Duncan Faulkner Head of Hydrology, JBA Consulting we safe from reservoir flooding? Duncan Faulkner...

Are we safe from reservoir flooding?

Duncan Faulkner

Head of Hydrology, JBA Consulting

A confession

Date Location % of estimated PMP

28 Jul 1917 Bruton, Somerset 102%

18-19 Aug 1924 Cannington, Somerset 103%

19 Jul 1955 Martinstown, Dorset 117%?

7 Oct 1960 Horncastle, Lincs 101%

19 May 1989 Halifax, W. Yorkshire 119%

Going over the top… rainfall

Source: Stewart, E. J., Jones, D. A., Svensson, C., Morris, D. G., Dempsey, P., Dent, J. E., Collier, C. G., and Anderson,

C. A. (2013) Reservoir Safety – Long Return Period Rainfall. R&D Technical Report WS 194/2/39/TR, Defra.

Date Location Catchment size

(km2)

% of estimated

PMF

17 Aug 1917 Red-a-ven, Devon 4.0 141%

12 Aug 1948 Stobshiel, East Lothian 4.1 111%

08 Aug 1967 Claughton, Lancashire 2.3 200%

16 Aug 1970 Dorback, Morayshire 365 139%

13 Jun 1980 Caldwell Burn, Dumfriesshire 5.7 381%

12 Jul 1982 Chulmleigh, Devon 1.7 270%

Going over the top… flood flows

Source: Acreman, M.C. (1989) Extreme historical UK floods and maximum flood estimation. J. IWEM 3, 404-12.

Upward trends in the uplands

1938 1943 1948 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013

Leven

Eamont

A look under the bonnet

1. PMP dated

Timeline of rainfall frequency models

1970s 1980s 1990s 2000s 2010s

Return periods up to 1000 years: fluvial flooding and drainage design

FSR rainfalls

FEH rainfalls

FEH13

10,000-year return period

FSR rainfalls

FEH13

PMP

FSR rainfalls

2. Flood Studies Report model superseded

3. Rapid response

3. Rapid response

3. Rapid response

The consequence of the observed nonlinearity in

response time is to increase design peak flow by … up

to 80% when considering the probable maximum flood.

Kjeldsen et al. (2016), Journal of Hydrologic Engineering

4. Snowmelt

5. Frozen ground

6. Errors in % runoff for some soil types

7. No allowance for climate change

Summary

duncan.faulkner@jbaconsulting.com

Duncan Faulkner and Jeremy Benn (2016). Reservoir Flood Estimation: Time for a Re-think. Proceedings of the British Dam Society Conference: Dams – Benefits and Disbenefits; Assets or Liabilities? ICE Publishing / British Dam Society.