The Flood Estimation Handbook, produced by the Institute of Hydrology in 1999 effectively replaced Flood Studies Report in the UK.
The following QMED equation is from a revision to the statistical approach in 2008 (Kjeldsen et al, 2008).
Qmed = 8.3062 x (0.01 x AREA)0.851 x 0.1536(1000 / SAAR) x FARL3.4451 x 0.0460(BFIHOST x BFIHOST), m3/s
where:
- Qmed is the median annual flow rate; the 1:2 year event.
- AREA is the area of the catchment in ha.
- SAAR is the standard average annual rainfall for the period 1941 to 1970 in mm.
- FARL is a reservoir attenuation function and is set at 1.0 and therefore has effectively been ignored. This means that areas with water bodies which attenuate the runoff will over-predict the greenfield runoff rate.
- BFIHOST is the base flow index derived using the HOST classification.
