Are you thinking 'Can I really write my own FRA?'
The answer is yes! Most likely. Probably. And with some guidance, but yes. It's not difficult, it just needs a little knowledge and the 'lingo' that will help with planning.
When you should write your own FRA
When your site is small, within Flood Zone 1 (low risk of fluvial flooding) and at low-medium risk of pluvial flooding - you should be able to submit your own FRA.
If you site is greater than 1 hectare but is within Flood Zone 1 and at low risk of pluvial flooding then you should be able to submit your own FRA but it will be more important for your site to have a sustainable drainage strategy (future blog post).
If your site is within FZ2/3 (medium to high risk) but it's a minor application like a change of use or an extension then you might be able to submit your own FRA (often it depends on the local council and how stringent they are).
We'll go into more detail about each type in a future blog post.
But first...
The Basics to ask yourself
Please note, the legislation and guidance is for the UK but the maps are split due to stupid reasons, so the links below will be relevant to sites within England and I'll do a separate post about Wales and Scotland.
There are 6 known sources of flooding to consider: tidal, fluvial, pluvial, groundwater related, from sewers and from artificial sources. I'll explain each one as we go through the outline process below.
Step 1: What Flood Zone is your site in? Check the flood map using the link below.
Step 2: What is the known flood risk to your site? Check the flood maps using the link below.
Use the drop down on this map to check tidal flood risk (from the sea), fluvial flood risk (rivers and watercourses), pluvial flood risk (overland flow or sometimes called surface water runoff), and flood risk from reservoirs (sometimes this is called flood risk from "artificial sources" and can include an assessment of canals too).
Step 3: What is the flood risk from sewers/highway drainage infrastructure? Check using the link. water.org.uk/advice-for-customers/find-your-supplier/
If you're based in the North-West like I am, there can be some confusing overlap between United Utilities and Severn Trent Water so for North-West sites it's worth checking this map too: unitedutilities.com/my-account/moving-home/check-if-you-are-in-our-supply-area/
To assess flood risk from sewers you'll need to order sewer records. You will be able to do this on the relevant company website. Your development type will decide what sewer records you need as they mostly inform the drainage strategy and not the FRA, example list below.
Extension of existing property - you will likely be able to submit an FRA without needing sewer records.
A new single house or two carried out by a small-scale housebuilder - you will likely only need the simplified (and less expensive) "lines-on-a-map" records.
A development with multiple houses, or an area over 1 ha. You will likely need the more expensive detailed sewer records which will not only show the lines on a map but also the cover level and invert levels of nearby manholes. This will be especially important for your drainage strategy.
For existing sites - it's always worth getting a CCTV survey carried out of your existing drainage infrastructure. This can prove the connection from your site to the public sewer network. If you don't think you need a full survey, a dye test may be enough to prove connectivity.
For surveys in the North-West (and beyond, within reason), I highly recommend Kevin and his team over at Invek, go to www.invek.com for more details.
If you're not sure if you need a survey to prove connectivity or which type of survey to go for, get in touch.
Step 4: Flood Risk from Groundwater
There's no map (that I know of) that checks flood risk from groundwater. On most development sites you will have a Ground Investigation Survey (or a site investigation) whether that's a Phase 1 SI (which is a desk based study) or a Phase 2 SI where the technical team actually go to your site to do sampling.
Firstly, what ground conditions do you have. Is it clay? sand? chalk? This will be described in your ground investigation study if you have one. If you don't find out here...
For bedrock and superficial deposits go to: geologyviewer.bgs.ac.uk
For soil type (this is more relevant) go to: landis.org.uk/soilscapes/
If your site is based on a soil type where groundwater ingress is likely (for example, sand or chalk) and a high water table is noted on the NSRI soilscape, then flood risk from groundwater sources is considered to be medium-high and you will need to check your trial pit records for the depth of groundwater strike that was recorded.
For clay sites (which most of them seem to be)... groundwater flood risk is considered to be low (because even if you have a permeable bedrock layer underneath, water is prevented from getting to the surface by the clay layers).
The soil type will also have a huge impact on your drainage strategy. But that's a topic for a future blog post.
Step 5: Now you should have a basic idea of whether your site is at significant risk of flooding.
The next stage is to make sure your site doesn't increase flood risk for anyone else...
Any questions, get in touch.
