Data Collection & Analysis Flashcards

A Parshall flume is used in stormwater monitoring primarily to:

Answer: Measure open-channel flow rate based on water depth

A Parshall flume is a calibrated flow measurement device that converts a depth reading (via stage-discharge relationship) into volumetric flow rate.

When using a rain gauge network to estimate watershed-average rainfall, the Thiessen polygon method accounts for:

Answer: The spatial area of influence attributed to each gauge

Thiessen polygons assign each gauge a weight proportional to the watershed area closer to that gauge than any other, giving a spatially weighted average rainfall.

In stormwater quality monitoring, the 'first flush' phenomenon refers to:

Answer: The disproportionately high pollutant concentrations occurring early in a runoff event

First flush describes the tendency for pollutant concentrations to peak early in a storm as accumulated surface pollutants are mobilized before dilution by continued rainfall.

Which QA/QC sample type is used to assess potential contamination introduced during field sampling and transport?

Answer: Equipment blank

An equipment blank (or field blank) is collected using reagent-grade water passed through all sampling equipment and containers to detect contamination introduced during collection, transport, or processing.

A stormwater manager wants to determine whether total phosphorus concentrations differ significantly between an agricultural sub-watershed and an urban sub-watershed. The appropriate statistical test for two independent groups with non-normal data is:

Answer: Mann-Whitney U test

The Mann-Whitney U test is the non-parametric alternative to the t-test, appropriate when data are not normally distributed and two independent groups are being compared.

Dry-weather field screening of storm drain outfalls is conducted primarily to:

Answer: Detect illicit discharges of sanitary sewage or industrial effluent

Dry-weather screening identifies outfalls with non-stormwater flow (sewage, wash water, industrial waste) by inspecting for flow, odor, color, or elevated indicator parameters during dry conditions.

The event mean concentration (EMC) of a pollutant is calculated as:

Answer: Total pollutant mass discharged divided by total runoff volume for the event

EMC equals total mass load divided by total runoff volume, effectively a flow-weighted average concentration that represents the storm event's overall pollutant contribution.