STORMWATER SEDIMENT AND LITTER TRAP

Abstract: Apparatus for trapping and retaining flotsam from flowing stormwater, comprising a movable perforated baffle (5) placed across the lower part of a culvert to direct the flow of stormwater downwards into a chamber. The chamber is roofed by a perforated deck (9) which rises and broadens gradually with increasing distance downstream, in such a manner as to constrain the flow and direct it into a meshed collection basket (10). Flow can escape the chamber and baskets only by passing through the mesh surface thereby being filtered to remove litter, detritus and particulate matter.

Description: STORMWATER SEDIMENT AND LITTER TRAP TECHNICAL FIELD This invention relates generally to improvements in devices for the removal of a range of pollutant materials from flowing stormwater and the retention of these materials for later collection and disposal. BACKGROUND ART The escape of a wide range of pollutant materials into water-bodies has become an important concern of stormwater managers and of the public generally in recent years, and various systems have been introduced to drainage systems for the purpose of mechanically removing litter and detritus from flowing stormwater and encouraging heavier materials to settle out so that they can be routinely removed for safe disposal.. One such prior art system is disclosed in my earlier International Patent Application No. PCT/AU97/00100 (WO 97/31162). Some systems incorporating screens have failed because their screens have become rapidly clogged by litter and detritus. Some systems have been unable to retain materials trapped during one storm during a later more intense storm, allowing them to be re-suspended in the more vigorous flow and thus pass downstream. Some have screening systems which are too coarse to consistently capture small litter items such as cigarette butts. Some systems have application only to partial flows diverted from the main stream for treatment because they are unable to safely convey the larger flows for which the main conduit is designed. Some systems have application only to conduits in the small to medium range, say up to 1200mm in diameter. Some have a significant retarding effect on flows either due to their intrinsic characteristics or due to some failure in their operation which may result in the reduction of conveyance capacity in upstream systems and cause flooding. Some systems are so configured as to totally confine flows downstream of some point in their construction such that a person or animal caught in the stream can be carried past that point and have no avenue of escape. OBJECTS OF THE INVENTION It s an object of the present invention to provide an improved means of trapping and retaining stormwater litter and sediments which goes at least some way towards overcoming or at least minimising the prior art problems or limitation outlined above, or at least providing a clear alternative choice for stormwater and pollution control authorities. It is another object of the present invention to provide an improved means of trapping and retaining floating and neutrally buoyant pollutant particles as small as a few millimetres in diameter and to provide an improved means of settling and retaining heavier, fine-grained pollutant particles while generally dealing with each of the difficulties of existing trash-rack and sediment-trap systems which have been identified above. It is a further object of the present invention to provide an improved means of trapping and retaining flotsam, neutrally buoyant particles down to several millimetres in diameter, and filtering and settling heavier particulate matter within the matrix of larger materials captured by filtration screens and retaining them through intense later flows while generally dealing with the difficulties of existing trash-rack and sediment-trap systems such as those which have been referred to above. It is yet another object of the present invention to provide a stormwater litter and sediment trap which is relatively simple in both construction and operation, relatively inexpensive to manufacture and which is easy to clean and to maintain. These and other objects of the present invention will become more apparent from the following descriptions and drawings. With the above objects in view, the present invention resides in certain novel features of the construction, combination and arrangement of elements or integers as will be hereinafter described in detail in the specification, particularly defined in the appended claims and illustrated in the accompanying drawings. DISCLOSURE OF THE INVENTION According to one aspect of the invention there is provided a pollution control device for removing litter and sediments from a flowing stream of water as it is discharged from a stormwater outlet, wherein a perforated baffle is placed across a lower part of said stream or outlet to direct the flow of water downwards and into a chamber roofed by a perforated deck which rises and broadens gradually with increasing distance downstream, in such a manner as to constrain the flow of water and direct it into an apertured or meshed collection container or basket, such that flow can escape the chamber and basket(s) only by passing through the apertured or mesh surface thereby being filtered to remove entrained litter, detritus and particulate matter. Preferably, a perforated barrier downstream of the above described assembly causes a weir pool to form which causes sediments to settle in the chamber and basket zone. One particular application of the present invention relates to the stormwater discharging from a box culvert into a water course, pond or other water body and it will be convenient to describe the invention with reference to that particular application. It is to be understood that this is not to limit the escape of the invention which has application to all other forms of open and closed conduit and may be used anywhere along the line of such conduits in a covered or open situation and in single or multiple configurations. When the chamber becomes clogged with materials removed from the flow or the flow becomes so great as to exceed the capacity of the mesh to pass it through, the water level builds behind the baffle until the force applied to the baffle is sufficient to raise it on its supports. When this occurs the hinged baffle is foreshortened in its dimension in the direction of the flow as it bends around its internal hinge point. The baffle is also hinged at its downstream support but is fixed both vertically and horizontally at this pivot point so that the foreshortening results in the upstream end of the baffle moving away from its supporting bosses on the culvert walls so that it is able to fall through the flow to take up a new stable position resting on the culvert floor or on some other supporting structure provided. As the baffle descends it is preferably trailed by a grill which is hinged at a point upstream on the culvert floor and leans upon the baffle during the active filtration phase to ensure that large debris does not pass into the lower chamber or that a person being carried along the stream is directed over the baffle to safety. The grill is preferably built in the form of a ladder to assist escape and is preferably sloped to encourage large debris to be upswept and pass over the baffle. The grill preferably is also so constructed as to house flush with the culvert floor after descending with the baffle, so as not to impede following flows. During the descent of the baffle, the assembly is damped in its fall by the need to expel water through the mesh surfaces which are its only escape, so that the fall is relatively gentle and litter which might lie against the underside of the baffle at the instant of release will continue to be contained and pass into the secure receiving chamber. The effect of the assembly assuming this altered stable position is that the obstruction to flow in the culvert is removed and a smooth transition to a widened channel is established downstream of the culvert so that there is little or no impedance to culvert flow as compared to conditions pertaining prior to device installation. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention will now be described by way of example only and with reference to the accompanying drawings, wherein:- FIG. l shows a longitudinal section of a stormwater culvert and litter trap assembly according to one embodiment of the present invention with the system in filtration mode; FIG.2 is a further longitudinal section of the culvert and trap assembly of FIG.l, immediately after release of the baffle; FIG.3 shows another longitudinal section of the culvert and trap with the baffle and safety gate in their major storm position; FIG.4 shows a longitudinal section of the baffle it its at-rest position braced between its two end supports; and FIG.5 shows a longitudinal section of the baffle of FIG.4 in its raised position just at the point where the striker plate is about to clear it support and allow the baffle to descend. BEST MODE OF CARRYING OUT THE INVENTION FIGs 1 to 3 show longitudinal section views of a stormwater culvert and litter trap assembly in different modes during a major stormwater flow event. FIG.l shows a longitudinal section of the culvert and trap assembly with the system in filtration mode. The culvert (1) has part full flow at water level (2) in the direction shown by the arrow (3). The grill (4) rests against the baffle (5) which has a vertically and horizontally fixed hinged support (6) and a second support (7) upon which the baffle is free to slide in the downstream direction but restrained from moving either upstream or downwards. The baffle has an intermediate hinge (8) which is arranged to maintain a slightly concave downward attitude in the assembly such that the baffle is supported by bracing action between support (6) and (7). The hinge (8) allows limited upward movement under the force of moving water as the water is deflected downward by the baffle such that the distance between the upstream and downstream baffle edges is shortened, to the extent that it is no longer supported by support (7). The baffle elements are so ballasted that, under normal operations, this state of foreshortening is reached just as the baffle begins to overtop as the water level in the culvert rises. The baffle overtopping level -is set with regard to leaving sufficient space above it for debris passage and for a person caught in the stream to escape. Water passing through the trap in filtration mode may exit through perforated baffle surfaces, through the perforated deck (9) or through the top, bottom, sides or downstream end of the litter receiving basket (10). A perforated fence (1 1) across the full flow width retains a stilling pool through the trap to facilitate sediment settlement while releasing water slowly to allow the assembly to drain fully when inflow ceases. FIG.2 shows the trap assembly a few moments after the release of the baffle from its upstream support as it descends to the culvert floor. Arrow (12) shows the baffle rotation about pivot point (6). The safety gate (4) follows the baffle (5) to the floor. FIG.3 shows the arrangement with the baffle (5) and safety gate (4) in their major storm position and the culvert flow at high level. The major part of the flow now passes over the deck and basket system after passing the smooth transition created at the culvert outlet by the lowered baffles. The disturbance to already captured litter and sediment is thereby minimised. FIG.4 shows a longitudinal section of the baffle (5) it its at-rest position braced between its two end supports (6) and (7). FIG.5 shows a longitudinal section of the baffle (5) in its raised position just at the point where the striker plate (14) is about to clear the support (7) and allow the baffle to descent. Stormwater with entrained litter is filtered or screened by means of the litter trap assembly. Litter reaching basket (10) includes a proportion of fine particles, some of which settle within the basket or on the basket walls. Those particles which pass through the mesh fall to the floor of the culvert and settle against the perforated fence (11) or weir. After the stormwater has subsided, and after each event or series of events over a period of time, the basket(s) and the weir (11) can be cleared of collected debris and litter. The stormwater litter trap is preferably fabricated from galvanised steel. The expanded metal mesh from which the letter collection baskets are fabricated is preferably an apertured louvered mesh such as 'Maximesh' from BHP Steel. Although the pollution control device of the present invention has been configured and described in relation to the preferred embodiment herein as a system to facilitate maintenance by hand, to favour its use where machine access is difficult or not possible, other embodiments of the invention adapted for mechanically assisted servicing but incorporating all of the inventive features of the embodiments described herein, are encompassed by the invention. Although an exemplary embodiment of the present invention has been shown and described, it will be apparent to those having ordinary skill in the art that a number of changes, modifications or alterations to the invention described herein may be made, none of which depart from the spirit of the present invention described herein may be made, none of which depart from the spirit of the present invention. All such changes, modifications and alterations should therefore be seen as being within the scope of the present invention. It should be appreciated that the present invention provides a substantial advance in the removal of a range of pollutant materials from flowing stormwater, providing all of the herein disclosed advantages without incurring any relative disadvantage.

Claims: CLAIMS 1. A pollution control device for removing litter and sediments from a flowing stream of water as it is discharged from a stormwater outlet, wherein a perforated baffle is placed across the lower part of said stream or outlet to direct the flow of water downwards and into a chamber roofed by a perforated deck which rises and broadens gradually with increasing distance downstream, so as to constrain the flow of water and direct it into an apertured or meshed collection basket, such that water flow can pass through the apertured or mesh walls thereof, said water thereby being filtered or screened to remove entrained materials. 2. A pollution control device for removing litter and sediments from a flowing stream of water as it is discharged from a stormwater outlet, wherein a perforated baffle is placed across said stream or outlet between an upstream end of said flowing stream proximal to said outlet and a downstream end of said flowing stream distal to said outlet, and wherein a perforated or meshed collection basket is provided adjacent to said downstream end and wherein said perforated baffle is adapted to hinge between a first position wherein a flowing stream of water discharged from the stormwater outlet is urged to pass through the perforated baffle and the collection basket, and a second position wherein a flowing stream of water discharged from the stormwater outlet is urged to pass over the perforated baffle and to bypass the collection basket. 3. A pollution control device as claimed in Claim 2, wherein the baffle is trailed by a grill which is hinged at a point upstream on a floor of said stormwater outlet and rests adjacent its opposite end against the upstream end of the baffle, whereby when said baffle adopts its second position the grill hinges to a substantially horizontal position to overlie the upstream end of the baffle. 4. A pollution control device is claimed in Claim 2 or Claim 3, wherein the baffle is hinged both at its lower or downstream end and at intermediate positions substantially centrally along each longitudinal side thereof, and is supported at its upper or upstream end by a ledge or latch means, whereby the hinges at the intermediate positions allow limited upward movement of the baffle under the force of the flowing stream of water as the water is deflected downwards by the baffle, such that the distance between the upstream and downstream baffle edges is shortened thereby dislodging the baffle from its upstream end supports. 5. A pollution control device is claimed in any one of the preceding claims, wherein one or more components thereof is fabricated from expanded metal mesh. 6. A pollution control device is claimed in any one of the preceding claims further comprising a sediment sump or a sediment weir at its downstream end. 7. A pollution control device is claimed in any one of the preceding claims, wherein the collection basket is of modular construction to enable expansion of the size of the collection chamber.

Inventors: NICHOLAS DOUGLAS IAN, NICHOLAS, DOUGLAS, IAN
Applicants: NICHOLAS DOUGLAS IAN, NICHOLAS, DOUGLAS, IAN
Application year: 2000
Main classification: E03F1
IPC codes: E03F5