An estuary has characteristics as follows: Depth = 4 m Velocity 250 m/hour = Width 100 m Flow = 100000 m/hour Dispersion Coefficient, E = 1*106 m/hour A degradable pollutant (k = 0.1 day) is leaking into the estuary. To anticipate the impact of the leakage, a time-variable numerical model will be employed. For the finite-difference approach in this model, a Forward Time-Backward Space scheme is chosen. Accordingly: a) What is the maximum cross-sectional length (critical section length) that can be used in the numerical model? b) After determining an appropriate section length, what is the longest time step (At) that can be used to ensure stability? c) What is the corrected dispersion coefficient that should be used to compensate for numerical dispersion?