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Timothy Reed's blog

Double Ditch Bank Stabilization Repairs Nearly Complete

Double Ditch Indian Village State Historic Site is one of the most spectacular archaeological sites preserved on the northern plains. The earthlodge village was a regional trading center occupied for nearly 300 years (AD 1490-1785) by the Mandan people. Due to its archaeological significance, the site is listed on the National Register of Historic Places.

Aerial view of Double Ditch

Aerial image of Double Ditch Indian Village State Historic Site taken by SHSND quadcopter – November 2013.

Readers of the State Historical Society of North Dakota blog will likely already be familiar with threats Double Ditch faced from severe erosion caused by the 2011 Missouri River flood (please see blog.statemuseum.nd.gov/blog/an-eye-in-the-sky-for-preservation, blog.statemuseum.nd.gov/blog/saving-double-ditch, and blog.statemuseum.nd.gov/blog/double-ditch-bank-stabilization).

Rotational erosion at Double Ditch

Image of rotational erosion of river bank at Double Ditch Indian Village State Historic Site. Image taken by SHSND quadcopter - October 2016.

The State Historical Society of North Dakota, partnering with the Mandan, Hidatsa, and Arikara Nation, the North Dakota Legislative Assembly, and other groups and individuals supporting preservation efforts mobilized after the 2011 flood to address this critical threat to the site. Left unaddressed the rotational erosion would have continued, eroding deeply into the village and causing catastrophic damage to the site.

Rotational erosion at Double Ditch

Image of rotational erosion front at Double Ditch from a trailcam that monitored the location from March 2015 - June 2017.

An engineering plan was developed to stabilize 2,200 linear feet of riverbank from the effects of rotational erosion exposing numerous burials at the site since the 2011 flood. The State Historical Society is grateful to the 2013, 2015 and 2017 North Dakota Legislative Assemblies for appropriation of the $3.5 million dollars necessary to move this important preservation project forward.

Monitoring topsoil removal

SHSND archaeologist monitoring topsoil removal by a track hoe during bank stabilization project at Double Ditch Indian Village State Historic Site – August 2017.

Bank stabilization began in July 2017, and was anticipated to last about five months. Prior to the start of construction, it was anticipated that additional burials would be identified. The State Historical Society and MHA leadership cooperated to follow state laws and the cultural practices of the Mandan to complete this sensitive work. Archaeologists from the State Historical Society were on hand daily throughout the construction period to monitor earth moving activities. All exposed burials were cared for according to proper protocol and will be interred in private ceremonies of the MHA nation after repatriation.

Heavy excavation equipment moving soil

An SHSND archaeologist monitors removal of soil by heavy excavation equipment during the bank stabilization project at Double Ditch Indian Village State Historic Site – August 2017.

The engineering plan implemented to stabilize the riverbank involved removing many tons of soil to reduce the weight on the bank slopes at the site. Installation of a rock -filled trench and hundreds of steel pipes vertically driven parallel to the river bank provide mass and strength to further stabilize the slopes.

Trackhoe working to stabilize slope

A trackhoe works to stabilize a slope during the Double Ditch bank stabilization project – August 2017. Quadcopter image by Dwayne Walker.

Heavy construction equipment installing steel pipe piles

Heavy construction equipment was used to install steel pipe piles parallel to the Missouri river bank during the Double Ditch bank stabilization project – August 2017. The rock key trench is already installed in this image, buried between the pipe piles and the river bank.

Aerial overview of crews working at Double Ditch

Aerial overview of the Double Ditch bank stabilization project – August 2017. The two trackhoes in this image are working to install a 20’ deep rock key trench as part of the stabilization plan. Quadcopter image by Dwayne Walker.

On a personal note, I’m humbled to have been involved with the bank stabilization activities at Double Ditch. Since 2002 I’ve been fortunate to be involved in archaeological research conducted at Double Ditch, and the site is very special to many people. It’s my belief that all those involved with the Double Ditch bank stabilization were part of a preservation project whose importance and sensitivity can hardly be overstated. Had the funding not been available and the project not been undertaken, the alternative would have been for the site to continue to be damaged and further eroded by the Missouri River.

Employees standing in front of construction equipment

Veit Construction employees Baldomero Castillo (Cabo) and John Fay pose with SHSND archaeologists Paul Picha, Brooke Morgan, Meagan Schoenfelder, and Timothy Reed during a break in the action of the bank stabilization project at Double Ditch State Historic Site – August 2017. (Not pictured: SHSND archaeologists Wendi Field Murray and Fern Swenson.)

The bank has been reshaped and landscaping with native plants was installed in early November. Interpretive aspects will be developed over the winter and installed in early summer, after the vegetation has had a chance to develop.

Arial view looking north of Double Ditch stabilization project

Aerial overview of the Double Ditch bank stabilization project – November 14, 2017. View is to the south. The dark patch on the landscaped slope marks the area covered with an erosion-control product called filter fabric. Filter fabric is used to help prevent erosion until the area develops heavier vegetation. Quadcopter image by Dwayne Walker.

Aerial view looking south of Double Ditch stabilization project

Aerial overview of the Double Ditch bank stabilization project – October 25, 2017. View is to the south. The dark patch on the landscaped slope is a portion of the area covered with an erosion-control product called filter fabric. The location of a non-motorized canoe and kayak access trail is also visible in this image. An erosion-control product called Geo Cell was used in the construction of the trail. Quadcopter image by Dwayne Walker.

Double Ditch Bank Stabilization to Begin Summer 2017

Extensive bank erosion since the 2011 flood has seriously impacted an important state historical site managed by our agency (http://blog.statemuseum.nd.gov/blog/saving-double-ditch). After a long process to determine possible alternatives for funding and a stabilization plan, we’re relieved to have the engineering work begin.

Situated on the east bank of the Missouri River nine miles north of Bismarck, Double Ditch Indian Village State Historic Site is one of the best preserved examples of an earthlodge village on the northern plains. The site was a regional trading center occupied for nearly 300 years (AD 1490-1785) by the Mandan people. At its peak the population of Double Ditch has been estimated to have been 2,000 or more people, with a richly developed culture based upon agriculture and seasonal bison hunting. Due to its archaeological significance, the site is listed on the National Register of Historic Places.

Bank Erosion at Double Ditch

Bank Erosion at Double Ditch Indian Village State Historic Site, October 2016. Photo courtesy Tim Reed, SHSND.

The Missouri River is powerful, perhaps never more so than when it’s in flood stage. This stretch of the river lies between the Garrison and Oahe reservoirs. Those living along the Missouri know this firsthand, as we’ve seen rising floodwaters on more than one occasion impact lives, property, and cultural and natural resources.

Double Ditch Indian Village State Historic Site was unable to escape the effects of the Missouri River’s catastrophic flooding in 2011. Large sections of the river terrace edge shifted in a process called rotational erosion. Rotational erosion simply means that large blocks of sediment at the site were rotating and shifting as slumping occurred along the river bank. This erosional process destabilized the bank and threatened a portion of the site, including parts of the public walkway/bicycle path.

Aerial view of geotechnical coring rig

Geotechnical coring rig operating on rotational erosion area at Double Ditch Indian Village State Historic Site, October 2015. Photo courtesy Tim Reed, SHSND.

To make matters even worse, the active erosion at Double Ditch has continued in an area known to contain human burials. Since 2013, 18 burials have been disinterred at the site as a result of this erosion. Because Double Ditch village was occupied for 300 years by thousands of people, more burials would be disturbed if erosion continued.

During the 2015 Legislative session, the State Historical Society of North Dakota partnered with the Mandan, Hidatsa, and Arikara Nation to raise awareness about the immediate threat posed to Double Ditch by erosion. Project funding was allocated during the 2015 legislative session to stabilize the site.

Geotechnical coring rig

Geotechnical coring rig operating on rotational erosion area at Double Ditch Indian Village State Historic Site , October 2015. Photo courtesy Tim Reed, SHSND.

A geotechnical study performed in October 2015 confirmed that the erosion was a result of the 2011 flood. The study further determined that the existing threat to the site was even more extensive than originally thought. A new crack was developing below the surface, with the potential to progress 400 feet into the heart of Double Ditch Village. Left unaddressed, this newly identified erosional fault could be catastrophic, causing twelve acres (half of the site) to be lost.

Geotechnical coring rig

Geotechnical coring rig operating at Double Ditch Indian Village State Historic Site, October 2015. Photo courtesy Tim Reed, SHSND.

Geomorphological trench being excvated

A geomorphological trench being excavated at Double Ditch Indian Village State Historic Site as part of the geotechnical study, October 2015. Photo courtesy Tim Reed, SHSND.

As the engineering plan was being developed in 2016, the project faced delays from a challenging permitting process. Thanks to the North Dakota Legislative Assembly, project funding not able to be used during the last legislative session was carried over into this biennium. We’re also grateful to tribal members from the Mandan, Hidatsa, and Arikara Nation and other groups and individuals who supported efforts to keep this critical project moving forward.

Stabilization plans involve terracing the slope and building a Rock Key and Pipe Pile Wall to prevent further erosion. Site improvements include a new nature trail and the addition of native plants. Construction will take about five months.

Double Ditch Indian Village State Historic Site bank stabilization diagram, March 2017. SHSND.

Various geotechnical studies and modeling were critical in developing plans for the bank stabilization. Ultimately the plan involved reshaping the bank by removing weight from the upslope and adding weight to the toe. The rock key/trench and pipe piles will provide mass and strength to stabilize the slope.

The riverbank will be revegetated with a variety of native grasses, forbs, shrubs, and trees. Interpretive signs will be installed along the bank highlighting natural resources. The stabilized and reshaped bank will protect the Mandan village and enhance fishing access to the river, bird/wildlife watching, and provide a non-motorized landing for kayaks and canoes. In addition, this will prove a safe walking/bicycle trail.

Construction fence

Construction fence at Double Ditch Indian Village State Historic Site, June 2017. Photo courtesy Tim Reed, SHSND.

As of the date of this blog, the bank stabilization at Double Ditch Indian Village State Historic Site is anticipated to begin in late June. Construction should be completed in about five months. We’ll keep readers informed in this blog as the project progresses.

 

*Fern Swenson, Director of Archaeology and Historic Preservation, and Kim Jondahl, Director of Communications and Education, were contributing authors to this post.

Advocates of Save Double Ditch

Advocates of Save Double Ditch, a grassroots organization, brave the cold in March 2017 to voice their support for bank stabilization funding. March- 2017. Courtesy Tom Stromme, Bismarck Tribune