List of top Water Resources and Environmental Hydraulics Questions

A BOD\(_5\) test is conducted. 25 mL wastewater with ultimate BOD of 75 mg/L is diluted to 300 mL. Initial DO = 6.5 mg/L. DO at 7th day = 1.25 mg/L. Find BOD\(_5\) of wastewater sample (mg/L, rounded off to two decimals).
The following figure (not to scale) shows a catchment (Q, S, U, T, Q) and adjoining raingauge stations P, Q, R, S, U, V. Due to a storm, rainfall depths were recorded as follows: - P = 20 mm, Q = 25 mm, R = 30 mm, S = 15 mm, U = 22 mm, V = 18 mm.
The corresponding mean rainfall over the catchment using Thiessen polygon method is ............... (in mm, rounded off to two decimal places).
A pipeline delivers 20 L/s of oil (kinematic viscosity = \( 6 \times 10^{-6} \, m^2/s \), specific gravity = 0.9) under laminar flow. Minimum diameter of pipe is ________________ (in m, rounded off to two decimal places).
A fully penetrating well is installed in a homogenous and isotropic confined aquifer. The aquifer has uniform thickness of 16 m and hydraulic conductivity of 25 m/d. Water is being pumped out from the well at a constant rate of 0.1 m$^3$/s till steady state condition is reached. If a drawdown of 3.5 m is observed at a distance of 75 m from the well then the drawdown at a distance of 150 m from the well will be ....................... (in m, rounded off to two decimal places).
In a 30 m$^3$ room, a stove in operation consumes wood at the rate of 0.25 kg/h. The inflow and outflow rate of air in the room is the same, i.e., 500 m$^3$/h. This stove emits a VOC species at a rate of 0.2 g/kg-wood. The VOC species gets converted to CO$_2$ at a rate of 0.4 per hour. Given: (i) the air in the room is completely mixed, (ii) initial concentration of the VOC species in the room is negligible, and (iii) concentration of the VOC species in the air entering the room is negligible. The concentration of the VOC species due to two hours of stove operation in the room is __________________________________ (in $\mu$g/m$^3$, rounded off to one decimal place).
A trapezoidal canal lined with cement concrete (\(n = 0.01\)) is designed to carry a discharge of 20 m\(^3\)/s at a bed slope 1 in 400. The bed width is twice the depth of flow and side slope of the canal section is 2 (1 vertical : 2 horizontal). The corresponding depth of flow will be ............. (in m, rounded off to two decimal places).
The critical depth in a 2 m wide rectangular channel carrying a discharge of 10 m³/s and taking $g = 9.81$ m/s² is __________ (in m, rounded off to two decimal places).