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Chapter 2 – Subsidence and Other Coastal Hazards at Kapoho One of the main objectives of this report and study was to determine the nature of subsidence in the Kapoho area and answer the key question -- is the subsidence episodic only -- or episodic and continuous? Once the nature of subsidence was determined, it would be possible to fit it into the overall determination of hazard risk in the Kapoho area, and create mitigation measures that are suited to the characteristics of this site. The development of mitigation measures for the area is dependant on the hazard risk and is covered in Chapter 4, which deals with administration of the Special Management Area. In this Chapter, insight into the hazard risk is provided. 2.1 Ongoing Subsidence at Kapoho A major portion of this project was to gather the information necessary that would be vital for planning purposes. Most importantly, it was necessary to determine if the subsidence at Kapoho was ongoing, and if so, what is the magnitude of the change. Dr. Ben Brooks and his team from the Pacific GPS Facility at the School of Ocean and Earth Science and Technology, University of Hawaii was contacted to assist for this issue. Using Synthetic Aperture Radar Interferometry (InSAR) techniques and radar data from the European Space Agency’s Envisat, an estimate for subsidence at Kapoho could be determined for the period from February 12, 2003 to March 8, 2006. The full body of the report, explaining the methodology, the results and limitations is found in Appendix A. This section contains a very brief description of the major findings. From the InSAR study, the immediate Kapoho region experienced average downward vertical motions, with respect to Hilo of between ~ -0.7 and -1.6 cm/yr +/- 0.6 cm/yr. The 0.6 cm/yr. represents 2 standard deviations. Combined with the rising sea levels measured in Hilo and believed to be representative for Kapoho, the relative sea level rise for Kapoho has thus been estimated to be ~0.8 to 1.7 cm/yr +/- 0.8 cm/yr (2 standard deviations). Several key points should be made from the study. First, the subsidence at Kapoho is at least an order of magnitude greater than the sea-level change recorded at the Hilo tide station. So local land motion dominates over relative sea-level change for this particular area and time interval. Also the authors do not attribute the subsidence to any particular cause as this was outside the scope of the study. Finally the authors note, and this report concurs that the area should continue to be monitored since so much is at stake. It is not known if there are variations in the rate of subsidence over time and to what extent the continuous subsidence relieves stress that over time may cause episodic larger events (see next section). In other 9