Long Valley Meadow Restoration Project

Transcription

1 Long Valley Meadow Restoration Project USDA Forest Service Mogollon Rim Ranger District Coconino National Forest Coconino County, Arizona T13N, R9E, Section 12 and T13N, R10E, Sections 6 and 7 Gila and Salt River Baseline and Meridian Description of Meadow Restoration Activities The following meadow restoration actions would be implemented by heavy machinery and/or volunteer crews with supervision by Forest Service personnel. Headcut stabilization Headcuts, if left untreated, will continue to migrate upstream, forming channels that will dissect the meadow and lower the local water table. Roots of grasses and forbs may become perched above the water table, resulting in drying or desiccation, reducing vegetative ground cover and its stabilizing effect. Several methods would potentially be used for stabilization of headcuts. The first method involves sloping the vertical portions of headcuts to a gentle angle of repose followed by either placement of angular rock above an erosion control mat to form an erosion resistant rock chute or through establishment of native grass on the newly established slope. Erosion control matting such as coir mat fabric (described below) would also be potentially used to assist with slope stabilization during establishment of native grasses. Where possible, the native sod would be stripped prior to sloping and replaced on the treated slope. The second method involves the use of angular rock typically ranging in size from 4- to 18- inches to construct Zuni bowls as described below. The third method of headcut stabilization involves the use of locally harvested logs to create a log step fall structure as described below. These headcut stabilization methods would require heavy machinery (small tracked excavator) or possibly hand crews to complete the work. Bank Sloping Where banks of streams or gullies are too steep (i.e., less than 2 feet of run to 1 ft. of rise) it is difficult to establish or maintain vegetative cover. Using heavy machinery or potentially hand crews, soils will be removed from eroding banks to create slopes with approximately

2 3:1 ratios. Excavated material would be removed from the banks and deposited on higher terraces away from channels or used to restore the longitudinal profile of a channel by raising the channel bed through placement and compaction of fill. Restoration of the longitudinal profile of a channel would re-connect incised channel segments with their floodplain while also preventing headcut migration. All disturbed areas would be reseeded, and protected with erosion control fabric. Grade Control structures Cross-Vane Weir Cross vane weirs will be used to control grade while centering flows and maintaining sediment transport (Rosgen, 2006). They consist of natural rock arranged in a v-shape across the channel, with the arms pointing upstream and the tip pointing downstream. The arms of the v extend from bankfull elevation upstream into the bed of the channel at a 2-7% slope relative to the bankfull slope. The arms extend out from the bank at an angle of less than 30º and extend approximately 1/3 the bankfull distance into the stream before arcing to intersect the other arm. Rock size will be determined using empirically based equations and designed shear factors. Larger, or feature rocks will be anchored in place using footer rocks on the downstream side to resist movement. The instream portion of the weir is tied to wings of rock buried in each bank. Installation of these structures should slow water velocities, reduce stream power and provide grade control. One-Rock Dams This grade control and energy dissipation structure is constructed with a single layer of rock, across the channel bed. The structure creates an artificial riffle in the channel. The structure extends up the banks of the channel, at least to the bankfull elevation. They increase channel stability and decrease erosion and scour by reducing water velocity and storing moisture in the inner spaces of rocks, providing suitable sites for vegetation to reestablish, which further increase channel stability and erosion resistance. See Figure 3. Zuni Bowl This grade control structure provides protection from erosive flow where a steep portion of the channel or headcut exists. The structure is built of rocks which line the channel and allow for energy dissipation without erosion by creating a step fall and plunge pool. See Figures 4 and 5.

3 Figure 3. Diagram of One Rock Dam. Figure 4. View upstream of a proposed Zuni Bowl placement.

4 Figure 5. Diagram of a Zuni Bowl. Log Step Fall A log step fall (see figure 6) is typically used as a type of grade control structure in which the energy of water at a headcut is dissipated through a gradual change in stream grade as opposed to the abrupt change in grade that occurs at a headcut. Figure 6. Log Step Fall Structure.

5 Figure 7. Rock Chute Structure Contour Plowing Contour Plowing with a Yeoman type plow develops a pattern of off-contour cultivation in which all the rip marks left in the soil will slope down towards the center of the ridge. This pattern of contouring, using a Yeoman plow allows more time for water to soak in. Contour plowing also enables controlled flood irrigation of undulating land, which further assists in the rapid development of deep biologically fertile soil, which improves soil nutrition and health. Tree Removal Conifers are encroaching into the meadow areas, threatening the integrity of the grassland ecosystem. Tree removal from the meadows and thinning of encroaching trees along margins is recommend to restore grasslands and promote overland flow. Point bar shaping Where the channel width is constrained by evolving point bars, reshaping of the point bars to allow for a proper bankfull channel width would occur. Point bar reshaping allows flood waters to flow through a meander without scouring and eroding outside banks and causing undercutting. This practice accelerates the channels progression toward stable dimensions by contouring the point bar to shallowly grade up from the thalweg to the floodprone elevation at an appropriate width. Erosion Control Matting

6 Coir mat fabric, a natural, biodegradable bristle coconut material would be placed over seeded areas or staked to disturbed areas to provide suitable protection of sites from scour and to provide favorable conditions for seed germination. Other non-biodegradable erosion control matting materials typically made from polypropylene fibers would be used to prevent loss of fines beneath grade control structures. Utility Constraints No utility constraints have been found within the project area. Prior to excavation, Arizona 811 will be contacted to verify there are no underground utility concerns and to have any utilities within the project area marked to prevent injury to workers or damage to utilities. Disturbed Areas All disturbed areas will be seeded with an approved native seed mix. Any access roads would be returned to a pre-construction condition upon completion of the restoration activities. Revegetation and use of natural fiber erosion control matting as described above would protect disturbed areas from scour and erosion. Tank Removal Heath Tank No. 1 and Heath Tank No. 2 are degraded stock tanks that are no longer functioning as initially designed(figure 7). Both are causing headward erosion through the meadow system, resulting in dissection of the meadow by channelized flow and a series of gullies. The spillway of Heath Tank No. 1 causes channelized outfall, which contributes to increased flow velocities resulting in channel incision and erosion. The removal of the tanks would promote overland flow and reestablish hydrologic conditions that will supports restoration of the downstream meadow reaches. Removal of the impoundments and regrading of the surrounding area would restore proper hydrologic function to this portion of the meadow system. Log sills may be used to maintain grade as vegetation re-grows and to keep large flood events from incising into the meadow. Pond and Plug Treatment As previously noted, the meadow downstream of Heath Tank No.1 has been dissected by a channel originating at the outlet of Heath Tank No. 1. A common restoration practice for this type of condition is known as Pond and Plug. Short segments of the incised channel are ponded through installation of earthen fill dams, or plugs. It is not necessary to completely fill the existing channel. The open channel portion creates a pond where runoff collects during runoff events and eventually spills out onto the meadow as overland flow. The area available for water to spill onto the meadow prevents surface scour and erosion. Figure 8 provides an aerial view of a pond and plug treatment on the Plumas National Forest in California.

7 Figure 7. View downstream from Heath Tank No. 1. Figure 8. The Red Clover-McReynolds Project on the Plumas National Forest, the first spring after construction (2008) (Photo: Jim Wilcox).

8 Disturbed Areas As with Phase I work, all disturbed areas would be seeded with an approved, weed free native seed mix. Given the types of restoration work to be performed, heavy equipment would be necessary and would result in the need for temporary access roads. These roads would be returned to a pre-construction condition upon completion of restoration activities, including but not limited to scarification and seeding. Media Luna Media Luna, or sheet flow spreaders would be used to spread concentrated flows. The structure is made up of rocks keyed into the channel and shaped to promote the dispersal of flow across a valley bottom or meadow in the form of sheet flow. Figure 9 provides an example of a Media Luna. Figure 9. Example of a Media Luna. Contour Plowing Contour Plowing with a Yeoman type plow may also be used during Phase II restoration. Areas for contour plowing would be integrated into the locations of channel plugs and overflow/inflow into ponded areas.