Automated Seepage Meters
The Lee-type manual seepage meter only measures the aggregated seepage gain or loss over a fixed time period. Various types of automated meters have been developed to record the time-series change in seepage flow. The same principle of an inverted chamber to isolate and direct seepage flux is used. However, instead of using a plastic bag or similar collection device, different instruments are used to continually measure the rate of water flow through the outlet tube. Some automated devices are compared in Table 1 and include the:
- continuous heat meter, which applies the "Granier" method commonly used in sap flow meters that measure water flux in trees. This is based on the effect of water flow velocity on a temperature gradient established along the flow tube - the temperature difference is at a maximum under no-flow conditions and progressively decreases with increasing water flow velocity (Taniguchi and Iwakawa, 2001);
- heat pulse meter which is based on the travel time of a heat pulse generated within the flow tube, which is also a function of water flow velocity (Taniguchi and Fukuo, 1993; Krupa et al, 1998);
- ultrasonic meter that is based on the relationship between water flow velocity and the travel time of an ultrasonic signal through the flow tube (Paulsen et al, 2001);
- dye-Dilution meter, based on the principle that the rate that a dyed solution is diluted is directly proportional to the water flow rate in the flow tube (Sholkovitz et al, 2003). The method involves the timed injection of a water-soluble dye and the subsequent measurement of the absorbance of the dyed solution;
- electromagnetic meter which is based on Faraday's law of induction and measures the voltage induced by the movement of a conductive material (water) perpendicular through a magnetic field, which is proportional to the flow velocity (Rosenberry & Morin, 2004); and
- a proximity switch which is tripped each time a collection bag is filled (Reay & Walthall, 1992).
| Continuous Heat | Heat Pulse | Ultrasonic | Dye Dilution | Electromagnetic | |
|---|---|---|---|---|---|
| Reference | Taniguchi and Iwakawa, 2001 | Taniguchi & Fukuo, 1993 | Paulsen et al, 2001 | Sholkovitz et al, 2003 | Rosenberry & Morin, 2004 |
| Area of seepage housing (m2) | 0.25 (can be changed) | 0.20 (can be changed) | 0.21 (can be changed) | 0.29 (can be changed) | 0.25 (can be changed) |
| Diameter of flow tubing (cm) | 1.1 | 0.95 | 0.85 | 5.1 | |
| Minimum time resolution | 5 min | 1 s | 5 min | 1 sec | |
| Maximum time resolution | Adjustable (up to days) | Adjustable (up to days) | Adjustable (up to days) | Adjustable | |
| Range of measurable flow rates (cm/d) | 2-40 | 0.9-300 | 0.5-150 | 5.6-5600 17-17000 |
|
| Able to measure forward and reverse flow | Not in current configuration | Yes | Yes | Yes | |
| Able to operate manually | No | No | Yes | No |
References
Krupa SL, Belanger TV, Heck HH, Brok JT, Jones BJ, 1998. Krupaseep- the next generation seepage meter. Journal Coastal Research 25, 210-213.
Paulsen RJ, Smith CF, O'Rourke DO, Wong T-F, 2001. Development and evaluation of an ultrasonic ground water seepage meter. Ground Water 39, 904-911.
Rosenberry DO, Morin RH, 2004. Use of an electromagnetic seepage meter to investigate temporal variability in lake seepage. Ground Water 42(1):68-77.
Sholkovitz E, Herbold C, Charette M, 2003. An automated dye-dilution based seepage meter for the time-series measurement of submarine groundwater discharge. Limnology and Oceanography: Methods 1, 16-28.
Taniguchi M, Fukuo, Y, 1993. Continuous measurements of ground-water seepage using an automatic seepage meter. Ground Water 31, 675-679.
Taniguchi M, Iwakawa H, 2001. Measurement of submarine groundwater discharge rates by a continuous heat-type automated seepage meter in Osaka Bay, Japan. Journal of Groundwater Hydrology 43, 271-277.