Recreating Natural Landforms

By Jodie Carter

Aerial view of the mitigated pond connected to the right bank of the Sacramento River. After a 32-mile levee project impacted the lands ecosystem, a restoration plan called to create a multi-habitat mosaic imitating the original oxbow from historic aerial photos of the river.

When work along 32 miles of levee near the Sacramento River in Sacramento, California eroded nearby land, the California Reclamation Board hired the Army Corp of Engineers to develop a restoration plan to re-create the previous landform and thriving ecosystem and return it to its original splendor.

Sid Jones, a landscape architect with over 16 years of service with the Corps, created the grading plan for the 123-acre site, establishing a habitat of 22 acres of open water, 22 acres of emergent marsh (together forming a 44-acre pond) and 79 acres of riparian upland. ?EUR??,,????'??We ended up moving about 360,000 cubic yards of soil,?EUR??,,????'?? says Jones, who designed the grading plan much like he would a golf course, by following free-form contours instead of a plan and profile approach.

These 22 acres of open water and 22 acres of emergent marsh together form the projects horseshoe-shaped 44-acre pond, surrounded by 79 acres of riparian upland forest. Cattails and bulrushes thrive in the shallow marshy area bordering the pond.

The devastated land was connected to the right bank of the Sacramento River so in order to recreate the lands original contours, Jones chose to mimic historic oxbow from old aerial photos of the river. Oxbow, says Jones, is best explained by envisioning a river that meanders, creating a big loop. Eventually, hydraulic evolution will shorten the river?EUR??,,????'???s path?EUR??,,????'???because the river will keep trying to jump to the shortest point downstream. Eventually the river will cut across that loop-leaving an abandoned thumbprint of land called an oxbow.

Landscape architect, Sid Jones, designed the project?EUR??,,????'???s grading plan by using freeform contours instead of a rigid ?EUR??,,????'??engineered?EUR??,,????'?? approach. Using up to 10 scrapers at one time, contractors took off the first 12 inches of topsoil, stockpiled it on site and graded toward the contoured lines forming the pond. Remaining topsoil was replaced over the newly graded 79 acres of riparian upland forest.

Using up to 10 scrapers at one time, contractors moved the dirt according to Jones cut and fill plan. After taking off the first 12 inches of topsoil and stockpiling it on site, contractors took the scrapers and started grading toward Jones contoured lines. After the elevation level neared the grade lines, contractors compacted the soil with sheepsfoot rollers, and then replaced the topsoil, spreading it over the remaining 79-acre riparian upland.

To create 22 acres of emergent marshland around the periphery of the pond, Jones graded the entire area at a depth elevation of zero to about three feet. To create another 22 acres of sustained open water in the center of the pond, Jones plan called to grade three feet deeper so that emergent marsh would not be able to ?EUR??,,????'??crawl?EUR??,,????'?? down in the soil and root.

Using local native seed, the Corps grew depot-size tree seedlings and planted valley oaks, mule fat, coyote brush, box elder, Fremont cottonwood, Oregon ash, California wild rose, California blackberry, California sycamore, California white alder and red, yellow, black and arroyo willow on the 79-acre riparian upland area. A temporary drip irrigation system was installed, watering the site for three years until the plants were ready to sustain on their own.

Jones took soil excavated from the 44-acre pond and mounded it up as containment around the edges of the pond, making it as natural looking as possible. To determine the top-water surface elevation of the new pond, Jones surveyed and adjusted the elevation to work with the existing adjacent land. ?EUR??,,????'??We set the top-water surface elevation of the pond at the same elevation of nearby drainage ditches-so as rainwater water filled into the pond it would flow out into these adjacent drainage ditches,?EUR??,,????'?? Jones remembers.

The recreated pond and riparian upland?EUR??,,????'???s revitalized ecosystem is maturing and functioning as designed, witnessed by the identification of at least 58 bird species.

Two concrete weirs built at the low part of the pond were created to drain into an adjacent runoff ditch. The advantage of a weir over a plain earth bank is that the concrete ?EUR??,,????'??spillboard?EUR??,,????'??, arranged to be lower than the bank takes the overflow rather than the easily eroded bank. ?EUR??,,????'??Even if it rained hard, water would flow over without undermining the structure,?EUR??,,????'?? assures Jones.

While rainwater dynamics were easily integrated into the strategic grading design, finding water to initially fill the newly dug pond posed a challenge.

This conceptual planting plan shows 22,000 plantings of emergent marsh species, riparian species, and upland species. Near the canal, the two concrete weirs were constructed to contain rainwater overflow from the pond. A well driven on the right side of the pond oxbow was necessary to fill and maintain the pond water. Total project area: 123 acres. Open water: 22 acres. Emergent marsh: 22 acres. Riparian upland: 79 acres. Shoreline length: 3.5 miles. Lake volume: 47,248,250 gallons. Soil moved to create lake: 400,000 cubic yards. Depth of lake: 5 ft. Highest elevation above lake: 14 ft.

?EUR??,,????'??We were disconnected from the river, recounts Jones, so we drove a well producing over 1,300 gallons-per-minute.?EUR??,,????'?? This one well fed the pond, sustaining all 22 acres of open water and 22 acres of emergent marsh.

After the grading was complete and the pond filled, it was time to introduce native plants back into the landscape. In the marshy area bordering the pond, Jones planted bulrushes.

?EUR??,,????'??We also wanted cattails but we knew that they would come in on their own, so we didn?EUR??,,????'???t plant and sure enough they came in quite readily,?EUR??,,????'?? says Jones who planted another 17,000 woody plants throughout the remaining dry 79-acre site. Using local native seed, the Corps grew depot-size tree seedlings (similar in size to a snow cone) and planted woody oaks, mule fat (a backress like coyote brush), box elders, willows cottonwood, sycamores, Oregon ash, California wild rose, and California blackberry.

After the site grading was complete and the pond was filled, native plants were introduced back into the landscape. Here, bulrushes and cattails thrive in the 22 acres of emergent bordering the pond.

A temporary irrigation system was also installed, watering the entire site for three years, until the plants were ready to sustain on their own. ?EUR??,,????'??Initially we had about a 91 percent survival rate of plants,?EUR??,,????'?? states Jones. ?EUR??,,????'??Now 13 years later we still have at the very least an 85 to 87 percent success rate.?EUR??,,????'??

?EUR??,,????'??Another good indicator that the revitalized ecosystem is in good shape,?EUR??,,????'?? says Jones, ?EUR??,,????'??is that we have identified at least 58 bird species on the land.?EUR??,,????'??

In retrospect, Jones remembers a few good lessons from grading this site. He knew the land had a high water table&an adjacent project had done groundwater soil excavations&so he knew at the back of the project there was groundwater five feet under the surface. But at the front of the project groundwater dipped to 15 ft. This was all good news, says Jones. ?EUR??,,????'??We only tested three or four different areas of the 123-acre area, but they all tested good for [water] holding capacity.?EUR??,,????'??

The Corps planted 17,000 woody plants throughout the 79-acre riparian upland. Due to the temporary irrigation system they initially had about a 91 percent survival rate of plants. Now 13 years later they still have an 85 to 87 percent success rate.

During the restoration, Jones uncovered a 10-acre area that looked like it was part of the old oxbow&because there was a lot of sandy material in it.

?EUR??,,????'??We wish we could have known that prior to our grading design because we would have treated the soil with bentonite (a very fine clay silt that has good water holding properties in it) to increase it?EUR??,,????'???s water holding capacity.?EUR??,,????'??

But after the fact, when the pond was receding faster than expected, Jones?EUR??,,????'??? crews went back into that same 10 acres, harvested the cattails and then incorporated a bentonite mixture into the soil. Other than that snag, the project went very well, says Jones who advises: ?EUR??,,????'??If you have time to do a soils investigation prior to a grading design it?EUR??,,????'???s well worth it&we could have uncovered the potential obstacles if we would?EUR??,,????'???ve only had the time to do it.?EUR??,,????'??