Profile of a weir on permeable foundation is shown in the figure I and an elementary profile of ‘upstream pile only case’ according to Khosla’s theory is shown in the figure II. The uplift pressure heads at key points $Q, R$ and $S$ are $3.14 \: m$, $2.75 \: m$ and $0 \: m$, respectively (refer figure II).

What is the uplift pressure head at $P$ downstream of the weir (junction of floor and pile as shown in the figure I)?

1. $2.75 \: m$
2. $1.25 \: m$
3. $0.8 \: m$
4. Data not sufficient