U.S. National Tsunami Warning System Tsunami gauge development and implementation

The U.S. National Weather Service (NWS) operates an independent array of Tsunami Gauges in Alaska and California. NWS Tsunami Gauges are designed to provide real-time monitoring capability to assess the hazard potential of tsunamis. The gauges are developed at the U.S. National Tsunami Warning Center (NTWC) and encompass two distinct designs. The Alpha version utilizes a high precision radar sensor, and has served the U.S. Tsunami Warning System through over 56 years of cumulative operation in challenging Aleutian environments with zero component failures. The Alpha version requires sturdy infrastructure, as the sensor must be rigidly positioned over the water. A typical installation would be found on a dock, bridge, caisson or piling. The All-Terrain (AT) version Tsunami Gauge utilizes a typical data logger and pressure transducer. The installation method of the AT version is unique. Component and materials selection, component integration, and system installation techniques have been developed to maximize reliability. The AT version is designed to be installed by two technicians in about 3 hours. This makes it ideal for remote coastal environments where hazards may prevent a more robust installation. Environments where the AT version is ideally suited include areas where tsunami generation may be caused by landslide, or volcanic activity, or remote coastal environments where hardened infrastructure is not available. Tsunami gauges are, by necessity, considerably different from a conventional tide gauge. A tsunami gauge should be exposed to open ocean where the wave is less distorted than in up-river or confined harbor settings. Tsunami forecasts typically provide a range of wave amplitudes at the main shore, and not at the rear of a jetty protected harbor. A tsunami gauge is installed with the expectation of inundating or high current events. Tsunami gauges need only report relative water levels. Tsunami forecasts are scaled in real time during an event based on wave crest heights as recorded by these gauges. The expectation of survival comes with specific installation practices and assembly techniques. Tinned wires, silicone grease, stainless steel installation hardware, and utilization of materials that exceed expected structural strength requirements are among the many techniques utilized. The tsunami gauge is fortified to be tsunami resilient, but it is not tsunami proof. The value of the NTWC Tsunami Gauge is realized by the reduction of travel to remote stations. The Alpha version Tsunami Gauge has required no hands on intervention, even after years of continual operation in demanding sub-arctic conditions.