Request for information – FOI14552
Thank you for your email of 23 May 2015, requesting the following information in accordance with the Freedom of Information Act (FOIA) 2000:
What the river level is it that you use to define the limits of the river.
Likely answers are:
1. No particular level
2. We avoid floods/droughts
3. We aim to use the average river flood 4. We aim to Q50% flow level (flow exceeded 50% of the time)
Under our duty to provide advice and assistance as stipulated in Section 16 of the FOIA, we can provide the following explanation which may assist you in this matter.
The OS MasterMap real-world object catalogue (page 409) PDF states that for non-tidal rivers “The width to be shown is that at normal winter level.” Expanding on this our current large scale capture specification states, "For features represented by Topographic Area features the limits of the water are captured in the location that represents their normal winter level, which can normally be determined as the point where vegetation ceases to grow."
Please be aware that our current capture specification also includes minimum survey distance rules for some types of features: The OS MasterMap Topography Layer user guide (page 36) PDF states that “Rivers, streams and drains are shown at their true scale width. A single line is normally used where their width is less than 1.0 m in urban areas and 2.0 m in rural, mountain and moorland areas.”
I hope the above is of use to you.
Your enquiry has been processed according to the Freedom of Information Act (FOIA) 2000. If you are unhappy with our response, you may request an internal review with our FOI Internal Review Officer, by contacting them as follows:
FOI Internal Review Officer
Customer Service Centre
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In the meantime, should you need to contact Ordnance Survey regarding your request at any time, please quote the allocated reference number FOI14540 in any correspondence.