The Inner Area Change Detection in Pak Panang Bay Before and After the Operation of the Uthokawiphatprasit Watergate using Aerial Photographs and Geographic Information System

This study investigates coastal changes in Pak Panang Bay, Nakhon Si Thammarat Province before and after the operation of the Uthokawiphatprasit Watergate over the Pak Panang River by using aerial photographs and geographic information system techniques. The aerial map on 1:15,000 scale produced by The Royal Thai Survey Department in 1974 was compared to the aerial photographs acquired in 1995, 1999 and 2003. The results revealed that from 1974 to 2003, the inner area of Pak Panang Bay increased by a total of 7 km2 (4,375 rai). However, it was found that between 1995 and 1999, 4 years before the operation of the watergate, coastal area increased by 1.89 km2 (1,181.25 rai) compared to 0.19 km2 (118.75 rai) of area expansion from 1999 to 2003, 4 years after the watergate was in operation. Sediment reduction due to the watergate operation may benefit the Pak Panang Bay by delaying the sediment filling of the bay. However, debate over the watergate as the main factor of sediment reduction calls for further investigation.