In-Situ Integrated Suspended Sediment Stream Sampler

1. Technical Field

This invention relates generally to the field of water quality analysis and geochemical prospecting, and more specifically to an in-situ sampler for collecting suspended stream sediment over extended time periods.

2. Background Art

Over the years a variety of samplers and procedures have been developed and used for sampling suspended and bottom sediment. In general, the requisites for sampling suspended or fluvial sediment are different from those for sampling bottom sediment.

Suspended sediment in streams is sampled for a variety of purposes. In general, the intent is to supply samples for analyses to provide information on the quantity, i.e. concentration, and on the physical and chemical characteristics of the suspended sediment. Sorptive characteristics of suspended sediments have been recognized as an important process in the transport of natural and anthropogenic trace constituents. Suspended sediments have been used extensively in geochemical mineral exploration. They are also becoming increasingly recognized as important transporters of trace organic and inorganic contaminents in streams, lakes and marine environments.

Prior art suspended sediment samplers can be categorized into three classes--integrating samplers, instantaneous samplers and pumping samplers. Integrating samplers accumulate a water-sediment mixture over a period of time by withdrawing water and associated suspended sediment from the ambient flow through a relatively small nozzle. Instantaneous or grab samplers essentially trap a volume of the water-sediment mixture by instantaneously closing off the ends of a flow-through chamber. Pumping samplers withdraw a mixture of water and suspended sediment through an intake by a pumping action. Generally, passive integrating samplers are preferred because they obtain a water-sediment mixture from a long filament of flow, can sample at more than one point, and require no energy input or complicated velocity sensing and adjusting apparatus.

In the past, a variety of hand-held and cable and reel integrated samplers have been used to assess suspended sediment concentrations in streams. These samplers were generally designed to sample relatively small quantities of water, usually less than one liter and therefore have limited application for environmental and geochemical exploration sampling.

Various filtering apparati have been used to separate suspended sediments which rely on collection of a water sample and then separating the suspended fraction by some mechanical process. Commonly, water samples are collected and either filtered at the site or the suspended material is separated at the laboratory. In either case, whole water samples are collected within short term periods and therefore reflect instantaneous or short term stream events or episodes. Continuous sampling pumps, coupled to an on-site centrifuge are able to sample large volumes of water for extended periods. This approach, however, requires an electrical source which limits application to relatively accessible areas, and is also personnel intensive requiring continuous monitoring.

In accordance with the present invention, an improved stream sampler capable of continuous collection of suspended stream sediment over extended time periods is provided, which overcomes many of the limitations of the prior art. The integrated sampler of the present invention is passive and relies on natural sedimentation principles and therefore requires neither ancillary operating power nor conventional filtration or centrifugation to remove the suspended fraction from collected water samples. The sampler is also lightweight, self-actuated, simple and inexpensive to construct, readily deployed and serviced, and can be used in remote areas, unattended, over extended time periods for environmental or geochemical sampling.

The sampler of the present invention is designed to capture a portion of a flowing stream containing sediment and direct said portion into a sedimentation chamber. In this chamber, the stream flow is slowed to induce settling of suspended sediment and the settled sediment is collected. Apertures in the chamber allow for discharge of water and accordingly sampling of the stream over an extended period of time. In a preferred form, the sampler includes a funnel to capture a portion of the flowing stream, a cylindrical housing having a water impermeable top member and a perforated base member for defining the sedimentation chamber, a receptacle in said chamber for collecting settled sediment and channeling means in said chamber for directing settling sediment into said receptacle. The outlet of the funnel is sized and the apertures in the base member are sized and positioned so as to reduce the flow in the chamber and induce sedimentation. The sampler is preferably constructed for ready disassembly, sample removal and cleaning. The receptacle for collecting settled sediment and other portions of the sampler may be made of inert material to avoid sample contamination. The receptacle can also accommodate a removable and replaceable beaker to minimize interruption of sampling, and a cross baffle to further inhibit flow if desired. The collecting funnel is preferably thread-mounted to the main body of the sampler allowing rapid change of funnel diameter.

The sampler may be positioned at any depth and oriented with the funnel facing upstream on a support rod secured, for example on or in the stream bed. The sampler is preferably supported such that it may be readily vertically repositioned or removed from the support rod. The sampler of the present invention can be used singly or in groups to determine lateral and vertical suspended sediment variations within a stream. The invention also encompasses the method of sampling advantageously implemented by the described hardware.

These and other objects, features and advantages of the invention will be more readily understood from the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings in which:

FIG. 1 is a vertical sectional view of a preferred embodiment of the sampler of the present invention;

FIG. 2 is a top plan view of a base member of the sampler of FIG. 1;

FIG. 3 is a perspective view of the top member of the sampler of FIG. 1; and

FIG. 4 is an elevational view of a support structure for the sampler of FIG. 1.

Referring now to the figures, an in-situ integrated suspended sediment stream sampler 10, constructed in accordance with the principles of the invention, is depicted in FIG. 1. (For purposes of this description, the term "stream" is intended to encompass any flowing body of liquid, whether natural or man-made.) The sampler includes a main body or housing 12, preferably of cylindrical configuration. Housing 12 includes side walls 14, a top member 16 and a perforated base member 18. The interior of housing 12 comprises a reduced flow sedimentation chamber generally designated 20.

A hollow adaptor 22 extends through and out of side wall 14 and is secured thereto by glue or other suitable means. The exterior surface of adaptor 22 is threaded to threadably engage cooperating threads on the interior of one end of a mounting sleeve 23. The other end of sleeve 23 frictionally engages the neck portion 24 of a funnel 26. In use, sampler 10 is oriented so that the mouth 28 of funnel 26 faces upstream to capture a portion of a flowing stream containing sediment. Arrow A indicates the direction of stream flow. The thread mounting of funnel 26 to main body 12 allows rapid exchange of funnels with different diameter openings. Larger diameter funnels may be more desirable for streams with small suspended sediment concentrations and/or low flows.

The side walls 14 and top member 16 of housing 12 are generally water impermeable while base member 18 is provided with a series of circumferentially spaced water discharge apertures 30. The number, size, and location of apertures 30 are selected, in conjunction with the restricted size of the outlet of funnel 26 to reduce the flow of water in chamber 20 to a level that permits settling of suspended sediment within this chamber. A receptacle 32 for collecting settled sediment is centrally mounted to base member 18. Receptacle 30 preferably is cylindrically shaped and extends substantially to the inner edges of appertures 30. To guard against contamination of the collected sample, receptacle 32 can advantageously be constructed of glass or other inert material. If desired, a beaker 34 made of glass, plastic or other suitable material may be inserted inside receptacle 32, which beaker can be readily removed and replaced to minimize interruption of sampling. A removable, axially extending cross baffle 33 preferably made of inert material can be advantageously employed in beaker 34 to further reduce flow therein.

Located in between receptacle 32 and side walls 14 of housing 12 is an intermediate channeling means 36 which serves to channel most of the settling sediment into receptacle 32. Channeling means 36 preferably takes the form of a hollow, concentric cylindrical tube secured near its upper end to side walls 14. Channeling means 36 is sized so as to be spaced from side walls 14 and preferably to be substantially aligned with the outer edges of apertures 30. The lower end of channeling means 36 terminates short of base member 18 and is open allowing water passage therethrough. As shown, nipple 22 connected to neck portion 24 of funnel 26 extends through channeling means 36 so that incoming sediment containing water is directed in the general direction of arrows B and C with sediment settling as shown by arrow D in receptacle 32 and excess water flowing out of the sampler through discharge apertures 30 as shown by arrow E.

As shown in FIG. 3, top member 16 preferably has a circular cross section with external threads for threadable engagement with matching threads provided on the interior of the top portion of side walls 14. A boss or protruding external cap 38 mounted on the exterior surface 40 of top member 16 provides a convenient handle for screwing in or unscrewing the top member 16 with respect to the housing. Cap 38 has a square cross section or other configuration which allows easy hand gripping and torque application. An aperture 42 extending through cap 38 provides a convenient channel for receiving a supporting rod, as more fully described hereinafter. Threaded base member 18 is also threadedly mounted to the side walls 14 of the housing and can be provided with a similar end cap 44 also having a through hole 46. The thread mounting of top member 16 and base member 18 allow ready disassembly of the sampler for ease of sample removal and cleaning.

Sampler 10 can be supported at a desired depth in flowing water by a support stake 50 mounted on or secured in stream bed 51, as shown in FIG. 4. Rods 52 extend generally horizontally from anchoring stake 50 to an adjustable positioning rod 54 which supports the sampler 10. U-shaped clamps or other suitable securing means 56 are attached to the distal ends of rods 52 and allow both vertical adjustment and ready removal of positioning rod 54 and the connected sampler 10. Sampler 10 is secured to positioning rod 54 by an upper threaded rod 58 and a lower threaded rod 60. Rod 58 extends through aperture 42 of top cap 38 while rod 50 extends through aperture 46 of bottom cap 44. Nuts threadably engaged with rods 58 and 60 can be used to position and secure sampler 10 to these rods.

The sampler of this invention can be used singly or in lateral or vertical nests. More than one sampler can be secured on positioning rod 54 to collect samples from varying depths. Similarly, a lateral array of samplers can be used to collect samples from within different areas of the stream profile. Samplers can also be located at various sites providing a means of determining sources of stream contaminants or metals of economic interest.

The sampler mounting system described was designed for shallow water (less than 1.5 m) and is best suited for positioning in alluvium, although it can be used in areas where bedrock joints or fractures enable wedging of the supporting stake. Other support structures for maintaining the sampler at a desired depth and with an upstream orientation in any body of flowing water can of course be used.

The operating principle of the sampler of the present invention is to funnel suspended sediment into the sedimentation chamber where flow is reduced sufficiently to allow sedimentation, with the settled sediment being collected in the receptacle within the chamber. A prototype sampler was constructed of poly vinyl chloride with the sediment collecting receptacle made of clear cellulose acetate butylate. The sediment receptacle had an inner diameter of about 5.8 cm, the intermediate cylindrical channeling means an inner diameter of about 7.6 cm and the housing a 10 cm inner diameter. The discharge apertures had a diameter of about 1.2 cm. The prototype was field tested by positioning it at about 0.75 m water depth in a running upstate New York stream with the funnel opening facing upstream at about 0.1 m above the stream bottom. Flow of the stream varied from about 3.5-5.0 m/sec. and the suspended sediment varied from 2.0-5.0 mg/l during the seven day test period. The sampler collected 1.2 dry grams of suspended sediment during this test period indicating that, if 100% of the suspended fraction was trapped by the sampler, between 600 and 240 liters of water passed through the sampler during the test period. A more realistic sampling efficiency of 10% suggests the sampler processed 6,000-2,400 liters of water during the seven day period.

From the foregoing, it will be appreciated that a suspended sediment stream sampler has been described which is capable of continuously sampling a flowing stream over an extended period of time. The sampler of the present invention collects sediment rather than a sediment-water mixture collected by prior art integrated samplers and therefore eliminates the need for subsequent filtering or centrifugation of the sample. This sampler is passive, self-activated and can be readily deployed and used without any ancillary power or accessories, at remote and otherwise inaccessible sites. The sampler is simple, inexpensive, lightweight and easily serviced and cleaned. It affords an efficient, independent sampling technique, relying upon the natural sedimentation process and facilitating collection of integrated samples. Although specifically designed to collect suspended sediments for environmental monitoring, the sampler can also be advantageously utilized to determine lateral and vertical suspended sediment variations within a stream and for geochemical prospecting. The sampler is simple to set up and can be left unattended for extended periods of time.

Although a preferred embodiment of the sampler has been described and depicted, it will be readily apparent to those skilled in this art that numerous modifications, substitutions, and the like may be made without departing from the spirit of the invention. By way of example, other funnel mounting mechanisms or sampler supporting structures can be employed. The invention is intended to encompass all such variations which fall within the scope of the appended claims.