Flood recovery is not a problem most of us have had to deal with before so we can only try to solve the problems individually and make adjustments in the future.
The main problems seem to be: 1) Soil washed away-erosion 2) Soil dumped on top of plants, trees and existing soil 3) Plants washed away
4) Weed seeds deposited on the soil 5) manure and sewage and unknown contaminants deposited on the land
Soil washed away: Soil can be hauled in or the remaining soil can be rejuvenated. Most topsoil for sale in Colorado is mostly screened clay, so if you have soil hauled in, unless you are filling deep holes, order Planter’s Mix that has at least 30% compost. If you are rebuilding the remaining soil where the topsoil was washed away, cover the soil with 2” of landscape-waste compost (composted manure is fine if only 1” is put down or if there are no plants to burn, 2” is good). Rototill or dig this into the soil along with an organic fertilizer (organic is longer lasting and contains important micronutrients). Or plant a cover crop and till it in at the proper time.
If soil was washed off tree roots, cover them with no more than 2” of soil because the roots need oxygen, and perhaps 2” of a fine wood chip mulch that will break down more quickly and add to the organic matter of the soil.
Soil dumped on top of plants, trees and soil: As soon as possible, remove soil that is piled on top of tree roots if it is more than 2” deep. If too much soil covers the roots, trees can decline or die. If the soil is over grass only, the grass can grow up through 1”-2” of soil and some people say grass can grow up through 5” of silty-sandy soil.
Soil on top of plants must be removed immediately or it may already too late to save them. After shoveling close to the plant, it is easier to use a hose to wash (or blast) off layers of mud. A layer of silty-sandy soil might actually be beneficial to let water through which will be held by the clay layer below, and it may provide better drainage than your original clay soil and therefore be easier to grow drought-tolerant plants. You will probably want to add some compost and fertilizer to these deposited soils. It could also be a good idea to get a soil test.
Plants washed away: If most of your soil is left intact, just replant. At the end of this article there is information on where to find a list of plants that are good frontier plants to establish on poor soils or in exposed, rugged sites. The list includes plants with tenacious root systems that prevent erosion and resist washing away.
Weed seeds deposited: Many plants will come up from seeds deposited by the flood water, and in the mud. Many of these volunteers will be weeds, but some near the foothills or open spaces will be natives. There can be several approaches: 1) let everything grow until it gets big enough to identify and cut down the undesirables before they flower and go to seed. They can be composted or left on the ground for mulch 2) plant no seeds and plant container shrubs, trees and perennials, then sow the area with Corn Gluten which will prevent all seeds from developing 3) weed everything, water and let the seedlings come up and weed again (maybe even a third time), then plant grass seed, cover crops or what have you.
Manure, sewage and other contaminants deposited on your land: Nature is a wonderful rebuilder/recycler all by herself, but she needs time to perform her magic of turning wastes into fertilizer. We humans can speed up the process considerably by feeding the existing microorganisms their favorite foods-carbon and natural nitrogen (plant wastes and animal wastes). And we can also inoculate our soils with beneficial bacteria, beneficial fungi and mycorrhizae to speed up the breakdown of wastes and to colonize the roots of plants. This is especially important where the topsoil was washed away along with the soil life.
The Biodynamic community has long relied on Pfeiffer’s Field Spray which is a combination of 55 selected microorganisms to rapidly breakdown organic matter like raw compost and cover crops. Also effective are compost tea, a biologically active compost spread over the ground and scratched in, and there are other microbial products that can speed up the composting process and purify organic contaminants.
In my personal experience, I have seen how the composting process, rich with soil microorganisms can even break down pesticides.
Rebuilding soil and preventing erosion can be accomplished with planting seed mixes of grasses that are adapted to our conditions. Mountain conditions are different than Plains conditions are require different grasses. For the Foothills, Lynn Reidel, from Boulder Open Space and Mountain Parks, recommended this mix: Western Wheatgrass, Thickspike Wheatgrass, Slender Wheatgrass, Green Needlegrass, Sideoats Grama, Blue Grama, Little Bluestem and Buffalograss
Plants to establish where the topsoil was washed away or to prevent erosion
Artemisia filifolia-Sand Sage
Artemisia frigida-Fringed Sage
Artemisia ludoviciana-Silver King Sage
Artemisia tridentata-Big Sage
Cercocarpus montanus-Mountain Mahogany
Cercocarpus ledifolius-Curlleaf Mt. Mahogany
Cornus sericea-Red Twig Dogwood
Ericameria-both Tall and Dwarf Rabbitbrush
Mahonia repens-Creeping Mahonia
Populus tremuloides- Aspen
Prunus Americana- Wild Plum
Prunus virginiana- Chokecherry
Quercus gambelii-Gambel Oak
Quercus undulata-Wavyleaf Oak
Rhus glabra cismontana– Smooth Sumac
Rhus trilobata – Threeleaf Sumac
Ribes aureum-Golden Current
Rosa woodsii-Wood’s Rose
Rubus deliciosus- Boulder Raspberry
Salix irrorata-Bluestem Willow
Shepherdia argentea- Buffaloberry
Symphoricarpus – Snowberry
Achillea lanulosa-Native Yarrow
Asclepias speciosa-Common Milkweed
Asclepias tuberosa-Butterfly Weed
Aster laevis-Smooth Aster(and other asters)
Eriogonum many species
Eriogonum umbellatum-Sulphur Flower
Fragaria americana-Wild Strawberry
Geranium viscossimum-Sticky Geranium
Helianthus pumilis-Dwarf Sunflower
Helianthus salicifolius-Willowleaf Sunflower
Iris missouriensis-Blue Flag Iris
Linum lewisii-Blue Flax
Mirabilis multiflora-Desert Four O’Clock
Oenothera caespitosa-White Evening Primrose
Oenothera missouriensis-Missouri Evening Primrose
Rudbeckia hirta-Blackeyed Susan
Solidago nana-Dwarf Goldenrod
Solidago rigida-Stiff Goldenrod
Thermopsis- Golden Banner
Achillea millefolium-creeping yarrow
Anacyclus depressus-Atlas Daisy
Chives and Garlic Chives and Garlic
Many Creeping Veronicas
Prunella vulgaris-Self Heal
Vinca major and minor-Periwinkle
Apples if not soggy soil
Buddlea alternifolia-Silver Butterfly Bush
Dwarf Flowering Almond-Prunus tenella
May Day Tree-Prunus padus