A procedure for monitoring the spread of water Hyacinth using remote sensing and geographic information system(GIS)
Date
2011-10-31
Authors
Namakando, Chrispin
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Abstract
Water hyacinth is, after eutrophication, the largest threat to waterways, lakes and dams throughout Africa. The aim of this study was to develop a procedure for monitoring the spread of water hyacinth on Lake Kariba using Remote Sensing and Geographic information System. The spread of water hyacinth on Lake Kariba is influenced by nutrients (phosphates and nitrates), climate, wind and wave action and lake level variation. On the Lake the weed is found as fringe on the shore line, free floating and thick mats. A procedure for monitoring the spread of water hyacinth on Lake Kariba was developed considering its occurrence, the use of Global Positioning System and satellite imagery. The spread of water hyacinth on Lake Kaiba was studied using satellite imagery and through boat surveys. Remote sensing software Idrisi 2.0 was used to process and classify the satellite image whereas ArcView GIS 3.2a software was used for analysis. Idrisi 2.0 and ArcView GIS 3.2a software were used to test specific steps of the procedure. The hybrid classification procedure (Using the ISOCLUST module of Idrisi) was found to be better suited for monitoring the spread of water hyacinth than the supervised and unsupervised methods of image classification. Seven (Two Spot and Five Landsat) satellite images were used to assess the spread of water hyacinth in this study. The extent of water hyacinth on Lake Kariba was estimated at 572 ha in 1995 (Spot), 1422 ha in 1999 (Spot), 455ha in 2001 (Landsat) and not detected by Landsat satellite images captured in 2004 and 2005. The weed spread was visually estimated to be 50 ha in January 2004, 10ha in December 2005 and 20ha in July 2007 through boat surveys. Overall, water hyacinth spread from 682ha in 1992 to 4510ha in 1998 after which it reduced to very low levels not warranting the use of satellite imagery in 2007.
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Keywords
Water Hyancith , Eichhornia Crassipes