鼓勵此網誌：0
| 加入書籤: |
 |  |  |  |  |  |  |  |  |  |  |
十二月初，來自於夏威夷的熱帶氣流「鳳梨快車」（Pineapple Express）例行性地又重擊了美國西北地區，鳳梨快車的暖流不但帶來了破紀錄的雨量，連帶也融化了山上的積雪，造成嚴重的水災。
整個西北地區，包括西雅圖都有災情傳出，尤其是位於華州首府附近的Chehalis River，水位暴漲，吞沒了與其平行的國道五號高速公路，讓這條華州主要的交通動脈被迫關閉三天，造成高額的經濟損失。當然，附近的城市和社區也被泡在深深的水中，居民被迫撤離家園，精神和實質財產損失慘重。
Image Source: The Seattle Times
住在西雅圖這幾年才知道，水患也是美西地區的常客。事實上，世界各地許多地方都飽受水患之苦，從以下這張由Dartmouth Flood Observatory製作的圖就可以看出水患影響之廣泛。紅色的部分代表今年十二月二十一日為止，水患波及的區域。
歐美國家和台灣一樣，一直以來砸下龐大的工程經費來防洪，卻可以說沒有什麼成效，水患仍然是人類最頭痛的問題之一。政府和水利工程師往往把每一次的水患歸咎於雨量高過預期，或是其他有的沒有的人為疏失，但很很少檢討治水邏輯背後假設的錯誤。歐美在飽嚐水患之苦後，許多國家開始思考新的方法，與其與自然對抗，不如順應自然來減少災害。在華州，當科學家對河流的作用力越來越瞭解、在有心人對舊治水觀的努力檢討下，管理水患的方式開始慢慢有了轉變，拆堤防、給河流足夠的行水空間，成了治水的前瞻方法。
以下轉載西亞圖時報十二月十八日的新聞報導：「國王郡（西雅圖的所在縣治）的新治水哲學：不再與自然對抗」，希望能夠給台灣一些啟示。
原文出處：http://seattletimes.nwsource.com/html/localnews/2004079529_flood18m.html
By Lynda V. Mapes
Seattle Times staff reporter
It's a sight only a biologist — or a fisherman — might love: a very big, and very ripe, spawned-out king salmon, tucked under a log in a side channel of the
This fish, this log and this meander wouldn't have been here even a year ago. A levee used to fence the river and the fish out. Then King County did what until recently was unthinkable: It ripped the levee out and gave this bit of land north of Highway 18 in Auburn back to the river.
The project, completed last year, reconnected the
It's just one of many projects planned to eventually return stretches of land totaling more than 33 miles along the county's major rivers back to nature — rather than fighting it.
The difficulty of trying to hold a swollen river to its banks was on frightening display earlier this month in southwestern Washington, where flooding damaged or destroyed hundreds of homes and dozens of businesses in the Chehalis River watershed, and closed Interstate 5 for four days.
Levees expected to protect roads and buildings were overtopped by the floodwaters.
The work along the
"Rivers don't negotiate with you. So you have got to figure out what the river's behavior is going to be, and accommodate that," said Ron Sims,
Increasing flood risk
And flood risk is only going to get worse, scientists say. That's because of two converging trends: climate change and development, in a place uniquely sensitive to both due to our topography and weather pattern.
The Cascades are low mountains. And our weather pattern sees most of its precipitation in winter. That means that if average temperatures rise just three degrees, about a third of the precipitation switches from snow to rain, said Philip Mote, research scientist with the Climate Impacts Group at the
"It's very likely that flood risk will increase in the future," Mote said.
Cliff Mass, an atmospheric scientist at the
And changes in land use will make flood risks — already heightened by more rain and runoff — worse. That's because as more land in the
No place in the country has undergone a bigger change in land use between 1973 and 2000 than what's called the Puget lowlands ecoregion. During that time, 29 percent of the land, or 1,943 square miles, converted from one type of use to another, according to preliminary findings of a study by the U.S. Geological Survey.
The study, which is still under review, analyzes changes in the landscape in 11 categories — such as forestland, water and development — in sample grids all over the country.
The Puget lowlands ecoregion stretches from the Canadian border to
The high rate of change is driven primarily by the turnover of forestlands. In all, about 337 square miles of forest have been converted to development between 1973 and 2000, according to the study. That does not include land that's been clear-cut but is still in forestry.
"Adaptation strategy"
In
Where it has billions of dollars of development to protect, the county is spending millions on a containment strategy, repairing levees that in some cases were cracked and vulnerable to failure.
The County Council last month increased property taxes by 10 cents per $1,000 of assessed value to raise money for levee repairs and other flood-control projects.
Where it's still possible, the county is giving the river some space to flood. In those places, instead of disaster, floodplains can actually deliver benefits: aquifer recharge, open space, recreation, wildlife habitat and farmland preservation.
The county also has severely restricted new development in the floodplain. Some new construction is banned, and new fill in the floodplain must be offset by excavation at the same elevation. The policy is intended to help prevent an increase in flooding due to new development.
It's a mixed approach to living with Mother Nature, in a place where a lot of choices have already been made. "This is an adaptation strategy," Sims said.
"There comes a time when nature speaks to remind us of our insignificance. I accept that," he said. "You are never going to constrain a river system in a way that says there is not going to be flooding. Sometimes you can let nature do what nature does best."
Lynda V. Mapes: 206-464-2736 or lmapes@seattletimes.com
-------------------------------------------
相關資訊：
2007十二月美國西北地區水災相關參考網站：
