Watershed Characterization & Sufficient Data. Anne McFarland Texas Institute for Applied Environmental Research (TIAER) Tarleton State University

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1 Watershed Characterization & Sufficient Data Anne McFarland Texas Institute for Applied Environmental Research (TIAER) Tarleton State University

2 Study Design Depends on the objective Why monitor? Identifying water quality problems Defining current vs desired conditions Estimating loadings for allocations (TMDLs & point source permits) Recommending & evaluating pollution control practices Assessing improvement

3 Study Design & Statistical Analysis Dictates the monitoring design Study scale Sampling frequency Location & # of stations Station type & sampling type Duration of sampling

4 Common Study Designs

5 Reconnaissance or Synoptic Used to obtain an overview of water quality Routine monitoring Can be used to target areas or sources of water quality problems Often considered a snapshot in time

6 Reconnaissance or Synoptic Advantages Allows a quick picture of water quality over a large area Fast approach and relatively cheap

7 Reconnaissance or Synoptic Disadvantages Often biased toward baseflow conditions Low sampling frequency limits application of statistics Sampling location often biased based on ease of access

8 Reconnaissance or Synoptic Data Evaluation Often only descriptive due to limited sample size Ranking of values for comparison Mapping helps with spatial targeting

9 Example: Map from Lake Granbury WPP gbwpp_reports.asp

10 Plot Studies Generally applied to small land areas (fractions of acres) Involves Replication - 3 to 6 plots of each treatment and control condition Objective evaluate differences between specific conditions and/or treatments

11 Source Diagram: NRCS, NWQH Plot Studies

12 Advantages Plot Studies Replication allows greater statistical power Statistical design depends on: Plot area available & # of plots # and types of treatments evaluated Blocking variables considered (e.g., soil type) Small plot areas allow greater control of environmental conditions

13 Disadvantages Plot Studies Results may not be easily transferable to the larger watershed area or to other watersheds May not represent the larger scale hydrologic or management system

14 Potential Problems: Plot Studies Plots need to be homogeneous but representative of the system being evaluated As plot size increases, control of environmental variables decreases

15 Plot Studies Example Quarry Study Report: Storm Water Best Management Practices (BMPs) Field Trials of Erosion Control Compost in Reclamation of Rock Quarry Operations

16 Plot Studies Example Rainfall Simulation

17 Single Watershed Objective evaluate effectiveness of a conservation practice Two General Approaches: Temporal Before and After Practice Implementation Spatial Above and Below Practice Location (Upstream/Downstream approach)

18 Single Watershed Before/After Temporal Before and After Practice Implementation Source Diagram: NRCS, NWQH

19 Single Watershed Before/After Advantages Simple needs only one monitoring station Relatively cheap to implement Source Diagram: NRCS, NWQH

20 Single Watershed Before/After Disadvantages Can be difficult to separate treatment effect from year-to-year variability in environmental conditions Transferability of results limited Source Diagram: NRCS, NWQH

21 Single Watershed Above/Below Spatial Above and Below Practice Location (upstream/downstream) Source Diagram: NRCS, NWQH

22 Single Watershed Above/Below Advantages Not susceptible to year-to-year climatic variation Relatively easy to implement Useful for isolating critical source areas

23 Single Watershed Above/Below Disadvantages Nested observations may not be independent Differences may be do to inherent differences within the watershed and not the practice

24 Single Watershed Above/Below Before monitoring helps account for inherent differences within the watershed Before Monitoring After Monitoring No Practice Source Diagram: NRCS, NWQH

25 Paired Watersheds Paired watershed or BACI approach (Before-After-Control-Impact) Two (or more) Watersheds Involves a Calibration & Treatment period At least one watershed serves as a control

26 Paired Watersheds Calibration period (monitor both without practice, treated identically) Calibration Period Source Diagram: NRCS, NWQH

27 Paired Watersheds Treatment period (implement practice on one, treat control as in calibration period, and monitor both) Treatment Period Source Diagram: NRCS, NWQH

28 Paired Watersheds Calibration period evaluates inherent differences between the two watersheds Treatment period control watershed serves as a check on changes due to changes in environmental conditions

29 Advantages Paired Watersheds Allows statistical control of environmental variation not associated with the treatment Water quality from the two watersheds does not need to be identical

30 Paired Watersheds Disadvantages Treatment effect may be gradual, thus, initially masking differences with the control Implementation costly and time consuming (calibration & treatment periods may each take several years) Long study period, more prone to gradual changes in control plot as well as catastrophic changes (fires, drought, insect infestations, etc )

31 Paired Watersheds Example: Manure Management Study

32 Multiple Watersheds Objective Evaluate treatments Use multiple watersheds representing each treatment Example: Comparison of commercial fertilizer on pasture vs manure spreading

33 Advantages Multiple Watersheds Transferability within the region where monitoring occurs Gets at the true variance of the treatment and variability among the watershed areas in a region

34 Multiple Watersheds Disadvantages Logistics - difficult to sample storm runoff across a large region Often difficult to obtain specific information regarding management practices

35 Trend Stations Single watersheds monitored over time Effectiveness of a group of practices implemented over time or having a gradual impact over time Works best when there are not data gaps Helpful to have a control or reference watershed for comparison

36 Advantages Trend Stations Long-term station relatively easy to establish, particularly in perennial streams Allows evaluation of practices that may take several years to see a water quality response Example: Residual storage of nutrients

37 Disadvantages Trend Stations Long-term commitment needed (often > 10 yrs) Greater chance for unwanted disturbances (not only within the drainage area but in sampling and laboratory analysis methods)

38 Depends on: Sufficient Data The monitoring objective Statistical design Environmental conditions before and after treatment implementation Variability in the constituent of interest

39 Sufficient Data Number of sites Number of samples Frequency of monitoring Duration of monitoring

40 Major References USDA-NRCS Chapter 4, Statistical Designs. In: National Handbook of Water Quality Monitoring. =17843.wba Helsel & Hirsch Statistical Method in Water Resources. USGS, Techniques for Water-Resource Investigations. TIAER, Strategies for Monitoring Nonpoint Source Runoff.

Statistical Tools for Analysis. Anne McFarland Texas Institute for Applied Environmental Research (TIAER) Tarleton State University

Statistical Tools for Analysis Anne McFarland Texas Institute for Applied Environmental Research (TIAER) Tarleton State University Monitoring Objectives Focus Watershed Scale Evaluating BMP Effectiveness