[milton-chat] Flooding

[Paul Oldham]

On 15/02/07 15:29 Clarke Brunt wrote:

> I'm no expert on this lot, but presumably the area between the railway and the
> river floods because it's scarcely any higher than the river 

Yup. When the river above Baits Bite is getting overfull they dump it as 
hard as they can below the lock (by opening both lock gates). So the 
land around and below the lock, which lies below the water level above 
the lock, floods. All the way down to Waterbeach. It's quite impressive. 
See http://the-hug.org/paul/flood/index.html for photos of the last two 
times.

> Whereas the centre
> of Milton doesn't flood because it's quite a lot higher. 

Well, hardly a lot. The edge of the flood plain is 5m above sea level. 
Our house (and yours I guess) are at about 6m. But that's a big 
difference in practice.

> It will remain this
> same amount higher regardless of the construction of the lakes, or indeed of
> anything else.
> 
>> This will obviously lower village property values
> 
> Doesn't sound obvious to me. Well not unless the flood risk altered in the
> way you presumed.

Actually the worry isn't the flood plain. The worry is local drainage 
which could produce local flooding above the present flood plain. There 
are two issues:

1. The surface drains run W-E into the river and the lake is it the way.
    The solution being proposed is to divert the land drains around the
    lake to a sump from where it will be pumped away. There's nothing
    very unusual in doing this: most of the Fens rely on pumps to keep
    from turning back into bog, but if you're a engineer like me you'll
    be muttering "single point of failure" to yourself at this point.

2. A lot of our drainage hereabouts is via ground water. Dig down 6' and
    you'll find two things: gravel and water. When it rains the water
    goes into the soil, down to the gravel layer and from there to the
    river. The lake cuts through this gravel layer and it will be
    "puddled" with clay so the gravel layer will no longer be able to
    drain into the river. The suspicion is that this will raise the local
    water table, already very close to the surface at 6' or less. If
    you've got cellars this may be an issue, as may rising damp.

I believe CSL are still undertaking or are intending to undertake 
hydrological surveys over these issues.
-- 
Paul