1. Sampling issues in river health
assessment
Dr Chris Gippel, Australia
Workshop on China’s national river health assessment program
Ministry of Water Resources
2012 February 22

2. Low Sensitivity to change High
Scale
100 – 1,000,000 km2 10 – 1000 km2 100 – 10,000 m 1 – 100 m 0.1 – 1.0 m
Basin and Functional process Reach Site Microhabitat
catchment zone
Report aggregated Report individual
site scores site scores

3. Border Rivers
Fish Macroinvertebrates

6. How many sites?
• Murray-Darling Basin
– 1,061,469 km2
– 506 fish sites; 773 invertebrate sites
• 1 site per 2,100 km2 for fish
• 1 site per 1,370 km2 for macroinvertebrates
• Victoria
– 227,416 km2
– 1,040 reaches/sites
• 1 site per 219 km2
• SE Queensland
– 22,420 km2
– 135 sites
• 1 site per 166 km2

7. How many sites?
• Budget
• Objective
– Confirm known issues (e.g. sewerage pollution)
• Wherever the issues are located
– Monitor catchment health change over time
• Sufficient statistical power to detect change

8. Variation in space Variation in time
low low
few
low high
Number of
sites required
to detect change
high low
high high
many

9. How often to sample?
• Budget
• Objective
– Seasonal variation important (depends on system)
– 2 times per year
– Fit in with annual reporting schedules
– 1 or 2 times per year
– Long term change is main priority
– Every 2 – 5 years
– Slowly changing parameters (e.g. vegetation, physical form)
– Every 2 – 5 years

10. Where to locate the sites?
• Budget
• Objective
• Random
– Most expensive
– Most statistically sound
– Mix of fixed and non-fixed sites
• Stratified
– Freedom to chose exact site within a specified zone
• Non-random
– “Data hunting” – looking for evidence of known issues
– Avoiding sites with poor health
– Selecting only large rivers, or high profile sites
– Risk of systematic bias (e.g. all sites near roads or bridges)

11. Sampling at the chosen site
• If chosen because of easy access, avoid unusual activity:
– vehicles crossing the stream;
– waste disposal;
– recreational angling;
– sand and gravel extraction;
– timber collection;
– washing clothing and vegetables
• Follow standard protocols

14. Summary
• Sampling strategy depends on:
– Budget
– Objectives
– Expected variability of the data
– Reporting scale
Need to establish these things before setting the sampling sites
• Program sampling strategy should be designed by a statistician
– As a minimum, report the sampling strategy
• Follow standard protocols at the site