Advancing Water Resources Research and Management

Hydrologic Data Collection and Accessibility for the USDA-ARS

Grassland Soil and Water Research Center at Riesel, TX

R. Daren Harmel, Clarence W. Richardson, Kevin W. King

INTRODUCTION

The USDA-ARS Grassland Soil and Water Research Center in Riesel, TX, is one of the most intensively monitored hydrological research sites in the country. Hydrologic data and management records for the site date from the 1930's. The 620 ac research site is divided into sub-watersheds under pasture and cropland management. The sub-watersheds range in size from 0.25 to 309 ac. Currently in operation are 18 runoff stations, 15 rain gauges (including a weather station), 1 lateral flow station, and 7 wells. Each flume or weir runoff station is instrumented with a pressure transducer for stage measurement and a Chickasha or ISCO sampler for water quality analysis. The rain gauge network consists of 15 rain gauges positioned to capture rainfall spatial variability on the site. The weather station uses a Campbell Scientific meteorological setup to measure air temperature, soil temperature, relative humidity, wind speed and direction, and solar radiation. At the lateral flow station, lateral subsurface flow is determined with a pressure transducer as a French drain releases into a sharp-crested v-notch weir. At the wells, pressure transducers provide a continuous record of piezometric head. Currently, data from these stations are stored on dataloggers, downloaded weekly, and placed on the USDA-ARS Grassland Soil and Water Laboratory, Temple, TX, website: http://arsserv0.tamu.edu/. Plans for Riesel in the near future include installation of radiotelemetry equipment for real time data acquisition and accessibility.

HISTORICAL PERSPECTIVE

In the mid 1930s, the Soil Conservation Service (SCS), now the Natural Resources Conservation Service (NRCS), realized a need to understand and analyze hydrologic data from agricultural fields and watersheds. Based on this need, the Hydrologic Division of the SCS was established and a number of experimental watersheds were formed across the US. The primary function of the facilities was to collect hydrologic data (precipitation, percolation, evaporation, runoff, etc.) and evaluate the hydrologic response from watersheds influenced by various agricultural land management practices. One of those watersheds was located in the heart of the Blackland Prairie near Riesel, TX, on the 5860 ac Brushy Creek watershed. During the height of activity at the Riesel center, 35 runoff sites and 35 recording rain gauges were in operation; and since 1937, hydrologic data have been collected throughout the watershed. These data sets have been used for numerous purposes such as water quality studies, farming practice evaluations, and model development and evaluation. The long hydrologic records (in excess of 60 years on some watersheds) make the data particularly valuable for studies designed to identify trends or changes caused by climate change or other factors. Current studies at Riesel include a watershed water balance study and a study of drought effects on native prairie pasture.

GENERAL SITE DESCRIPTION

The Blackland Prairie in Texas is a region of fertile agricultural land extending from San Antonio north to the Red River. Houston soils, which exhibit a strong shrink/swell potential, dominate the region. The slopes generally range from 1-3 % and are classified as gently rolling. Mean annual rainfall for the region is approximately 33 in. In Waco, 12 miles north west of Riesel, the average annual precipitation is 32 in, and daily high temperatures range from a minimum of 60 ^oF in January to a maximum of 95 ^oF in July and August (NOAA, 1990). Present day agricultural land use in the region consists of pasture and rangeland, and corn, grain sorghum, and oat production under a wide range of tillage and management operations.

RUNOFF STATIONS

Collection of runoff data began at the Riesel site in 1938. Historical data from 40 runoff stations are accessible via the web at: http://arsserv0.tamu.edu/runoff.htm. This internet site lists the stations, their watershed size, and the years for which runoff data are available. Specifically, flow rate (cfs and in/hr) and corresponding date and time (min) data are available. Currently, 18 runoff stations are in operation. These operational structures (Table 1 and watershed map) are instrumented with a pressure transducer located in each structure’s stilling well to measure stage and a datalogger to record instantaneous flow data.

WEATHER STATION

Weather data have been collected from the weather station at Riesel since 1938. Historical data such as rainfall, maximum and minimum temperature, and potential evapotranspiration (PET) are currently being converted into electronic form and should be accessible in the spring of 2000 at: http://arsserv0.tamu.edu/climate.htm. In 1995, a Campbell Scientific weather station was installed at Riesel. This equipment allowed additional weather parameters to be gathered. Daily data on maximum and minimum air temperature (°C), solar radiation (kJ/m²), wind speed (m/s) and direction (°), precipitation (mm), maximum and minimum soil temperature (°C), and heating and cooling degree days will be accessible in 2000 at: http://arsserv0.tamu.edu/climate.htm.

RAIN GAUGE NETWORK

Collection of rainfall data at the Riesel Center began in 1938. Historical data from 57 rain gauges is currently under quality control analysis and should be accessible in the spring of 2000 at: http://arsserv0.tamu.edu/rainfall.htm. Rainfall estimates for individual watersheds and runoff stations can be calculated from Thiessen polygon weights, which are also available. This internet site will list the stations and the years for which rainfall data will be available. Specifically, accumulated rainfall (in), intensity (in/hr), and corresponding date and time (min) data will be available. Currently, 15 rain gauges are in operation. These operational gauges are instrumented with a tipping bucket rain gauge to measure precipitation and a datalogger to record instantaneous data. A standard rain gauge is also used at each site as backup device.

LATERAL FLOW STATION

Available data for the lateral flow station are currently being processed into electronic form and should be accessible in 2000 at: http://arsserv0.tamu.edu/lateral.htm. The lateral flow station was installed in 1970 to measure lateral subsurface flow from a portion of watershed Y. Flow from a French drain is released into a boxed sharp-crested v-notch weir. Currently, instantaneous flow over the weir is determined with a pressure transducer and recorded with a datalogger.

WELL STATIONS

Nine shallow groundwater wells were monitored at Riesel in the 1950’s to 1970’s. Available water level data from this period is currently being processed into electronic form and will be accessible in 2000 via the web at: http://arsserv0.tamu.edu/oldwells.htm. In 1998, 7 new wells were installed at Riesel to monitor shallow aquifer water levels and recharge properties. Currently, 5 of the new wells are instrumented with pressure transducers to provide a continuous record of piezometric head, and two of the wells are monitored periodically with a hand-held "e-line" water depth gauge. These two wells will be equipped with pressure transducers in the near future to provide instantaneous data. Data from these 7 wells will be accessible in 2000 at http://arsserv0.tamu.edu/newwells.htm

FUTURE PLANS

Installation of a Campbell Scientific Radiotelemetry Network (Campbell Scientific, Inc., 1995) is underway. A total of 41 field stations will be established at the 18 runoff stations, 15 rain gauges, lateral flow station, and the 7 new wells. A base station will be established at the Riesel Center headquarters building. This station will communicate with the field stations with a VHF radio signal and will receive instructions (via phone modem) from a computer located at the USDA-ARS Grassland Soil and Water Laboratory in Temple, TX. Once operational, this network will acquire and make available near real-time hydrologic data. This system is unique in its location, the Blackland Prairie, and is useful for its ability to provide an up-to-date hydrological data record dating from the 1930’s.

REFERENCES

Campbell Scientific, Inc. 1995. Radiotelemetry Network Instruction Manual. Campbell Scientific, Inc. Logan, Utah.

National Oceanic and Atmospheric Administration. 1990. Climatography of the United States #84: Daily Normal Temperature, Precipitation, and Heating and Cooling Degree Days, 1961-1990.

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