Shoreline Change in Response to the Construction of a Flood Canal in Jaro, Iloilo City, Philippines

Understanding shoreline change due to engineering modifications and how it compares with the long-term trends is vital for future development plans. In this study, we focused on the Jaro Floodway, which was constructed in 2012 to mitigate the yearly floods experienced by Iloilo City. Shoreline positions were extracted from geometrically corrected historical maps (1947, 1955, and 1988) and Landsat images (1998, 2004, 2006, 2008, 2010, 2014, 2016, and 2018) for change analysis. Between 1947-1988, the coastline prograded by ~1 km due to channel avulsion most likely induced by fishpond construction at the river mouth. Between 1988-1998, erosion occurred likely due to the compounding effects of loss of mangrove cover and an increase in the number of typhoon events during the period. The majority of the coastline became relatively stable from 2004-2006. Progradation occurred at the mouth of Jaro River from 2006-2010. By the end of 2018, shoreline prograded by as much as 1.4 km. Rapid progradation is attributed to both large sediment input and the low accommodation space in the area of new discharge. The estimated volume of sediment deposited annually from 2010 is 4.11 x 105 m3, while the annual sediment input during the progradation phase between 1947-1988 is estimated at 2.70 x 104 m3. The shortened floodwater route likely contributed to the one order magnitude increase in sediment input but an increase of sediment yield in the upper stretches of Jaro River likely had a greater contribution.