Graham Macky – Peer-review of Bob Hall’s Pinehaven Hydrology

Graham Macky, of Macky Fluvial Consulting Ltd, peer-reviewed Bob Hall’s Pinehaven Hydrology in which Bob Hall finds that future development on the Pinehaven hills will increase runoff five-fold. Macky states: “I concur with Mr Hall’s conclusions … The general hydrological method adopted in Mr Hall’s report is sound” and agreeing that Jacobs model has “assumed an exceptionally impervious catchment.” Bob Hall relied on on-site infiltration tests by Alex Ross which differ significantly from desktop infiltration rates in Cardno’s map for the Pinehaven area.

For comparison, Hall re-did his calculations (see R J Hall - ADDENDUM A) using Cardno’s questionable rates yet still found a doubling of runoff from the SKM / Jacobs ‘future development scenarios’ on the Pinehaven hills, not 1% as asserted in the work by SKM, Jacobs and Beca. Macky comments that, “Regardless of which model results are preferred [five-fold increase in runoff using Alex Ross’s infiltration rates, or two-fold increase using the Cardno map] the increase in runoff [from the SKM / Jacobs ‘future development scenarios’ on the Pinehaven hills] is significant …”, and not 1% as claimed by SKM, Jacobs and Beca. Bob Hall concluded there are “substantive discrepancies” in the Pinehaven flood model and flood maps, and that “the flood modelling … should be … corrected before any reliance is placed upon it as the baseline modelling for assessing post-development runoff of future Guildford development in the upper Pinehaven catchment.”