Revitalizing Riparian Systems

Problem: Our current stream channel management techniques in Yolo County have left us with mostly narrow, thinly vegetated streams that house little wildlife and are unable to carry the high flows of winter storms. The bare, eroding banks serve as excellent substrate for propagation of noxious weeds such as yellow starthistle, giant reed, and peppercress and allow tons of sediment to be carried away downstream, only to clog channels or be deposited on adjacent fields. Standard winter maintenance efforts of excavating silt and weeds only perpetuate the problem by leaving the banks bare again for further erosion and weed establishment.

Solution:One solution to the problem of constant maintenance and degradation of our streams is to reintroduce some of the original natural bank structure and plant systems. The original native riparian plant species that once populated these streams can be reintroduced to serve multiple functions of stream bank stabilization, weed suppression and wildlife habitat. Re-grading banks to a more natural benched slope increases the flood capacity of the stream while making room for vegetation and wildlife. Depending on each individual situation, such channel re-sloping may or may not be necessary. Most landowners will find that "pulling back the levee" for such a project is only necessary on one side of a channel, minimizing the amount of land that would be taken out of production and leaving one side accessible for channel maintenance. If land adjacent to a stream is marginal, often flooded or difficult to farm anyway, such a channel alteration may have little impact on farm income beyond the cost of the project. The rest of this article gives a brief description of some of the steps required to enhance a stretch of stream on your property.

Ideally, any stream restoration project should be part of a coordinated effort along the entire stream or watershed. The California Department of Fish & Game (CDFG) is required to include an environmental review under the California Environmental Quality Act (CEQA) as part of the Streambed Alteration Agreement process (see below). Cost-sharing opportunities exist for riparian improvement projects through the Natural Resources Conservation Service (NRCS), CDFG  and the California Wildlife Conservation Board. The funding from different sources can be combined and increased, especially when multiple landowners cooperate on a project. 

Permits
Depending on the scale of your project, you will need to consult with different natural resources agencies to do the job with minimal negative environmental impact. This is the step that most growers dread, but it is not necessarily the ordeal it is made out to be. A good first step is to start with your local Resource Conservation District (RCD) and county planning department for some basic direction. Permit-wise, the first agency to consult is the CDFG. The local game warden for the CDFG can make a site visit to help you determine what environmental review permits you might need other than a Streambed Alteration Agreement ($500-$1100 for our typical projects, depending on size). There is also often an additional fee for the associated CEQA documentation.  If you intend to leave any disturbed earth or gravel within the stream channel or banks, you should apply for a Nationwide Permit #27 (no cost, one month process) from the Army Corps of Engineers (ACOE). Their Nationwide Permits are pre-approved and involve little paperwork. As part of that permit you will also have to contact the California State Water Resource Control Board (SWRCB) for Clean Water Act Section 401 Water Quality Certification (Base fee is $500 with additional fees for dredging and filling). Depending on the recommendation of your CDFG contact, you may also need to consult with the US Fish and Wildlife Service regarding potential sensitive wildlife and seek a Cultural Resources review of the site. Your local RCD and NRCS Field Office should be able to assist you with all of these. Some RCDs have developed permit coordination programs to streamline this process for conservation projects of this type, so checking with them first can save you considerable time if there's such a program in place in your county. Yolo County RCD should have a permit coordination program available by early 2008. Two handy on-line guides are available through the Sacramento River Watershed Program and the California Association of Resource Conservation Districts.

Breaking Ground
Once you have determined your project location, scope of work and have dealt with the appropriate agencies, you're ready to break ground. The ideal time for such work in Yolo County is from late summer through mid-October, when most ephemeral streams have dried down enough that you don't have to worry about equipment getting stuck. If your project includes reshaping the stream channel, an engineer or landscape architect can help you in determining how best to balance your cutting and filling work. For any permit-approved project, the NRCS provides this service free of charge. (If you have watched the stream in question over a number of years, you are probably aware of its "Ordinary High Water Line"  -- how high the water gets in an average year after a winter storm. If you can limit your earthwork to the bank above this line, you will decrease your chances for needing an ACOE or SWRCB permit.) You can improve the likelihood of revegetation success if you stockpile your topsoil during earth moving and replace it as the top layer of soil on the planting surfaces of your new levee when filling and shaping. The soil in the lower soil horizons may have good texture, but it is poor in nutrients and organic matter, which will be vital to the success of your revegetation effort.

Why reshape the channel?
The primary reasons for channel shaping are to increase the flood capacity of the stream and make planting and maintenance work easier. Streams in lowlands typically develop a channel form that is stepped, consisting of a small, incised, low-flow channel that carries year-round flow and a broader high-flow channel (or flood plain) that carries storm flows. The earth (spoils) that is removed in creating a high-flow channel can be used to build up the levee along the stream to further protect adjacent land from flooding. Key factors in developing your channel cross-section should be desired stream channel capacity (with the added vegetation), long-term maintenance needs (equipment access, etc.), and the desired slope or grade for the 'set back' levee bank to facilitate planting and maintenance. A typical 'flood plain' bench is at least 10-15' wide to accomodate equipment for mowing and channel maintenance. A typical levee should not be graded any steeper than 3:1 to allow planting, with more gradual slopes such as 4:1 or 6:1 even more preferable. The engineer at your NRCS or RCD office should be able to design a channel cross section that meets these criteria and further consult for the hydrological information to support the design. If you also desire to re-align your stream (such as from a straightened channel back to a meandering form), that involves a much higher level of engineering and potential liability than this article covers, but through consultation with your local NRCS or RCD field office you should be able to determine if they can provide such a service or if you need to work with a private engineering or environmental consulting firm.

Vegetation
Vegetation of the site is key to a project's long-term success. A successful revegetation effort will stabilize your new banks and suppress noxious weeds. Riparian plant systems may be more complex than those in traditional agriculture, but any farmer should be able to manage them easily. All vegetation should be selected to match the soil and hydrologic conditions of the site -- i.e., light or heavy soils, alkalinity and proximity to the water table. The existing plants near the site are a good indication of what grows best there. The RCD and local NRCS can assist you in developing an appropriate plant list for your site.

Establishing groundcover vegetation for bank stabilization and weed control is an essential aspect of revegetation. Ground cover vegetation includes native grasses, sedges and rushes, which can be planted either by direct seeding or plugs. These plants will require "farming" for their first 2-3 years to aid their establishment, during which weed control is essential. Herbicides, mowing, grazing, and fire are all useful weed management tools. The Yolo County RCD has a detailed article available with specific information on perennial grass establishment.

There are many native, riparian trees, shrubs and forbs that can be included in a riparian enhancement project to increase biodiversity and habitat value. These can be propagated either from cuttings, seeds or starts. Native plant nurseries and most RCDs have lists and information about them available to the public. Many of these plants need some protection from herbivory and weed competition, for which tree shelters, weed mats, manual weeding, and careful herbicide application are useful tools. A short list of recommended native plants is below.

Planting Zones
Planting should be made in zones to facilitate water movement and maintenance access, and to ensure planting success. Four basic zones are briefly described below, moving from the stream channel up to the bank top.

Bank of Low-Flow Channel: Plants that are tolerant of saturated soils and frequent inundation such as Spikerush, Baltic rush, Alkali bulrush, Slender sedge, Barbar's sedge and Creeping wildrye are best in this zone. These plants have an important role in bank stabilization and are the hardest hit by stream flow. Their low profile and ability to fold over minimize restriction of water flow. A number of shrubs and trees can tolerate these conditions to a degree, but placed near the center of the stream channel, they would represent a real reduction in channel flood capacity.

High Flow Channel or Flood Plain: Naturally-occurring stream benches are typically inundated only during high flows following winter storms when the stream spills over its low-flow channel. During the rest of the year, this portion of the channel typically remains dry. To facilitate storm flows, plantings in this zone should be of low stature. Candidate plantings are any moisture-tolerant perennial grasses (e.g., Meadow barley, Creeping wild rye, and Slender wheatgrass) or low-growing shrubs such as Wild rose and Poison oak. (Note: for property owners concerned about trespassers, brambles and Poison oak look better than a fence and work as well or better.) This zone can also host a two-tire access road for maintenance and should be configured to accommodate equipment the landowner envisions using in the future.

Bank of High-Flow Channel:  For soil stabilization and ground cover, this zone should be seeded with perennial grasses similarly tolerant of seasonal flooding. This is the best site for flood-tolerant trees and shrubs such as willows, Cottonwood, Mulefat, Box elder, Valley oak, Black walnut, California sycamore, brambles, and vines. If flood capacity is a concern, the shrubby plantings can be kept higher on the bank. Trees provide valuable weed suppression by shading and, with some training, their trunks provide minimal water flow restriction. The extensive roots of shrub and tree plantings fortify the stability of the bank and levee.

Levee: The top and field-side portion of the levee are appropriate sites for planting shrubs and grasses that are less tolerant of inundation, such as Toyon, Elderberry, Blue wildrye, Purple needlegrass and Onion grass. Many plants could be included in this mix that might provide insectary benefits to the adjacent fields as well. Many farmers use the top of their stream levee as a field access road, which need not be left bare of vegetation. Roads can be maintained with low-stature perennial grasses down their middles and sides, though an extra pass with a mower may be needed in the summer.

Mulches
Immediate bank stabilization and weed suppression is aided by the use of mulches and mulching fabrics, which reduce the exposure of soil to moving water but allow plants to grow through them. Loose straw and wood chip mulches are common mulching materials but typically only an anchored fabric would hold up against a consistent stream or sheet flow of water.  There are many mulching fabrics available that can withstand various intensities of flow, consisting of materials from woven straw to geotextiles. These require careful anchoring to be effective and are not recommended for streams with high flows. In situations with highly erosive flows, special armoring with bioengineering structures  that incorporate live willow cuttings and quarried rock may be necessary.

Plant List for "Riparian" Hedgerows
The following is a list of possible plants for hedgerow designs in riparian-type situations. Abundant water is a prerequisite for establishment and normal growth. The plant's proximity to standing water should vary from species to species (e.g., locate most trees higher on slopes than shrubs). One should consult a planner for appropriate planning schemes. The notes provide information to help determine planting combinations that allow individual species appropriate sunlight and adequate space. General growth habits may also be included. Hedgerows comprised of a mix of trees and shrubs are generally long-lived. Trees are typically longer-lived than shrubs. Many shrubs, however, can have life spans of more than 15-20 years. All of these plants require summer irrigation during their establishment period.

Trees (Evergreen)

The following list of native species is for general information only. NRCS does not imply or consent to the use of this information as a recommendation for species selection. Plant establishment is not implied. Varying environmental and human factors such as soil type, climate, topography, weed management and watering regime will invariably affect the establishment of these plants.

Proper stream channel habitat and flow improvements require thoughtful planning, but yield very satisfying results in terms of aesthetics, flood control, animal visitation and maintenance reduction. Although the task may appear overwhelming, your local RCD and NRCS field offices have skills to support you in your effort. They can also provide direction in dealing with other agencies and contractors.

California Department of Fish & Game
Gary Hobgood
Region 2 - 1701 Nimbus Road, Suite A
Rancho Cordova, CA 95670
Phone: 916.983.6920

US Army Corps of Engineers
Marc Fugler
Regulatory Branch, Sacramento District
1325 J Street, Rm. 1480
Sacramento, CA 95814-2922
Phone: 916.557.5255

Regional Water Quality Control Board

Patrick Gillum
Central Valley Region
11020 Sun Center Drive #200
Rancho Cordova, CA 95670
Phone: 916.464.4709

US Fish and Wildife  Service
Michelle Tovar
Endangered Species Division-Sacramento Valley branch
2800 Cottage Way, Suite W2605
Sacramento, Ca 95825-3901
Phone: 916.414.6645