Watershed Management: The Path Traversed and the Way Forward

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WETTING CHARACTERISTICS OF SOME TROPICAL TREE SPECIES

Interception is a physical process, which represents a definite loss of rain-water,since most plants can absorb water only through their roots. 771e quantity lostdepends on how the canopy is wetted by the falling rain, and the amount of waterstored on the vegetation after the rain stops. Information on these points is needed inmodelling studies aimed at estimating the interception loss under varying climaticconditions. This study compared the welling characterisitics of Acacia decurren,Artocarpus heterophyllus, Eucalyptus microcorys, Hcdyotis confertiflora, Pinuscaribaca, Rhododendron zeylanicuni, Syzygiun! rotundifoliunt, and Tectono gram/is./1 rainfall simulator was used 10 generate three drop sizes. Maximum interceptionand interception loss for each species and for each drop size were measured on abranch representing a projected canopy area of one square metre. The resultsshowed that the interception loss depends on the species and not on the raindrop sizeand that it is inversely proportional to leafsize. Front the point ofview ofmaximizingthe catchment water yield, the species with larger leaves, such asjak and teak, whichgive the least interception losses, are more suitable Jhr planting in drier areas, whilespecies with smaller leaves are more suitablefor wetter areas

QUALITY MEASUREMENTS IN CLOUD WATER, RAIN, THROUGHFALL, AND STREAM WATER, AT HORTON PLAINS

Die-back of natural forests in the Horton Plains has been of some concern inrecent times. One of the possible causes is atmospheric pollution. Since clouds(jog) carry greater amounts of pollutants than rain, an assessment was made ofboth rain and cloud water quality, as well as that of throughfall and streamwater. Samples were collected and analysed at weekly intervals from November1995 to May 1996. They were tested for pH, electrical conductivity (EC), nitratenitrogen (NOrN), ammonium nitrogen (NHrN) and sulphate sulphur (,'-,·(Jr-S).Plastic buckets were used to collect rain water and throughfall. A collector wasdesigned and constructed to collect cloud water. The average pH of cloud waterlVas 5.0 and the values as low as 3.9 was observed during certain periods ..According to the literature, this latter high acidity could be injurious, burningtender leaves. The highest concentrations of NOrN, NH4-N, and S(Jr-S incloud water were 10.23, 5.04 and 9.40 mg/litre respectively; vet:y IIIl1ch higherthan those of the rain water. These pollutant levels and high acidity may causestress on the plants. The concentration (if chemicals is also high in thethroughfall. However, the soil acts as a buffer and provides good quality waterto the streams, as shown by the vet:y low concentration of chemicals there

IMPACT OF LAND USE CONVERSIONS ON WATER YIELD

Trees use more water than shorter vegetation due to comparatively high interception and evaporation losses. These losses also vary with the different tree species and climatic conditions. In high elevations, trees could offset the interception losses by capturing horizontally driven fog into the catchment system. Therefore, it is important to study the hydrological processes which would help to estimate water use of different land cover types which in turn is required to find the effect of land use conservation on water yield.Only two studies with limited duration have been carried out to find the effect of land cover on a few hydrological processes in 1977 and 1988. Therefore, a long-term research project has been carried out since 1993 at two sites, namely at Dodangolla and Horton plains, to monitor the hydrological processes in detail under different land use types. Home gardens, grass and Acacia are being selected at the low elevation site, while montane forests, grassland and Pinus are being selected for the high elevation site.These two sites are instrumented with automatic weather stations which monitor rainfall at 5 minutes intervals and other climatological parameters at hourly intervals. Net rainfall gauges with tipping buckets are installed to measure interception. Soil moisture is being monitored with access tubes and neutron probes at the two sites. A fog collector is installed at the Horton plain site to measure the horizontally driven fog at hourly intervals.The results from this study will be used to calibrate a water use model for different land use types. Once this is accomplished, the model can be used to predict the effect of land use conservation on water yield

Runoff Prediction in an Ungauged Catchment of Upper Deduru Oya Basin, Sri Lanka: A Comparison of HEC-HMS and WEAP Models

Runoff prediction from ungauged catchment has always been a challenging task, requires transfer of hydrologic information from gauged to ungauged catchments. However, it is not clear whether information transfer among nearby catchments is suitable across a wide range of climatic and geographic regions. In this study, stream flow data of a gauged catchment (Tittawella tank) were used for calibration and validation of HEC-HMS (Hydrological model) and WEAP (Water resource model). Watershed area ratio technique was adopted to simulate runoff from an ungauged catchment (Hakwatuna Oya) and the results were compared. The simulated flows generated by both models in calibration and validation showed good agreement with observed flows. Monthly flows simulated by both models were quite similar. Although HEC-HMS enables runoff simulation on daily basis with better prediction of peaks, necessary for flood forecasting, monthly simulation is adequate for water managers to take management decisions. Therefore, WEAP as a single model can be used for both runoff simulation and taking management decisions in Hakwatuna Oya catchment

Resilience of farmers at water shortage situations in minor irrigation systems: a case study in Kurunegala District, Sri Lanka

Farmers in Minor Irrigation Systems (MIS) experience many difficulties due to severe seasonal or year-round absolute water scarcity that affects their livelihoods. In order to address this problem, the resilience of the vulnerable communities needs to be enhanced through smart investments and appropriate adaptation strategies. Since there is no well-established method for assessing the resilience of the farmers in MIS, this study was aimed to develop a framework and prospective methodology to assess resilience and factors determining the resilience to shocks and stresses of MIS. A structured questionnaire survey was carried out among 188 households belong to eight farmer organizations under 16 MIS located in three Agrarian Service Divisions in the IL3 agro-ecological region in Kurunegala District. The resilience of farming was measured using adaptive capacity or the risk management strategies used at household levels related to farming practices using 20 indicators. Analysis of factors was performed with the principle component method and rotated (from Varimax with Kaiser Normalization technique) factor loadings were extracted to compute resilience index. Using the empirical equation derived from the study, the resilience of MIS was quantitatively determined. The results showed that there is an adequate space to enhance the resilience of farming in MIS by introducing and adapting various risk management strategies. It appears that capacity of the tank, accessibility of services and the trust of farmers both on farmer organizations and the agency officials are some of the key factors which govern the resilience of farming in MIS