Flume testing of underwater seep detection using temperature sensing on or just below the surface of sand or gravel sediments

Temperature anomalies can identify locations of seeps of groundwater into surface waters. However, the method’s sensitivity to details such as thermometer burial depth, sediment material, seep velocity, and surface water current are largely unknown. We report on a series of laboratory flume experiments in which controlled seeps under variable sediment texture, surface currents, burial depth, and temperature differentials were imposed. The focus of the study is temperature effects at the sediment surface to a few centimeters below the sediment surface, as these locations are of particular interest when using fiber-optic distributed temperature sensors (DTS). The data demonstrate: (1) without surface water flow, seep-related thermal anomalies were apparent in all cases, i.e., the method is feasible in such cases; (2) probe burial is helpful for fine sediment although not effective with coarse bed sediment, i.e., the method is strongly sensitive to sediment properties; (3) placing a thin rubber sheet over an unburied thermal probe increases detection of seeps in some circumstances, but not in others, and is generally not as robust as probe burial; and (4) local surface flow velocity, details of probe position and depth, and seepage velocity all influence observed temperature anomalies, limiting the opportunity to quantify seepage velocity, particularly with unburied temperature sensors. Overall, these findings suggest optimal installation would be at a well-defined depth within fine sediment, that installation in gravel and coarser sediment is not suited to the method if there are any significant surface currents, and that more data would be required to obtain accurate estimates of seepage velocity, though a single sensor may be sufficient to identify the location of seepage.Keywords: Temperature, Gravel, Sand, Flow, Sediment, Seepag

Active-distributed temperature sensing to continuously quantify vertical flow in boreholes

We show how a distributed borehole flowmeter can be created from armored Fiber Optic cables with the Active-Distributed Temperature Sensing (A-DTS) method. The principle is that in a flowing fluid, the difference in temperature between a heated and unheated cable is a function of the fluid velocity. We outline the physical basis of the methodology and report on the deployment of a prototype A-DTS flowmeter in a fractured rock aquifer. With this design, an increase in flow velocity from 0.01 to 0.3 m s−1 elicited a 2.5°C cooling effect. It is envisaged that with further development this method will have applications where point measurements of borehole vertical flow do not fully capture combined spatiotemporal dynamics

A simple accurate method to predict time of ponding under variable intensity rainfall

The prediction of the time to ponding following commencement of rainfall is fundamental to hydrologic prediction of flood, erosion, and infiltration. Most of the studies to date have focused on prediction of ponding resulting from simple rainfall patterns. This approach was suitable to rainfall reported as average values over intervals of up to a day but does not take advantage of knowledge of the complex patterns of actual rainfall now commonly recorded electronically. A straightforward approach to include the instantaneous rainfall record in the prediction of ponding time and excess rainfall using only the infiltration capacity curve is presented. This method is tested against a numerical solution of the Richards equation on the basis of an actual rainfall record. The predicted time to ponding showed mean error ≤7% for a broad range of soils, with and without surface sealing. In contrast, the standard predictions had average errors of 87%, and worst-case errors exceeding a factor of 10. In addition to errors intrinsic in the modeling framework itself, errors that arise from averaging actual rainfall records over reporting intervals were evaluated. Averaging actual rainfall records observed in Israel over periods of as little as 5 min significantly reduced predicted runoff (75% for the sealed sandy loam and 46% for the silty clay loam), while hourly averaging gave complete lack of prediction of ponding in some of the cases.Keywords: Infiltration, Variable rainfall, Pondering, Runof

Technical Note: Bed conduction impact on fiber optic DTS water temperature measurements

Error in Distributed Temperature Sensor (DTS) water temperature measurements may be introduced by contact of the fiber optic cable sensor with bed materials (e.g., seafloor, lakebed, stream bed). Heat conduction from the bed materials can affect cable temperature and the resulting DTS measurements. In the Middle Fork John Day River, apparent water temperature measurements were influenced by cable sensor contact with aquatic vegetation and fine sediment bed materials. Affected cable segments measured a diurnal temperature range reduced by 10% and lagged by 20–40 min relative to that of ambient stream temperature. The diurnal temperature range deeper within the vegetation–sediment bed material was reduced 70% and lagged 240min relative to ambient stream temperature. These site-specific results illustrate the potential magnitude of bed-conduction impacts with buried DTS measurements. Researchers who deploy DTS for water temperature monitoring should understand the importance of the environment into which the cable is placed on the range and phase of temperature measurements.This discussion paper has been under review for the journal Geoscientific Instrumentation, Methods and Data Systems (GI). Please refer to the corresponding final paper in GI. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.geoscientific-instrumentation-methods-and-data-systems.net/ The final revised paper is available at: http://hdl.handle.net/1957/5657

Different frequencies of RIP among early vs. late ascospores of Neurospora crassa

We have noticed that the frequency of RIP can be quite variable, even in crosses of the same strains. One possible source of variability is the time at which ascospores are harvested. We reasoned that the earliest ascospores shot from a perithecium might contain DNA that went through relatively few mitotic divisions in pre-meiosis. RIP occurs between fertilization and premeiotic DNA synthesis (Selker et al. 1987 Cell 51:741-752). Thus, early spores might have less exposure to RIP than late spores. Since all ascospores from a perithecium are thought to arise from a single fertilization event, a minimum of 7- 10 divisions are required to account for the number of ascospores normally produced (Perkins and Barry, 1977 Adv. Genet. 211:541-544). It is likely, however, that some ascospore lineages contain fewer divisions than others

Bed conduction impact on fiber optic distributed temperature sensing water temperature measurements

Error in distributed temperature sensing (DTS) water temperature measurements may be introduced by contact of the fiber optic cable sensor with bed materials (e.g., seafloor, lakebed, streambed). Heat conduction from the bed materials can affect cable temperature and the resulting DTS measurements. In the Middle Fork John Day River, apparent water temperature measurements were influenced by cable sensor contact with aquatic vegetation and fine sediment bed materials. Affected cable segments measured a diurnal temperature range reduced by 10%and lagged by 20–40 min relative to that of ambient stream temperature. The diurnal temperature range deeper within the vegetation–sediment bed material was reduced 70% and lagged 240 min relative to ambient stream temperature. These site-specific results illustrate the potential magnitude of bed-conduction impacts with buried DTS measurements. Researchers who deploy DTS for water temperature monitoring should understand the importance of the environment into which the cable is placed on the range and phase of temperature measurements.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.geoscientific-instrumentation-methods-and-data-systems.net

In-Situ Performance and Usability of a Distributed, Wireless Sensor Network via Mesh Connectivity at a Production Container Nursery

Many nurseries are considering soil moisture sensor networks to improve water application efficiency. Due to the necessarily wide distribution of sensors at a nursery, a wireless network is easier to install, more flexible, and can be scaled up as needed without re-design as compared to a traditional wired sensor network. When choosing a wireless network, a matter of critical importance is the network reliability. This study examined the reliability and usability of a commercially available, mesh-style wireless network used at a container nursery. We found that the network failed to record approximately 20% of scheduled sensor readings and that usability was limited due to a fixed 15-min reading interval. However, the system function was sufficient for calculating irrigation set-time and monitoring net irrigation and evapotranspiration when overhead irrigating containerized nursery crops. Results led to discussion of optimum characteristics of a wireless monitoring network system and to what extent this system embodied each of them.This is the publisher’s final pdf. The published article is copyrighted by the American Society of Agricultural and Biological Engineers and can be found at: http://elibrary.asabe.org/toc_landing.asp?conf=aeaj.Keywords: Mesh network, Sensor networks, Wireless network, Network reliability, Container nursery, Nurser

Thermal-Plume fibre Optic Tracking (T-POT) test for flow velocity measurement in groundwater boreholes

International audienceWe develop an approach for measuring in-well fluid velocities using point electrical heating combined with spatially and temporally continuous temperature monitoring using Distributed Temperature Sensing (DTS). The method uses a point heater to warm a discrete volume of water. The rate of advection of this plume, once the heating is stopped, equates to the average flow velocity in the well. We conducted Thermal-Plume fibre Optic Tracking (T-POT) tests in a borehole in a fractured rock aquifer with the heater at the same depth and multiple pumping rates. Tracking of the thermal plume peak allowed the spatially varying velocity to be estimated up to 50 m downstream from the heating point, depending on the pumping rate. The T-POT technique can be used to estimate the velocity throughout long intervals provided that thermal dilution due to inflows, dispersion, or cooling by conduction do not render the thermal pulse unresolvable with DTS. A complete flow log may be obtained by deploying the heater at multiple depths, or with multiple point heaters

Experimental investigations for trapping oxygen gas in saturated porous media for in situ bioremediation

Oxygen is often the rate-limiting factor in aerobic in situ bioremediation. This paper investigates the degree to which air or oxygen gas can be emplaced into the pore space of saturated porous media and provide a significant mass of oxygen. Column experiments were performed to test three emplacement methods: direct gas injection, injection of water supersaturated with gas, and injection of a hydrogen peroxide solution. The direct gas injection method fills 14–17% of the pore space with trapped gas. Water supersaturated with gas fills 18–27% of the pore space with a trapped gas phase, and hydrogen peroxide solution injections emplaces trapped gas in 17–55% of the pore space. In addition to supplying oxygen, gas entrapment causes a decrease in hydraulic conductivity which could be an advantage by decreasing the flow of contaminants offsite. The relative hydraulic conductivity of porous media with a trapped gas volume of 14–55% was 0.62–0.05.Keywords: Hydrology: Groundwater hydrology, Hydrology: Groundwater qualityKeywords: Hydrology: Groundwater hydrology, Hydrology: Groundwater qualit