No water crisis anytime soon, scientists say
May 19, 2011 · Updated 3:52 PM
Bainbridge Island water levels don’t appear to be facing an imminent crisis during the next 25 years, even with a dramatic scenario of climate change and runaway population growth.
“In this location between now and 2035, even with rapid population growth, we don’t expect wells to begin to run dry or have water quality issues,” said Matt Bachmann, a U.S. Geological Survey hydrologist who addressed the City Council Wednesday. “Even (a) worst-case scenario is not something that can’t be managed by your current (water) system.”
Since groundwater is the sole source of drinking water for islanders, the uncertainty about available water has created an escalating level of concern for island development.
The USGS study simulates the potential impacts of increased groundwater pumping from 2008 to 2035, using best- and worst-case scenarios.
The report did conclude that the island’s main sources of drinking water have declined by 25 feet in some places since the island was first settled.
However, the hydrologists say Bainbridge is still in good position to manage and protect its resources. The city can use this computer model to better plan for the island’s future.
The 95-page final report presented Wednesday is the compilation of a two-year study that looked at a range of historical data, more than 400 current wells and weather. It was jointly prepared by the city and the USGS.
The results show that water usage has varied with island topography. In some places, groundwater has increased by five feet where septic systems are taking water from the deep aquifers and returning it to the shallow, surface aquifers.
In other places, such as the 1,000-foot-deep Fletcher Bay aquifer that pumps groundwater for about 38 percent of the island, the water levels have drawn down about 25 feet.
Bachmann said their computer simulation estimates that the Fletcher Bay aquifer will most likely drop between four and 10 feet by 2035. Future groundwater declines were generally less than 10 feet with some parts higher or lower.
The worst-case scenario manipulated the island population to 70,000 and created high-rise buildings dotting Winslow with much of the island becoming paved impervious surfaces.
“Our current land-use code would radically change in order to have 70,000 people on this island,” said Interim City Manager Brenda Bauer. “But it’s something to have in mind as we go through land-use changes. We have finite resources on the island and we need to consider that in relation to density... that is in our best interest.”
Bachmann said they didn’t want to imagine too far into the future because of the rapid rate of change.
“I think water refugees are something to think about, this island may feel an artificial pressure to rezone [in the future] and it’s good to have defensive data to say this is how much we can bear,” said Mayor Kirsten Hytopoulos. “This will be helpful to determine a tolerable capacity of population.”
Salt water intrusion in the water system was not predicted in the main wells that provide city water through 2035.
“In some parts of the state we are seeing 800 or 1,000 feet wells go dry and there is no more water available,” said Bachmann. “Places where you can’t pump water out fast enough without salt water intrusion, which means the water isn’t suitable for home use and has to be pre-treated. There are cases where further (land) development is just not manageable without more money.”
On average, islanders use 65 gallons per person per day of water, Loanna Frans, USGS hydrologist said, and that figure is almost doubled in the summer. This is a common trend everywhere, she said.