LiDAR

The Changing Water’s Edge - 06/23/2011 – 8:30AM-12:30PM

Simulated LiDAR Survey

On June 23, 2011, experts, researchers, and governments officials came together to discuss the potential effects and implications of sea level rise. Every aspect of sea level rise and its results were examined during the four hour meeting held at Save the Bay in Providence. The meeting was composed of three major sections: maps and resources for local managers, case study presentations and discussions, and a view from the private sector.

Rhode Island does not have a plan to deal with sea level rise; however, it is crucial that one be developed, as the Newport Tide Gauge shows that the rate at which the sea level is rising is increasing. Planning is currently in Phase 1, consisting of data consolidation as well as the identification and quantification of vulnerable assets. Storm surge and spring high tide in Wickford can be viewed as precursors of impacts from sea level rise.

The LiDAR data was collected on May 2, 2011 and the product delivery is expected by the fall of2011. The deliverables should include raw point cloud data as well as classified points that specify ground, non-ground (trees, buildings, etc.,) water, and noise (ie. birds.) The existing data from 1997-2009 consists of maps of different scales, formats, and quality. Those maps have been compiled to make one accurate map available for viewing on ArcGIS. The information derived from LiDAR data can help standardize the accuracy of our understanding of the terrain of Rhode Island. It has such precise resolution, its margin of error is only +/- 6inches. The previous map had a margin of error of greater than +/- 3 feet.Recently a LiDAR(Light Detection and Ranging) survey of RI took place. The data from these surveys can provide a foundation for elevation data of the state, which can allow for predictions of areas that will be most impacted by sea level rise. LiDAR has a number of benefits. First of all, it is very precise, recording over 100,000 points per second. It has the ability to get multiple returns from a single pulse: in other words one pulse could detect a bird, the trees over which it is flying, and the ground beneath that tree canopy. The two major LiDAR products are digital surface models and digital elevation models, the latter of which can create bare earth digital elevation models(DEMs) which are used to calculate the areas impacted by sea level rise. The bare earth DEMshave 10 foot cell sizes and are hydroflattened, showing neither contour lines nor bathymetry.

A one foot sea level
rise in Wickford Harbor

LiDAR data will be particularly useful when examining the state’s tidal marsh areas. The total area and actual location of tidal marshes is important for a number of reasons. Tidal marshes are quite vulnerable to sea level rise and their locations and total area can change as a result of sea level rise. Many roads are blocking their retreat and if those roads are not moved, the marshes will inevitably be inundated. South County is a prime example of where this is likely going to be an issue. In order to model the potential effects of sea level rise, Kevin Ruddock of the Nature Conservatory presented models of how a 1 feet, 3 feet, and 5 feet sea level rise would impact different areas of the state. He depicted the scenarios using SLAMM (Sea Levels Affecting Marshes Model.) This modeling program takes into account inundation, erosion, overwash, saturation, and accretion on the topography of the state. It presents data on a1:12,000 scale.

Following the presentation and discussion of the compelling SLAMM maps, there was a discussion with North Kingstown town officials. After a short break, panelists from Bristol,Newport, and Warwick discussed the potential impacts of sea level rise in their respective areas. Diane Williamson, the Community Development Director in Bristol, discussed concerns regarding storm surge and the infrastructure in the Poppasquash/Hope Street infrastructure where culverts are being blocked by the receding seawall. There is a question of whether or not to repair the road, as it is at such a risk for flooding, it may be a waste of money.

A three foot sea level
rise in Wickford Harbor

In terms of flooding, she succinctly said it “hits you at home because it is your home.” Her talk was followed by a presentation by Newport Planning Director, Paige Bronk. He discussed how storm surge is also a concern in the area, as Newport lies well within a 100-year floodplain. Storm surge threatens retail business on Thames Street; however, due to the historic nature of those buildings, raising them remains controversial. Bronk called for a stronger state building code that will consider flooding. He also encouraged zoning relief for properties at risk of coastal flooding. Finishing this portion of the meeting, Janine Burke from the Warwick Sewer Authority discussed how the floods of 2010 presented a true challenge to the wastewater infrastructure in the city. She provided forceful pictures and statistics about how the Sewer Authority faced an unprecedented challenge from the floods; her office was evacuated on March30^th and water levels there rose to six feet. The floods tested pumping stations that were “built like submarines,” completely wiping out six of them. The biggest impact of the floods could be seen in sanitary sewer overflows and electrical system problems. As a result of the floods, the wastewater treatment employees are now actively involved in emergency planning. Burke suggested that in planning for climate change, the following are major points to be addressed:energy efficient initiatives, renewable energy, consideration of future hydrology, and avoidance of construction in floodplains.

A five foot sea level
rise in Wickford Harbor

Finishing up the day, Sandy Taft, Director of US Climate Change Policy for National Grid discussed adjusting to climate change and addressing the risks associated with it. He said we must consider the impact of weather – wind, water, and temperature – on infrastructure. Taft suggested looking at long term threats and prioritizing based on how long each asset will be in place. In terms of flood types, he mentioned four types: coastal/tidal, fluvial/river, groundwater, and flash flooding and that they have been focusing on river flooding. While Federal Emergency Management Agency ranks areas in terms of risk as either low, medium, or high, the maps being used to categorize those areas may be outdated or based on historical events and therein lies several problems which we all face. LiDAR is a very helpful data source but National Grid found that sometimes it is not enough. For example, LiDAR cannot record inside a structure and therefore National Grid has had to conduct surveys of the equipment inside a building to determine if they will be flooded based on their elevation. Once flood implications are understood, several construction alternatives can be deployed which Taft described as avoidance, resistance, resilience, and reparability. Since National Grid is a UK-based company, Taft shared the different data sources that are made available in the UK versus the US and, as a result, the different internal design standards deployed.

Overall, the day was hugely informative for all of those involved. The speakers highlighted the extent to which sea level rise will have far-reaching implications, many of which are often not immediately obvious.

Elizabeth Gooding