Theme 7-10-Assessment and mitigation of hydrological hazards in Sri Lanka.

Abstract

In assessing Hydrological hazards emphasis be given to impact on land resources as it plays a very important role. Floods, water logging, acid sulphate conditions, iron toxicity, soil salinity, alkalinity, soil erosion, land slides and water pollution are the major hydrological hazards in Sri-Lanka.

Soil Erosion and land degradation is a very series aspect of hydrological disasters. Present day soil erosion is estimated for various land use categories and in certain categories like vegetables in mid and up country, tobacco in the mid country intermediate zone and slash and burn cultivation practices under low country dry zone it is alarmingly high. Monitoring is done in different catchments using absolute measurement estimation methods and cesium fallout method. Erosivity of rains decreases with increase in elevation of the country. Erodability of soil decreases in the following sequence. Red yellow latosolic soils or nitisols are the most stable followed by Red Yellow Podsolic soils(Ultisol), and Reddish Brown Earth soils(alfisol)

Land slides is another major aspect which cannot be disregarded. These are mostly activated by very heavy rains within very short time about 200 mm of rain within two days. Soil salinity and alkalinity is monitored in many tanks and in the command area of major irrigation projects in order to take necessary precautions.

Hydrological hazards can be minimized by educating rural people with awareness programmed and also to provide them with enough subsidies for results oriented active participation in this exercise.