Getting Results: Measuring Postwildfire. Treatment Effectiveness

Transcription

1 Getting Results: Measuring Postwildfire Erosion Control Treatment Effectiveness BAER Burned Area Emergency Response Pete Robichaud, R. Brown, P. Wohlgemuth, J. Wagenbrenner Rocky Mountain and Pacific Southwest Research Stations, USDA Forest Service

2 Probabilities Greater RISK Less Life Property Water Quality Habitat Soil Productivity BAER Team Treatment Objectives

3 Pro: Immediate ground cover $ /ha Cons Breaks down quickly Expensive ($7100/ha) Hillslope Treatments Pros Immediate ground cover Con: Pros Longer lasting On site materials Possible introduction of Cons Effective for small invasive species Expensive events $ /ha $ /ha Ag. Straw Cons Woodstraw Not effective for large events Pros Failures common Uniform application Small runoff/sediment Pros capacity Works well in areas w/ fast Inexpensive ($50/ha) vegetation response Contour-Felled Logs Immediate ground cover Cons No reduction in erosion post-fire year one. Precipitation dependent Hydromulch Aerial Seeding

4 Our Research Sites 2000 Bitterroot Fire

5 Mitigation Effectiveness Rainfall Simulation Bitterroot Valley Simulated Rainfall Intensity 20 mm/hr

6 Waugh Creek, MT Rainfall Simulation 7 0 Sediment Yield (t/ha) Sediment Yield Total Runoff Runoff (mm) 0 Untreated Control Contour Log Straw Wattle Contour Trench 6

7 Waugh Creek,MT Natural Rainfall Results Sediment yield (t/ha) Untreated control Contour log Straw wattle Contour trench Year Ground cover (%) 5 a 4 a 19 b 55 c

8 Hayman, CO 2002 Postfire Recovery Treatments Straw Wood Straw Contour raking Control How effective are these treatments?

9 Hayman, CO Rill Experiment Sediment Concentration Sediment concentration (g L -1 ) Sediment Concentration (g/l) A Contour Contour Raked raked 2002 Sediment concentration (g L -1 ) Sediment Concentration (g/l) B B A A B A B Straw Wood 0 Wood strandscontrol Control Control Control Control Natural Mulch Strands Contour Straw Wood Contour 2003 Wood strands Raked Mulch Strands Control raked A Treatment, year Year Treatment, Year A C Trea C D

10 Control Silt Fences for Measuring Hillslope Erosion Wood straw Raked Straw mulch

11 Gap Fire Silt Fences on Los Padres NF, CA Sediment (t/ha) I10: 38 mm/hr I10: 21 mm/hr Max I10 (mm/hr) and Max Total Precip (mm) Wood Shreds (n=6) WS Control (n=6) Hydromulch (n=10) HM Control (n=6) I10 (mm/hr) Total precip (mm)

12 Jesusita Fire Silt Fences on Los Padres NF, CA Sediment Yield (t/ha) Max I10 (mm/hr) and Max Total Precip (mm) Control Hydromulch 30% Wood straw 60% Wood Straw Max I10 (mm/hr) Total Precip (mm) Cleanout Date

13 Mulch effectiveness from Northern Rockies Log-normalized Predicted Sediment Yield Control Hydromulch Control Straw A B BC CD BC CDE Post Fire Year Control Wood A B A A Post Fire Year Post Fire Year B D B B BC CD DE E

14 Hayman Fire, CO Control Cheeseman reservoir Paired watersheds Salvage logged Burn severity map High Moderate Low Unburned

15 Hayman, CO Paired Watersheds Full Empty

16 Hayman, CO watershed E

17 Hayman, CO Small Storm vs. Large Storm Year 1 Storm Date 18-Jul 9-Aug I10 (mm/hr) Treatment Sediment (t/ha) Contour Felled Logs 0 9 Untreated Control Untreated Control Storm date 18-Jul 29-Jul I10 (mm/hr) Treatment Sediment (t/ha) Straw Mulch Untreated Control Hydromulch

18 Sediment Yield (t/ha) Hayman Annual Sediment Yields Untreated Control Untreated Control Hydromulch Contour-Felled Logs Salvage Log Straw Mulch Year 8 0 t/ha Year

19 Cedar Fire, Watersheds on Cleveland NF, CA Watershed Means Post Fire Year Rainfall Annual Rainfall (mm) Storm Peak I 10 (mm/hr) Sediment Yields (t/ha) Control % Hydromulch <2.2 0 <2.2 < % Hydromulch <2.2 <2.2 <2.2 <2.2

20 Watershed: Runoff Cedar (CA) Hayman (CO) Treated runoff (mm) % Hydromulch yr 3 1 yr 4 yr 5 yr 6 50% Hydromulch 0.1 yr 3 yr 4 yr 5 yr 6 1: Control runoff (mm) Treated runoff (mm) 10 Hydromulch 1 yr 0 yr 3 yr 4 yr 5 yr yr 7 Straw yr 0 1: Control runoff (mm)

21 Watershed: peak flow 10 Cedar (CA) Hayman (CO) 10 Treated peak flow (m 3 s -1 km -2 ) 1 100% Hydromulch yr 3 yr 4 yr 5 yr % Hydromulch yr 3 yr 4 yr 5 yr 6 1: Control peak flow (m 3 s -1 km -2 ) Treated peak flow (m 3 s -1 km -2 ) 1 Hydromulch yr 0 yr 3 yr yr 5 yr 6 yr 7 Straw yr 0 1: Control peak flow (m 3 s -1 km -2 )

22 Watershed: Sediment yield 100 Cedar (CA) Hayman (CO) 100 Treated sediment yield (t ha -1 ) % Hydromulch 1 yr 3 yr 4 yr 5 yr 6 50% Hydromulch 0.1 yr 3 yr 4 yr 5 yr 6 1: Control sediment yield (t ha -1 ) Treated sediment yield (t ha -1 ) 10 Hydromulch 1 yr 0 yr 3 yr 4 yr 5 yr yr 7 Straw yr 0 1: Control sediment yield (t ha -1 )

23 Understanding Erosion bucket by bucket Fires Happen, Then Erosion Happens... Variability Burn Severity Rainfall Events Hillslope/Soil Conditions Treatment Effectiveness Ground Cover Better Than Barriers Decay Rates Vary