A hydroelectric scheme comprises an upper storage lake and a lower impounding reservoir connected by a tunnel of $1\mathrm{.}3$ km total length, internal finished diameter of $0\mathrm{.}9$ m and Darcy friction factor of $0\mathrm{.}01.$ The tunnel delivers water to an on$-$line turbine hall at a normal operating rate of $850$ liters per second. A surge tank constructed within a circular shaft is positioned $100$ m upstream of the lower impounding reservoir and has an internal finished diameter of $2300$ mm$.$ In the event that the turbines experience shutdown, derive the maximum likely instantaneous water level within the surge tank. Take a time interval of $20$ sec$.$