GB2415455A

GB2415455A - Drainge channel assembly

Info

Publication number: GB2415455A
Application number: GB0413922A
Authority: GB
Inventors: Quintin Anthony Murfin
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-06-22
Filing date: 2004-06-22
Publication date: 2005-12-28
Anticipated expiration: 2024-06-22
Also published as: GB2415455B; GB0413922D0

Abstract

A drainage channel assembly for receiving water from a paved surface (1) comprises a valved drainage channel (2), one or more vegetated filter strips (3) and, optionally, one or more modular cellular redistribution weir strips (4), wherein outfall from the drainage channel (2) is controlled by of a shut-off valve, such that, in the event of a rainstorm the valve can be closed in order to retain polluted water in the channel for subsequent treatment and disposal, and excess water overpasses the channel and flows across a vegetated filter strip (3) and, optionally, into a redistribution weir strip unit (4). A redistribution weir strip (4) is formed from water retaining modular units (6) filled with gravel up to at least the retained water level (9). The unit is characterised in having a water retaining downstream edge with a level weir edge crest that creates weir flow. Preferably, the weir strip units are provided with closely space v-notch weirs along the level weir edge that redistribute water across the vegetated filter strip in a uniform manner.

Description

iv - 24 15455

CONTROLLED FILTER STRIP

Background to the Invention

A filter strip consists of a vegetated verge, often grass, adjoining a paved area, receiving water from the paved surface and used as an element of a surface water treatment and disposal system. The paved area is laid to surface falls so that the flow of precipitation generated surface water runs off the paved area and across the vegetated strip. A filter strip is laid to a shallow fall so that with the high frictional resistance of the vegetation the water flow rate is slower than across the paved surface. The slowing of the velocity of flow causes silt entrained in the flow to precipitate out. Some entrained pollutants will attach to the grass and soil and may break down by aerobic biodegradation. Some of the water may infiltrate into the soil if it has a well-managed biological structure, disposing of the water to the soil where it is lost to evapotranspiration of the vegetated soil and to groundwater by peculation down through the soil.

Problem of the invention Areas such as Airfield Runways and Taxiways, and other paved areas, may be subject to the deposition of activity-generated pollutants such as hydrocarbons or the application of de-icing chemicals such as glycols. The initial flow offa surface washes off deposited pollutants which results in the first flush of water arising from a rainfall event being significantly more polluted than runoff in the later part of the storm event. Where such pollutants raise the runoffpollutant levels above the limit for infiltration to meet the local requirement to protect groundwater, filter strips are not acceptable as a receiving system for the first flush of runoff from a rainfall event and hence filter strips cannot be used with in such circumstances. Filter strips require a uniform flow of water across the vegetated surface to enable the greatest efficiency of treatment and infiltration. Flow in filter strips will tend to concentrate to flow lines as the distance travelled increases because of the variability in constructed surface profile and the variation in resistance of the vegetation due to species mix and growth variations. This will leave gaps in the flow that prevent the utilisation of some of the area for infiltration. This problem increases with increasing filter strip width.

Solution of the Invention in accordance with the present invention it has been appreciated that by designing a pavement edge drainage system that diverts the initial first flush of runoff from a pavement to an appropriate treatment process, the remainder of less polluted runoff may be disposed of by infiltration in a filter strip with a biologically well managed vegetated soil surface. The separated more highly polluted first flush runoff is treated before appropriate disposal. An object of the invention is to provide a system that collects the first flush of more polluted runoff from a paved surface and diverts it to treatment system, allowing the post first flush flow to be disposed of by flow across a profiled wide vegetated soil filter strip where evaporation and infiltration to soil can occur. When the flow exceeds the capacity of the filter strip to take up water, the excess runoff is collected at the end of the filter strip for re-application to the filter strip or disposal, if necessary, via an appropriate treatment process.

The diversion of the first flush flow can be by either of the two following methods.

The first method consists of a drainage channel system with a shut off valve- controlled outlet. The channel has a volume equal to the first flush runoffvolume for the cathchment. At the start of a storm event the channel outlet is closed and the first flush ofthe rainfall event runs off the pavement into the channel until such time as it is full. When the channel is full it overtops and the remainder of the storm event runoff flows over the channel to the adjoining filter strip. After the storm event is over the channel is emptied by the opening of the valved outlet to allow the polluted water to flow to an appropriate treatment and disposal system. The valve is then closed and the system is then able to receive the next storm first flush. The second method is to have a drainage channel system sized to be able to discharge the maximum design first flush flow rate. The channel receives the flow and discharges it via an open outfall to appropriate treatment until such time as the flow has been measured by monitoring equipment to have completed the first flush volume for the storm profile that is occurring. The channel outlet is then closed and the channel backs up and the overtopping flow from the channel runs over the weir edge of the channel to the adjoining filter strip. After the storm event end the channel first flush content is discharged to by opening the outlet to appropriate treatment and disposal. Either of these first flush collection channel systems could be combined with a second downstream channel as a separating system for traditional drainage.

It is also appreciated that by providing within a filter strip level redistribution weir strips that the flow down the filter strip can be directed to have a more uniform coverage of the available vegetated surface, with the benefit of better utilisation of the infiltration capacity of the vegetated surface. The strips consist of a linear collecting face that feeds a ponded distribution channel, which has on the outlet face with regularly spaced discharge weirs that are set at a uniform level to create a uniform redistribution of flow to the next band of filter strip. The channel may be gravel filled for convenience of access and the avoidance of open water attraction of birds.

A preferred embodiment of the system is shown in the following diagrammatic drawings: Figure I shows a vertical cross section through the system.

Figure 2 shows a vertical cross section through the head channel Figure 3 shows a vertical cross section through a redistribution weir strip Figure 4 shows an isometric sketch of a modular redistribution weir strip container unit In Figure I a Paved Surface 1 is laid to a standard paving drainage fall so that rainfall runoff flows toward a Head Channel 2 which is a channel with a continuous slot entry sized to hold the volume of the first flush of runoff from the pavement. The first flush is the amount of rainfall that is deemed to generate runoff containing pollutants exceeding the level acceptable for disposal to the grass filter strip. The Head Channel has an outlet that is valve controlled. Prior to a rainfall event the valve is closed so that the first Rush of a rainfall event is retained in and fills the Head Channel 2.

When the Head Channel 2 is full it will overtop over the right hand side in Figure 1,2 over the longitudinally level edge, which may have closely spaced v notch weirs formed along the top edge and distribute the water across the first band of I;ilter Strip 3, Figure 1. In Figures 1,3 the Redistribution Weir Strip 4 shown with the right hand edge forming a Level Weir. The Redistribution Weir Strip 4 is formed from water retaining Modular Units 6, Figure 4 which are preferably made of durable plastic designed to accommodate any vehicular loading the units are expected to experience in operation. The Modular Units 6 are filled with open graded Gravel 7, Figure 3 up to at least the retained Water Level 9, Figure 3. The gravel reduces the amount of open water and hence reduces the attractiveness to water birds. The Modular Units 6, are laid level and butted and sealed together to create a continuous water retaining channel with a Level Weir Edge 8 with v notches a frequent regular intervals to uniformly distribute the water leaving the Redistribution Weir Strip 4 to the next band of Filter Strip 3, Figures 1,3. This sequence of Filter Strips and Redistribution Weirs Strips can be replicated to suit the grassland width utilised. The Redistribution Weir Strips are spaced so as to ensure reasonably uniform flow is achieved between Redistribution Weir Strips across the Filter Strip for efficiency of utilization of the grassland. The grassland should be managed to ensure a good biological soil structure that allows infiltration to occur. Infiltration of some of the water occurs as the water passes over the filter strips. The runoff from larger rainfall events may exceed that which can be infiltrated by the Filter Strips and an excess runoff may flow to the Tail Channel 5, Figure 1. This excess runoff may be and re-circulated by pumping to irrigation sprays that apply the water to the grassland or disposed of in other appropriate ways.

Once the storm event is complete the Head Channel outlet valve is opened and the first flush content is disposed of via the outlet to an appropriate treatment and disposal -- method. The valve is then closed again and the system is set for the next rainfall event.

Claims

1. A pavement edge drainage channel that detains or diverts rainfall event first flush flow resulting in subsequent overtopping of post first flush runoff to vegetated filter strip disposal, the channel contents being emptied for separate treatment and disposal following the rainfall event.

2. Redistribution weir strips consisting of modular weir units that evenly redistribute water across a vegetated filter strip. 5

Amendments to the claims have been filed as follows

I. A drainage channel (2) and filter strip (3) for receiving water from a paved surface ( I) characterized in that the channel outfall is controlled by a shut off valve that is closed before rainstorm events so that the first flush of more polluted water running off the paved surface detained in the channel for treatment and disposal after the cessation of the storm event fills the channel causing post first flush surface water flow from the paved surface to overtop the channel and flow across a vegetated filter strip.

2. A filter strip as claimed in claim I, wherein there is means of redistributing water across the vegetated filter strip in a more uniform manner consisting of modular cellular redistribution weir strip units (4) characterized in that the units have a water retaining downstream edge with a level weir edge (8) crest that creates weir flow.

3. A Channel as claimed in claim I which has closely spaced v notch weirs along the downstream level crest of the channel side that distribute water across the vegetated filter strip in a more uniform manner.

4. Redistribution weir strip units as claimed in claim 2 which have closely spaced v notch weirs along the level weir edge (8) that redistribute water across the vegetated filter strip in a more uniform manner.

5. Redistribution weir strip units as claimed in claim 2 which are constructed of durable plastic.

6. Redistribution weir strip units as claimed in claim 2 which are filled with inert media to reduce the amount of open water surface and attractiveness to birds.

7. A drainage channel and filter strip as herein described and illustrated in the accompanying drawings.