The Life and Death and Consequences of Canals and Spoil Banks in Salt Marshes

Turner, R. Eugene; Swenson, Erick M.

doi:10.1007/s13157-020-01354-w

Cited by 9 publications

(6 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is probably because, as shown in Figure 3a, the dredged waterway widened beyond the footprint of the former spoil bank, whereas the natural channels were relatively stable. The lower elevation at locations once having spoil banks compared to natural waterways is, we hypothesized, because the weight of the spoil bank pulled the salt marsh lower adjacent to where the spoil bank once existed [39]. There was no ponding behind the spoil banks because they had eroded by 2002, but it is common where spoil banks remain [40].…”

Section: Dredged Waterways Erode With Timementioning

confidence: 98%

Salt Marsh Elevation Limit Determined after Subsidence from Hydrologic Change and Hydrocarbon Extraction

Turner

2020

Remote Sensing

Self Cite

View full text Add to dashboard Cite

Levee construction aboveground and hydrocarbon removal from belowground in coastal wetlands can create hydrologic changes that increase plant stress through flooding. But the significance of the subsidence they cause individually or in combination is contested. This study untangled them to demonstrate elevational limits of salt marshes by studying dredged and natural waterways in two salt marshes in Louisiana, USA. The areas had a homogenous plant cover before drilling for oil and gas extraction peaked in the 1960s, and now are a mixed network of natural waterways and dredged canals used to drill wells with an average drill date of 1965.8 ± 2.7 (µ ± 1 SEM; n = 18) and well depth of 4661.0 m ± 56.6 (µ ± 1 SEM; n = 18). Aerial imagery was used to document how canals widened to become 2 to 4 times larger than their original construction width at the high production site and 50% larger at the low production site, whereas increases at the nearby natural channels were much less. Light detection and ranging (LIDAR) measurements at the high production site from 2002 showed that the marsh surface near wells subsided by 34 cm compared to undredged sites. Elevation in marshes at producing and dry wells were equal at the low production site, but high production well locations were even lower than at dry wells. An elevation vs. percent open water curve developed from these data overlapped with an independent analysis of a brackish marsh. A relative subsidence rate between 7.4 to 10.4 mm y−1 transformed these salt marshes to an open water habitat within a few decades. The local creation of accommodation space through hydrocarbon removal and leveed wetlands is a parsimonious explanation for the spatial and temporal land loss rates on this deltaic coast over the last 80 years of oil and gas exploration. Substantial losses from the accelerating rates of sea level rise are indicated to occur before 2050.

show abstract

Section: Dredged Waterways Erode With Timementioning

confidence: 98%

Salt Marsh Elevation Limit Determined after Subsidence from Hydrologic Change and Hydrocarbon Extraction

Turner

2020

Remote Sensing

Self Cite

View full text Add to dashboard Cite

show abstract

“…Unplugged canals were 68% restored after 39 years and the total area disturbed by dredging (canal + spoil bank area) was 75% restored after 39 years. The difference is due to the reduced water exchange between canal and surrounding landscape that is blocked by plugs at the entrance of the canal and because the spoil banks made of the high-density mineral soils that were put on top of the marsh compresses the underlying material (Turner and Swenson, 2020); a "bathtub" of standing water is created with minimal drainage. Migratory fish do not have access to the canal, but grassbeds may be more abundant there that birds may be attracted to Neill and Turner, 1987a,b.…”

Section: Restorationmentioning

confidence: 99%

“…Pond formation from 1955 to 1978 in the Biloxi marshes of southeastern Louisiana was three times higher in marshes with weirs than without weirs (Turner et al, 1989) and pond formation is directly related to their distance to canals (Turner and Rao, 1990). A key inhibiting agent of restoration results from spoil banks blocking belowground flow and inhibiting aboveground flows (Turner and Swenson, 2020) and occurs in forested wetlands too. Megonigal et al (1997), for example, described how artificial controls on natural flooding reduced the aboveground productivity of forested bottomland forests.…”

Section: Restorationmentioning

confidence: 99%

“…Thirty-three canals were backfilled in the early 1980s, and there are others in the Barataria Preserve of the Jean Lafitte National Historical Park and Preserve (the "Park") near New Orleans, Louisiana, that were done from 2001 to 2002 and in 2010. Information on the restoration success of these few backfilled sites is important, not only because of the paucity of information but also because spoil banks may last 100 years (Turner and Swenson, 2020). The influences of the accelerating sea level rise across the coast, of course, may override restoration efforts at the local and regional scale (e.g., Horton et al, 2018;Schepers et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Wetland Restoration Progress 39 Years After Canal Backfilling

Turner

2022

Front. Ecol. Evol.

Self Cite

View full text Add to dashboard Cite

Dredging to create canals and channels in wetlands is widespread and is a major cause of dramatically high wetland loss rates in coastal Louisiana. The dredged material placed alongside the canal forms continuous levees and can be dragged back into the canal to start wetland restoration (backfilling) but is rarely done. Thirty-three canals backfilled in the 1980s as opportunistic permit requirements were examined to determine their re-vegetation after 39 years. Sixteen of the 33 disturbed areas are now mostly restored to wetlands, and seventeen were compromised by re-dredging and other factors such as being surrounded by other canals or embedded within water level control structures. Success occurred where the natural hydrology was not artificially constrained by these structures. The re-vegetation of these 16 canals were compared to backfilled canals in the Barataria Preserve of the Jean Lafitte Historical National Park. The spoil bank was restored wetland habitat within a few years, and the open water of the canal was 70% re-vegetated after 39 years if there was no soil “plug” placed at the canal entrance during backfilling. Backfilling canals can be done on the 27 thousand abandoned canals across this coast for a low cost compared to other restoration strategies.

show abstract

“…Due to the migration of water and salt, the salinity distribution in practical engineering is quite different, which causes enormous harm to large-scale water diversion projects, such as canals and slopes etc. [22][23][24][25][26][27]. At present, there are many studies on the loess in the monsoon area in the reports [28][29][30][31], and the research on Ili loess mainly focuses on the mechanical properties under cycling test conditions of dry-wet [32,33] and freeze-thaw [34,35], respectively.…”

Section: Introductionmentioning

confidence: 99%

Study on the Unified Mechanical Properties of Ili Undisturbed Loess under the Influence of Soluble Salt

Niu,

Zhao

et al. 2023

Sustainability

View full text Add to dashboard Cite

Through three stress path tests of unsaturated Ili undisturbed loess, the effect of soluble salt content on the deformation of net mean stress, suction, and deviated stress were investigated. The mechanical properties of the normalized compression curve, soil water characteristic curve and critical state line were revealed. The test results indicate that: in the isotropic compression test, the normal compression curves controlling different suctions can be characterized by using the initial void ratio and the yield net mean stress, and can be described as a two-parameter exponential function. In the triaxial shrinkage test, the soil water characteristic curves controlling vary net mean stresses are dimensionless by using saturated moisture and air entry value, and the normalization formula can be characterized by a single parameter exponential function. In the consolidation shear test, the corresponding effective net mean stress is calculated by suction and saturation. The critical state lines under the unsaturated condition controlling vary suctions can be described as the critical state line under the saturated condition on the plane of effective net mean stress and deviator stress. When the effective net mean stress is constant, the critical state lines under the unsaturated condition can be characterized by the degree of gas saturation and the ratio of unsaturated void ratio to saturated void ratio. The research will offer reference pointing at the regulation and utilization of water and salt in the loess region of Central Asia, so as to better guarantee the sustainable development of saline-alkali land project construction.

show abstract

The Life and Death and Consequences of Canals and Spoil Banks in Salt Marshes

Cited by 9 publications

References 23 publications

Salt Marsh Elevation Limit Determined after Subsidence from Hydrologic Change and Hydrocarbon Extraction

Salt Marsh Elevation Limit Determined after Subsidence from Hydrologic Change and Hydrocarbon Extraction

Wetland Restoration Progress 39 Years After Canal Backfilling

Study on the Unified Mechanical Properties of Ili Undisturbed Loess under the Influence of Soluble Salt

Contact Info

Product

Resources

About