Wawona South Fork of the Merced River Gage Installation
The purpose of this project is to install a permanent USGS-type river gage downstream of Highway 41, on the South Fork of the Merced River. The gage would be located in the vicinity of a former USGS gage site, approximately 300 meters downstream from the Highway 41 bridge on river right. This gage would measure and transmit the full range of flows on the river. The gage would be installed and maintained by the USGS or Merced Irrigation District with oversight and quality assurance provided by the USGS.
The gage house would be a 4 foot by 4 foot by 8 foot tall metal building resting on a concrete pad on the top of a terrace north of the river. The building will be sided with wooden lap siding similar to that used on the Pohono gage house in Yosemite Valley and painted Wosky brown (standard NPS brown). A 24 inch by 36 inch solar panel will be mounted to the south side of the building (or the roof if less conspicuous)using anodized black metal brackets. An antenna will be mounted to a pole attached to the building extending up to 5 feet above the roof of the building.
Two 2-inch steel conduits (40 feet long) would extend from the gage house to the bottom of the river. The conduit would be nested into the riverbed and bank sediments and secured using metal stakes. Two or three staff plates would be installed in the river and up the bank to span the range of flows. A temporary cable tramway would be placed on the foundations of the former tramway at the site during periods of high flows for measurement of peak flows.
As the lowest major drainage basin in Yosemite National Park, the South Fork of the Merced River is particularly vulnerable to the effects of predicted climatic warming over the next century. Long-term river flow data are needed to effectively manage surface water withdrawals for water supply in the Wawona area (as called for in the 1985 Environmental Assessment for the reconstruction of the Wawona Water System)as well as for water supply predictions further down river outside of the park. Current water resource planning for drought conditions is based on only 10 years of data (1958-1968) and indications are that this is insufficient for understanding drought conditions in the future.