Watershed Experiments

Lab 3

Watersheds

• Several different designs – Single watershed (data for modeling) – Nested (evaluate accumulated effects) – Paired (cause and effect) • Watershed studies were important for detection of environmental problems such as acid rain and climate change.

• Very Expensive and difficult to do process research • Look at long-term trends, cumulative-impacts, and develop models with data.

• Most of our knowledge on the impact of land use on watershed scale processes are from paired watersheds. Processes include: – Runoff volume (water yield) – Peak Flows (flooding) – Sediment Yield – Other water quality parameters (N, P, K, etc.)

• Nested Design • Can Evaluate: – Scale effects – Hillslope to channel – Spatial processes – Cumulative impacts Watersheds Walnut Gulch Experiment Watershed

Paired Watershed

• Watersheds should be similar (geology, soils, terrain, vegetation, etc.) • Need to develop a relationship between watersheds before treatment (i.e pre-treatment) • You need to collect data for years before the treatment is implemented.

• This is an experiment in an uncontrolled environment. • Potential disturbance can disrupt the experiment.

H.J. Andrews Experimental Forest Oregon, USA

Paired Watersheds • Multi-factorial experiment is where more then one factor varies over time.

• To understand the relationship between response and treatment we must take measures over different levels of all the factors. In our case we are looking at response over a series (i.e. years) of environment conditions (e.g. climate).

• Develop relationships for two time periods, pre-treatment and post-treatment. Test to see if they are statistically difference.

Statistical Test

• We will develop two regression model for pre- and post treatment time periods where: – SF F-pre = a1 + b1 * SF D-pre – SF F-post = a2 + b2 * SF D-post • SF = Annual Streamflow (inches) • F = Watershed F • D = Watershed D • We will test to see in the equation coefficients are equal where the HO: a1=a2 and b1=b2.

• If one of the tests is rejected the equations are not equal which indicates we may have a treatment effect.

• Watershed D is the Control watershed and Watershed F is the Treated watershed. Watershed F was treated with herbicides to kill deep-rooted shrubs and was converted to grass.

b1 ≠ b2 Post Pre Watershed D Statistical Tests a1 ≠ a2 Post Pre Watershed D

Water Yield Increase

• If there is a treatment effect that the Increase in water yield can be computed as: – WYI = SF f-post – [a1+b1*SF d-post ]