Stormwater gullies are used to collect surface water run off, usually from non-porous ground surfaces such as roadways, pavements and other paved areas. Water from the ground surface flows into the gully through an opening at the surface, usually covered by a grating. The gully may also receive flow from underground drains. The gully has an outlet, which is usually connected to a main sewer or outfall.
The gully outlet is usually above the bottom of the gully, so that the lower region of the gully serves as a sump in which solid contaminants of the flow are retained for periodic extraction, so that the water passing to the main sewer is free of at least some of the original contaminants. Also, in periods of heavy flow when the inflow is greater than the maximum capacity of the gully outlet, water will build up in the gully to be discharged later when the incoming flow rate subsides. Such a gully is disclosed in U.S. Pat. No. 7,005,060. In that gully, water flowing from the gully chamber to the outlet passes through an up-flow filter and into an outlet housing, from which the gully outlet extends. Because flow through the filter is upwards, solid contaminants are caught on the underside of the filter and so can fall from the filter into the sump at the bottom of the gully when incoming flow rates subside. The filter restricts the rate of flow towards the gully outlet, and consequently, under periods of heavy incoming flow, the water level in the gully will rise above the filter. A bypass is provided which comprises a weir over which water can flow directly into the outlet housing, and thence to the gully outlet without passing through the filter.
A problem with such gullies is that the flow rate over the weir under conditions of high flow may be inadequate to avoid flooding of the overlying surface. Also, when flow into the gully eases so that the level drops below that of the weir, discharge from the gully then takes place only through the filter. Consequently, the level of water in the gully falls only slowly, leaving little safety margin if one period of heavy rainfall is closely followed by another.
According to the present invention there is provided a stormwater gully comprising a chamber in which an outlet assembly is disposed, the outlet assembly comprising an outlet housing having a primary inlet, provided with a filter unit, for admitting stormwater from the chamber into the outlet housing through the filter unit, and a bypass unit comprising a weir situated at a higher level than the primary inlet for enabling flow of stormwater from the chamber into the outlet housing over the weir, thereby bypassing the filter unit, the outlet housing having an outlet extending from the chamber, the weir being enclosed by a top cover of the outlet housing so as to define a siphon through which liquid may flow from the chamber into the outlet housing.
The provision of a siphon means that, once the water level in the gully chamber has risen to a sufficient extent to prime the siphon, the discharge of water through the bypass inlet will take place rapidly under the siphon effect. Furthermore, the entrance to the bypass inlet can be positioned below the level of the weir so that rapid water discharge will continue even after the water level has dropped below that of the weir.
The top cover may have an arched region which extends over the weir so as to define up-flow and down-flow legs of the siphon, which legs communicate with each other over the weir.
The weir may be one of two weirs of the outlet assembly, which may be situated generally opposite each other on the outlet assembly, each weir having a respective arched region of the top cover to define respective siphons.
The arched regions of the two weirs may be connected to each other at a valley region of the top cover. The valley region may extend downwardly generally to the level of the top edges of the weirs. Beneath the valley region, the down-flow legs of the siphons merge to form a single duct extending to the outlet.
The outlet housing is preferably disposed adjacent a wall of the gully chamber.
The wall may be cylindrical, and the outlet housing may have an arcuate housing wall configured to conform to the inner surface of the cylindrical wall. In addition, the weirs, and the lower edge regions of the arched regions of the top cover, may lie in planes which extend radially with respect to the cylindrical wall. The weirs may be disposed approximately mid-way between the lower edge regions of the respective arched regions.
According to another aspect of the present invention there is provided a stormwater gully comprising a chamber in which is disposed a vessel comprising a primary inlet from the chamber, having a lower edge at a first level, and a secondary inlet from the chamber, having a lower edge at a second level higher than the first level, the vessel also comprising a drain-down outlet comprising a duct in the form of a siphon, the duct having a first portion which extends upwardly within the vessel from a first end of the duct to a crest of the siphon and a second portion which extends downwardly from the crest of the siphon to a second end of the duct disposed within the chamber outside the vessel, the crest of the siphon being disposed at a level below the lower edge of the secondary inlet.