A developer wants to develop a $12$ ha site $($IDF curves for the site are shown below$).$ You are required to estimate the change in peak discharge from this catchment for a $1$ in $20$ AEP design storm using the Rational Method.

Existing catchment $($pre$-$development condition$)$: Dense bushland, low soil permeability. Tc $=25$ min.

Proposed development $($post$-$development condition$)$: Residential land uses, medium density, lot sizes $>450$ and $<600$ m$2($fraction impervious $=0\mathrm{.}80).$ Tc $=15$ min.

Determine the peak discharge for the existing catchment $($pre$-$development condition$).$ Express your answer in m$3/$s in the box below. Please do not show any work or attach any files to your response as these will not be marked.