Hetch Hetchy Meteorological Station Consolidation and Automation
Air temperature and precipitation have been measured near O'Shaughnessy Dam since before construction of the dam, starting in 1919. While the location of measurements has not changed in this time, the individual gages have throughout the history of the site. Hetch Hetchy Water and Power (HHWP) is proposing to remove the manual precipitation and temperature gages and replacing them with automated gages that can be accessed online. National Oceanic and Atmospheric Administration (NOAA) did not support letting HHWP automate their existing precipitation gage on site.
The new precipitation gauge will be slightly larger than the current gauge (about the same size as the NOAA gauge nearby), but will occupy the same footprint. A small (12" x 12") solar panel mounted with the precipitation gage will power the radio, which will be collocated with the temperature probe inside the existing temperature gauge housing. The solar panel will be mounted on the stand holding the precipitation gauge. Installation of the precipitation gage will require digging a shallow hole and installing a base using hand tools. A small diameter (1") flexible jacketed steel conduit will run 60 feet from the precipitation gage to the temperature gage housing to transmit power and precipitation gage signal. The conduit will be buried in a shallow 4" deep trench dug by hand tools.
A radio, data logger, antennae and battery will be installed inside or attached to the existing temperature gage housing. The footprint of the housing will not change.
To ensure continuity of the long term data record, the existing manual precipitation gauge will need to remain on site for a period of time. Depending on precipitation conditions (drought, snow, rainy periods), this collocation may need to continue for 2-4 years. After we are assured that the new precipitation gauge matches the old, the old gauge will be removed. This will be performed using hand tools and will not require any additional ground disturbance.
The evaporation pan nearby is no longer in use, and will be removed during installation of the new precipitation gage. Removing the fence poles will require some digging using hand shovels. The pan itself is mounted on a small wooden platform, which will be removed by hand.
This work will also involve removing the current automated weather station that is located on a granite outcrop overlooking Evergreen Road at the Hetch Hetchy compound. The entire station will be removed during the installation of the new weather station.
The project also involves the removal of three trees that partially encroach on both the NOAA and HHWP precipitation gauges. Two of the trees are dead cedars (dbh = 43", height = 85'; and 48", height 90'; respectively) and the third tree is a dead oak (dbh of main stem = 15", height = 40').