Upper Section (Capps Bridge to Lancing Brook)

A combination of new channel creation and increased wetting of the floodplain is proposed to enhance this reach. The three principal constraints comprise the road bridge, the access track to Pound Farm and the footpath route from Trollards Barn to Tenchford Cottage.

7.2.1 Floodplain wetting

Within two hundred metres of Capps Bridge a tributary stream (Spring Wood Stream) joins with the main river from between Capps and Charlwood woods. It is reported by the landowner that this tributary flows for much of the year, but no data is available. Above the farm track,

enhancement work will centre on diverting this tributary stream onto the eastern side of the floodplain, following the low areas identified in the topographic survey (Plan A). Initially a shallow ‘swale’ may need to be excavated to provide a route for this diverted flow, but in general the principle is to allow shallow surface wetting by overland flow. At times of high flows the increased volume of surface water may flow far enough to the south to rejoin the (new) River Adur, just above the access track. At other times evapotranspiration may exceed inflow and only keep wet the upper floodplain.

7.2.2 New Channel

Just above the weir at Pound Farm, a new channel will lead off to the left of the existing course. This is shown following the low depressions and old drainage network on a sinuous course across the floodplain. This new course picks up an area where standing water persists after high flows and heavy rainfall. In some areas the new channel will invariably drain these

communities, but similar hollows and depressions can be excavated in the adjacent floodplain. Although the main depression in this area currently holds vegetation of wetland interest, such as water crowfoot (Ranunculus peltatus) and water starwort (Callitriche sp.), it is expected that such species will colonise similar wet depressions created to the north by the diversion of Spring Wood Stream.

The new channel will re-enter the Adur approx. 50m further downstream from the Lancing Brook confluence. This entry point needs to be designed to reduce headward erosion if bed and flow levels differ significantly between the two channels.

Along the new channel, two woody debris jams will be constructed from whole trees, branches and twigs. These features will require a ‘standard’ design for costing and construction purposes. On-site supervision will be needed to ensure that this basic design is interpreted into the

naturalistic features envisaged (Figure 7. 4)

7.2.3 Footpath and farm access track

Shortly after the start of the new channel it will cross the existing access track to Pound Farm. A ford will need to be constructed to maintain continued access.

Half way along the new channel, at approx. chainage 1350, the footpath crosses the floodplain. Old structures indicate that the footpath may have been raised above the floodplain level to allow access when the surface was waterlogged. Reinstatement of this raised footpath, in conjunction with a bridge over the new channel is likely to be necessary to accommodate the requirements of the West Sussex Rights of Way Officer. This will provide a restored and (for the purposes of those who now use the path) a significantly more usable route.

7.2.4 Old course

Ensuring that Capps Bridge and the road are no more prone to flood risk than at present requires careful siting of the off-take to feed a new channel. Currently a weir exists at the farm access

crossing. This crest level will define the overspill into the new channel. Above the weir, no major alterations will be undertaken that could affect the potential for river levels to back up and impact on the bridge. Small woody material, twigs and branches will be incorporated into this section to provide source material for the new channel (Appendix F2).

Below the farm sluice the old course is retained. This channel is still valuable as an additional flood channel in flood flows, and as a still/slow water habitat. The existing riparian trees will continue to provide leaf litter, branches and the occasional whole tree to the river system. This is important in the short to medium term as any new planting/colonising growth will take at least 10 years to provide such input to the river system.

7.2.5 Tenchford Cottage

Tenchford Cottage requires flood proofing to protect it from current and future flood risk. A specific study of the property, flooding routes and possible solutions should be undertaken. It is likely that a flood bund and a small sump and pump system will be needed to manage risk to the property. A brief inspection of the cottage revealed an existing barn in a state of disrepair with signs of road runoff entering the garden from the road through the barn wall. There appears to be room to create a flood bund around the property tying in with the high ground, except where the barn sits tightly between the cottage and road. It may be necessary to rebuild the barn, incorporating a low floodwall into the structure to link in with the bunds.

As the cottage is outside the project floodplain boundary, detailed solutions for its protections have not been drafted. Such bunding, etc. is likely to be undertaken locally to the property.