Rehabilitation of Alluvial Gully Erosion in the Normanby Catchment

Transcription

1 Rehabilitation of Alluvial Gully Erosion in the Normanby Catchment Jeff Shellberg and Andrew Brooks Australian Rivers Institute, Griffith University, Queensland, Australia

2 Factors Controlling Alluvial Gully Erosion Inherited Landscape Floodplain geomorphology, landscape evolution Elevational Relief Floodplain to channel and degree of incision Monsoon Climate and Hydrology Tropical rainfall, floodplain hydrology Soils texture and chemistry Sodic, alluvial, silts/clay soils, hardsetting, dispersible Vegetative cover Grass woodlands, drought, fire, animal grazing Land use Cattle grazing, fire regime changes, weeds, roads Relief Landscape Hydrology Cattle Grazing Fire Soil Chemistry

3 Land Use Can Accelerate Water Runoff and Gully Erosion in River Frontages Over-Grazing / No Cover Increase In Gully Area Cattle Pads on Flats Hot Fires Cattle Pads on Banks Land Clearing Fences Roads Invasion by Annual Weeds

4 Cumulative Effects And Scale Cumulative impact (CEQ 1971) Impacts from incremental actions (past, present, future) regardless who makes them Individually minor but collectively significant actions taking place over time Cumulative watershed effects (Swanson 1986) Downstream changes in hydrology, sediment production, transport, and storage in response to land management practices Not one hotspot or sub-catchment, but many Not one land use, but many.. Not a specific gully or road or cattle pad or paddock but.. Thousands

5 Rehabilitation of Alluvial Gully Erosion (Breakaways) Along River Frontages 1. Reduce Water Runoff Into Gullies (Drivers) 2. Increase Vegetation in Gullies (Resistance) 3. Reduce Slope (Grade) of Gully Channels (Resistance) Fence river frontage away from high banks Full cattle exclusion or wet season spelling Install water diversion/retention banks above gully heads Divert excess water to safe disposal areas Reduce cattle pads over steep banks Reduce water concentration Install grade control structures Only at narrow gully outlets or finger headcuts Increase perennial grass cover on river flats Cover Target >75% at BOS, >1000 kg/ha Redcue water runoff Fire management in river frontage Cool winter fires (3-5 yrs) Infrequent hot fires (> 7-10 yrs) Active rehabilitation gully slopes Re-grade gully slopes with machinery Amend sodic soils with gypsum (CaSO 4 ) Add compost or mulch for soil protection from rain drop Add fertilizer or compost for plant nutrients Sow gully with perennial grass seed (native or exotic) Increase grass cover in gullies Fence out cattle Aerial, hand or spray grass seed in the wet season Weed management and control

6 Intensive Active Gully Rehabilitation Trials Before: Nov 2011 After: Dec 2011

7 7 Erosion Control Treatment Plots (7m x 30m x 10% Slope) (CRGC1-29/30) 1. No Treatment (status quo, highly sodic, infertile silty clay soils) 2. Gypsum, Compost, Native Grass (~80t/ha gypsum, 25mm compost; 180 kg/ha Native grass: Kangaroo, Black spear, Queensland bluegrass) 3. Gypsum, Compost, Exotic Grass (~80t/ha gypsum, 25mm compost; 180 kg/ha Exotic grass: Indian bluegrass, Saraji Sabi grass, Jap millet) 4. Gypsum, Hydromulch, Exotic Grass (~90t/ha gypsum, 25mm compost; 100 kg/ha Exotic grass: Indian couch, Sabi grass, Jap millet, verano stylo) 5. Gypsum Only (~80t/ha gypsum) 6. Compost, Native Grass (25mm compost; 180 kg/ha Native grass: Kangaroo, Black spear, Queensland bluegrass) 7. Straw, Exotic Grass ( 25mm straw; 180 kg/ha Exotic grass: Indian couch, Saraji Sabi grass, Jap millet) Before Dec 2011 After April 2012

8 Plot 2 & 3 (Compost) Rainfall-Runoff and Erosion Re-initiation Plot 4 (Hydromulch) Rainfall-Runoff Only No Runoff From Above Scarp Plot 5 (Gypsum Only) Plot 6 & 7 (Straw & Compost)

9 April 2013 Results [After Two (2) Wet Seasons] Experimental Treatment Plots: CRGC1-29/30 Upper Plot Lower Plot 1 upper 2 upper 3 upper 4 upper 5 upper 6 upper 7 upper 1 lower 2 lower 3 lower 4 lower 5 lower 6 lower 7 lower Battered Control No Treatment Battered Gypsum Compost Native Grass Battered Gypsum Compost Exotic Grass Battered Gypsum Hydromulch Fertilizer Exotic Grass Battered Gypsum Only Battered Compost Native Grass Battered Straw Exotic Grass

10 Ground Cover: April 2013 Results Vegetation Cover After Two (2) Wet Seasons Experiment # 1: Gully 29 Dead Organic Ground Cover Live Weed Cover Live Grass Cover % Ground Cover Battered, Control, No Treatment Battered, Gypsum, Compost, Native Seed Battered, Gypsum, Compost, Exotic Seed Battered, Gypsum, Hydromulch, Exotic Seed Battered, Gypsum Only Battered, Compost, Native Seed Battered, Straw, Exotic Grass

11 Exchangeable Sodium (Na) With Gypsum Treatment Surface Soils ONLY Experiment # 1: CRGC1 Gully 29/30 09/Dec/ /Dec/ /Jun/2012 ESP (%) Battered, Control, No Treatment Battered, Gypsum, Compost, Native Seed Battered, Gypsum, Compost, Exotic Seed Battered, Gypsum, Hydromulch, Exotic Seed Battered, Gypsum Only Battered, Compost, Native Seed Battered, Straw, Exotic Grass Adding gypsum to surface soils reduces ESP compared to control Why did these change? Organic influence? Soil Variability? Error?

12 30 Infiltration Rates Aug/Sept 2012 Following Treatment (Double Ring Infiltrometer) Experiment # 1: CRGC1 Gully 29 Average Infiltration Rate (mm/day) Day NET 5-Day NET Battered, Control, No Treatment Battered, Gypsum, Compost, Native Seed Battered, Gypsum, Compost, Exotic Seed Battered, Gypsum, Hydromulch, Exotic Seed Battered, Gypsum Only Battered, Compost, Native Seed Battered, Straw, Exotic Grass Adding Gypsum, Compost, or Grass or Combination Improves Infiltration..But.. Improved Infiltration Rates (<25mm/day) still do not match rainfall rates (> mm/day)

13 LiDAR Changes by Plot CRGC1-29 Plots 1 to 7 Dec 2011 to November Plot 4 = Hydromulch, Gypsum = Least erosion, but poor long-term cover Plots 2,3 = Compost, Perennial Grass, Gypsum = Best long-tem cover, minor erosion

14 Summary: Gully Slope Stabilization Re-grading gullies does not stop erosion Just reinitiates. Adding gypsum, mulch and grass reduces erosion by protecting and binding the soil and increasing infiltration Rill erosion continues to be persistent.. Rainfall > Infiltration promotes water runoff, sheet flow, rilling.. Gully head-cutting from the bottom still a major threat to slope stability Can add grade control structures to improve stability Hydromulch, gypsum best for short term erosion reduction Compost, gypsum, perennial grass best for long-term vegetative cover PHYSICAL INTERVENTION IS EXPENSIVE!!!!!! ~ $6,000 to bulldoze, gypsum, hydromulch a 0.2 ha (50x40m) gully slope ~ $60 million to treat 2000 ha of mapped alluvial gullies in the Normanby Would this actually reduce erosion or accelerate it???

15 Cattle Exclusion Trials and Passive Rehabilitation Will Grass Vegetation Recover and Reduce Erosion if Cattle Are Excluded From These Sites for Years? Rely on Natural Resilience of Vegetation Applicable at Large Scales Potential to Destock Larger Areas of Erosion? Cumulative Sediment Reductions?

16 Trial Fenced Cattle Exclusion Sites #1) West Normanby River Frontage Study Design 2-5 ha exclusion areas Before-After Control-Impact design Control vegetation plots (outside) Treatment vegetation plots (inside) Different geomorphic units Before Fence: Nov-11, Apr-12 After Fence: Nov-12, Apr-13, ongoing??? LiDAR Topography 2009 & 2011 #2) Crocodile Old Hay Paddock Metrics At Vegetation Plots % cover # of species Tussocks counts Pasture yield Soil condition Overall land condition rating Grass & weed species ID and diversity #3) Granite Normanby River Frontage

17 Best to Not Initiate Gully Erosion in the First Place!!!! Reduce land use pressures in erosion sensitive areas

18 Acknowledgments Stations Crocodile Station and Indigenous Land Corporation Springvale Station and Outback North Kings Plain Olivevale/Fairview Normanby Station People CYSF: Isha Segboer,Trish Butler, Peter Thompson South Cape York Catchments: Jason Carroll CYMAG: Ian, Malcolm and Lynette McCollum DEEDI: Joe Rolfe Ted Lee and Sue Marsh and Laura Rangers Western Yalangi Landcare and Andrew Hartwig Christina Howley Zoe Lieb Anglea Gleeson Amanda Hogbin Materials and Equipment Mo Jenkins Mario Puccini Excavating Oz Earthmoving Swiss Farms Compost Native Seeds Tony Illling Seeds Jones Mobile Crushing and Screen Revegetation Contractors Miriwinni_Lime Far North Earthmoving Analysis RPS: Nick McKelvey Australian Tropical Herbarium: Gerry Turpin & Darren Crayn Environmental Analysis Laboratory: Graham Lancaster & Kris Saville Griffith University: Rawaa Abdul Jabbar, Bahar Nader Al-Uzairy, Scott Byrnes, Daniel Borombovits Terranean Mapping Technologies/RPS: David Moore

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