Forecast: Groundwater and river levels in the Pang Valley

Date: 20 January 2017

Produced by: Peter McGeehin

We have a PVFF meeting next week so I thought I would update you: 'radio silence' on my part has been due to the fact that nothing much has been happening with regard to river and groundwater levels.

Rainfall in September and November was relatively high, but in October and especially December it was low. I have access to a forecast that suggests that January is a also likely to be a relatively dry month overall. Beyond that uncertainties rise, but a forecast that I have seen suggests rainfall in February-March will be ~ 60% of normal. Below I consider the likely effects of rainfall 300% of normal so you would be entitled to form the opinion that my expectations are reasonably robust.

Groundwater levels began to rise in early December from a relatively high seasonal minimum, but the rate of rise has slowed significantly due to the low rainfall since then.

My model predicts that with average rainfall in January overall and 300% of the average in subsequent months the level of the Pang at Frilsham and downstream of there is likely to be ~250mm higher than it is at present. This rises to ~ 325mm higher if we have a monsoon in January that results also in 300% of average rainfall for that month as a whole. In this worst case scenario the Pang would be flowing in Compton but there would be no backing up at infrastructure spanning the watercourse, and probably similarly downstream of Compton. Remember I've seen a forecast that suggests January rainfall will be more like 50% of normal. All to do with the orientation of the jet stream, I believe.