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.)

Watersheds

• Nested Design

• Can Evaluate:– Scale effects

– Hillslope to channel

– Spatial processes

– Cumulative impacts

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 ForestOregon, 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:

– SFF-pre = a1 + b1 * SFD-pre

– SFF-post = a2 + b2 * SFD-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.

Statistical Tests

Watershed D Watershed D

Watershed F

b1≠ b2 a1 ≠ a2

Pre

Post

Pre

Post

Water Yield Increase

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