The 3D Elevation Program in South Carolina: $4.3 Million a Year in Benefits

Why elevation data

Elevation data serve a wide range of work — forest and wildlife management, national security, recreation and much more. In South Carolina they matter most for flood risk management, natural resources conservation, agriculture and precision farming, infrastructure and construction, and forestry. Today most elevation models are built from high-density lidar (light detection and ranging). Federal, state, tribal and local agencies work together to replace older, lower-quality data and to cover places with no public data, aiming for consistent statewide coverage.

The National Enhanced Elevation Assessment (NEEA; Dewberry, 2011) weighed options for data quality and how often to refresh it against cost. The best benefit-to-cost ratios came from quality level 2 lidar for the conterminous United States and quality level 5 ifsar (interferometric synthetic aperture radar) for Alaska, refreshed every 6 to 10 years. The 3D Elevation Program (3DEP) chose an 8-year cycle. It is managed by the U.S. Geological Survey, the federal lead agency for land elevation data.

The national programme

3DEP aims to cover the whole United States with high-resolution elevation data by the end of 2022, depending on funding and partners — more accurate and more current than the National Elevation Dataset. The USGS and its partners will collect quality level 2 or better lidar over the conterminous United States, Hawaii and the U.S. territories, and quality level 5 ifsar in Alaska, over eight years, all made public.

Conservatively, 3DEP could deliver $1.2 billion a year in new benefits, and potentially $13 billion a year, through better government services, fewer crop and flood losses, more efficient vehicle routing and more. A funded national programme brings:

• Economy of scale — collecting larger areas cuts costs by 25 percent;
• A systematic plan — collecting at a higher quality level lowers the cost for state and local governments of "buying up" to what they need;
• Consistency across state and watershed lines, meeting more needs;
• More federal money, so state and local partners pay less;
• Help with acquisition through ready contracts and published specifications.

Benefits for South Carolina

NEEA respondents in South Carolina estimated that 3DEP would bring at least $4.3 million a year in new benefits, against a cost of about $10.4 million — a payback of 2.4 years and a benefit-to-cost ratio of 3.3 to 1 over eight years. Because not every benefit was given a dollar value, the real total is probably much higher. About 73 percent of the identified needs fall in flood risk management, natural resources conservation, and agriculture and precision farming.

Closer coordination between 3DEP and government and private organisations in the state could capture more than these conservative figures.

How the data would be used

• Floods. Lidar gives better, cheaper terrain for flood modelling; for designing bridges and culverts that can carry heavy runoff; and for dam design, dam-breach studies and stormwater engineering. It also helps find vulnerable properties in floodplains and show people their true flood risk. On the Saluda River below Saluda Lake Dam near Greenville, a lidar-derived elevation model helped map flooding along a 3.95-mile reach at different river stages at USGS streamgage 02162500. Dynamic 3D models with lidar show flood effects in more detail.
• Conservation. Better elevation data would help governments carry out conservation practices and save the public money. With lidar available, public and private organisations would use it more for planning and site engineering — cutting field work for conservation ponds, grassed waterways, pipelines and terracing, calculating runoff accurately, finding drained historic wetlands and restoring wetlands.

Next steps

Reaching national coverage in eight years depends on:

• more partnerships among federal, state, tribal and local governments;
• partnerships that collect data to 3DEP's specifications over larger project areas;
• more awareness of the programme's benefits and goals;
• support from government and other stakeholders.

Sources

• Carswell, W.J., Jr., 2015, The 3D Elevation Program — Summary for South Carolina: U.S. Geological Survey Fact Sheet 2015–3029. https://pubs.usgs.gov/publication/fs20153029
• Map: U.S. Geological Survey, from the U.S. Interagency Elevation Inventory (October 2014). The fact sheet's Saluda River flood maps are drawn over aerial photography with no credit and are left out.
• Rewritten in hubnx's own words.