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FLOODING

Hassocks is a village that floods. Just in this century, flooding has occurred in 2000, 2003, 2008, 2012 and 2014. 685 Hassocks homes are at risk of surface water flooding. 

See the image of Lodge Lane in flood.

With climate change we can expect more intense weather events – more flooding and more droughts.  Existing problems are likely to become worse.

See the image of Dale Ave flood.

Streams:

The major cause of flooding in Hassocks is the Herring stream and its tributaries, which drain northwards from the Downs to join the River Adur near Twineham.  The chalk downs act as a giant sponge absorbing and holding rainwater, releasing it slowly via springs into the streams.  When the sponge gets full any additional rain runs off quickly into the streams, which can increase from a few inches deep to several feet within a few hours. 

 

See the stream flood map 

 

There are two main ‘pinchpoints’ that constrain the stream flow: one at Spitalford Bridge and the other at the top of Woodsland Rd where the stream goes under the railway.  At times of high flow the water can’t get through the pinchpoints and backs up, flooding neighbouring gardens and even houses.

Surface water drains:

The water in the stream is only part of the problem. In urban areas rainwater is collected by roofs, driveways, roads and car parks and drains into the storm water drain system – which discharges straight into the nearest stream. During rainstorms this adds to the volume of water already running in the stream, increasing the likelihood of flooding.

What can be done?

Natural flood management can ‘slow the flow’ of water through the streams by planting trees to absorb rainfall, digging seasonal ponds to allow streams to overflow in winter, creating debris dams to reduce peak flows.  We are working with the Ouse and Adur Rivers Trust on projects like these.

See Lagg Wood debris dam

Rainfall runoff from roads, roofs, driveways and other paved surfaces can be slowed down by simple projects that anyone could do at their own home – water butts, rainbox planters, garden ponds.  We also need larger projects like rain gardens and swales. Collectively these measures are known as Sustainable Drainage Systems or SuDS. See our dedicated page for more ideas on what can be done.

Rain gardens

Rain gardens are dug into the ground, filled with permeable materials and topped with permeable soil, then planted with vegetation that can withstand occasional short-term flooding.  

Street rain gardens can be installed in the verges along roads to collect rainwater. They can be planted with grass, wildflowers or other kinds of plants.

Our first Hassocks rain garden has been completed in Adastra Park [add photo]. It takes rainwater from the roof of Adastra Hall and holds it temporarily, allowing it to be absorbed slowly into the ground.

The second demonstration rain garden in Adastra Avenue is in the planning stages and should be created later in the spring of 2019. See more on our dedicated page on rain gardens.

Your rain pics please

Hassocks has been identified as a West Sussex ‘wet spot’ with 685  properties at risk of flooding ‘in frequent to extreme rainfall events’. Can you help to highlight the problem by taking a quick photograph next time there is a really heavy downpour and your garden, your road, is subject to flash flooding?  Your Suds group (Sustainable Urban Drainage Systems), led by HKD Transition and Hassocks Community Organisation hope to build up a picture of the worst ‘wet spots’ in our ‘wet spot village’ and perhaps come up with some ideas to reduce the problems.   So it’s important to indicate clearly both when and where the picture was taken. The most useful photos will show the cause of the flooding as well as the result. Either email to us at herring@hkdtransition.org.uk or if you use Instagram you can follow us at hkdtransition and add #Hassocksfloods to your images.

HERRING STREAM

Last winter volunteers became beavers for the day and made some experimental ‘debris dams’ in Butchers and Lag woods – these worked effectively to slow down the flow of water in the Herring Stream in times of heavy rain, while still allowing fish to swim through.  So this winter we’ll be making more.  If you’d like to join the volunteer team who get to play in the woods with sticks and splash around in streams, please email herring@hkdtransition.org.uk and we’ll let you know when projects are happening. 

 

Many of us have seen the brown trout by Spitalford Bridge. But what about the stream life that is harder to see?  Volunteers from HKD Transition and the Hassocks Amenity Association have been surveying aquatic life in the Herring stream where it enters the village in Parklands Copse, and where it leaves at Friars Oak.  After quarterly stream surveys we have a much better sense of stream life than when we started in January 2016.

Shrimp are the only species we found in every sample at both sites, but Bullhead fish are almost always present. 

 

We commonly find larvae of different species of mayfly, caddis fly, blackfly and midges, sometimes cranefly and demoiselle larvae.  There are worms, segmented or flat, and snails or bivalve molluscs.  Often Riffle beetle or Diving beetle larvae appear (and sometimes the beetles themselves), and we have found leeches several times.

All of these creatures are fascinating to watch.  There was the time that a mayfly larva hatched out in the warmth from the microscope (we put it outside but it probably didn’t survive the cold).  Some Caddis fly larva make a ‘case’ from sticks and stones to protect themselves from predators: one of our favourites had incorporated a tiny piece of gold tinsel into its home.  There have been rarities like the larva of Atrichops crassipes, the Least Water-snipefly.

We have found differences between our two sites: contrary to expectations, Friars Oak consistently has more species (and more of the species that are especially sensitive to pollution) than Parklands Copse.  It may be because there is more water in the stream by Friars Oak, as five more tributaries join the Herring through the village.  It may be that there are issues relating to the upstream farmland.  We’re now changing our sampling sites so we can get a better sense of the whole stream.

We volunteers are learning as we go along, with a lot of training and support from the Ouse and Adur Rivers Trust.  We start wading in the stream, measuring water depth and speed, then use our dipping net to gather a sample from the stream bed.  The bullhead fish are counted and put back in the stream immediately, and the rest of the sample is returned to the same site after identification.

Indoors a digital microscope linked to a laptop allows us to identify the tiny invertebrates hiding in the sample.  It looks like mud and sticks when we spread it in trays, but study closely and things start to move. The shrimp are easy: they dart about in a characteristic sideways movement.  Others are harder to spot.  Only with a long look does a piece of twig suddenly appear to have legs, identifying it as one of the Cased Caddis fly larvae. A tiny black dot reveals itself under the lens to be a water mite. A puzzle over which species of mayfly larva we’re looking at requires working through keys in several reference books.

For non-biologists the quarterly glimpse of what lives alongside us in the Herring stream is captivating. 

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