New satellite measurements show that the city of Venice is continuing to sink, albeit at a relatively slow rate of about 2mm a year. The famous city in north-east Italy experienced major subsidence in the last century due to the constant extraction of water from below ground.
That was stopped and subsequent studies in the 2000s suggested the decline had been arrested.
But work by a US and Italian team indicates Venice is still descending, even tilting to the east slightly.
With waters rising in the Venetian lagoon also by about 2mm (0.08in) a year, the combined effect is a 4mm-a-year increase in sea level with respect to the land.
The city is already subjected to regular floods, which require citizens sometimes to walk on raised boards. These floods, however, should be better constrained by a new system of barriers set for completion in 2014.
The value of the latest data is in how it helps local authorities plan defences much further into the future, says team-member Yehuda Bock from the Scripps Institution of Oceanography in California.
"It's critical information that they need to take into account," he told BBC News.
Dr Bock worked on the Venice project with colleagues from the University of Miami in Florida and Italy's Tele-Rilevamento Europa, a company that specialises in the measurement of ground movement from space-borne sensors. The team used a combination of GPS and satellite radar to map how Venice and its lagoon were shifting over time.
The analysis indicated that the city through the 2000s was subsiding on average by 1-2mm a year, with some other lagoon locations dropping by up to 3-4mm per year. No-one can really state how the trend will behave in the future, but if the current rates of subsidence and sea level rise are maintained, the city can expect to drop up to 80mm (3.15in) with respect to the average height of the water in the lagoon over the next 20 years. The new inflatable gates should be able to handle this, though.
Longer-term, Venice is always likely to have a problem, says Dr Bock's group.
Large-scale geological processes are pushing the ground on which the city sits down and under Italy's Apennine Mountains. And although subsidence from groundwater pumping is no longer an issue for Venice, compaction of sediments under the built environment will remain a factor for some time, the scientists say.
As part of a decade-long partnership called the Sustainable Rivers Project, the US Army Corps of Engineers and The Nature Conservancy are collaborating in eight river basins across the U.S. to modify dam operations for the benefit of downstream river and estuary health. In five of those basins – the Savannah River in Georgia and South Carolina, the Green River of Kentucky, the Bill Williams River of Arizona, the Big Cypress Bayou of Texas, and the Willamette River in Oregon – the Corps is releasing ‘designer floods’ from their dams.
According to river scientists, muddy, raging flood waters can be good for regeneration and growth. They can encourage fish migration and spawning, weltand plant and floodplain regeneration, the formation of aquatic habitats, and nourishment of food chains and fisheries from essential nutrients being carried in to coastal estuaries.
The more than 50,000 large dams built on the world’s rivers have been quite effective in dampening or completely eliminating all but the biggest floods. The aquatic life in dammed rivers has suffered greatly. Nearly 40% of US fish species are imperiled or extinct, and dams are a leading cause.
That’s why the Corps of Engineers, historically the biggest dam-builder in the U.S., is now in the business of making floods. They do it by intentionally releasing large volumes of water from their dams at specific times of the year to reinvigorate river ecosystems in a carefully controlled manner that promises maximum ecological benefit while avoiding damage to structures, roads, and farms.
Photo credit: US Army Corps of Engineers
The first Wild Salmonid Management Zone for steelhead has been designated in Washington State by the Department of Fish and Wildlife. The new zone covers the entire Sol Duc River on the Olympic Peninsula, spanning nearly 227 square miles. The river drains directly into the Pacific Ocean from the west coast of Washington and is one the most productive systems for wild steelhead in the state.
“Maximizing genetic diversity in salmon and steelhead populations is the key to preserving fishing opportunities,” said Guido Rahr, President of the Wild Salmon Center. “Managing the Sol Duc as a wild steelhead zone is the critical first step of investing in our future fisheries.”
Wild Salmonid Management Zones (or WSMZ’s) provide fish an excellent opportunity to adapt to ever‐changing environmental conditions. The zones are only selected for salmon and steelhead populations that are the most productive, genetically diverse, and abundant and where their habitats are healthy enough for rearing and spawning.
The establishment of this new management zone was the result of many organizations and concerned citizens working together. Though the zone is official, there is still more work to be done.
“The designation has good potential, but it is important to determine what management actions should be put into place to protect spawning steelhead from increasing fishing pressure,” said Mel Moon, Director of Natural Resources for the Quileute Tribe.
Over the coming years, the Wild Salmon Center will be working with its partners to improve fishery regulations, pursue long‐term monitoring funding, and to identify other candidate rivers for Wild Salmonid Management Zone designation.
Incredible [pictures have emerged of the frozen Danube River as the ice finally begins to break up. The Danube River - one of Europe’s key waterways — has this winter been stuck in the longest freeze in recent memory.
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