When ice covers a river, it severely limits the reaeration. There is some compensation for the reduced aeration because of the reduced water temperature. The lower temperature reduces the biological activity and, thus, the deaeration rate and, at the same time, the DO saturation level increases. Assuming a winter condition, rework Problem 9–29 with the reaeration reduced to 0 and the river water temperature at 2°C.
The town of Edinkira has filed a complaint with the state department of natural resources (DNR) that the city of Quamta is restricting its use of the Umvelinqangi River because of the discharge of raw sewage. The DNR water quality criterion for the Umvelinqangi River is 5.00 mg · L−1 of DO. Edinkira is 15.55 km downstream from Quamta. What is the DO at Edinkira? What is the critical DO and where (at what distance) downstream does it occur? Is the assimilative capacity of the river restricted? The following data pertain to the 7-year, 10-day low flow at Quamta.
Parameter | Wastewater | Umvelinqangi River |
Flow (in m3 · s−1) | 0.1507 | 1.08 |
BOD5 at 16°C (in mg · L−1) | 128.00 | N/A |
BODu at 16°C (in mg · L−1) | N/A | 11.40 |
DO (in mg · L−1) | 1.00 | 7.95 |
k at 20°C (in day−1) | 0.4375 | N/A |
Speed (in m · s−1) | N/A | 0.390 |
Depth (in m) | N/A | 2.80 |
Temperature (in °C) | 28 | 28 |
Bed-activity coeff. | N/A | 0.200 |
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