Measuring hyro & metereo parameters - Walnut Gulch

It was an early morning on October 27th, 2009 that I joined a small tour to Walnut Gulch and San Pedro with David C. Goodrich (Research Hydraulic Engineer, USDA-ARS) and Stephen Miller (student, UOA). Walnut Gulch is an experimental watershed at Tombstone, Arizona. It is taken as an outdoor laboratory for the Southwest Watershed Research Center (SWRC) program of USDA-ARS (United States Department of Agriculture - Agriculture Research Services).

Our trip started at 6 am in the morning. In around 1.5 hrs we reached the field office of USDA at Walnut Gulch experimental watershed. We were first given few introductory information about the different works done by USDA at the site.

Photo-1: Walnut Gulch - a glance

Photo-2: Activities at Walnut Gulch

Then Dave described us about how different hydrological and meteorological parameters were being measured regularly. An interesting thing to be noticed was how analogical methods of measurement were being substituted by digital measures with time. As in Photo-3, the cylindrical rain gauge is supplemented by the squared metallic strip on the ground. It helps in measuring the precipitation.

Photo-3: Rain Gauge

The circular apparatus in Photo-4 measures evaporation rate. As shown in the photo, effect of wind on evaporation is also taken into account. Rate of evaporation is measured by the change in water level in the small triangulated feature inside water body.

Photo-4: Measurement of evaporation

The apparatus shown in Photo-5 measures CO2 flux. Since all these apparatus are attached to the computers, digital measure of all parameters are obtained directly and instantly.

Photo-5: Measurement of CO2 flux

After the informative introduction, we moved to Flume 6 of the Walnut Gulch where we saw how sediment flow rate is measured.

Photo-6: Flume 6

The concreted area is made for measuring actual amount of deposit collected. Sediment deposited is now being recorded using sensors indicated by yellow markings in Photo 7.

Photo-7: Way for Sediment

Initially, the metal shown in Photo-8 was used to collect sediments within the flow and measured.

Photo 8: Metal collecting Sediment

Sediment recorded by the sensors is used to measure the sedimentation rate electronically. The video below describes how the recording works directly.

It was really an informative trip. Though not much to be done by myself, it was my first field exposure in AZ. I found it fruitful and came across how some important measures of hydrological parameters are being collected from the field.

My sincere thanks to David C. Goodrich and Stephen Miller for the opportunity and wonderful company.