How big should my wild detention pond be?

[jen and mark]

Looking for a bit of info and any tips from those who have built a detention pond.

 

Originally we had planned for 2 soakaways however because our roof is so large (not sure exactly how big - double steel barn with total floor area of 366m2) these would have to be massive. We have an existing pond on our field about 75m from our steel barn conversion. I think the original roof discharged into this alongside the other field drainage pipes. It has now run dry (due to lack of rain and the barn roof no longer connected to it) so we thought we could extend the pond and half pond line it (so it wouldn't run dry). We would then build up the sides to allow slow release. We have a straight run from the barn and the field is sloping towards the pond. The ground is clay. We are going to use 100m solid twin walled drainage pipe from the gutters at the barn and then straight to the pond. 

 

How deep should the land drain be? Does it need bedding in gravel as with foul? What gradient? - I have read 1 in 100 - does it matter if it is more like 1 in 30? Do we need it to be roddable at any distance across the field?

 

Happy for any advice!

Edited July 31, 2022 by jen and mark

[twice round the block]

A pond will still run dry even if has a liner in it. The only time they retain water is if they are spring fed or on the water table

[jen and mark]

Didn’t know that - thanks

[Jilly]

Did you have to submit a plan of it for SUDs as a planning condition?  Some people have found it a pain to do, for others it seems to be ignored. 

It would be worth checking BC are happy for you to do this instead of a soakaway?  As it's a conversion things are a lot easier,  as there likely was a soakaway dug at the time, they'll be assuming  you'll use that (I think). 

Edited July 31, 2022 by Jilly

[jen and mark]

1 hour ago, Jilly said:

Did you have to submit a plan of it for SUDs as a planning condition?

No planning conditions for our class Q - apart from Bat mitigation. Haven't spoke to BC yet but plan on asking him what he would like to see.

 

1 hour ago, Jilly said:

As it's a conversion things are a lot easier,  as there likely was a soakaway dug at the time

No. Just a main valley gutter on an old clay pipe 75m to pond between the 2 steel barns. No guttering at all on the eaves that I could see! Your traditional square/round modern house soakaway pits are only suitable up to 100m2 See BR Section H 3.26 Soakaways for areas less than 100m² are generally formed from square or circular pits, filled with rubble or lined with dry-jointed masonry or perforated ring units. Soakaways serving larger areas are generally lined pits or trench type soakaways. Our roof is much bigger than this so would rather land drain to pond and have a nice feature for the wild life 😃

 

1 hour ago, Jilly said:

It would be worth checking BC are happy for you to do this instead of a soakaway?

The Regs for England state: Soakaways and other infiltration drainage systems 3.23 Infiltration devices include soakaways, swales, infiltration basins and filter drains......  So I dont think he would object - who knows?!?! - Would I catagorise our pond as an infiltration basin?

 

 

Could do with some ideas on how to build the thing 🤪🤪🤣