The River Arun has a network of tributary streams some of which rise in the area of north of Horsham where Liberty (and Cllrs Dawe, Vickers, Rae and Croft) want to build 2,500-plus houses and a large industrial/commercial park.
In the natural state, heavy rainfall drains into these streams and is carried away. There was a time when landowners ensured these streams allowed clean passage for water and wooded slopes slowed the rate of run off.
The Environment Agency has responsibility for dredging and cleaning larger waterways and drains but most of their budgets seem to go on building defences. Where natural drainage is hindered by buildings, car parks for gardens, concrete foundations etc, rapid run off combined with sodden ground – means the natural drainage can’t cope.
The Environment Agency is responsible for taking measures to mitigate the risk of flooding. The Agency produced a report in 2009 (‘The Environment Agency Flood Management Plan for the River Arun and Western Streams’) in which it looked at flood risks in Horsham and throughout the Arun Valley.
This report constantly refers to the ‘increased risk (of flooding) due to climate change’, the impact of ‘urban development’ and the agency not having quantified ‘the risk associated with surface water flooding’.
For Horsham the report states ‘Urban development and increased flows will place considerably more pressure on the existing drainage network and will result in more surface water flooding, urban drainage capacity being exceeded with greater frequency and more extensive flooding from urban water courses’.
For the Pulborough area, the report lists the remedial work done and then says ‘The current level of flood risk is assessed as relatively low, although we have not quantified the risk associated with surface water flooding’.
Looking at the pictures in your paper (02.01.14) I am not sure the residents of Pulborough, Wisborough Green, Bury and Rookwood Park will feel reassured. (It is really worth looking at http://maps.environment-agency.gov.uk/ and then click on ‘Flood map for planning’. Start with RH12 4RT and then follow the course of the Arun and its tributaries southwards).
Not being able to quantify the risk seems quite unacceptable. Are there going to be major infrastructure developments to carry this excess water away from houses?
I don’t see any plans for that. Horsham District Council has not published any impact assessment for the proposed Liberty development plan on heightened flood risks down the Arun Valley.
If all these building developments go ahead in the Arun catchment area north of Horsham, I can’t see the flooding risk getting less – quite the reverse particularly if the Environment Agency goes ahead with substantial job cuts.
As climate continues to warm and these severe episodes in the weather increase, maybe there will be further infrastructure spending by the Environment Agency to contain the swollen Arun within its banks.
But surface water flooding where hard surfaces have replaced the natural drainage can affect any of us. Existing drains cannot cope and polluted water lifts off the drain covers and floods.
Is there to be a major spending on modernising the drainage infrastructure? What will be the impact on those living in the mid and lower Arun Valley of building all these structures in the upper Arun catchment? Do we know?
Owlscastle Close, Horsham