Măsuri de întărire a capacității de adaptare la schimbările climatice a ecosistemelor acvatice

The current article presents a bibliographic overview of green infrastructures and their role in strengthening the adaptive capacity of aquatic ecosystems to the adverse effects of climate change (high temperatures, heavy rains, droughts). Different types of ecological infrastructures are presented: forest buffer strips, rain gardens, permeable pavement, drainage ditches; bioengineering structures for bank stabilization. Also the functions performed by green infrastructures to maintain ecosystem services were presented: mitigating the effects of floods, stabilizing banks, preventing landslides and water caused erosion, stormwater management, reducing the load of pollutants. For the implementation of this approach in the hydrographic basin of Dniester River or the Prut River a more detailed study is necessary on the state of habitats, identification of hotspot areas of aquatic biodiversity, particularly those species important for maintaining of ecosystem functions, highlighting of the areas at high risk of floods or erosion.

A low-cost subsurface drainage technique to enhance gully bank stability in the sub-humid highlands of Ethiopia

Gully erosion is the leading cause of elevated sediment yields in the world. Few low-cost techniques are available for rehabilitating gullies. The objective of this research was to evaluate the applicability of a low-cost horizontal sub-surface drainage system for decreasing gully erosion by stabilizing gully banks. The study was conducted in the sub-humid Ethiopian highlands in two active gullies, one in a Vertisol and another in a Nitisol. One bank was drained with a plastic pipe, and the other bank acted as the control. The two opposite banks are hydrologically isolated from one another. The surrounding groundwater tables were continuously monitored for two years. Over two wet seasons, the average bank retreat in the Vertisol gully was 0.62 m for the control and 0.15 m for the drained bank. Similarly, in the Nitisol gully, in 1.1 m for the control and 0.29 m for the drained bank. The average groundwater table of the drained bank was 20% lower than the non-drained banks during the monitoring periods. These results suggest that bank dewatering maintained higher levels of stability of gully banks and promoted lower rates of bank retreat on both soil types. The initial cost of the dewatering treatments was significantly less than the conventional bank stabilization measures. Bank dewatering could be one of the technologies for gully rehabilitation. Gully management techniques in Ethiopia and elsewhere could benefit from integrating bank drainage with other physical and biological protective measures.

Impact of Bank Stabilization Structures on Upstream and Downstream Bank Mobilization at Cedar River, Nebraska

HighlightsStabilization structures are only effective at stabilized segments.Erosion increased in two of the six segments in the post-stabilization period.Deposition decreased in all six segments in the post-stabilization period.Jetties are effective at reducing erosion but are also prone to fail.Abstract. The effectiveness of streambank stabilization structures is insufficiently quantified. Although such structures clearly reduce or eliminate streambank erosion at the local scale, little is known about associated effects on unstabilized reaches immediately upstream and downstream. This study measured streambank erosion and deposition in stretches of the Cedar River, 1.5 meander wavelengths upstream and downstream from 24 stabilization structures that included jetties, rock vanes, root wads, and gravel protection. We also measured erosion and deposition on the streambanks directly opposite the stabilized locations. We compared measurements from the pre-stabilization period (1993-2005) with those from the post-stabilization period (2005-2018) using historical imagery in ArcGIS. Upon completion of this analysis, we were able to reject an initial hypothesis that local and adjacent streambank segment erosion rates would be significantly less after stabilization, and that deposition rates would be greater in stabilized locations and adjacent stream segments. Instead, the differences in erosion from pre- to post-stabilization showed little or no statistical significance. Rather, our data indicated that streambank erosion decreased in only four of the six stream segments and was predominantly confined to the stabilized segment. Overall deposition decreased in all six stream segments after bank stabilization. In reaches where wooden jetties were installed, partial or total failure was common, and further increases in erosion and decreases in deposition were more pronounced. We conclude that streambank stabilization on the Cedar River is effective only at the location of installation; there is no measurable effect on adjacent unstabilized reaches. Our results demonstrate the need for improved streambank monitoring practices and better understanding of how streambank stabilization impacts an entire river system. Such advances will enhance stream restoration design and implementation, as well as support future river management efforts. Keywords: Adjacent stream reach, Deposition, Jetty, Erosion, Streambank stabilization.

Comparative Analysis on Environmental Adaptability of Two Types of Bank Stabilization Structures along the Middle and Lower Reaches of the Yangtze River

With the aim to prevent channel incision and migration and provide protection at the riverbank, a series of ecological bank stabilization projects have been carried out in the middle and lower reaches of the Yangtze River. In this study, nine ecological bank stabilization areas using two different techniques, Steel mesh gabion (Type 1) and Chain-type bricks (Type 2), were compared in terms of environmental adaptability on the basis of the survey data of vegetation and substrate. There were no significant differences between the two types of dominant species before and after the flood season. Annual or biennial herbaceous plants had clear spatial competitive advantages while perennial herbs had clear temporal competitive advantages. While Type 1 was better than Type 2 in overall vegetation restoration and growth, Type 2 was more sensitive to periodic flood disturbance. Redundancy Analysis was used to determine the main environmental impact factors that caused differences on biotic indices of the two types. The clay content in the substrate was an important factor affecting vegetation cover and diversity for Type 1 while the substrate nutrient composition was important for Type 2. Generally, Type 1 presented stronger environmental adaptability in channel regulation projects.

Nitrate, Total Ammonia, and Total Suspended Sediments Modeling for the Mobile River Watershed

This paper presents details of a water quality model of the Mobile River watershed that estimates total suspended sediments at the outlet of the watershed. The model is capable of simulating Nitrate (NO3), Total Ammonia (TAM), and Total Suspended Sediments (TSS) for extended periods of time at a daily temporal resolution (1970-1995). The Hydrological Simulation Program Fortran is used for modeling the hydrological, nitrogenous constituents, and sediment processes. Based on the nutrient simulation and exploration of the effects of two management practices (filter strips and stream bank stabilization and fencing) on nutrient removal, the resulting sediment model is used to implement the most efficient nutrient management practice and explore its effects on TSS concentrations in the Mobile River. Results show that the implementation of the management practice “stream bank stabilization and fencing” to agricultural lands in sub-watersheds that had intense agricultural activities produced the highest reductions of NO3 concentration (up to 14.06%) and TAM concentrations (8.01%). Based on the nutrient simulation and identification of “stream bank stabilization and fencing” as the most efficient BMP for nutrient concentration reduction, the sediment model was used to explore its effects on TSS concentrations in the Mobile River. Implementing “stream bank stabilization and fencing” produced monthly median TSS concentration reductions ranging from 3.6% to 10.6% in the Mobile River.

Cultural Resources Survey for the Proposed MUD 121 Brazos River Levee Protection Project in Fort Bend County, Texas

This report summarizes the results of a cultural resources survey by Gray & Pape, Inc. of an approximately 14.8-hectare (36.6-acre) property in Fort Bend County, Texas, planned for a bank stabilization project on behalf of their client, Berg-Oliver Associates, Inc. The goals of the survey were to determine if the proposed project would affect any previously identified archaeological sites as defined by Section 106 of the National Historic Preservation Act of 1966, as amended (36 CFR 800), and to establish whether or not previously unidentified buried archaeological resources were located within the project’s Area of Potential Effect. Portions of the project are on property owned by Fort Bend County Municipal Utility District Number 121, political subdivisions of the state, as such, a Texas Antiquities Permit (Permit Number 8734) was required prior to the commencement of fieldwork. All fieldwork and reporting activities were completed with reference to state (the Antiquities Code of Texas) and federal guidelines. Prior to fieldwork mobilization, a background literature and site file search were conducted to identify the presence of recorded sites and previous cultural resource surveys within or near the project area. The search indicated that no previously identified archaeological sites, cemeteries, historic markers, or National Register properties are located within the project area. The same research identified that eight previous cultural resource surveys had been conducted within the study radius of the project area, one of which overlapped with the current project area. In addition, 14 previously recorded archaeological sites are located within the study radius, none of which are located within or immediately adjacent to the current project area. Field investigations were carried out in two mobilizations in January and December 2019 and consisted of a combination of pedestrian survey and subsurface testing, resulting in the excavation of 32 shovel tests. Five planned tests were left unexcavated due to inundation, and eight planned tests were left unexcavated due to significant surface disturbance. All shovel tests were negative for cultural resource material and no historic-age resources were identified during survey. After a revised scope of work was submitted to the Texas Historical Commission, investigation of deeply buried soils took place tandem with construction by regular monitoring of construction excavation. When the construction schedule allowed, traditional deep testing, by means of mechanical excavation, was carried out in five of six areas anticipated to have deep impacts from the proposed bank stabilization project. A total of 22 trenches were excavated. No buried features or deeply buried paleosols were encountered. Gray & Pape, Inc. archaeologists are of the opinion that the shovel test survey and deep testing completed within the Area of Potential Effects has adequately assessed the potential for surface and near surface intact, significant cultural resources, as well as determining the potential for deeply buried resources or paleosols. No artifacts or cultural features were encountered during the course of the survey, and no new archaeological sites were identified. No negative impacts on any previously identified sites are anticipated from the proposed project. Based on these results, Gray & Pape, Inc. recommends that no further cultural work be required and that the project be cleared to proceed as planned. As required under the provisions of Texas Antiquities Code Permit 8734, all project records are housed at the Center for Archaeological Studies at Texas State University, San Marcos, Texas.

Bank Processes and Revetment Erosion of a Large Lowland River: Case Study of the Lower Tisza River, Hungary

Stone and concrete revetments are widely constructed to control bank erosion and thus stabilize river banks. The consequences include accelerated erosion at unrevetted downstream channel sections and in-channel incision at revetted sections. The studied section of the Tisza River (Hungary) was revetted along 49% of its banks in the 20th century with stepped-block and placed-rock revetments. We therefore aimed (1) to study the effects of revetment constructions on channel processes and (2) to evaluate the state and collapse of revetments using a DEM of the channel and ADCP measurements. In the late 19th century, the river had an equilibrium meandering channel, with alternating eroding and aggrading banks. Currently, erosional processes dominate. Thus, 65% of the total channel length is affected by bank erosion. The revetments reduced the active lateral erosional processes only temporarily, as 58% of the revetments, mainly placed-rock, are already damaged. The flow characteristics at the revetted sections were found to depend on the rate and type of revetment collapse. Large pools developed in front of the revetments, playing an important role in initiating their erosion. The placed-rock revetments can collapse by slides or by stones falling into the pool one-by-one. In this case, a knickpoint develops, propagating upstream. Thus, the collapse and accelerated bank erosion also propagate upstream. The increased hazard created by the failure of the revetments requires the re-planning of bank stabilization practices.