Thursday, June 12, 2008

Bailing Out Alviso from the Guadalupe River Delta

Alviso has an unfortunate geographical and geological position that it always must battle.

Alviso is our Netherlands. Ever since the water pumpers (that's everyone) pulled the artesian pressure from the gravels below the valley floor, the clay deposits dewatered and then compressed and the ground sank 10 to 12 feet all the way from downtown to the Bay.

Alviso is now that much below sea level and will remain that way until the watersheds and/or we humans fill it in again to sea level. That can be observed in short enough history as the Guadalupe River bottom filled right back to almost sea level between the new District-built levees within just 10 years. Sort of a public-natural partnership, without the watershed actually signing anything, just dumping its sediment load while the water was seeking sea level.

Every river on the planet forms a delta as it reaches the sea. Except in South San Francisco Bay, where our rivers were channelized through the salt ponds for the last 100 years, where the river deltas would otherwise be forming and doing their geomorphology thing. Add that to the adjacent, upstream and below-sea-level Alviso District, and you form the huge real estate blind spot that begs & demands flood protection NOW before you spend any more money upstream.

If we are going design with nature, (Parcel tax is funding CLEAN, SAFE CREEKS AND NATURAL FLOOD PROTECTION) we need to first see what nature would do in Alviso it we weren't here. It would first fill it in with sediment from the watershed, and then form a delta fanning along the bay to distribute sediment across the tidelands, which would then move out through the estuary to the ocean.

The Water District can either work with that natural course of events or just throw away money trying to reverse it temporarily, remembering the sediment that showed up within 10 years between the newest set of levees.

Maybe I'm foolish to think that the District Board or staff can think this big before they spend money. But at least I know that looking at it with a planetary view, this delta approach should be a natural.

Never Thirst!

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