Currently, routine observations of the water cycle mainly consist of precipitation and streamflow data collected daily or weekly by federal and state agencies. Precipitation and streamflow represent the excess water that the atmosphere and soils cannot hold. Measurements of these surpluses do not inform us about other complexities of the hydrologic cycle such as the origin of the water, or its transformation and redistribution in the atmosphere and the soils.

 

The situation is akin to weather observations before satellites, when technician-intensive observations were limited to the lowest part of the atmosphere, linkages between distant observations were seldom made, and the predictive horizon was only one to two days. For example, time series observations of chemical constituents in streams, an important window into the processes that control streamflow and the transport and fate of constituents, are currently based on hourly or sub-hourly measurements of water fluxes, but only weekly or monthly samples of rainfall and streamflow chemistry. This stark mismatch in measurement timescales is a fundamental obstacle to understanding the interaction between hydrological and geochemical dynamics in watersheds.

 

Some of the key goals of the Hydrowatch Center include:

 

Two sites in the UC Natural Reserve System are currently being used for field deployments. Sagehen Creek Field Station in the Sierra Nevada is fed by snowmelt runoff to Sierran streams in mid-summer, while the Elder Creek Watershed in the Angelo Coast Range Reserve is dominated by winter storms from the ocean and summer dry spells. Furthermore, Elder Creek has no floodplain, while Sagehen runs through a meadow. Elder Creek is very steep, with a boulder strewn bed, while Sagehen is gravel bedded. Elder Creek’s bedrock is crumbly sedimentary rocks, while the Sagehen is volcanic; and the forest around Elder Creek is mostly uncut whereas the forest around Sagehen was cut in the early 1900’s.  The field deployment can be conceptually separated into two synergistic components: “before rainfall” and “post rainfall.” The components will focus on atmospheric and ground water parts of the hydrologic cycle, and will be linked by the near-surface humidity and soil moisture measurements.

 

Tiny wireless sensors known as motes, complete with software and low-power communication systems onboard will be deployed in test site watersheds from above (sensing atmospheric humidity along the way), mounted on trees or structures, or embedded in the soil. The first analyzers will be deployed at the gauging station at Angelo Reserve along the South Fork of the Eel River during the rainy winter months (to study watershed response to rainstorms), then be relocated to the gauging station at the Sagehen Creek Field Station from late spring through mid-Autumn (to study watershed response to snowmelt and to summer drought conditions). Once the instruments have been “proofed”, they will be deployed along tributaries at both sites to document and understand the spatial structure of runoff generation and the spatial evolution of water chemistry.

 

Water isotopes (HDO, H218O) are signatures of both the sources (e.g. continental versus oceanic, tropical versus high latitudes) and the transformations (e.g. condensation, evaporation) of water in the environment. The isotopes of U can be used to establish the weathering rates within catchments, and to determine the extent that water in streams at any time represents runoff versus water that has been resident in soils. A new automated precipitation sampling-archiving system will produce isotopic records of unprecedented temporal resolution. At present, there is no low-cost accurate instrument for in situ isotope analysis, so the water samples will be returned to the Center for Isotope Geochemistry at UC Berkeley for analysis.

 

The data and model made possible by this project will be a gold mine for addressing long-standing questions about how the water cycle functions and how it may change. Some of those we will address include: