Lundquist et al., Online supplement for Measurement Paper, page 1. Electronic .... page 6. Table 2: Step-by-step instructions to build your own stilling tube ...
Lundquist et al., Online supplement for Measurement Paper, page 1
Electronic Supplement to: Strategic use of stream stage recorders as proxy rain gauges in complex terrain For Water Resources Research Measurement Methods Issue 2008 Jessica Lundquist, Brian Huggett, Heidi Roop Submitted April 3, 2008 Electronic Supplement: Guidelines for measuring stream stage in remote wilderness locations
I.
Introduction
Detailed, thorough instructions for deploying stream gages have been developed by the Department of Agriculture [Brakensick et al., 1979] and the USGS [stage and discharge, Rantz et al., 1982; pressure transducers, Freeman et al. 2004; Doppler current profilers, Oberg et al., 2005; Oberg and Mueller, 2007]. However, traditional monitoring stations generally require substantial investments of time, money, and infrastructure, effectively limiting the number of locations that can be monitored. Regions of complex topography and remote wilderness terrain have spatiallyvarying patterns of streamflow, but due to inherent difficulties of access, are often very poorly sampled. Because many distributed measurements are needed to represent the environment, individual installations must be robust and inexpensive, be easy to construct and install in remote regions, and need infrequent site visits. Stream stage records, particularly temporal fluctuations of water level, are much easier to obtain than discharge and allow for faster, less expensive deployment to multiple sites. Freeman et al. [2004] provide a detailed description of how pressure transducers work and recommendations for their proper use. Key steps require that the pressure transducer be held stationary at the bottom of the water column and be calibrated to
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represent actual water depth, which may include correcting for barometric pressure fluctuations and for temperature dependencies. If measurements are designed to monitor streamflow timing, with no plan to develop a rating curve or determine discharge, the fastest method of deployment is to place the pressure sensor within a section of PVC pipe (for protection) and then anchor it to the bottom of the stream (Figure 1). Anchors can consist of concrete poured around a PVC pipe (Figure 2b and c), such that the instrument can be inserted and removed from the structure, or a mesh bag filled with local rocks (Figure 1d). In either case, the pipe should be cabled to a secure tree trunk or bridge abutment, as anchors are prone to move in large flood events. At locations where a rating curve is being developed, with the goal of relating stage to discharge, a stilling tube, combined with a corded sensor and adjacent staff gage, should be used to provide a stable datum for the stage record relative to the stream bed from one year to the next. Details for construction and installation of a wilderness stilling tube follow.
II.
Wilderness stilling tube
The wilderness stilling tube is designed to emulate a larger scale stilling well gaging station but with parts that can be obtained from a local hardware store (Table 1). This design houses and protects a self-recording water level logger from ice or floating debris while decreasing exposure to turbulent water levels and pressures. The stilling tube provides a consistent platform from which to monitor water levels while offering a visually discrete, compact and mobile enclosure (Figure 2). A 1”-diameter perforated tube houses the instrument, which is in turn fixed inside a 2” -diameter perforated tube.
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The inner tube is held in place by a conduit hanger (on the lower end) and an automotive hose clamp (on the upper end). The hose clamp can be loosened and tightened to allow the inner tube to be removed for service. Appropriate lengths of rebar are driven into the stream bed and bank and are attached to the stream tube via hose clamps. Any instrument cords are routed out the top of the tube and hidden on the stream bank in a weatherproof container.
III.
Conclusions
These techniques, which include low cost and rapid deployment, are well-suited to make measurements of opportunity; for example, to monitor how different basins respond to a catastrophic event, such as a volcanic eruption, a forest fire, a dam removal, or a logging operation. These techniques provide a means to make preliminary measurements at many locations before designing a more-permanent monitoring network, and provide spatial information on precipitation locations and runoff timing to aid in checking distributed models.
IV.
References
Brakensick, D. L., Osborn, H. B., Rawls, W. J. (1979), Field Manual for Research in Agricultural Hydrology: Agricultural Handbook No. 224, U.S. Dept. of Agriculture. 547 pgs. Freeman, L. A., M. C. Carpenter, D. O. Rosenberry, J. P. Rousseau, R. Unger, and J. S. McLean (2004), Use of Submersible Pressure Transducers in Water-Resources Investigations. Chapter A of Book 8, Instrumentation, Section A, Instruments for
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Measurement of Water Level, Techniques of Water-Resources Investigations 8-A3. pp 65. [Available at: http://pubs.usgs.gov/twri/twri8a3/] Oberg, K. A., S. E. Morlock, and W. S. Caldwell (2005), Quality-Assurance Plan for Discharge Measurements Using Acoustic Doppler Current Profilers. U.S. Geological Survey Scientific Investigations Report 2005-5183. 46 pp. [Available at: http://hydroacoustics.usgs.gov/] Oberg, K., and D. S. Mueller (2007), Validation of streamflow measurements made with acoustic Doppler current profilers. J. Hydraulic Eng. ASCE, 133, 1421-1432. Rantz, S.E., and others, (1982), Measurement and computation of streamflow: Volume 1, Measurement of stage, and Volume 2, Computation of discharge: U.S. Geological Survey Water-Supply Paper 2175, v. 1, p. 1-284, v. 2, p. 285-631.
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Table 1: Parts list for the wilderness stilling tube Supplies Needed: 2.5’ length of 2” ABS TUBE 2.4’ length of 1” Schedule 40 PVC (2) 2” ABS pipe caps (2) ½” stainless Phillips head self drilling screws (for fixing caps to tube) (5) 4” stainless steel hose clamp (automotive type) (1) 1” conduit bracket (electric type-either 1 or 2 hole clamp will suffice) (1 or 2) ½” ¼ 20 bolts with locking nylon nuts (quantity depends on style of conduit bracket) 1.2’ length of nylon string Appropriate* length of ¼” rebar (1) 1 ¼” galvanized deck screw
Tools Needed: cordless drill 3/8” chuck ¼” drill bit Phillips screwdriver ¼” socket and rachet file 2 lb hammer (for driving rebar) hacksaw
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Table 2: Step-by-step instructions to build your own stilling tube
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CONSTRUCTION •
PERFORATION OF BOTH TUBES: Drill 2 ¼” holes into each tube cap. Drill ¼” holes at 6” intervals along the vertical axis of both tubes. For reference, the side with holes will be referred to as the “front,” and the side without holes will be referred to as the “rear.”
OUTER TUBE : •
LOWER TUBE ATTACHMENT: Place the conduit hanger into the bottom end of the larger diameter tube (Figure 2c). Check to ensure fit of the inner tube by pushing the 1” tube through the hanger.
•
UPPER TUBE ATTACHMENT: One inch from either side of the rear of the outer tube, 2.5” down from the top, drill 2 ½” holes. These will be the slots to thread the hose clamp through. Open the hose clamp, and thread one end into the outer tube and feed it out through the other hole. Reconnect the hose clamp. The tightening screw of the clamp should remain on the outside of the outer tube to facilitate the tightening of the clamp once the inner tube is emplaced.
INNER TUBE •
HANDLE LOOP: Drill a ¼” hole near the upper end of the inner tube. Thread the nylon rope through the hole, and tie the ends to form a loop. This allows the inner tube to be pulled out easily, if necessary.
•
INSTRUMENT REST: Approximately ½” from bottom of smaller diameter tube, thread a deck screw through the center of the tube so that its exit point is 180 degrees from its entry point (Figure 2a). It is critical that the screw head is flush with the outside diameter of the smaller tube, or this can result in difficulty in
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removing the inner tube as it may hang up on the lower conduit bracket. Flushing the screw can be accomplished by countersinking the hole, or more crudely, drilling a portion of the tube away with a larger diameter drill bit. If using the larger diameter drill bit, be careful not to drill through the tube. File off the end of the screw that protrudes out the other side of the tube. SLOTTING OF THE TUBES: •
Slide the smaller tube through the upper hose clamp, and slide the tube through the lower conduit hanger (Figure 2b). Tighten the hose clamp until the inner tube is securely held next to the outer tube.
TOP/BOTTOM CAP ATTACHMENT: •
Place the bottom cap over the lower end of tube, and use a self drilling screw to fix the cap to the tube.
OPTIONAL-DRILLING HOLE FOR DOWNLOAD CORD: •
Drill a ½” hole in outer tube below the level of the cap. Remove the cap and use a hacksaw to connect the hole to end of the tube. The end result will be a slot that the data logger cord can exit the tube with the cap attached.
TUBE EMPLACEMENT •
Place a length of rebar (or two) into the streambed to serve as the vertical support for the tube (Figure 1a). Use stainless hose clamps to attach the tube to the rebar.
•
Pound at least two lengths of rebar into the streambed to serve as the horizontal supports for the tube. Attach tube to rebar with hose clamps.
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Figures:
Figure 1 (a) Wilderness stilling tube, (b) anchor with pipe and rebar, with cable connected to a tree, (c) small concrete anchor, (d) Brian Huggett with PVC pipe attached to a cable and attached to large river rock with a mesh bag.
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Figure 2 (a) Pressure transducer placed inside 1” diameter PVC pipe, with screw to keep it resting in place. (b) Inserting the 1” diameter pipe inside the 2” diameter pipe. (c) Conduit hanger to keep inner tube in place.
