Tuesday, February 26, 2008

New Kauai shoreline erosion bill among nation's most conservative

Kaua'i County has adopted the most aggressive shoreline building setback law in the state, a powerful policy that aims to protect coastal structures against 70 to 100 years of erosion.

(Image: Kaua'i map with red boxes showing areas where erosion studies have been completed. This interactive image is available online at www.soest.hawaii.edu/asp/coasts/kauai/index.asp. Courtesy Chip Fletcher.)

Coastal geologist Chip Fletcher, of the University of Hawai'i's School of Ocean and Earth Science and Technology, said the Kaua'i legislation may represent the most conservative coastal erosion position in the nation.

The new law, passed by the County Council and signed by the mayor, declares its provisions to be both a public safety and a planning measure.

Pushing buildings back from eroding waterlines, the law says, “is critical to the protection of life and property, the mitigation of coastal hazards, and the preservation of coastal resources.”

The issue, in part, is that if government allows people to build within a few dozen feet of the shore, and erosion threatens to undermine foundations, then there are powerful financial incentives to protect the structures—and you end up with rock walls instead of sandy beaches. Coastlines where people can't pitch their beach umbrellas, where anglers can't set up poles and beach chairs and coolers, where monk seals and turtles can't haul out, and where the classic look of a tropical beach is destroyed.

Under the new legislation, there are two potential ways of calculating how close to the water a structure can be erected.

On shallow lots whose depth from the certified shoreline to the back of the lot averages 100 feet or less, a building could be built as near as 40 feet. On deeper lots, the setback grows. If the lot depth is 130 feet, the setback is 60 feet. If it's 180 feet, the setback is 80 feet.

On larger lots, a coastal erosion study would be required, and it would establish the rate at which the shoreline is eroding.

For structures of less than 5,000 square feet, the setback would be 40 feet plus 70 times the annual erosion rate. The goal is that 70 years from now, if the erosion continues, the building would presumably be near the end of its useful life, and would still be 40 feet from the water.

For bigger buildings, with square footages greater than 5,000, the setback would be 40 feet plus 100 times the erosion rate.

So, on a coastline that's eroding at a foot a year, a normal-sized house would require a 110-foot setback, and a big hotel would require a 140-foot setback.

The Kaua'i bill is considerably stronger than the state's first such legislation, Maui's bill. The Maui setbacks are 25 feet plus 50 times the erosion rate.

For comparison, on a beach with one foot of erosion per year, a Maui home would be set back 75 feet from the certified shoreline (25 feet plus 50), while the same house on Kaua'i would be set 110 feet back (40 feet plus 70).

To learn more about coasts, see the University of Hawai'i Coastal Geology website at http://www.soest.hawaii.edu/coasts.

Erosion maps, showing coastlines where the erosion rates have been determined, are available:

For O'ahu: www.soest.hawaii.edu/asp/coasts/oahu/index.asp.

For Maui: www.soest.hawaii.edu/asp/coasts/maui/index.asp.

For Kaua'i: www.soest.hawaii.edu/asp/coasts/kauai/index.asp.

One of the interesting features of the maps is that they indicate that on many shorelines, land is actually building up. Accretion and erosion both are features of Hawaiian shorelines, and some shores have some of both, depending on where along the coast you look.

As a result of this, on many coastlines, the dramatic Kaua'i setback legislation would not take effect. If there's no documented erosion, then the issue doesn't come into play.

© 2007 Jan W. TenBruggencate