Lidar Elevation Data for New Hampshire: The 3D Elevation Program

Publicly available lidar in New Hampshire, March 2015. USGS, from the U.S. Interagency Elevation Inventory.

Why elevation data matters

Elevation data serve many needs in New Hampshire: flood mitigation, land development, agriculture, transportation planning and design, and managing infrastructure. The state's most valuable uses are flood risk management, natural resources conservation, forest management, agriculture, infrastructure and construction and geologic hazards.

High-density lidar is now the main source of elevation models. Federal, state, tribal and local agencies work together to replace older, lower-quality data and to fill gaps, aiming for consistent statewide coverage.

By the numbers

Because not every benefit had a dollar value, the true total is likely much higher. About 78% of the identified needs fall in flood risk management and conservation.

How lidar helps New Hampshire

Floods. Lidar gives better, cheaper terrain for flood studies and hydrologic modeling; for designing bridges and culverts to carry runoff from big storms; and for dam design, dam-breach studies and stormwater engineering. It identifies vulnerable properties in floodplains, supports better floodplain decisions, shows the public their true risk, and can avoid costs when floods come. Dynamic 3D models show what a flood could do. (The fact sheet recalls the Cold River flood of October 10, 2005, which wrecked the Route 123 bridge and road near Drewsville.)

Conservation. Better elevation data would help state, regional and local governments carry out grade stabilization, dam safety, habitat easements, pipelines, terracing and wetland restoration at lower cost — and would let organizations do more planning and engineering from the desk, with less fieldwork.

About 3DEP

The National Enhanced Elevation Assessment (Dewberry, 2011) found the best return from quality level 2 lidar for the conterminous United States and quality level 5 radar (ifsar) for Alaska, refreshed every 6 to 10 years; 3DEP chose an 8-year cycle. The USGS runs it as the federal lead for land elevation data.

• Goal: complete national coverage by the end of 2022, depending on funding and partners.
• Value: conservatively $1.2 billion a year nationally, with the potential for $13 billion a year.
• Why a national program: larger purchases cut costs by 25%; buying high quality once avoids paying to "buy up" later; consistent data across state and watershed lines; more federal money reduces state and local shares; and ready contracts and specifications simplify buying.

Sources

Based on William J. Carswell, Jr., "The 3D Elevation Program: summary for New Hampshire," U.S. Geological Survey Fact Sheet 2014–3110, version 1.1 (2015); a work of the United States government in the public domain. The map and tables are taken from the fact sheet's PDF; its photograph of the Cold River flood damage, courtesy of the New Hampshire State Police, is not reproduced. Benefit figures come from Dewberry's National Enhanced Elevation Assessment (2011, revised 2012).