Data Collection & Analysis Flashcards

Which sensor technology is commonly used for continuous in-situ turbidity monitoring in stormwater channels?

Answer: Optical nephelometer or infrared scatter probe

Optical nephelometers measure light scattered by suspended particles at a defined angle and are routinely deployed as submersible probes for continuous turbidity monitoring.

A stage-discharge rating curve becomes invalid when:

Answer: Channel cross-section geometry changes due to scour or deposition

Rating curves are developed for a specific channel geometry; scour, deposition, or vegetation changes alter hydraulic controls, requiring recalibration with new discharge measurements.

In the context of stormwater data analysis, 'censored data' refers to:

Answer: Values reported only as less than the detection limit (non-detects)

Censored data are measurements below the method detection limit, reported as '<MDL'; special statistical techniques (e.g., Kaplan-Meier, substitution methods) are needed to handle them in analysis.

Which remote sensing product is most commonly used to map impervious surface area across an entire watershed efficiently?

Answer: Multispectral satellite imagery classified using NDVI and spectral indices

Multispectral imagery (e.g., Landsat, Sentinel-2) distinguishes impervious surfaces from vegetation and soil using spectral indices, enabling watershed-scale impervious cover mapping at low cost.

A stormwater manager finds a strong negative correlation (r = -0.85) between vegetated buffer width and outfall total suspended solids (TSS) concentrations. This means:

Answer: As buffer width increases, TSS concentrations tend to decrease

A negative correlation coefficient means the two variables move in opposite directions — wider buffers are associated with lower TSS, consistent with buffers trapping sediment before it reaches the outfall.

The primary purpose of maintaining a chain of custody (COC) form for stormwater samples is to:

Answer: Document sample possession and handling to ensure legal defensibility of data

A COC form tracks who collected, transferred, and analyzed a sample, providing an auditable record that demonstrates sample integrity and is required for regulatory enforcement actions.

GIS-based watershed delineation using digital elevation models (DEMs) determines drainage area by:

Answer: Tracing the direction of steepest descent from each grid cell to define flow paths and catchment boundaries

Flow direction algorithms assign each DEM cell a drainage direction toward its lowest neighboring cell; accumulating these paths downstream delineates the contributing area above any outlet point.