Assessment of channel dynamics, in-stream structures and post-project channel adjustments in North Carolina and its implications to effective stream restoration (original) (raw)

Use and performance of in-stream structures for river restoration: a case study from North Carolina

Environmental Earth Sciences, 2012

In-stream structures including cross-vanes, J-hooks, rock vanes, and W-weirs are widely used in river restoration to limit bank erosion, prevent changes in channel gradient, and improve aquatic habitat. During this investigation, a rapid assessment protocol was combined with post-project monitoring data to assess factors influencing the performance of more than 558 in-stream structures and rootwads in North Carolina. Cross-sectional survey data examined for 221 cross sections from 26 sites showed that channel adjustments were highly variable from site to site, but approximately 60 % of the sites underwent at least a 20 % net change in channel capacity. Evaluation of in-stream structures ranging from 1 to 8 years in age showed that about half of the structures were impaired at 10 of the 26 sites. Major structural damage was often associated with floods of low to moderate frequency and magnitude. Failure mechanisms varied between sites and structure types, but included: (1) erosion of the channel bed and banks (outflanking); (2) movement of rock materials during floods; and (3) burial of the structures in the channel bed. Sites with reconstructed channels that exhibited large changes in channel capacity possessed the highest rates of structural impairment, suggesting that channel adjustments between structures led to their degradation of function. The data question whether currently used in-stream structures are capable of stabilizing reconfigured channels for even short periods when applied to dynamic rivers.

Invited commentary for Hydrological Processes Evaluating 'natural channel design' stream projects

We need a coherent, deliberate process to learn from failures and successes in stream rehabilitation projects. Insightful evaluations comparing projects in varied regions have been limited by the diversity of approaches and some scientific uncertainty as to how to best accomplish longer-term monitoring (Bernhardt et al., 2005; Giller, 2005; Palmer et al., 2005; Palmer and Bernhardt, 2005; Reid, 2001, Reid and Fur niss, 2002). Addressing just the critical issue of biological assessments would take an entire paper but with hundreds of natural channel design (NCD) projects completed across the country, simply evaluating their performance and impacts on bank erosion would be a step forward. Too often critiques of NCD projects have returned continually to the same few locations, and have yet to grapple with many other projects with different designs, disturbance histories, and environments. I hope this brief review will encourage better dialogue between scientists and stream rehabilitation practitioners.

Post-project geomorphic assessment of a large process-based river restoration project

Geomorphology, 2016

This study describes channel changes following completion of the Provo River Restoration Project (PRRP), the largest stream restoration project in Utah and one of the largest projects in the United States in which a gravel-bed river was fully reconstructed. We summarize project objectives and the design process, and we analyze monitoring data collected during the first 7 years after project completion. Post-project channel adjustment during the study period included two phases: (i) an initial phase of rapid, but small-scale, adjustment during the first years after stream flow was introduced to the newly constructed channel and (ii) a subsequent period of more gradual topographic adjustment and channel migration. Analysis of aerial imagery and ground-survey data demonstrate that the channel has been more dynamic in the downstream 4 km where a local source contributes a significant annual supply of bed material. Here, the channel migrates and exhibits channel adjustments that are more consistent with project objectives. The upstream 12 km of the PRRP are sediment starved, the channel has been laterally stable, and this condition may not be consistent with large-scale project objectives.

Evaluating stream restoration projects

Environmental Management, 1995

River and stream restoration projects are increasingly numerous but rarely subjected to systematic postproject evaluation. Without conducting such evaluation and widely disseminating the results, lessons will not be learned from successes and failures, and the field of river restoration cannot advance. Postproject evaluation must be incorporated into the initial design of each project, with the choice of evaluation technique based directly upon the specific project goals against which performance will be evaluated. We emphasize measurement of geomorphic characteristics, as these constitute the physical framework supporting riparian and aquatic ecosystems. Techniques for evaluating other components are briefly discussed, especially as they relate to geomorphic variables. Where possible, geomorphic, hydrologic, and ecological variables should be measured along the same transects. In general, postproject monitoring should continue for at least a decade, with surveys conducted after each flood above a predetermined threshold. Project design should be preceded by a historical study documenting former channel conditions to provide insights into the processes suggest earlier, potentially stable channel configurations as possible design models.

Conducting Rapid Fluvial Geomorpic Assessments Based on the Channel Evolution Model: A Case Study in Griffin, Georgia

2005

A variety of fluvial geomorphic assessment methods, such as TMDL development, biological habitat quality assessment, and overall channel characterization, have been developed and are being adopted by organizations for use in assessing stream conditions for a variety of purposes. This paper first summarizes available stream geomorphic assessment methods, detailing their strengths and weaknesses. Then we describe an actual project conducted by Tetra Tech in Griffin, Georgia to show how assessment methods were selected to suit a particular application and how the results were presented to maximize usefulness to the client. The stream channel stability study was conducted on Shoal Creek for the City of Griffin, Georgia, Public Works and Stormwater Department. The focus of the study was to qualitatively assess the potential availability of sediment from channel sources so that the findings could be used to address downstream sedimentation issues. Time and funding constraints led to choosing a qualitative rapid geomorphic assessment method whereby channel evolution and other easily observable field data were collected for the entire watershed. Assessed reaches were then classified by degree of channel stability with results presented as a set of correlated maps, data tables, photographs, and reach narratives. This data set enabled stormwater management decision makers for the City of Griffin to prioritize the specific erosion hot spots for mitigation.

Geomorphic Classification and Assessment of Channel Dynamics in the Missouri National Recreational River, South Dakota and Nebraska

Scientific Investigations Report, 2006

A multiscale geomorphic classification was established for three segments of the Missouri River on the border of South Dakota and Nebraska: the 39-mile and 59-mile segments of the Missouri National Recreational River administered by the National Park Service, and an adjacent segment, Kensler's Bend. The objective of the classification was to define naturally occurring clusters of geomorphic characteristics that would be indicative of discrete sets of geomorphic processes (process domains), with the intent that such a classification would be useful in river-management and rehabilitation decisions. The statistical classification was based on geomorphic characteristics of the river collected from 1999 digital aerial orthophotography. Persistence of classified units was evaluated by comparison with similar datasets for 2003 and 2004. Changes in channel location and form were also explored using imagery and maps from 1993 to 2004, 1941, and 1894. The multivariate classification identified a hierarchy of naturally occurring clusters of reach-scale geomorphic characteristics. The simplest level of the hierarchy divides the river from segments into discrete reaches characterized by single and multithread channels. Additional hierarchical levels established 4-part and 10-part classifications. The utility of the classifications was established by exploring persistence of classified units over time and by evaluating variation of bank erosion rates by geomorphic class. The classification system presents a physical framework that can be applied to prioritization and design of bank-stabilization projects, design of habitat-rehabilitation projects, and stratification of monitoring and assessment sampling programs.

CONCEPTS - A Process-Based Modeling Tool to Evaluate Stream-Corridor Restoration Designs

Wetlands Engineering & River Restoration 2001, 2001

The success of proposed stream-corridor restoration measures to effectively restore stream structure and function is greatly aided by a thorough analysis of the potential geomorphic responses of the stream to the measures. Complex hydrologic and geomorphic processes determine channel form. Simple analysis tools are available for restoration practitioners, however few are process-based and dynamic. As a response to this, scientists at the US Department of Agriculture, Agricultural Research Service, National Sedimentation Laboratory (NSL) have developed the CONCEPTS model. CONCEPTS (Conservational Channel Evolution and Pollutant Transport System) is a process-based, dynamic computer model that simulates open-channel hydraulics, sediment transport, and channel morphology. CONCEPTS includes research conducted during the past five years by NSL scientists to improve our understanding of the processes controlling channel width adjustment and streambank mechanics. The streambank erosion component of CONCEPTS has been enhanced to include bank-material stratigraphy. Tests of the new component are underway with data obtained over a five-year period from a reach (a bendway) of Goodwin Creek, Mississippi. Initial results show that the enhanced component is able to predict undercutting of streambanks. It underpredicts the retreat of the top of the outside bank at the apex of the bendway by approximately 2 meters because critical shear stresses to initiate lateral erosion at the toe of the bank were too small.

The Long-Term Stability and Morphologic Influence of the Use of Instream Structures in Channel-Restoration Design

Widespread use of instream structures in the United States occurred as early as the 1930s under the direction of the Civilian Conservation Corp. Specific designs of instream structures were well developed in the 1930s with prototype versions of most currently employed designs. The Civilian Conservation Corp and U.S. Forest Service helped to standardize the designs in the 1930s and subsequent decades, and promote their use throughout the country. Many modern designs of instream structures show little or no variation in materials, construction methods and placement specifications relative to the 1930s prototypes. Consequently, surviving instream structures from projects in the last seventy years provide an opportunity to assess the long-term stability and morphologic impact of these devices. Field studies in the northeastern U.S. show that decay of structures can create site conditions that adversely impact aquatic and riparian habitat. Loss of streamside trees and reduced bank cover were both noted with certain designs of instream structures. Additional literature-based findings show that instream structures require expensive yearly maintenance to insure continued function of the devices as designed. These results show that the use of instream structures do not always provide a cost-effective long-term approach to channel-restoration design. Furthermore, the detrimental long-term impacts of certain designs of instream structure may reduce the amount of specific habitat areas stream managers try to enhance.

Hydraulic Design of Stream Restoration Projects

2001

Purpose 1 Definition of a Stream Restoration Project 3 Design Philosophy Project Study Teams 2-Project Objectives and Constraints Project Objectives Flood Damage Reduction Techniques Project Constraints 3-Hydrology General Frequency Analysis Peak discharge analysis Regional regression Errors in regression analysis Flow-Duration Curves Hydrologie Models Channel-Forming Discharge Concept Bankfull discharge Discharge with a specific recurrence interval Effective discharge Examples of channel-forming discharge representations Channel-forming discharge related to drainage area Channel-Forming Discharge Summary Stormwater Management General hydrologic effects of urbanization and stormwater management Conventional dry ponds Extended detention ponds Wetland-pond systems Infiltration basins and bioretention Stormwater management guidance 4-Stability Analysis Geomorphic Assessment Data assembly Field investigations Identification of geomorphologically similar reaches Assessment of reach condition 51 Channel typing and classification Methods for assessing historical channel stability Specific gage analysis Comparative surveys and mapping Hydraulic Geometry Assessment Background Developing hydraulic geometry relations Choice of independent variables Use of stream typing systems to refine hydraulic geometry relations Transfer of hydraulic geometry relations from one watershed to another Special problems of urbanized streams Uncertainty in hydraulic geometry relations Application of hydraulic geometry relations to assess channel stability Analytical Stability Assessment Hydraulic calculations Bed stability 61 Sediment rating curve analogy analysis 61 Sediment budget analysis Nonequilibrium sediment transport Integration and application of results 64 5-Hydraulic Design Methodology Design Discharges Design discharge for low flows 66 Main channel discharge 67 Habitat and hydraulic structure design discharge Threshold Channels Alluvial Channels 69 Alluvial channel design variables 70 Analogy methods 70 Hydraulic geometry methods Extremal hypotheses 80 Constrained dependent variables 80 Calculation of the remaining unknown design variables 80 Planform Natural variability in morphology around meander bendways 87 Practical channel design equations for meander bend geometry Sediment Impact Assessment 95 Topics to report 95 Sediment budget analysis 96 Sediment rating curve analysis 96 IV

Invited commentary for hydrological processes evaluation 'natural channel design' stream projects

2007

Received 5 June 2007 Accepted 6 June 2007 We need a coherent, deliberate process to learn from failures and successes in stream rehabilitation projects. Insightful evaluations comparing projects in varied regions have been limited by the diversity of approaches and some scientific uncertainty as to how to best accomplish longer-term monitoring (Bernhardt et al., 2005; Giller, 2005; Palmer et al., 2005; Palmer and Bernhardt, 2005; Reid, 2001, Reid and Furniss, 2002). Addressing just the critical issue of biological assessments would take an entire paper but with hundreds of natural channel design (NCD) projects completed across the country, simply evaluating their performance and impacts on bank erosion would be a step forward. Too often critiques of NCD projects have returned continually to the same few locations, and have yet to grapple with many other projects with different designs, disturbance histories, and environments. I hope this brief review will encourage better dialogue b...