Dike Restoration Monitoring

How fast is the beach and dike recovering after the timber sill repairs, rock seawall repairs and other recovery efforts? Where were sills or the seawall damaged by floating logs during last winter's storm surges? Did any shoreline properties adjacent to the dike have significant damage? Currently, where are the weakest and lowest points along the seawall?

Annual programmed scan flights and high-accuracy 3D geospatial models over the next 15 years enable detailed measurements of the volumes of sand along the base of the dike and along the repaired timber sills. The data and imagery in the progression of models provides evidence of sand accumulation and erosion from the previous year, and detailed visualization of any damage to the dike and homes from winter storms. Each year, the current elevations along the top of the dike indicate the lowest areas or weakest points where there is potential for a sustained breach of the dike during extreme winter weather conditions. The dike currently prevents flooding of over 700 acres of residential properties, farm lands, recreational lands (a golf course), wetlands, livestock grazing lands, and freshwater aquifers tapped by the wells of several local, residential water supply systems.

This project is being coordinated with the WA State Department of Ecology, the US Army Corps of Engineers, other regulatory agencies, local tribes, and property owners in and near the dike. As contracted by the local Diking District, Aerial Whidbey authored the long-term Monitoring and Adaptive Management Plan for the project, and is responsible for developing the annual progress reports based primarily on georeferenced aerial imagery and data from high-accuracy 3D geospatial models. Aerial Whidbey was among the first to acquire a proven, high-accuracy system from Klau Geomatics, based in Australia. Aerial Whidbey developed additional capability by adapting industry-leading software from Switzerland and Belgium. Extensive field and office procedures have been developed to reduce operational risks and enable rapid training and assumption of contractual responsibilities. Outcome: A complete system with procedures for high-accuracy geospatial modeling and monitoring of changes in the visible state of a property, and without placing and retrieving any ground targets. The 3D models are readily explorable by project participants and stakeholders without extensive photogrammetry, land surveying or civil engineering background, and without significant software training or cost.

Project images/videos - select for more details

Repaired timber sills and rock seawall from east to west. Littoral drifting sand has begun to re-accumulate along the sills and the base of the seawall. Top boards in the sills are added to increase sand accumulation toward the target restoration elevation of sand relative to NAVD88.

A 5 foot grid of measurement points has been established between each pair of sills. The elevation of the points along the east and west sides of each sill is tracked and described in each Annual Monitoring Report.

The shape and size of the long sandspit in the foreground evolves with tidal changes and varying weather conditions, most significantly during winter months. The opening in the spit that servies as the mouth of a lagoon also shifts in location over time.

The orthomosaic image (part of the 3D geospatial model of the dike and adjacent beach areas) aligns with Google Earth satellite imagery from a previous summer. The orthomosaic was developed from recent, low-altitude aerial images to provide significantly more detail.

The orthomosaic image (part of the 3D geospatial model of the bay and shoreline area that is mostly east and south of the dike) aligns with Google Earth satellite imagery from a previous summer. The orthomosaic was developed from recent, low-altitude aerial images to provide significantly more detail.

As needed, the total modeled area can be expanded to 125 acres by including a model of the mouth of a lagoon near the western end of the sandspit and dike. The level of sand and sediment in the lagoon has been rising for years.