H53G-1503
Measuring Moisture Dynamics in Soil and Rock Along a Steep Forested Catchment
While it is recognized that bedrock groundwater is a contributor to the hydrology of hill-slopes, very little is known about how water from the overlying soil moves into, and is distributed through the rock profile. The near surface bedrock zone is usually fractured and weathered to a much greater porosity and permeability than at depth. Water availability to plants and to runoff dynamics may be significant along this zone. We have instrumented a steep forested catchment underlain primarily by deeply fractured mudstone to investigate moisture dynamics along the soil-bedrock continuum. The site, which is located within the Elder Creek Watershed in the Angelo Coast Range Reserve (CA) (http://angelo.berkeley.edu/visiting.htm), is dominated by winter storms from the ocean and summer dry spells. Using a combination of established techniques (e.g., Time Domain Reflectometry) and a proof-of-concept measurement system, we are monitoring moisture in both soil and the underlying bedrock (up to a depth of 2.0 m) at high spatial (centimeters) and temporal (minutes-hours) resolution in multiple locations. The hydrology of the deeper rock profile is being evaluated with a series of boreholes that intercept an underlying water table. This effort is part of a larger project (The Keck Hydrowatch Center) which is targeted to dramatically expand observations of all aspects of the water cycle by developing cost-effective, rapid-response, and accurate sensors and techniques to monitor water quality, quantity, and pathways (i.e., atmosphere, trees, soil/rock and streams).
H53G-1504
Asymptotic Response of Shallow Groundwater and Interactions Among Precipitation, Throughfall, and Stem Flows
Pore pressure head dynamics and heterogeneity were examined monitoring piezometric responses at 83- locations during three seasons (2004 ¨C 2007) in a rain dominated Doe Creek headwater watershed (13.4 ha) in Northern California. Also, during the hydrological year 2006-2007, throughfall and stemflows were monitored at 20 and 4 locations, respectively, to examine the dynamics of net rainfall amount reaching the forest floor and subsequently their potential influence on dynamics of piezometric responses. Soil depth in the study area varies from 0.7 m \¨C\ 1.8 m, and the soil is derived from rocks belonging to Wildcat geological group. No Hortonian or saturated overland flows were observed in the study area throughout the study period (2004- 2007) during which about 1,150 (return period 1.4-yr), 1780 (return period 20-year), and 1200- mm (return period 1.5-yr) annual rainfalls were recorded in 2004-5, 2005-6, and 2006-7, respectively. Positive pressure head occurred at all but four sites located in the divergent hillslope. Interestingly, none of the 83 locations exhibit full soil column saturation during the period. The ratio of pressure head to soil depth was > 0.5 only at five (6% of total sites), eleven (13% of total sites), and six (7% of total sites) piezometric locations in 2004-5, 2005-6, and 2006-7, respectively. The maximum piezometric response varied from site to site ranging from P/D values of 0.1 to 0.72. The peak pressure head during a storm was dependent on the short-term characteristics of rainstorm events and short-period antecedent conditions (¡Ü 2-weeks). The striking difference in the seasonal piezometric responses among hydrological years was on the base levels of piezometric responses than on the peaks. Due to continuous input of rainfall, positive pressure head persisted in most piezometers almost throughout the season during the wet year 2005-6. Despite incessant positive pressure head throughout the mid-winter in 2005-6 in most piezometers, many large rainstorms, occurred at the time when large positive pressure head persisted at the onset of a storm, did not generate dramatic peak pressure heads. The observed scenarios highlight the maxima related to upper limit of increase in pressure head with increasing rainfall. Such a peak threshold may be related to the increased efficiency of preferential flow pathways at higher soil water contents. This kind of asymptotic response for highly reactive piezometers was observed for pressure head return period > 8.4- months. Moderately and least responding piezometers, however, depict asymptotic pressure head return period threshold of 2.4-months. During large storms, the difference in net rainfall amount reaching the ground surface between open space and under the canopy was not significant. Therefore, owing to asymptotic nature of piezometric responses, interception was found less likely to affect the peak pressure head during a large storm.
H53G-1505
The Use of Distributed Temperature/Light Probes to Capture the Spatio-Temporal Dynamics of Snowmelt and Headwater Stream Discharge
Knowing how wet or dry the landscape is provides a valuable piece of information. It can tell us what pathways are active or provide insight to how long water resides in a catchment or help close a water balance. Traditional methods to monitor the hydrologic state of the landscape are often too temporally sparse (e.g., snapshots from remote sensing) or spatially coarse (e.g., point measures from data-logging piezometers) to reflect the dynamic nature of water as it moves through and interacts with the landscape. In this study, we employ inexpensive temperature/light sensors to monitor the distribution of snowmelt and headwater stream discharge as a proxy for hydrological state of the landscape with high spatial and temporal resolution. This is done at Redondo Peak which offers the largest (local relief over 1,100 m) of the resurgent domes within the caldera complex of the Valles Caldera National Preserve located near Los Alamos, New Mexico, USA. The first-order streams that drain Redondo Peak do so through different aspects and thus receive, on average, different amounts of solar energy. This impacts groundwater recharge through variations in sublimation, evaporation, and transpiration. To monitor the role this variation plays with respect to spatio-temporal dynamics of snowmelt and headwater stream discharge, we have installed 150 temperature/light probes in seven different streambeds draining through unique aspects of the peak. The variation of daily temperature/light levels relative to seasonal change in mean temperature/light levels provides a metric of the spatial distribution of surface waters and snow cover. Based on a conceptual model of a groundwater "mound" within the peak that roughly follows the shape of the land surface, such a metric relates directly to the amount of water in the landscape. http://hwr.arizona.edu/~surface/fieldsites/valles.html
H53G-1506
Field-Scale Distributed Wireless Network for Monitoring Dynamic Hydrologic Processes
Measuring and monitoring field-scale hydrology is important to understanding the fate of water in the vadoze zone, especially in concert with pedological information. Historically, single point measurements of hydrologic and pedological information have been straightforward to obtain, while monitoring widely distributed locations over time has been more challenging, both in expense and labor. As radios have become more available, distributed wireless networks have been developed and constructed to meet this need. However, there remain relatively few commercially available, inexpensive, and simple options. The objective of this study was to test the viability of a distributed wireless network to monitor soil parameters (moisture, temperature, and electrical conductivity) across a growing season on the 36.5 hectare Cook Agronomy Farm in Eastern Washington. Using landscape analysis, 12 representative sites were selected using a stratified random procedure and sensors were installed at 30, 60, 90, 120, and 150 cm depths. Radio frequency wireless transmitters linked sensors to a central data station where data were made available anywhere in the world via a cell modem link. Data were analyzed to show relationships between soil features, crop type, and water use. Results show that a system can be assembled from commercially available components with excellent reliability across all communication links. Data from the system showed correlations between water use, directly sampled static soil features and crop type.
H53G-1507
Pore Space Statistics From the X-ray CT of Large Undisturbed Soil Columns
Large soil columns need to be studied to infer geometric properties of macropores and their role in flow and transport phenomena, especially when colloid or colloid-facilitated transport is of interest. We have sampled and studied undisturbed columns (7.5 cm ID, 20 cm length) of the Taylor soil from a grassed floodplain. A FlashCTTM - 420 kV system (HYTEC Inc.) was used for X-ray computer tomography (CT) scanning. The FlashCT-DAQ, the FlashCT-DPS, and the FlashCT-VIZ software was used for reconstruction. A MatLab® software with GUI for processing, analyzing and visualizing of 3D X-ray CT scans was developed. It was used in the binarization process on each of 1480 cross-section images obtained for each column. The resolution of about 100 mkm was sufficient to distinguish macropores. The high-connectivity macropore space was reconstructed from the imagery, as well. The "porosity-depth" data series have been investigated. The R/S (rescale range) analysis indicated that these series did not have a simple structure that might be understood as a persistent or antipersistent fractional Brownian motion using the Hurst exponent. More complex behavior had been detected that could be characterized by means of multifractal analysis. The water retention data were obtained for column sections and were related to the CT characterization of these sections. Large columns present feasible objects for CT if macroporosity is of interest.
H53G-1508
Measurement of soil water potential over an extended range by polymer tensiometers: comparison with other instruments
In water scarce areas, plant growth and productivity can be severely hampered by irregular precipitation and overall water shortage. Root water uptake is mainly driven by matric potential gradients, but measurement of soil water matric potential is limited by the measurement range of water-filled tensiometers (-0.085 MPa). Other measurement techniques indirectly measure soil water potential by converting soil water content with the use of the water retention curve. In dry soils, the water content measurements may become insensitive to small variations, and consequently this conversion may lead to large errors. We developed a polymer tensiometer (POT) that is able to measure matric potentials down to -2.0 MPa. The POT consists of a solid ceramic, a stainless steel cup and a pressure transducer. The ceramic consist of a support layer and a membrane with 2 nm pore-size to prevent polymer leakage. Between the ceramic membrane and the pressure transducer a tiny chamber is located, which contains the polymer solution. The polymer's osmotic potential strongly reduces the total water potential inside the polymer tensiometer, which causes build-up of osmotic pressure. Hence, the water in the polymer tensiometer will cavitate at a much lower matric potential than the nearly pure water in a conventional tensiometer. Direct observation of the potential of soil water at different locations in the root-system will yield knowledge about the ability of a plant to take up the water under conditions of water shortage or salinity stress. With this knowledge it will be possible to adjust existing unsaturated flow models accounting for root water uptake. We tested 8 POTs in an experimental setup, where we compared matric potential measurements to TDR water content measurements, matric potentials derived from measured water contents, and matric potentials measured by water-filled tensiometers. The experimental setup consisted of two evaporation boxes, one filled with sand (97.6% sand, 1.6% silt, 0.8% clay), and the other with loam (42.8% sand, 38.8% silt, 18.4% clay). The uniformly repacked soils were saturated at the beginning of the experiment, then drained, and left to dry out. Results show that polymer tensiometer data are comparable to the other instruments in their measurement ranges, and highlight the risks of converting water contents to matric potentials. This research is funded by the Dutch Technology Foundation (STW). Contributing companies are: ECO Ceramics BV (www.ecoceramics.nl), ENRIN (www.enrin.nl) and KELLER Meettechniek BV (www.keller-holland.nl).
H53G-1509
Using an RC Circuit Model to Determine Soil/Water Content
Accurate soil/water content measurements are essential for water conservation. We have developed a soil/water content measurement probe that is simple to deploy, not affected by the salinity, and is corrosion proof leading to extremely long field life. The measurement takes advantage of the high dielectric constant for water (~80) compared to that of soils (3 to 7) to determine the soil/water content. The RC circuit model for the soil/water mixture consists of a bulk conductivity resistor, a double-layer capacitor, and a bulk dielectric capacitor. Since our electrodes are not directly exposed to the soil, the overall RC circuit model includes a blocking capacitor. Measurements of the differential phase angle are acquired across an on-board drive resistor at a single frequency (70 MHz). Measurements are proportional to bulk soil/water dielectric constant for salinities as high as 5 dS/m. The slight temperature dependence of the dielectric constant is compensated for by an on-board temperature sensor. Water content is determined using a soil/water mixing model. Using the RC circuit model, we will show that our choice of measurement frequency is optimal in achieving a salinity-independent measurement of soil/water content.
H53G-1510
Fingerprinting Dissolved Organic Carbon (DOC) Sources with Specific UV Absorbance (SUVA) and Fluorescence
DOC is an important water quality constituent because it is an important food source for stream biota, it plays a significant role in metal toxicity and transport, and protects aquatic organisms by absorbing visible and UV light. However, sources of stream DOC and changes in DOC quality at storm and seasonal scales remain poorly understood. We characterized DOC concentrations and SUVA (as an indicator of aromaticity) at the plot, hillslope and catchment scale during and between five storm events over the period Fall 2004 until Spring 2005, in WS10, H.J. Andrews, Oregon, USA. This study site has hillslopes that issue directly into the stream. This enabled us to compare a trenched hillslope response to the stream response without the influence of a riparian zone. The main result of this study was that SUVA in addition to DOC was needed to fingerprint sources of DOC. Stream water and lateral subsurface flow showed a clockwise DOC and SUVA hysteresis pattern. Both organic horizon water and transient groundwater were characterized by high DOC concentrations and SUVA values, while DOC concentrations and SUVA values in soil water decreased with depth in the soil profile. This indicates transient groundwater was an important contributor to high DOC concentrations and SUVA values during storm events. During the falling limb of the hydrograph deep soil water and seepage groundwater based on SUVA values contributed significantly to lateral subsurface flow and stream water. Preliminary results showed that fluorescence of stream water and lateral subsurface flow continuously measured with a fluorometer was significantly related to UV-absorbance during a December storm event. Finally, SUVA of lateral subsurface flow was lower than SUVA of stream water at the seasonal scale, indicating a difference in mixing of water sources at the hillslope and catchment scale. Overall, our results show that SUVA and fluorescence are useful tracers for fingerprinting DOC sources.
H53G-1511
An In Situ Analyzer for Accurate Dissolved Carbon Dioxide and Total Inorganic Carbon Measurements
Inland waters have generally been viewed as passive conduits for carbon (C) movement to the sea. However, recent estimates suggest that approximately half of the C entering aquatic systems from the land actually reaches the ocean. Understanding the processes and mechanisms responsible for net C losses en route to the sea is a leading challenge in biogeochemistry. Formulation of an integrated C budget for inland waters will require advances in chemical sensor networks for both organic and inorganic forms of C. We describe here a new in situ chemical analyzer for the inorganic carbon system and illustrate findings for lake and stream deployments. In conjunction with thermodynamic acid/base equilibrium calculations, a complete characterization of the dissolved inorganic carbon system can be accomplished by accurately measuring both pCO2 (partial pressure of dissolved CO2) and TCO2 (total inorganic carbon). Unfortunately, due to the expense and complexity of current instruments, continuous (e.g., hourly) pCO2 in situ monitoring has been performed for long periods only in ocean systems. Affordability and complexity still hinder routine deployments of similar pCO2 instrumentation in freshwater systems. Moreover, in situ devices for continuous TCO2 monitoring are still in development and are not yet practical for routine deployments in freshwater or marine ecosystems. Further, though manual monitoring of CO2 (via headspace sampling and laboratory analysis) and TCO2 (via grab sampling and laboratory analysis) are both feasible, high frequency sampling programs are difficult to sustain long-term; thus, the diurnal and seasonal cycles of events are not resolvable practically with such an approach. Our new device provides for continuous (high resolution) or manual in situ measurements of both pCO2 and TCO2 in groundwater and surface water, allowing complete characterization of the inorganic carbon system. Initial lake and stream deployments for continuous and manual sampling were performed in 2006 and 2007. Accuracy and precision (<0.15% coefficient of variation) met or approximated the data quality requirements for large-scale biogeochemical research initiatives (e.g., Joint Global Ocean Flux Study). A continuous buoy deployment for pCO2 provided a high resolution (30 minute intervals) record of diurnal lake metabolism during the summer of 2007. In a 24-hr test deployment we obtained a 3 minute temporal resolution. Synoptic surveys of 51 northern Wisconsin lakes revealed that pCO2 was sub-atmospheric (<370 ppm) in a majority of lakes (n=40), suggesting the lakes generally served as atmospheric C sinks, rather than atmospheric C sources, during early and mid summer. Further, TCO2 data suggested that carbonate anions helped suppress pCO2 below atmospheric levels during periods when R > P. Surface maps (0.5 m depth) of selected lakes revealed dynamic and heterogeneous pCO2 in near shore areas and relatively homogenous patterns in deeper zones. High resolution spatial patterns along the perimeter of one lake revealed likely entry points of groundwater discharge. Similarly, longitudinal surveys along a small stream corridor revealed patterns of pCO2 and TCO2 consistent with known groundwater discharge and recharge features and showed the primary importance of the groundwater discharge segments as sources of CO2 efflux to the atmosphere.
H53G-1512
Optimizing Wastewater Reuse in Agricultural Fields via Merging of Embedded Network Sensor Data and Flow and Transport Models Using Data Assimilation
Wastewater re-use via crop irrigation has the potential to be an effective means of wastewater disposal. However, nitrate in wastewater may contaminate groundwater if it does not decay before reaching the groundwater table. In order to dispose of wastewater while preventing long-term groundwater pollution, irrigation rates need to be optimized based on the current and predicted states of the soil, such as soil moisture content and/or nitrate concentration. A real-time soil states estimation system using the Ensemble Kalman Filter (EnKF) has been developed for application to a test bed for wastewater re-use in Palmdale, CA. This test bed, covered with alfalfa, is a 30-acre irrigation plot with a 200-meter long rotating pivot arm that irrigates the area with reclaimed wastewater. A sensor network is deployed in the soil near the surface. The data assimilation system has shown the ability to characterize soil states and fluxes from sparse measurements. The real-time estimation system will then be used to explore the potential feedback for optimizing the sprinkler operation (i.e. maximizing the magnitude of wastewater release while minimizing the ultimate groundwater pollution). In optimization models, soil states and fluxes can be regarded as functions of irrigation rate. Through optimization, the irrigation rate in a finite horizon can be maximized while still satisfying all criteria in soil states and fluxes to ensure the safety of groundwater. Since the data assimilation system provides reliable estimation of soil states and fluxes, it is expected to define the optimal irrigation rate with higher confidence compared to using models or sensors only.
H53G-1513
Using Satellite Imagery to Predict Salinity in a Large Oligohaline Estuary
Ecosystem conditions in and around estuaries are directly affected by fluctuation of their salinity changes. This study utilized satellite imagery and field measurements to develop a model for predicting salinity changes in Lake Pontchartrain, the largest estuary in the Northern Gulf of Mexico. Field salinity measurements from the lake were collected on 30 Oct. 2001, 25 Oct. 2005, and 8 May 2007. Landsat-5 TM images for these dates and additional three dates were pre-processed through "banding" noise reduction and radiometrical correction. Multivariate regression was performed to determine the relationships between measured salinity levels and water reflectance derived from TM bands 1, 2, 3, 4, 5, and 7. The regression model developed was then applied to evaluate the immediate effects of Hurricanes Katrina and Rita on saltwater intrusion into Lake Pontchartrain. The results show that the modeling achieved a high prediction power (R2 =0.83 and RMSE=0.45), with a relatively low prediction error (5.9 %). A close relationship between salinity levels and water-leaving reflectance was found (R2= 0.89), with TM bands 3 and 5 being the most important predictors. The modeled spatial pattern and magnitude of the salinity levels following Katrina and Rita show a strong, immediate effect of the hurricanes on saltwater intrusion across the lake up to the mouths of the freshwater rivers. This study demonstrates that remote sensing techniques can be a powerful tool for predicting salinity changes in large estuaries. The model, if successfully validated, should be applicable for other estuaries in the Northern Gulf of Mexico.
H53G-1514
Soil Moisture, Salinity, and Nitrate Control for Soil and Groundwater Protection in Support of Wireless Sensor Networks and Optimal Irrigation Strategy
Over-irrigation with reclaimed water may cause crop yield reduction and groundwater quality degradation. Continuous and automatic monitoring strategies are desirable as a means of guiding management schemes to avoid these problems. In this work, an optimal irrigation management scheme known as Receding Horizon Control (RHC) is proposed to balance water reuse and soil/groundwater quality. In this scheme, a wireless networked sensor array is deployed to provide on-line feedback to the simulators on which the management algorithm depends. A simulation model including a one- (vertical) dimensional form of the Richards equation coupled to energy and solute transport equations is automatically updated with real-time soil moisture, temperature, nitrate, and salinity sensor data on a regular basis. A genetic algorithm-based control scheme determines the optimal irrigation rate using current observations which continuously maximizes the reclaimed water usage while maintaining salinity and nitrate in soils at a certain level. Results from simulated soil moisture/nitrate control where maximum soil moisture/nitrate level throughout the soil depth is maintained are presented. On-site soil moisture control in Palmdale, CA, where reclaimed water is irrigated with center-pivot irrigation system at an agricultural site, is also demonstrated. An on-going field experiment in Merced, CA where automatic irrigation system is set up to control salinity level in soils is presented as well. The results demonstrate that coupling in situ observations with RHC process control algorithm is a viable strategy for achieving water reuse and agricultural objectives while minimizing negative impacts on environmental quality.
H53G-1515
Robotic Stream Flow and Solute Mass Balance Measurements Guided by a Non-Stationary Gaussian Process Model
Spatially distributed hydraulic and water quality property characterization is important to understanding a broad range of river issues including confluence and discharge mixing phenomena, groundwater-surface water exchanges, and flow and temperature distributions in the context of habitat restoration efforts. Such characterization efforts often need to be completed rapidly to avoid complications associated with transient upstream conditions ( e.g., reservoir operational changes, time-variable irrigation drainage). In this work, we test a non-stationary Gaussian Process (GP) model for increasing sampling efficiency during a robotic deployment of velocity (ADV) and electrical conductivity (EC) sensors across a river transect. GP modeling is a common statistical approach for addressing spatially distributed phenomena. We first develop velocity and salinity observations within the mixing zone of the Merced-San Joaquin River confluence robotically in the form of high resolution (114 point) raster scans. We train the GP model by dividing the river cross-section into three sub- regions corresponding to Merced river side (east), mixing zone (center), and San Joaquin River side (west). An information criterion was selected that assigned each observation location a quantitative value in terms of the uncertainty about our prediction of the EC value given the measurement made at that location. We then executed a path-planning algorithm optimizing 16 locations out of the original 114. Using the observations from these 16 locations, and the trained GP model, we predicted the values at the rest of the 98 unobserved locations. EC distributions are compared for the raster- and GP-based data and suggest that the GP modeling strategy is viable for enhancing sampling efficiency in the context of spatially distributed river characteristics.
H53G-1516
Characterising the Hyporheic Environment and Inferring Groundwater-Surface Water Interactions with Continuous Monitoring of Dissolved Oxygen Using Optical Sensors
The recent development of optical sensors that facilitate continuous, accurate in situ measurement of dissolved oxygen (DO) levels have revolutionised our ability to monitor the hydrochemistry of the hyporheic zone; an important ecological and biogeochemical hot spot in streams. In addition, this has also provided invaluable insight into the nature of local groundwater – surface water exchange in stream-aquifer systems. This contribution will report the use of optode technology over a 2 year period in a gravel-bed stream draining a 30km2 montane watershed in the Scottish Highlands. Laboratory calibration of the optodes before and after installation confirmed excellent reliability and data quality. Two contrasting sites were monitored where previous work had suggested the hyporheic zone was respectively characterised by upwelling groundwater and downwelling surface water. At each site, replicated logging optodes recorded DO levels in the stream and in hyporheic water at depths of 15cm and 30cm in the stream bed. At the upwelling site, DO levels in the stream were close to 100% throughout the 2 years; levels in the hyporheic zone were highly dynamic and could range between 0 and 100% saturation in a matter of hours. Associated piezometry indicated that such changes were strongly influenced by high water table levels in hillslope groundwater, which resulted in positive pressures allowing the discharge of groundwater through the hyporheic zone. As such, hyporheic DO levels exhibited marked seasonal and inter- annual variability with values close to 100% saturation for prolonged periods during summer and other times when rainfall was low and there was poor connectivity between groundwater and the stream. In contrast, winter and wetter times, when hillslope groundwater-hyporheic connectivity was good, resulted in prolonged periods – up to several months – when hyporheic DO levels were at or close to zero. In addition, short transient spells of low DO followed some small summer events where in site O2 consumption might be expected from microbial respiration following the influx of organic material. At the downwelling site, streamwater was also close to 100% saturation throughout, and hyporheic DO levels also remained high, with no apparent relationship with water tables, though there was also evidence of transient O2 consumption following small summer spates. The optode technology characterised the dynamics of the hyporheic environment in a way that traditional ex situ sampling at weekly or fortnightly intervals could not. The 15 minutes time series data were statistically analysed to show the loss of information and resulting uncertainty that would have occurred had samples been collected at the daily, weekly, fortnightly or monthly intervals that are common in hyporheic studies. The additional information gained was found to be fundamentally important to hydroecological interpretation, as well as invaluable in indicating groundwater – surface water dynamics.
H53G-1517
Use of the "smart tracer" resazurin to identify biological activity and quantify sediment-water interaction in a stream in Catalonia, Spain
A smart tracer is a tracer that provides, directly or through measurement of its concentration or in combination with another compound, at least 1 bit more information than a conservative tracer. In other words, the tracer provides information about conditions in the hydrologic system in addition to arrival time – location history, chemical conditions, biological activity, physical interactions, or other information. We have developed a smart tracer for quantifying biological activity and sediment-water interaction in streams. We will present a hands-on demonstration of the resazurin (Raz) test of biological activity and show results from an injection of the tracer in the Riera de Santa Fe de Montseny, Catalonia, Spain. In the presence of living bacteria (in many streams these are most common as biofilms on sediment), mildly fluorescent blue resazurin reduces irreversibly to strongly fluorescent resorufin. Using the information provided by this reaction along a 125- m stream reach, in conjunction with a chloride tracer, we were able to qualitatively identify bacterial growth and to quantify sediment-water interactions.
H53G-1518
Using Electrical Resistance Sensors for High Resolution Monitoring of Channel Network Expansion
It has long been recognized that the volume of water in a channel network can vary greatly over single storm events. This increase in drainage network volume may be expressed as changes in stream stage, an increase in the wetted perimeter as streams expand laterally onto their floodplains and an increase in the flowing length of channels as the stream head migrates upstream into ephemeral portions of the channel network. Monitoring the increase in the flowing length of channels over entire catchments is tremendously difficult. However, it has been found that Electrical Resistance (ER) sensors can used to detect the presence or absence of stream flow at any point in a stream network. During flow conditions, there is a continuous circuit between the sensor electrodes, so the measured electrical conductivity is high. When there is no flow, the circuit is broken and conductivity is low. This enables a binary level flow/no flow distinction to be made. These sensors are robust and inexpensive with on-board data loggers. As such they can facilitate distributed measurements at fine spatial and temporal resolutions. Therefore, extensive instrument networks could be installed to monitor the spatial pattern of stream network expansion and contraction within an entire catchment. This could enhance our understanding of hydrological response to rainfall and the controls governing runoff generation. Dynamic-extent drainage networks could eventually replace the static networks currently used in runoff, erosion, sediment, and pollution transport models with potentially significant improvements to prediction accuracy. This paper presents results from an extensive sensor network established to monitor stream network expansion and contraction in a peatland catchment in the South Pennines, UK, over the autumn of 2007.