CSM Assessment & Monitoring Methods 3 — Questions and Answers
Question 1: A bioassay is used in stormwater assessment programs primarily to evaluate which characteristic?
- Hydrologic peak flow timing
- Toxicity of stormwater to aquatic organisms (Correct answer)
- Nutrient loading from impervious surfaces
- Sediment particle size distribution
Correct answer: Toxicity of stormwater to aquatic organisms
Bioassays use living organisms (e.g., Daphnia, fathead minnow) to assess the acute or chronic toxicity of stormwater or receiving water samples.
Question 2: In a watershed assessment, what does the term 'effective impervious area' (EIA) represent compared to total impervious area (TIA)?
- The total area covered by pavement and rooftops
- Impervious surfaces directly connected to the storm drain system (Correct answer)
- Surfaces with pervious pavement overlays installed
- Areas where rainfall infiltration exceeds runoff generation
Correct answer: Impervious surfaces directly connected to the storm drain system
EIA includes only those impervious surfaces hydraulically connected to the drainage network, which is a better predictor of stormwater runoff volume and stream impacts than TIA.
Question 3: Which remote sensing tool is most commonly used to delineate impervious surfaces and measure land cover changes in a watershed?
- Acoustic Doppler current profiler (ADCP)
- Satellite or aerial multispectral imagery (Correct answer)
- Piezometer network data
- Portable turbidimeter readings
Correct answer: Satellite or aerial multispectral imagery
Multispectral satellite or aerial imagery allows analysts to classify land cover types, including impervious surfaces, vegetation, and water, across large watershed areas.
Question 4: A stormwater manager reviews a stage-discharge rating curve for a stream monitoring station. What condition would cause the curve to be unreliable?
- Stable bed and bank conditions
- Consistent vegetation along the channel
- Shifting channel bed due to scour and deposition (Correct answer)
- Regular calibration with current meter measurements
Correct answer: Shifting channel bed due to scour and deposition
A stage-discharge rating curve assumes a stable relationship between water surface elevation and flow; shifting bed conditions alter channel geometry and invalidate the curve.
Question 5: Which biological indicator is most commonly used to assess stream health impacts from stormwater in the US?
- Benthic macroinvertebrate community index (B-IBI) (Correct answer)
- E. coli bacteria counts
- Total dissolved solids (TDS) concentration
- Dissolved oxygen depletion rate
Correct answer: Benthic macroinvertebrate community index (B-IBI)
Benthic macroinvertebrate index of biotic integrity (B-IBI) scores are widely used because these organisms integrate long-term stream conditions and are sensitive to stormwater-related stressors.
Question 6: During a dry-weather screening inspection of a storm drain system, what would constitute a potential illicit discharge finding?
- Stormwater flowing in the channel after 72 hours of dry weather (Correct answer)
- Clear water draining into the outfall during wet conditions
- Sediment deposition at a catch basin inlet
- Vegetation growing near a detention pond outlet
Correct answer: Stormwater flowing in the channel after 72 hours of dry weather
Flow observed at a storm drain outfall more than 72 hours after the last rainfall event is a strong indicator of an illicit non-stormwater discharge connection.
Question 7: What is the purpose of a 'control watershed' in a paired watershed stormwater study?
- It receives all best management practice treatments first
- It remains untreated to provide a baseline for comparing changes in the treatment watershed (Correct answer)
- It is monitored only during dry-weather low-flow periods
- It represents the most urbanized catchment in the study area
Correct answer: It remains untreated to provide a baseline for comparing changes in the treatment watershed
A control watershed with no management interventions allows researchers to account for natural variation and climate effects when evaluating BMP effectiveness in the paired treatment watershed.
CSM Assessment & Monitoring Methods 3
A bioassay is used in stormwater assessment programs primarily to evaluate which characteristic?