Source Controls: Remediation of Scarred LandscapesVic Claassen, research soil scientist

Regeneration of soil hydrologic function on disturbed sites increases erosion resistance and supports sustainable vegetative cover.

Can engineered / constructed installations be coupled with natural field processes?

165,000 mine features; 47,000 abandoned mine sites

CA DOC OMR

Few sites will receive formal treatment

Can sediment be immobilized using intensive revegetation rather than by constructed projects?

As an example, a precise grading job can be a potential infiltration problem.

Without infiltration, rainfall accumulates as overland flow.

Runoff mobilizes sediment, including surface sorbed, colloidal mercury.

Low infiltration rates cause rainfall to accumulate at the surface.

Splash detachment disperses smaller particles and plugs pores.

Disturbance breaks down soil aggregates

Smaller particles have smaller pores and slower infiltration.

Aggregate regeneration requires 1) sustained plant growth 2) minimal erosion.

Design elements for sustainable revegetation of drastically disturbed sites

1. Select a Reference Site.

2. Correct the site’s soil hydrology to provide adequate:a. infiltration rate for short term target storm eventsb. infiltration capacity for multi-day target storm eventsc. moisture retention for summer plant growth

3. Correct chemical and fertility

4. Use site adapted plant and microbes

Case study: Highway 20 Colusa County. Coast Range annual grass/oak woodland are in the foreground, with serpentine chaparral in the background around the gray serpentine cutslope. (BLM; Bear Creek watershed)

Center and left foreground shows an engineered earth buttress. Right half and background show cuts into serpentine geology (1.8:1 slope).

Rills and gravel pedestals indicate insufficient infiltration and chronic surface erosion.

Surface infiltration was characterized with a rainfall simulator, bulk density, constant head permeameter, and tension infiltrometer.

Red arrows indicate jackhammer fracture row locations to 24 or 36 inches depthHydrus 2d* software integrated field–

measured hydrology into a dynamic model of water infiltration and lateral flow. The existing slope was simulated as well as a hypothetical treatment of fractured substrate on a level base.*Simunek, J., M. Sejna, and M. Th. van Genuchten, 1999

Key to color representation of pore pressure in the modeled soil volume: values in cm of water pressure: negative pore pressures (strengthens soil) blue -30 to - 60 cm light blue -30 to -15 cm dark green -15 to - 5 cm light green - 5 to - 0 cm positive pore pressures (weakens soil) yellow + 0 to 2 cm orange + 2 to 5 cm red + 5 to 15 cm dark red + 15 to 25 cm black > 25 cm head

Simulation of a 25 year 1 hr storm shows vertical flow (upper left), then lateral flow down slope (upper right) after the surface horizon saturates. Lower graphic shows positive pore pressures above the compacted horizon.

The upper graphic shows the untreated condition with a lateral slippage plane. The lower graphic shows pooling of rainwater on the ± horizontal bench, retaining 3 times the incident rainfall volume.

Key to color representation of pore pressure in the modeled soil volume: values in cm of water pressure: negative pore pressures (strengthens soil) blue -30 to - 60 cm light blue -30 to -15 cm dark green -15 to - 5 cm light green - 5 to - 0 cm positive pore pressures (weakens soil) yellow + 0 to 2 cm orange + 2 to 5 cm red + 5 to 15 cm dark red + 15 to 25 cm black > 25 cm head

Vector flow output for a 25 year 1 hr storm event shows no flows on the fractured bench since pores are larger and have not yet saturated.

(Arek Fristensky, UCD)

Approximately 15 minutes into the 25-year, 1 hour IDF storm event, lateral flow increases in the porous, low density surface layer becomes saturated (lighter colors). Flow at the toe of the bench is reduced.

About 20 minutes into the storm, overland flow starts to be captured in the fractured bench. Surface run-off is reduced on the plot surface and the untilled area immediately downslope from the plot toe.

At the end of the 25-year, 1 hour IDF storm event, flow starts to seep from the fractured bench at the toe (yellow arrows) indicates maximum infiltration capacity under these slope and storm scenario conditions.

Caltrans xsc diagram Colusa 20 cutslope mile 1.5

Geotechnical global stability analysis Colusa 20 cutslope mile 1.5

Plot construction: Remote locations require powered hand tools to avoid need for access roads. Holes were 2 - 3 ft deep, backfilled with 10% compost by volume. Cracks radiate out from the hammered holes (right photo).

The third aspect of site substrate hydrology is retention of adequate moisture in soil pores for summer plant growth.

Evapotranspiration is estimated by: ETa = ETo x Kc x Ks

Comparision of modeled ETo and ETa of coyote bush on a coast range soil

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1/1 2/20 4/11 5/31 7/20 9/8 10/28 12/17

Date

ET

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m)

ETa

ETo

ETo

Kc

Ks

Design elements for sustainable revegetation of drastically disturbed sites

1. Select a Reference Site.

2. Correct the site’s soil hydrology to provide adequate:a. infiltration rate for short term target storm eventsb. infiltration capacity for multi-day target storm eventsc. moisture retention for summer plant growth

3. Correct chemical and fertility

4. Use site adapted plant and microbes

Many mined sites have unique substrates that are selective for plant type. Here the typical coast range plants are displaced by serpentine adapted species in the shrubby area in the foreground.

Serpentine substrates with low calcium : magnesium levels select for serpentine-adapted plants. Lime or fertility amendments can reduce this selective condition, promoting weedy infestation of the site.

(Ryan O’Dell, BLM )

SUMMARY CONCEPTS

1) ‘Stability’ includes both surface erosional and geotechnical stability.

2) Erosional stability requires sustained plant growth.

3) Design elements for sustainable revegetation of disturbed sites

1. Select a Reference Site.

2. Correct the site’s soil hydrology to provide adequate:a. infiltration rate for short term target storm eventsb. infiltration capacity for multi-day target storm eventsc. moisture retention for summer plant growth

3. Correct chemical and fertility

4. Use site adapted plant and microbes