A new, more stringent Kauai law aims to protect the island’s coastline by folding erosion data into calculations used to set limits on shoreline construction.

A shoreline setback bill was signed into law last week.

Supporters laud it as a means to tighten an ordinance established in 2008 by swapping static measurements for figures subject to changes based on ongoing coastal erosion data.

Others, however, maintain the law is flawed because it now allows construction closer to the water’s edge on properties in rocky coastal areas.

In a letter to the County Council, Kauai Mayor Bernard Carvalho, who signed the bill Friday, described the county’s law as having "the most aggressive shoreline setback requirements in the state of Hawaii," noting it is recognized as one of the most progressive for coastal protection in the nation.

Nearly two years in the making, Bill 2461, now Ordinance 979, also bans landscaping that artificially alters the shoreline as well as construction that can accelerate erosion, such as sea walls. Such shoreline hardening projects, however, may be constructed if approval is obtained by the state Office of Conservation and Coastal Lands.

Councilwoman JoAnn Yukimura sees the law as an effort to help avoid what property owners on Oahu’s North Shore endured last year when large winter swells caused extensive damage to homes.

The new ordinance incorporates scientific data from a study conducted by the University of Hawaii Coastal Geology Group titled "National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands," which charts shoreline changes from 1927 to the present for Oahu, Maui and Kauai.

According to the study, beaches on those three islands are eroding at an average rate of 4.8 inches a year.

Maui has the highest average erosion rate, more than 6 inches per year, due to the island’s high rate of sea level rise. Kauai’s rate is just under 6 inches and Oahu’s is 2.4 inches.

Under the new law, construction on most properties included in the UH ongoing study will be pushed back at least 20 feet from the shoreline — a buffer zone intended to account for future accelerated sea level rise.

Construction on coastal properties not threatened by erosion — and not included in the shoreline change study — could move closer to the edge of rocky areas if proposed structures are at least 30 feet above sea level.For property owners meeting that condition and others, the setback will be as close as 60 feet from the certified shoreline.

Under the previous law, construction was not allowed within 100 feet of the certified shoreline.

Opponents argue that allowing construction to move up to 40 feet closer to the lip of coastal bluffs and cliffs will mar the scenic view for the benefit of private landowners and developers, such as eBay founder Pierre Omidyar, who owns land north of the Hanalei River that’s being eyed for a resort.

Last month, before the Council passed the bill with a 4-3 vote, Councilman Tim Bynum expressed concerns about reducing the setback in rocky areas.

"Who is this serving?" Bynum asked, pointing out, along with some coastline conservationists, that the provision could result in negative visual impacts.

Councilman Mel Rapozo countered, "I don’t see it as protecting a few landowners." He added, "The primary purpose of the bill is to protect life and property, and I believe it does this."

Yukimura and Rapozo along with Council Chairman Jay Furfaro and Councilman Ross Kagawa voted for the bill. Bynum and Councilmen Mason Chock and Gary Hooser voted no.