Connection between rivers and their floodplain is critical to the function of fluvial systems; however, there has been little research quantitatively examining the dynamics of this interaction for large, alluvial rivers. Critical questions include the following: What are the rates and mechanisms of materials and energy exchange, and in what ways does the exchange impact ecosystem functioning? To address these questions, we built a simple model of a hypothetical reach of the Lower Mississippi River (LMR) containing a single backwater. The model is based on empirical data obtained from the LMR system. Our primary objectives for the model were to assess potential backwater impacts on river nitrate transport and in subsidizing phytoplankton biomass to the main channel. Simulations run over a 10‐year period suggest that on an annual basis, (a) LMR backwaters remove NO3–N, and it would require a temporal mean of 34,400 ha functioning like the model backwater, or 2.8 times the current area of oxbow lakes, to eliminate 100% of the river flux of NO3–N of our study region; (b) it would require inputs of phytoplankton from a mean of 5,242 ha of sites functioning like the model backwater to produce observed river flux of phytoplankton biomass; and (c) backwater function is sensitive to the controlling elevation in linking channels hence subject to management. Although simple, this model is a useful first step in quantifying the significance of river–backwater connectivity on ecological processes of the LMR system.

Numerical simulation of surface runoff is used to understand and predict watershed sediment transport and water quality and improve management of agricultural watersheds. However, models currently available are either simplified or parameterized for efficiency. In this chapter, CCHE2D, a physically based hydrodynamic model for general free surface flow hydrodynamics, was applied to study watershed surface runoff and channel flows. Multiple analytical solutions and experimental data were used to verify and validate this finite element model systematically with good results. A numerical scheme for correcting the bilinear interpolation of the water surface elevation solutions from the cell centers to the computational nodes was developed to improve the model. The correction was found necessary and effective for the sheet runoff simulations over the irregular bed topography. The modified numerical model was then used to simulate storms in a low-relief agricultural watershed in the Mississippi River alluvial plain. This physically based model identified the channel networks, watershed boundary automatically, and helped to develop rating curves at the gage station of this complex watershed. The numerical simulations resolved detailed runoff and turbulent channel flows, which can be used for soil erosion and gully development analyses.

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Storms cause a substantial increase in the fecal indicator bacteria (FIB) concentrations in stream water as a result of FIB-laden runoff and the release of FIB from stream sediments. Previous work has emphasized the association between FIB and bed sediments finer than sand. The objectives of this work were to elucidate the effect of various velocities on the entrainment of bed-dwelling coliforms in sand-bed streams and to refine methodologies for quantifying sandy streambeds as sources of FIB. Pump-induced hydrographs were created using a stainless steel nonrecirculating flume. Experiments consisted of simulating four storm hydrographs and collecting water samples upstream and downstream of a sand bed at selected intervals. Bed sediment samples were collected before and after each event. The highest concentrations of total coliform and suspended sediments generally occurred in the downstream samples during the rising limb of the hydrographs as a result of entrainment of coliforms and sand from the bed to the water column. There was a first flush effect in the system, as the upper layer of sand was influenced by a rapidly increasing velocity at ∼0.2 m s. Coliforms downstream of the sand bed increased rapidly as velocity exceeded this threshold but then declined even as velocity and discharge continued to increase. This likely reflects the depletion of coliforms as the more densely populated sediment layer was flushed out. There is evidence that streams with sand beds harbor enough FIB that development of total maximum daily loads (TMDLs) should include consideration of them as a source.

This report evaluates and assesses existing guidelines for the design, installation, monitoring, and maintenance of environmentally sensitive stream bank stabilization and protection measures, and develops quantitative engineering design guidance for selected treatments. Updated design guidelines for three widely used treatments are presented: live siltation and live staking with a rock toe, vegetated mechanically stabilized earth, and vegetated rip rap. For the engineer involved in the multidisciplinary design of an environmentally sensitive treatment, this report also includes current guidance from the Federal Highway Administration on the use of biotechnical treatments in proximity to transportation infrastructure. In addition, for the Professional Engineer (PE) on a design team, the report explores aspects of professional liability in environmentally sensitive design.

Selected watershed studies of the Conservation Effects Assessment Project (CEAP) are reviewed and findings are interpreted from the perspective of potential conservation outcomes due to climate change scenarios. Primary foci are runoff, soil erosion, sediment transport, and watershed sediment yield. Highlights, successes, and challenges with regards to climate change impacts on soil erosion, runoff, and watershed sediment yield are presented. The covered information adds to the existing knowledge base of climate change impacts and provides another piece of information that may be useful in the planning and management of agricultural watersheds; assessment of conservation needs; and development, funding, and implementation of conservation programs. The selected conservation assessment studies include, among others, a thought experiment on the sensitivity of soil erosion, runoff, and sediment yield to changes in rainfall; a computer-based investigation of potential climate change effects on runoff and soil erosion in a southeastern Arizona rangeland; the complex response of northern Mississippi watersheds to runoff variations and channel stabilization measures; the impact of conservation practices and a persistent pluvial period on watershed runoff and sediment yield in Oklahoma; and stream bank erosion during major flooding in Iowa and river corridor management. A study of rainfall-runoff in an north-central Missouri watershed and a curve number analysis in a northern Appalachian experimental watershed are included herein. Findings showed that climate change scenarios of increased precipitation intensity lead to an exponential increase in soil erosion, runoff, and watershed sediment yield, thereby stressing current conservation practices or future practices designed with present day practice standards. This diminishes conservation practice effectiveness and increases sediment supply to the stream network. The sensitive response of the watershed hydrologic system may lead to renewed soil erosion that is large enough to offset the reduction in soil loss achieved by current conservation practices. However, in alluvial-floodplain environments with non-cohesive bed and bank material, watershed sediment yield is controlled by channel discharge and energy slope, neither of which is influenced by traditional in-field conservation practices or channel bank stabilization structures. Thus, control of sediment yield will gradually shift in the downstream direction from sediment supply to sediment transport capacity and blur any existing relation between a climate change signal, in-field conservation outcomes, and sediment yield at watershed outlets. Targeting conservation practices to erosion prone areas, expanding conservation coverage, and adapting agronomic practices may be necessary to prevent excessive soil erosion and downstream sedimentation under climate change scenarios that include intensified precipitation.

Complex habitats such as sloughs, oxbows, and wetla nds provide important ecosystem services for fish communities. While human manipula tion of rivers and streams for flood control often reduce this complexity, some construc tion practices may provide an unexpected benefit. Structures such as borrow pits excavated for levee construction may mimic the functions of other back water features li ke oxbows or sloughs. Fish were collected in both Abiaca Creek channel and borrow p its created during the construction of a 360 ha floodway to examine the value of borrow pits as a backwater resource. Taxa richness, true diversity and other diversity indice s were calculated to compare the communities of fish at the various sample locations . Lentic habitats created by borrow pit excavation contributed to the overall diversity. Gr eatest fish diversity was in the unaltered upper channel site while lowest was in the lower ch annelized sample reach. One of the borrow pits with relatively low diversity was found to support a strong sports fishery and exhibited characteristics of a managed resource. Ca tch per unit effort was higher in the pits which contained a higher proportion of species that re ched larger adult sizes while number per unit of effort was higher in the upper channel sit .

DOI: 10.1061/(ASCE)HY.1943-7900.0000814IntroductionThe practice of stream restoration has become widely accepted asan essential component to improving ecosystem function andenhancing aquatic biodiversity (Wohl et al. 2005). Despite theabundance of projects being implemented, a lack of definitivetrainingrequirements,designprocedures,andmonitoringprotocolsremain for the practice of stream restoration. Given the lack ofconsistency, many restoration projects end in frustration, excessivecosts, and poor results (e.g., Williams et al. 1995; Kondolf 1998;Johnson and Brown 2001; Roni et al. 2002; Wohl et al. 2005;Bernhardt et al. 2007; Roni et al. 2008). The fact that methodand experience are both varied and even poorly defined in anew and emerging profession is not surprising; however, the com-bination of diverse and inconsistent training and methodologymakes progress in transforming the practice of stream restorationinto a mature profession difficult. The widespread practice of re-storation, now a billion dollar a year industry in the United States(Bernhardt et al. 2005), coupled with highly inconsistent results,demands its conversion into a profession with broadly acceptedprinciples and methods of tested reliability.As a profession advances, it must have ways to assess andassure the adequacy of education and training curricula and thecompetency of individual professionals (Ford and Gibbs 1996;Pomeroy-Huff et al. 2009). At the core of the process of maturinga profession is the establishment of a body of knowledge (BOK), adocument generated by experts to identify and delineate theconcepts, facts, and skills that practitioners in that profession areexpected to master (Morris et al. 2006; Pomeroy-Huff et al.2009). For example, project management professionals saw a clearneed to formulate a common and consistent set of core competen-cies on which they could base a project management certificationand advance their emerging profession (Morris et al. 2006; Winteret al. 2006). In the emerging profession of stream restoration, asimilar call exists for the establishment of consistent training stan-dards, standards of practice, and professional certification, drivenlargely by the lack of agreed on criteria for judging restoration suc-cess and highly inconsistent project results (Palmer et al. 2005;Marr 2009; Kite 2009; Fischenich 2009). The development of aprofession with standards of practice and/or certification first re-quires establishment of a training and education structure that pro-vides consistency and can support and incorporate advances inunderstanding (Morris et al. 2006).A fully effective symbiosis among research, training, andpractice has yet to emerge in stream restoration; however, severalattemptsweremadeduringthepast10yearstoestablishthecurrentandfutureneedsinstreamrestoration educationandtraining [RiverRestoration Northwest (RRNW) 2003; (AFS Curriculum WorkingGroup, unpublished data, 2003); P. Wilcock, unpublished internalreport, December 2006 RRNW, in cooperation with Oregon StateUniversity and Portland State University, sought to advance thequality of the river restoration practice by identifying restorationeducational needs (RRNW 2003). In 2003, RRNWand its partnersimplemented a survey to assess the job tasks, educational back-grounds, and training needs of professionals working on river re-storation projects in the northwestern United States and Canada.The key results are as follows.1. Available training is multidisciplinary with most universityand short courses focused on ecology, fluvial geomorphology,fisheries, restoration, and soils. Fisheries biologists and civilengineershavethegreatestrangeoftrainingacrossdisciplines.2. Improved skills and competence in fluvial geomorphology,field techniques, restoration techniques, and biology/ecologywere identified as important for a practicing professional.

Agricultural runoff often contains pollutants with antagonistic impacts. The individual influence of nutrients and atrazine on periphyton has been extensively studied, but their impact when introduced together and with multiple agricultural pollutants is less clear. We simulated a field-scale runoff pulse into a riverine wetland that mimicked pollutant composition typical of field runoff of the Mississippi River Alluvial Plain. Periphyton biomass and functional responses were measured for 2 weeks along a 500 m section. Additionally, laboratory chamber assays were used to identify potential periphyton changes due to nutrients, atrazine, and their interactions. Generally, nutrients stimulated, and atrazine reduced chlorophyll a (Chl a ) in chambers. In the wetland, nutrient and atrazine relationships with periphyton were weaker, and when found, were often opposite of trends in chambers. Total nitrogen (TN) was inversely related to Chl a , and total phosphorus was inversely related to respiration (R) rates. Atrazine (10–20 μg L −1 in the wetland) had a positive relationship with ash-free dry mass (AFDM), and weakened the relationship between TN and AFDM. Wetland periphyton biomass was better correlated to total suspended solids than nutrients or atrazine. Periphyton function was resilient as periphyton gross primary production (GPP)/R ratios were not strongly impacted by runoff. However, whole-system GPP and R decreased over the 2-week period, suggesting that although periphyton metabolism recovered quickly, whole-system metabolism took longer to recover. The individual and combined impacts of nutrients and atrazine in complex pollutant mixtures can vary substantially from their influence when introduced separately, and non-linear impacts can occur with distance downstream of the pollutant introduction point.

Earthen flood control levees are often built using soil excavated from borrow pits lying parallel to and riverward of the finished levee. After construction, these pits can provide valuable floodplain habitats, and their value along corridors of larger rivers is well established. However, levee borrow pits along smaller streams have not been studied. Six waterside levee borrow pits were studied for about three years along Abiaca Creek, which drains a 202km2 watershed in central Mississippi. Fish were sampled annually from six pits using boat-mounted electrofishing, and water quality samples were collected weekly from four pits. Continuous records of stream and borrow pit water levels were coupled with topographic and bathymetric survey data of the floodway to compute the frequency of connection between each pit and temporal distributions of aquatic habitat characteristics. Pit water surface areas ranged from 0.4 to 11.7ha, and mean depth ranged from 0.5 to 1.8m. Pits were hydraulically connected to the stream 1–34% of the time. Dissolved oxygen concentrations ranged from 0.30 to 13.7mg/L and were inversely related to water depth. Fish collections yielded 1768 individuals representing 26 species. Larger-bodied fishes and some piscivores were more common in larger, more elongated pits with more sinuous shorelines and lower turbidity. Setback levees with waterside borrow pits are a viable stream corridor restoration concept for smaller streams as well as major rivers.

Doyle, Martin W. and F. Douglas Shields, 2012. Compensatory Mitigation for Streams Under the Clean Water Act: Reassessing Science and Redirecting Policy. Journal of the American Water Resources Association (JAWRA) 48(3): 494‐509. DOI: 10.1111/j.1752‐1688.2011.00631.xAbstract: Current stream restoration science is not adequate to assume high rates of success in recovering ecosystem functional integrity. The physical scale of most stream restoration projects is insufficient because watershed land use controls ambient water quality and hydrology, and land use surrounding many restoration projects at the time of their construction, or in the future, do not provide sufficient conditions for functional integrity recovery. Reach scale channel restoration or modification has limited benefits within the broader landscape context. Physical habitat variables are often the basis for indicating success, but are now increasingly seen as poor surrogates for actual biological function; the assumption “if you build it they will come” lacks support of empirical studies. If stream restoration is to play a continued role in compensatory mitigation under the United States Clean Water Act, then significant policy changes are needed to adapt to the limitations of restoration science and the social environment under which most projects are constructed. When used for compensatory mitigation, stream restoration should be held to effectiveness standards for actual and measurable physical, chemical, or biological functional improvement. To achieve improved mitigation results, greater flexibility may be required for the location and funding of restoration projects, the size of projects, and the restoration process itself.

Shields, F. Douglas, Jr. and Scott S. Knight, 2011. Significance of Riverine Hypoxia for Fish: The Case of the Big Sunflower River, Mississippi. Journal of the American Water Resources Association (JAWRA) 48(1): 170‐186. DOI: 10.1111/j.1752‐1688.2011.00606.xAbstract: Degraded streams draining low‐relief, intensively cultivated watersheds may experience periods of hypoxia or anoxia. A three‐year study of water chemistry, fish, and physical habitat in the Big Sunflower River in northwestern Mississippi coupled with continuously logged physicochemical and hydrology data provided by others showed prolonged periods of hypoxia associated with higher flows. Fish species richness was directly related to dissolved oxygen (DO) concentration (r2 = 0.35, p = 0.00004), and ordination using nonmetric multidimensional scaling (NMS) indicated strong association between fish community structure and DO. Low‐head weirs supported relatively dense and diverse fish communities and thus provided local habitat enhancement, but may create stagnant zones upstream due to backwater effects that exacerbate low DO problems. Although hypoxia has been reported for some lightly degraded rivers and floodplains, our observations suggest hypoxia in Big Sunflower River and similar systems alters fish species composition and should be remediated. Cost‐effective remediation will require better understanding of autotrophic and heterotrophic processes that control DO and the relationship of these processes to discharge.

Agricultural runoff carries high nutrient loads to receiving waters, contributing to eutrophication. Managed wetlands can be used in integrated management efforts to intercept nutrients before they enter downstream aquatic systems, but detailed information regarding sorption and desorption of P by wetland sediments during typical inundation cycles is lacking. This study seeks to quantify and elucidate how inundation of wetland sediments affects bioavailability of P and contributions of P to downstream systems. A managed wetland cell in Tunica County, Mississippi was subjected to a simulated agricultural runoff event and was monitored for bioavailable phosphorus (water-extractable P [P], Fe-P, and Al-P) of wetland sediments and water level during the runoff event and for 130 d afterward. Inundation varied longitudinally within the wetland, with data supporting significant temporal relationships between inundation and P desorption. Concentrations of P were significantly higher at the site that exhibited variable hydroperiods (100 m) as compared with sites under consistent inundation. This suggests that sites that are inundated for longer periods of time desorb less P immediately to the environment than sites that have periodic or ephemeral inundation. Concentrations of iron oxalate and NaOH-P were significantly higher at the least inundated site as compared with all other sites (F = 5.43; = 0.001) irrespective of time. These results support the hypothesis that increased hydraulic residence time decreases the bioavailability of P in wetland sediments receiving agricultural runoff. This finding suggests that the restoration of wetlands in the mid-southern United States may be hydrologically managed to improve P retention.

We examined the mitigation efficiency of a managed riverine wetland amended with a mixture of suspended sediment, two nutrients (nitrogen and phosphorus), and three pesticides (atrazine, metolachlor, and permethrin) during a simulated agricultural runoff event. Hydrologic management of the 500m-long, 25m-wide riverine wetland was done by adding weirs at both ends. The agrichemical mixture was amended to the wetland at the upstream weir simulating a four-hour, ~1cm rainfall event from a 16ha agricultural field. Water samples (1L) were collected every 30min within the first 4h, then every 4h until 48h, and again on days 5, 7, 14, 21, and 28 post-amendment at distances of 0m, 10m, 40m, 300m and 500m from the amendment point within the wetland for suspended solids, nutrient, and pesticide analyses. Peak sediment, nutrient, and pesticide concentrations occurred within 3h of amendment at 0m, 10m, 40m, and 300m downstream and showed rapid attenuation of agrichemicals from the water column with 79–98%, 42–98%, and 63–98% decrease in concentrations of sediments, nutrients, and pesticides, respectively, within 48h. By day 28, all amendments were near or below pre-amendment concentrations. Water samples at 500m showed no changes in sediment or nutrient concentrations; pesticide concentrations peaked within 48h but at ≤11% of upstream peak concentrations and had dissipated by day 28. Managed riverine wetlands≥1ha and with hydraulic residence times of days to weeks can efficiently trap agricultural runoff during moderate (1cm) late-spring and early-summer rainfall events, mitigating impacts to receiving rivers.

We examined the effects of an amended mixture of three pesticides, atrazine (72.7 g), S-metolachlor (54.5 g), and permethrin (both cis and trans isomers; 11.4 g), on 10-day sediment toxicity to Hyalella azteca in a managed natural backwater wetland after a simulated agricultural runoff event. Sediment samples were collected at 10, 40, 100, 300, and 500 m from inflow 13 days prior to amendment and 1, 5, 12, 22, and 36 days post-amendment. Background pesticide concentrations ranged from <1 to 977, <1 to 119, and <1 to 2 μg kg−1, for atrazine, S-metolachlor, and permethrin, respectively. Average post-amendment atrazine and S-metolachlor were 2,915–3,927 and 3–20 μg kg−1, respectively at 10–40 m and 538–872 and <1 μg kg−1, respectively at 300–500 m. Average post-amendment permethrin was 65–200 μg kg−1 at 10–40 m and 1–10 μg kg−1 at 300–500 m. H. azteca 10-day survival varied spatially and temporally up to 100 m from inflow. Animal growth, independent of survival, was reduced 40 and 100 m from inflow on day 36, showing continued sediment toxicity of up to 100 m from inflow more than 1 month after amendment. Animal survival and growth were unaffected at 300 and 500 m from inflow throughout the study period. Correlations of pesticide concentrations and H. azteca responses indicated that observed sediment toxicity was primarily from permethrin with potential additional synergistic toxicity from atrazine and methyl parathion. Study results indicate that natural backwater wetlands can be managed to ameliorate pesticide mixture 10-day sediment toxicity to H. azteca within 300 m of inflow and smaller wetlands (≤100 m) may require several months of effluent retention to mitigate effects.

We assessed the aqueous toxicity mitigation capacity of a hydrologically managed floodplain wetland following a synthetic runoff event amended with a mixture of sediments, nutrients (nitrogen and phosphorus), and pesticides (atrazine, S-metolachlor, and permethrin) using 48-h Hyalella azteca survival and phytoplankton pigment, chlorophyll a. The runoff event simulated a 1h, 1.27cm rainfall event from a 16ha agricultural field. Water (1L) was collected every 30min within the first 4h, every 4h until 48h, and on days 5, 7, 14, 21, and 28 post-amendment at distances of 0, 10, 40, 300 and 500m from the amendment point for chlorophyll a, suspended sediment, nutrient, and pesticide analyses. H. azteca 48-h laboratory survival was assessed in water collected at each site at 0, 4, 24, 48h, 5d and 7d. Greatest sediment, nutrient, and pesticide concentrations occurred within 3h of amendment at 0m, 10m, 40m, and 300m downstream. Sediments and nutrients showed little variation at 500m whereas pesticides peaked within 48h but at <15% of upstream peak concentrations. After 28d, all mixture components were near or below pre-amendment concentrations. H. azteca survival significantly decreased within 48h of amendment up to 300m in association with permethrin concentrations. Chlorophyll a decreased within the first 24h of amendment up to 40m primarily in conjunction with herbicide concentrations. Variations in chlorophyll a at 300 and 500m were associated with nutrients. Managed floodplain wetlands can rapidly and effectively trap and process agricultural runoff during moderate rainfall events, mitigating impacts to aquatic invertebrates and algae in receiving aquatic systems.

Large wood (LW) exerts an important influence on the geomorphology and ecology of streams and rivers. The magnitudes of flow forces on LW are needed to support stream management activities and are typically computed using time mean lift and drag coefficients determined in laboratory flumes using small, smooth cylinders. Herein we report measurements of forces on LW of varying complexity (simple cylinder, branching, and complex root wad) and surface (bark) roughness made in an outdoor grassed channel under steady and unsteady flows. LW orientation relative to the primary flow direction and LW relative submergence were varied. Drag and lift coefficients for cylindrical (unbranched) LW followed patterns reported by others for metal cylinders in wind tunnels. Drag coefficients for cylindrical (unbranched) LW, corrected for blockage effects, ranged from −0.05 to 1.29, and lift coefficients ranged from −0.88 to 0.52, varying systematically with LW position relative to the channel bed and incident flow direction. Measured drag coefficients for the noncylindrical LW, corrected for blockage effects, ranged from 0.22 to 6.27, while lift coefficients varied from −3.65 to 30.84. Systematic relationships between the relative submergence and orientation of branching LW and the drag and lift coefficients were not observed, but coefficients were greatest for LW with few branches and converged on smaller values typical of blunt bodies as LW complexity increased. For both simple and complex LW, maximum lift and drag forces during the rising limb of unsteady flows were about 2–3 times greater than steady flow temporal mean values.