9%. The elemental distributions were compared with those of the average upper continental curst, and it was found that, with a few exceptions, most of the studied elements are either comparable or depleted. Correlation and principal component analyses were applied to identify the relationships among studied elements. Major elements, most trace and light rare earth elemental distribution show strong positive correlation with Al2O3 and TiO2, which indicate that the phyllosilicates and heavy minerals in the sediments are the probable hosts for these elements. The results also indicate that the sediments in the Malagane tank are representative of the materials from the metamorphic rocks in the watershed and were subjected to changes within the tank ecosystem. The results obtained from this study are vital for future pollution management of tank ecosystems in Sri Lanka, since information on elemental distribution within the sediments of tank ecosystem is lacking.

Using the BC “Guidance for Assessing the Design, Size and Operation of Sedimentation Ponds used in Mining" to comply with federal/provincial sediment control legislation

British Columbia (BC) mining companies and federal/provincial regulators have the most stringent international minesite total suspended solids (TSS) standard to contend with. Addressing the generation, mitigation and compliance of sediment release from existing and proposed minesites means end-of-pipe and runoff must not exceed a TSS standard of 30 mg/L for a grab sample (and 15 mg/L for a monthly average) – this is a requirement of the Metal Mining Effluent Regulation (MMER) under the Fisheries Act. Add to this requirement in BC: minesite discharges must not cause exceedence of the stringent BC Water Quality Guidelines (BCWQG), exceedence of which may result in pollution, as defined in the BC Environmental Management Act (EMA). A frequent use of flocculants to achieve compliance with the MMER, a BC effluent permit, and the BCWQG TSS standards, may result in flocculant-induced toxicity, which is a contravention of the MMER, the EMA, and a BC mine effluent permit. Achieving compliance with these TSS requirements requires the application of a Best Achievable Technology (BAT). In 2002, the MMER was enacted and the Ministry of Environment (MOE) developed their Guidance for Assessing the Design, Size and Operation of Sedimentation Ponds Used in Mining. An essential part of designing for federal/provincial sediment release compliance for proposed mines is the preliminary sampling/testing of minesite soils and determining the need for a flocculant addition and control system. Sampling and testing is required for: (a) prediction of sediment pond discharge and runoff quality, and (b) execution of a well-designed Sediment Pond Management Plan (SPMP) and an Erosion and Sediment Control Plan (ESCP). Failure to follow a plan which uses a predictive methodology, using site specific soils and settling testing, leaves the issue of legislative compliance to chance. If existing mines are not in compliance, it may often be the result of not performing the recommended testing and planning. The MMER is currently under review to include coal mines, Al, Fe, ammonia, Se, and may potentially generate additional onerous requirements as Environment Canada (EC) recently asked for more stringent government rules to prevent water pollution from mines. This paper will comment on and provide conclusions related to the effectiveness of the following in predicting and preventing water pollution caused by TSS: (1) BC effluent permitting, (2) the BC sediment pond design approach, (3) proposed MOE guidance on designing erosion and sediment control plans, (4) the BC TSS/turbidity Water Quality Guidelines, (5) the MMER, and (6) other applicable prediction, design and operating strategies.

Water Quality Variation in a Tank Cascade Irrigation System: A Case Study from Malagane Cascade, Sri Lanka

Tank cascade irrigation system (TCIS) is a water management practice developed in order to match the nature of the rainfall and landscape in the dry zone of Sri Lanka. The series of interconnected tanks in this system serves multiple functions, including irrigation. This study was carried out to investigate the water quality variation in a tank cascade system and study the role of hydrophytes found in the upper periphery (Thaulla). The Malagane Tank in the northwestern intermediate zone of Sri Lanka was selected for the study. Fairly high levels of nutrients and metal concentrations were recorded in the upstream paddy fields and main inflow of the tank. The concentrations of most of the chemical parameters were showed a decreasing trend while passing the thaulla area which is one of the most important hydrologic regime in a tank system. However, the runoff from the either sides of the tank has polluted the lake water particularly during the rainy season. The hydrophytes in the thaulla area play a major role in the hydrology of the tank system.