Vishnu B, KAU

Hydrological modelling is a commonly used tool to estimate the basin's hydrological response to precipitation. It also allows to predict the hydrologic response to different watershed management practices and to have a better understanding of the impacts of these practices. HEC-HMS is hydrologic modelling software developed by the US Army Corps of Engineers-Hydrologic Engineering Centre (HEC). It is a physically based semi-distributed model designed to simulate the rainfall-runoff processes in a wide range of geographic areas for scenarios such as large river basin water supply and flood hydrology to small urban and natural watershed runoff. The system encompasses losses, runoff transformation, open channel routing, analysis of meteorological data, rainfall-runoff simulation and parameter estimation. HEC-HMS uses separate models to represent each component of the runoff process, like models that compute runoff volume, models of direct runoff, and models of base flow. Every model run combines a basin model, meteorological model and control specifications with run options to obtain results. The Nash Sutcliffe-model efficiency criterion, percentage error in volume (PEV), the percentage error in peak (PEP) and Net difference of observed and simulated time to peak were usually used for evaluating the model performance. When the model has to be applied to a watershed, the model parameters corresponding to that watershed should be estimated and calibrated. The sensitivity of the model parameters are also determined. Finally, the model validation with a known input-output time series is carried out before testing the model in a particular watershed. A model, calibrated and validated for a watershed, can be used for several design estimation purposes and planning and management functions with regard to the water resources utilization in that watershed.

A study of aquatic invasive plants in the Kuttanad Wetland Ecosystem (Vembanadlake [south of Thannermukkam bund] and AC canal) using multispectral imageries was undertaken to assess the temporal variation in aquatic weed distribution, its extent and trends in the region of study. The study employed medium resolution LANDSAT imageries for mapping and monitoring of aquatic weed distribution. The digital image processing software used for image classification and area estimation of aquatic weed was ILWIS 3.3 Academic version (Integrated Land and Water Information System) by ITC. The spatiotemporal variation in aquatic invasive plants shows a cyclic trend in weed distribution. The mean distribution of aquatic weed is 3.25 km 2. In monthly mean aquatic weed distribution it is seen that September month is having maximum weed distribution that is about 5.4 km 2. In season wise distribution, the southwest monsoon season (5.4km 2) has the maximum aquatic weed distribution, followed by winter season (4.0 km 2), Northeast monsoon (3.4 km 2) and summer season (2.3 km 2).