ON THE GROUND · modeling methods are generally employed in the absence of other alternatives. The...
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ON THE GROUND Measuring Ephemeral Discharge by Dye Tracer Michael L. Meyer and S. Amina Sena – New Mexico Highlands University, and David Shaull – Los Alamos National Laboratories Streamflow measurements in arroyos of the arid Southwest are complicated by the ephemeral nature of runoff events, complex cross-sectional channel geometry, and steep slopes. The short duration of runoff events makes manual, on-site discharge measurements difficult or impossible to use for developing stage-discharge relationships. Manning’s empirical equation for uniform, open- channel flow or other mathematical modeling methods are generally employed in the absence of other alternatives. The purpose of this project was to develop stage-discharge rating curves at selected Los Alamos National Laboratory (LANL) stream monitoring sites using a dye tracer. Rhodamine WT dye was purchased as a 20 percent solution and diluted to 0.5 percent and 1.0 percent for injection purposes. Four arroyo sites were equipped with event-activated dye injection equipment and automated water samplers. Dye injection equipment was located 50 to 200 feet upstream of the point of collection to ensure homogenous mixing of the dye with stream water. A datalogger system at the downstream point of collection was equipped with an ISCO water contact sensor, stream stage recorder, and ISCO sampler (see photos). The sampler contained 24 one-liter bottles and was programmed to collect 250 milliliters (mL) of water every 10 minutes when the water sensor was submerged by event runoff. Dye injection was initiated at a predetermined stage threshold during each runoff event. The dye pump was calibrated to deliver dye at a rate of 40 mL per minute. Varying dye concentrations were analyzed with a fluorescence spectrophotometer and converted to discharge in cubic feet per second (cfs). Stage was regressed against discharge to develop a rating curve. Dye injection and sampling were successfully activated Aug. 24, 2005 during a runoff event in Acid Canyon. Stage values recorded from 12:00 to 18:00 varied from 1.0 foot (no flow) to a peak of 3.1 feet at 13:35 (see chart, below left). The signal from the water sensor, recorded every five minutes, indicated continuous contact with water from 13:35 to 15:00. Continuous dye dripping occurred during the same period. The ISCO sampler collected samples at 10-minute intervals starting around 13:00. Dye concentrations were quantifiable for flow calculations from seven bottles collected between 13:55 and 15:05. Dye concentrations were used to calculate discharge (Q, in cfs) and to develop a rating curve with stage versus discharge: Stage = 0.3596 lnQ + 1.2; R 2 = 0.96. Seven discharge and stage values and one additional point representing 0.0 cfs with a stage of 1.0 feet were included in 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 12:30 13:00 13:30 14:00 14:30 15:00 15:30 Stream stage (ft) and water sensor (volts) 0 10 20 30 40 50 60 70 80 90 100 Stream dye conc. (ug/L), Q calculated from dye (cfs), and predicted Q (cfs) Stage Sensor Q from Dye Predicted Q Dye Conc. 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 12:30 13:00 13:30 14:00 14:30 15:00 15:30 TSS concentration (mg/L) and load (kg) 0 10 20 30 40 50 60 70 80 90 100 Predicted flow (cfs) TSS (mg/L) TSS Load (kg) Predicted Q (cfs) Event hydrograph (predicted Q) determined from stage-discharge rating curve, discharge determined from stream dye concentration, stream dye concentration, water sensor voltage, and stream stage. Total suspended solids (TSS) concentration, TSS load, and event hydrograph (predicted Q). Dye and pump (top) and actuator to release dye into the stream. Acid Canyon Event 8/24/05 • January/February 2007 • Southwest Hydrology
Transcript of ON THE GROUND · modeling methods are generally employed in the absence of other alternatives. The...
ON THE GROUNDMeasuring Ephemeral Discharge by Dye Tracer Michael L. Meyer and S. Amina Sena – New Mexico Highlands University, and David Shaull – Los Alamos National Laboratories
Streamflow measurements in arroyos of the arid Southwest are complicated by the ephemeral nature of runoff events, complex cross-sectional channel geometry, and steep slopes. The short duration of runoff events makes manual, on-site discharge measurements difficult or impossible to use for developing stage-discharge relationships. Manning’s empirical equation for uniform, open-channel flow or other mathematical modeling methods are generally employed in the absence of other alternatives. The purpose of this project was to develop stage-discharge rating curves at selected Los Alamos National Laboratory (LANL) stream monitoring sites using a dye tracer.
Rhodamine WT dye was purchased as a 20 percent solution and diluted to 0.5 percent and 1.0 percent for injection purposes. Four arroyo sites were equipped with event-activated dye injection equipment and automated water samplers. Dye injection equipment was located 50 to 200 feet upstream of the point of collection to ensure homogenous mixing of the dye with stream water. A datalogger system at the downstream point of collection was equipped with an ISCO water
contact sensor, stream stage recorder, and ISCO sampler (see photos). The sampler contained 24 one-liter bottles and was programmed to collect 250 milliliters (mL) of water every 10 minutes when the water sensor was submerged by event runoff. Dye injection was initiated at a predetermined stage threshold during each runoff event. The dye pump was calibrated to deliver dye at a rate of 40 mL per minute.
Varying dye concentrations were analyzed with a fluorescence spectrophotometer and converted to discharge in cubic feet per second (cfs). Stage was regressed against discharge to develop a rating curve.
Dye injection and sampling were successfully activated Aug. 24, 2005 during a runoff event in Acid Canyon. Stage values recorded from 12:00 to 18:00 varied from 1.0 foot (no flow) to a peak of 3.1 feet at 13:35 (see chart, below left). The signal from the water sensor, recorded every five minutes, indicated continuous contact with water from 13:35 to 15:00. Continuous dye
dripping occurred during the same period. The ISCO sampler collected samples at 10-minute intervals starting around 13:00. Dye concentrations were quantifiable for flow calculations from seven bottles collected between 13:55 and 15:05. Dye concentrations were used to calculate discharge (Q, in cfs) and to develop a rating curve with stage versus discharge:
Stage = 0.3596 lnQ + 1.2; R2 = 0.96.
Seven discharge and stage values and one additional point representing 0.0 cfs with a stage of 1.0 feet were included in
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Event hydrograph (predicted Q) determined from stage-discharge rating curve, discharge determined from stream dye concentration, stream dye concentration, water sensor voltage, and stream stage.
Total suspended solids (TSS) concentration, TSS load, and event hydrograph (predicted Q).
Dye and pump (top) and actuator to release dye into the stream.
Acid Canyon Event 8/24/05
� • January/February 2007 • Southwest Hydrology
the regression. The rating curve was used to calculate discharge for each 5-minute stage value recorded by the datalogger and develop the event hydrograph.
Total suspended solids (TSS) concentration (milligrams per liter) and load (kilograms) were determined for each sample collected. The right hand chart below
shows that TSS concentration was greatest in the first sample and generally decreased through the remainder of the hydrograph. The high initial TSS concentration had little effect on the total TSS load for the event due to small discharge values. TSS load was greatest (3,200 to 3,300 kg) near the peak of the hydrograph. Contaminant transport associated with or adsorbed on TSS would also be greatest near the peak discharge of event runoff. Total TSS load for the event was 12,309 kg.
This study demonstrated that automated tracer injection and collection during a storm runoff event can be successfully used to develop stage-discharge rating curves and to estimate contaminant mass transport during short events in arroyo streams with difficult accessibility or complex cross-sectional morphology.
This article is LANL report no. LAUR-06-7338. Contact Mike Meyer at [email protected].
Dye test collection site contains datalogger (end of bridge) and sampler (round container).
January/February 2007 • Southwest Hydrology • �
ON THE GROUND (continued)
Isotope Measurements Help Estimate Recharge Distributions in the Verde River Watershed Jeannie R. Bryson, Kyle W. Blasch, and John P. Hoffmann – U.S. Geological Survey Arizona Science Center
In 1999, the U.S. Geological Survey began a cooperative investigation with the Arizona Department of Water Resources to help quantify the hydrologic system of the upper and middle Verde River watersheds in north-central Arizona (Blasch et al., 2006). These watersheds encompass an area of about 5,000 square miles (see map) and range in elevation from around 3,000 to 12,000 feet. As part of this study, precipitation samples were analyzed for stable isotopes of oxygen and hydrogen (δ18O and δ2H) in order to determine the local meteoric water line (LMWL), seasonal variations in isotopic values, and isotopic gradients with elevation. This information was used
in conjunction with stable isotope data of groundwater to estimate seasonality and areal distributions of recharge.
Establishing the New LineTwenty-five rainfall and snowfall samples were collected between July 2003 and January 2005 from 11 stations at elevations ranging from 3,100 to 9,100 feet. Sample collections were timed to isolate the summer North American monsoon from winter frontal-storm precipitation. Seasonal
Precipitation and snowfall collection sites in the upper and middle Verde River watersheds (elevations of sites in feet).
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composite samples were created with precipitation contributions from each of the events within a season. Stable isotope samples were analyzed by the USGS Isotope Fractionation Project Laboratory in Reston, Virginia, and at the University of Arizona’s Laboratory of Isotope Geochemistry-Environmental Isotope Research.
Isotope compositions are reported as deviations from an international standard, the Vienna Standard Mean Ocean Water (VSMOW). Values are expressed in parts per thousand or per mil using standard delta notation. Values of δ18O and δ2H in worldwide fresh waters are shown to be linearly correlated on the Global Meteoric Water Line (GMWL), defined by
δ2H = 8.13 δ18O + 10.8 per mil
using data from all stations in the Global Network of Isotopes in Precipitation (GNIP) database (Craig, 1961; Rozanski and others, 1993).
The Flagstaff Meteoric Water Line (FMWL) is the local relation derived from samples collected by the International Atomic Energy Agency at a station in Flagstaff, Arizona (IAEA/WMO 2001; see chart) from 1962 to 1974. It is defined by
δ2H = 6 δ18O + 14 per mil.
The LMWL for the upper and middle Verde River watershed study area developed from the 2003-2005 data is defined by
δ2H = 7.48 δ18O + 9.15 per mil.
Stable-isotope values for winter precipitation samples are significantly lower than for summer precipitation samples (see chart above), reflecting temperature conditions during precipitation.
The relation of stable isotopic ratios to temperature also translates into a relation to elevation: stable isotope values decrease with increasing elevation. Measured stable-isotope elevation gradients for the study remained nearly constant between years and seasons. IAEA stable-isotope values spanning a 14-year period were
used to calculate average stable-isotope values at an elevation of 7,020 feet. The 14-year mean δ2H and δ18O values for the Flagstaff site were -41 and -4.2 per mil, respectively, in the summer and -80 and -11 per mil, respectively, in the winter.
Long-term stable-isotope values were calculated for elevations within the Verde watershed by using the measured gradient during this investigation and the IAEA stable-isotope values at 7,020 feet. The resulting elevation gradient is described by the following equations (z is elevation in meters):
δ2H = -0.019z – 39.04 per mil
δ18O = -0.0026z – 5.36 per mil.
Implications for RechargeUsing the average isotopic values of the groundwater from the subbasins within the watershed, these relationships were used to estimate the contributing recharge areas for subbasins within the watershed (Blasch and Bryson, in press). For example, in the Little Chino subbasin of the upper Verde River watershed, recharge to groundwater comes from precipitation falling at elevations greater than about 5,250 feet, while in the Big Chino subbasin, recharge comes primarily from precipitation falling at elevations
greater than 6,230 feet. In the middle Verde River watershed, precipitation falling at elevations greater than 6,900 feet is the predominant contributor to recharge. In addition, isotope values for groundwater from the entire watershed indicate that about 95 percent of the recharge occurs from winter precipitation.
The LMWL and stable-isotope elevation gradients are useful tools for determining groundwater flow paths to the Verde River as well as locating potential areas of recharge to each subbasin.
Contact Jeannie Bryson at [email protected].
ReferencesBlasch, K.W., and J.R. Bryson, in press.
Distinguishing sources of ground-water recharge by using δ2H and δ18O; Journal of Hydrology.
Blasch, K.W., J.P. Hoffmann, L.F. Graser, J.R.Bryson, and A.L. Flint, 2006. Hydrogeology of the Upper and Middle Verde River Watersheds of Central Arizona, USGS Scientific Inv. Report 2005-5198, 101 p.
Craig, H., 1961. Isotopic variations in meteoric waters, Science, 133: 1702-1703.
IAEA/WMO, 2001. Global Network of Isotopes in Precipitation: The GNIP Database. Accessible at: HTUisohis.iaea.orgUTH.
Rozanski, K., L. Araguás-Araguás, and R. Gonfiantini, 1993. Isotopic patterns in modern global precipitation, in Continental Isotope Indicators of Climate, ed. by P. K. Swart, K. C. Lohman, J. MacKenzie and S. Savin, American Geophysical Union Monograph 78.
ON THE GROUND (continued)
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Stable isotope values in precipitation collected in the study area (LMWL) compared to the Global Meteoric Water Line (GMWL) and meteoric line for precipitation collected at the IAEA station in Flagstaff, Arizona (FMWL).
January/February 2007 • Southwest Hydrology • 11
