Subsurface Erosion in Response to Land Management Changes and Soil Hydropedology. G.V. Wilson, J. R. Rigby, S.M. Dabney

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1 Subsurface Erosion in Response to Land Management Changes and Soil Hydropedology G.V. Wilson, J. R. Rigby, S.M. Dabney USDA-ARS National Sedimentation Laboratory

Soil Pipeflow & Internal Erosion Impacts Rapid flow through

, 2001) when blockage of the soil pipe by eroded material

Photo by Joe Gartner, USGS Foster et al.

pipe flow was the leading cause of embankment failures.

2 Soil Pipeflow & Internal Erosion Impacts Rapid flow through soil pipes causes landslides and mud/debris flow (Uchida et al., 2001) when blockage of the soil pipe by eroded material causes internal water pressures to jump. Photo by Joe Gartner, USGS Foster et al., (2000, 2002) concluded that internal erosion of soil pipes by pipe flow was the leading cause of embankment failures. Internal erosion of soil pipes occurs undetected until a mature gully is suddenly formed by tunnel collapse (Swanson et al., 1989)

3 Pipes Form Over Restrictive Layers A common feature for pipe-erosion is the existence of water-restrictive layers, which Faulkner (2006) termed duplex soils, that focus flow through soil-pipes. Lateral Flow Lateral Flow Perched water Perched water Water-Restricting Horizon Water-Restricting Horizon Preferential flow can be so rapid that the shear forces exceed the soil strength binding particles and the pore erodes internally to form a soil-pipe. Pipeflow can be occurring even when no surface runoff. Internal erosion of soil pipes can be occurring undetected on the surface. If IE continues, the shear strength of the soil can be exceeded by the overburden forces and the pipe collapses producing an ephemeral gully at an advanced stage of development or sink holes/pipe openings.

4 Pipe Collapse Features

Agriculture (cotton) was historically practiced over the majority of the watershed, but is

5 Field Site Description C1 C2 C3 GCEW The 2,132 ha Goodwin Creek Experimental Watershed is located in Panola County, MS. Agriculture (cotton) was historically practiced over the majority of the watershed, but is currently only in flat (slope < 2%) alluvial plains occupying only 6% of the area whereas the hilly forest and pasture lands occupy 39 and 55 %, respectively. MS

6 Soils of GCW Pasture Site Loring silt loam C1 C2 C3 Catchment 1 = 5.0 ha, 72% Loring, 28 % gullied Catchment 2 = 6.5 ha, 98% Loring, 2% gullied Catchment 3 = 1.4 ha, 55% Loring, 45% gullied (fine-silty, mixed, active thermic Oxyaquic Fragiudalf) A p 0 to 18 cm, SiL, 10YR 4/3, moderate fine granular B t1 18 to 36 cm, SiL, 7.5YR 4/4, medium subangular blocky B t2 36 cm to 71 cm, SiL, 7.5YR 4/4, medium subangular blocky B tx1 71 cm to 81 cm, SiL, 7.5 YR 4/4, prisms to medium subangular blocky, iron accumulations (10YR 5/6) and depletions (10YR 6/2) B tx2 81 to 102 cm, SiL, 7.5 YR 4/4, prisms to medium subangular blocky, iron depletions (10YR 5/1) and accumulations (10YR 5/4) B tx3 102 to 127 cm, SiL, coarse prisms, iron depletions (10YR 5/1) and accumulations (10YR 5/4)

7 Pipe Collapses in GCW Pasture Site C1 C2 C3 Catchment 1 (purple) has no pipe collapse features, density=0 Catchment 2 (green) has 100 pipe collapse features, density=15.4 ha -1 Catchment 3 (orange) has 40 pipe collapse features, density=29.4 ha -1 WHY?

8 Pipe Collapses in GCW Pasture Site C2 Total Depth Length Width Volume Feature number cm cm cm m 3 Flute hole Sink Hole Small GW Large GW

9 Pipe Collapses in GCW Pasture Site C3 Total Depth Length Width Volume Feature number cm cm cm m 3 Flute hole Sink Hole Small GW Large GW

10 Soil Characterization of GCW Pasture Site

Classify Soil according Pinhole to test: flow rate, effluent Pinhole color, (2mm and final diam) hole through size as: center

11 Soil Characterization of GCW Pasture Site Soil cores have water retention determined using Tempe Cell apparatus, and K sat by constant head method. Then Pinhole test. Classify Soil according Pinhole to test: flow rate, effluent Pinhole color, (2mm and final diam) hole through size as: center Dispersive Constant Moderately heads (50, Dispersive 180, 380, 1020 mm) Measure flow Slightly rate, sed. Dispersive conc, effluent color Nondispersive (Non Erodible) 1 min intervals for 5 minutes at each head

12 Soil Characterization of GCW Pasture Site C1 Swale/thalweg positions Anthropic soil A p 0 to 5 cm, SiL, 10YR 3/4, granular, 5YR 5/6 flakes L1 5 to 19 cm, SiL, 10YR 6/6, weak subangular blocky, 10YR4/4 fragic pieces, L2 19 to 40 cm, SiL, 10YR 5/6, weak subangular blocky, occasional fragic pieces and gravel L3 40- cm, SiL, 10YR 4/3, weak subangular blocky, mottles, concretions, occasional gravel C1 Catchment Severely Eroded Hillslopes positions Natural Loring silt loam A p 0 to 4 cm, SiL, 10YR4/4, granular B t1 3 to 18 cm, SiL, 10YR4/6, weak subangular blocky B t2 24 to 32 cm, SiL, 10YR5/6, subangular blocky, mottles B tx1 25 to 38 cm, SiL, 7.5 YR 5/6, subangular blocky, weak iron depletions (10YR 6/2) B tx2 28 to 41 cm, SiL, 10YR 4/4, prismatic, iron depletions (10YR6/2) B tx3 41 to 48, SiL, 10YR4/4, prismatic, strong iron depletions (10YR7/1) Hillslopes have severely eroded Loring soil with upper layers missing Swale positions have Anthropic soil: sediment deposition

13 Soil Characterization of GCW Pasture Site C2 Swale/thalweg positions Anthropic soil A p 0 to 14 cm, SiL, 10YR 5/2, granular L1 14 to 33 cm, Si, 10YR 6/2, blocky, charcoal L2 33 to 46 cm, SiL, 10YR 5/4, 5YR5/6 flakes, subangular blocky, charcoal L3 46 to 65 cm, SiL, 10YR 5/6, 5YR5/6 flakes, subangular blocky, charcoal, concretions L4 65 to 88 cm, SiL, 10YR 5/6, 10YR4/4 fragic pieces, massive, charcoal, concretions C2 Catchment Hillslopes positions Natural Loring silt loam A p 0 to 11 cm, Si, 10YR 4/4, granular B t1 11 to 30 cm, Si, 7.5YR 4/6, subangular blocky B t2 30 to 48 cm, SiL, 7.5YR 5/8, subangular blocky B tx1 48 to 62 cm, SiL, 7.5 YR 4/6, subangular blocky, iron depletions (10YR 6/2) B tx2 62 to 74 cm, SiL, 7.5 YR 4/6, prismatic, iron depletions (10YR 7/1) B tx3 74 -, SiL, prismatic, iron depletions (10YR 7/2) Hillslopes have eroded Loring soil Swale positions have Anthropic soil: charcoal, artifiacts,

14 Soil Characterization of GCW Pasture Site All layers present, A p severely eroded C3 C3 Catchment All positions Natural Loring silt loam A p 0 to 5 cm, Si, 10YR4/4, granular B t1 5 to 27 cm, SiL, 10YR5/6, subangular blocky B t2 27 to 45 cm, SiL, 10YR5/4, weak subangular blocky, concretions, mottles B tx1 45 to 61 cm, SiL, 10YR4/4, subangular blocky, weak iron depletions (10YR 5/2), concretions B tx2 61 to 81 cm, Si, 10YR4/4, prismatic, iron depletions (10YR 5/2) B tx3 81-, Si, 10YR4/4, prismatic, strong iron depletions (10YR 7/1)

15 Soil Characterization of GCW Pasture Site Horizon Bulk Density mg m -3 SV kpa SPR kpa Pinhole Erodibility Natural Soil A p Non Erodible B t Non/Slightly Dispersive B t Slightly Dispersive B tx Slight/Mod. Dispersive B tx Slight/Mod. Dispersive B tx Slightly Dispersive Anthropic Soil A p Non Erodible Slightly Dispersive Moderately Dispersive Moderately Dispersive Moderately Dispersive Surface layer is non erodible due to high OM and root density Subsurface layers more erosive, especially the Anthropic soils Surface layer forms a bridge over soil pipes formed below Lower fragipan layer is erosion resistant and forms lower boundary

Soil Characterization of GCW Pasture Site 104 102 Elevation (m) 100 98 96 94 92-25 -20-15 -10-5 0 5 10 15 20 25 Distance (m) 104 Elevation (m) 104 102 100

16 Soil Characterization of GCW Pasture Site Elevation (m) Distance (m) 104 Elevation (m) Distance (m) Elevation (m) Distance (m) Anthropic material

and burnt C1 was smoothed and in C2 the burnt trees pushed into gullies and the

17 Past Land Use of GCW Pasture Site C1 in pasture, C2 in forest, C3 still in cotton with terraces C1 was pure gullies and raw banks late 1950s trees removed from C2, piled up and burnt C1 was smoothed and in C2 the burnt trees pushed into gullies and the gullies were filled in Trees removed from C3 swale All three catchments converted to pasture

18 Past Land Use of GCW Pasture Site 1977 no pipe collapse features 1978 Pipe collapse features first appear in C Pipe collapse features first appear in C over 100 pipe collapse features

19 Soil Pipe Erosion Processes Vertical Macropores: Increased from 12 to 40 ha -1 with depth Lateral Macropores on gully sidewalls: 30 ha -1 (0.1 to 0.5 cm diameter) Mostly between depth Pinhole goes from 2 mm to >10 mm in 20 minutes with 5 to 100 cm heads

Soil Pipe Erosion Processes 70 60 P19 14.0 12.0 10.0 P23 Pressure (cm) 50 40 30 20 10 0 4/18 4/19 4/20 4/21 time 35.0 P8 30.0 25.0 Pressure (cm) Pressure (cm) 8.0 6.0 4.0 2.0 60.0 P13 4/18 4/19 4/20 4/21 time 50.

20 Soil Pipe Erosion Processes P P23 Pressure (cm) /18 4/19 4/20 4/21 time 35.0 P Pressure (cm) Pressure (cm) P13 4/18 4/19 4/20 4/21 time Pressure (cm) /18 4/19 4/20 4/ P2 time /18 4/19 4/20 4/21 time Pressure (cm) Heads of cm that last for hours to days /18 4/19 4/20 4/21 Time

21 Soil Pipe Erosion Processes Pinhole goes from 2 mm to >10 mm in 20 minutes of 5 to 100 cm heads Comparable heads and flow rates that last for hours during numerous storm events annually.

22 Summary Erosion can take place in subsurface without evidence of erosion on surface Fragipan layers can restrict vertical water movement and foster lateral flow The surface layer is non-erodible and forms a bridge over more erosive subsurface layers Lower fragipan layer is erosion resistant and forms bottom of gullies Sediment deposited in old filled-in gullies are highly susceptible to piping Susceptibility to piping is dependent upon land use history as well as soil properties 20 to 40 year transition period following conversion of forest/cropland to pasture, combined with filling-in gullies, for pipe erosion to be evident on surface

Updating Slope Topography During Erosion Simulations with the Water Erosion Prediction Project

Updating Slope Topography During Erosion Simulations with the Water Erosion Prediction Project This paper was peer-reviewed for scientific content. Pages 882-887. In: D.E. Stott, R.H. Mohtar and G.C. Steinhardt (eds). 2001. Sustaining the Global Farm. Selected papers from the 10th International