Monitoring the Spread of Water Hyacinth Using Satellite Imagery a Case Study of Lake Victoria

Abstract

Water hyacinth is aquatic vegetation that is believed to have been introduced to Lake Victoria in 1988. Using satellite images from 1988 to 2016, this research identifies the trend in the spread and how human activities have contributed to the trend of spread of the water weed. Landsat satellite images were obtained from internet open sources. Mosaicking and classification were done to the images. During classification, six classes comprising of water, water hyacinth, built up area, bare ground, other vegetation and unclassified were obtained. Built up area is captured in the study because a 10 km buffer along the shores of the lake was included. This was used to monitor the growth of urban centers around the lake. Growth in urban centers is due to population pressure resulting from rural urban migration, and this resulted in increase in pollutants draining into the lake. From the satellite images used, it is observed that water hyacinth occupied very small area of Lake Victoria in 1988. In this year, the area of the lake covered by water hyacinth was 2,846 m2, this is approximately 3.4% of the total area of the lake. The weed spread over the years and in the year 2000, it was occupying an area of 19,122 m2, which is approximately 23% of the whole lake. This shows a tremendous spread of the weed. After the year 2000, the government took some steps to counter the spread. And in the years 2004, 2008, 2012 and 2016, there was a continuous reduction in the spread of the weed, whereby in the year 2016, it occupied an area of 4.9% of the whole lake. The weed is observed to be occupying mostly along the shores of the lake where the water is shallow. This has greatly affected the fishing industry since navigation is not possible in the areas occupied by the water weed. Where the fishermen find small entry or navigation, overfishing is done due to small area available for fishing and the demand is high. The results show that growth in urban areas is proportional to the amount of spread in water hyacinth. Several efforts to curb the spread have been employed by different countries but none has been totally successful. Human activities have been clearly demonstrated in this study to be the major cause of the spread. NDVI maps were used to demonstrate where the water hyacinths were healthy as compared to other regions. This study recommends that human activities around the lake should be monitored and controlled so as to reduce the pollutants entering the Lake. The study further recommends on further study to discover other possible propellers of the spread of water hyacinth in the Lake.