Civil: Water Resources and Environmental PE

Always check units carefully - pressure must be converted to head units (divide by specific weight). Remember that gauge pressures are relative to atmospheric pressure. For velocity head calculations, don't forget the factor of 2 in the denominator. When solving for velocity, check that the result under the square root is positive.

The Chick-Watson model is fundamental for water treatment design. Remember that n≤1 for this form, and different pathogens have vastly different k values. Cryptosporidium is extremely resistant to chlorine (very low k), while bacteria are more susceptible. CT concept (concentration × time) is critical for disinfection credit calculations.

This equation appears frequently on the PE exam for disinfection problems. Remember that decay constants are often given in different time units (per minute, per hour, per day) - always check units match. The equation assumes first-order kinetics, which is valid for free chlorine in most treated waters.

The continuity equation is fundamental to all fluid flow problems. Often appears as part of larger problems involving energy equations, pipe networks, or channel design. Remember that velocity is average velocity across the entire cross-section.

Critical depth problems appear frequently on the PE exam. Remember that critical flow occurs at minimum specific energy. When flow depth equals critical depth, the flow transitions from subcritical to supercritical. Always check if the actual depth is above (subcritical) or below (supercritical) critical depth.