Weep visit mystifies


On 15 May, Wayne and I joined Peter and Susan from the Exploratorium and a couple of students from Stanford to hike out to the weep. Among other things we carried a lovely old K+E Transit out to shoot an elevation profile along a transect that crosses the weep perpendicular to the railroad grade.

Wayne framed by an old K&E transit

Parking lot transit play before the hike (taken with my new Peleng 8mm fisheye).

In general, we have been wondering about the physical mechanisms that drive the weep’s cycles of moisture. Sometimes the weep is relatively dry, sometimes wet. Sometimes the moisture seems to come predominantly from the railroad grade, sometimes from the levee for Salt Pond A15. The patterns do not seem to follow our general winter wet and summer dry seasons. The weep lies along the west-side ditch between the railroad and Salt Pond A15. A similar ditch on the east side of the railroad may be open to tidal flow. I am beginning to think moisture variations we observe on site are related to the (salt) water level in our flanking salt ponds (A15 & A16) but the ditches and patterns of tide and weather offer interesting alternatives. Perhaps they all combine to produce the weep’s moisture dynamic.

In any event, the current Google Earth image of the site (January 2007) shows flow patterns from the A15 levee to the weep that were not there in December. These flow patterns were evident, but not dominant in a March 2007 visit. So, it was a bit of a surprise to see them so clearly in May 2007.

Alviso Weep May 07-29.jpg

Flows to the weep emerge from the ground on the left. Salt Pond A15 lies just out of view on the left.

You can see more images from the May 2007 visit in this Flickr set:


One of my next steps will be organizing, as best I can, a chronological collection of views showing weep flow.

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