The water quality in Al Thawra Lake was getting worst recently because of the
increscent of the concentration of nutrients, which reached the lake from point and
nonpoint sources. The Geographic Information System GIS was widely used in the last
d
ecades in evaluating quality of water depending on models operates within GIS one of
these models is The BASIN software (Best Assessment Science Integrating Point and
Nonpoint sources)which used in this research .The Pload model(Pollution load) which is
one of the BASIN models was used to estimate the pollution loads. The Pload was run by
using satellite image, Digital Elevation Model (DEM30), land use map, and export
coefficient values. The result showed that the total annual pollution loads of TP&TN are
TP=11543 kg/yr ,TN=61367 kg/yr that came out of the watershed of the lake, Open maki
and rock out crops are the dominate contributors to TP load in the watershed for about 30
%of total TP load, while Olives and citruses are the dominate contributor to TN load in the
watershed for about 33 %of total TN load, the model results also indicated that the
nonpoint sources are the main contributor to TP&TN loads in the watershed for about
80%of the total TP loads while only 20% from point sources, and for about 75%of the total
TN loads from nonpoint sources while only 25% from point sources.
