13. The velocity of the water in a river soon after a strong storm event. (choose 2) (8pts) A. the velocity remains the same unless solids payload increases in which case velocity decreases B. increases drastically C. increases marginally such that it can be considered unaffected during calculations D. is only a function of the flow rate Q E. decreases as the cross sectional area of flow increases F. you can tell the velocity of the river by how wide the river is (Please note: if your answer to the above question is wrong, you will most probably get wrong answers for questions 15 and 16 ). 14. Which of the following statements is true about the Thomas Slope Method for Statistical determination of ultimate BOD, Lo, and biodegradation rate coefficient, k : (8 pts ) A. It is based on the simplified form of the convergent Taylor Series for the termLn(1e) B. It is based on the second derivative of the BOD removal term L0(1ett) which yield the term L[kt(1+6kt)1] C. It is based on the simplified form of the convergent Taylor Series for the term L[kt(1+6kt)3] D. The series for the BOD term L(1ekt) and the term L[kt(1+6kt)3] are equal up to the third term, thus the latter term can be used to calculate BOD as a function of time. 15. Explain why removal rates for both conservative and non-conservative substances in natural water bodies is assumed to follow first-order decay rate kinetics. Indicate the risks posed by the over-reliance on the first-order kinetic model in a broad range of scenarios. (8pts) 16. Following the example on the "Distributed loading in a river" (Lecture Notes), evaluate how far downstream of Point B could a point source outfall be allowed into the river with an in-stream impact of 14mg/L if the stream UBOD concentration must never exeeed 20mg/L. (Use rough approximations wherever possible). ( 8 pts)