Quantifying Effectiveness of Streambank Stabilization Practices on Cedar River, Nebraska

Excessive sediment is a major pollutant to surface waters worldwide. In some watersheds, streambanks are a significant source of this sediment, leading to the expenditure of billions of dollars in stabilization projects. Although costly streambank stabilization projects have been implemented worldwide, long-term monitoring to quantify their success is lacking. There is a critical need to document the long-term success of streambank restoration projects. The objectives of this research were to (1) quantify streambank retreat before and after the stabilization of 18 streambanks on the Cedar River in North Central Nebraska, USA; (2) assess the impact of a large flood event; and (3) determine the most cost-efficient stabilization practice. The stabilized streambanks included jetties (10), rock-toe protection (1), slope reduction/gravel bank (1), a retaining wall (1), rock vanes (2), and tree revetments (3). Streambank retreat and accumulation were quantified using aerial images from 1993 to 2016. Though streambank retreat has been significant throughout the study period, a breached dam in 2010 caused major flooding and streambank erosion on the Cedar River. This large-scale flood enabled us to quantify the effect of one extreme event and evaluate the effectiveness of the stabilized streambanks. With a 70% success rate, jetties were the most cost-efficient practice and yielded the most deposition. If minimal risk is unacceptable, a more costly yet immobile practice such as a gravel bank or retaining wall is recommended

STREAMBANK EROSION PHENOMENA AND UNDERSTANDING: CURRENT RESEARCH AND FUTURE DIRECTIONS

Streams are in dynamic equilibrium with their environments, and as that environment is altered by human development and changing climate, streambank erosion is a common, but little understood, result. This article highlights the contributions of the special collection “Streambank Erosion, Sediment Dynamics, and Restoration (SER),” which assembled six studies that represent key advances in streambank erosion research, highlight current research in the field, and identify directions for future research. The studies in this special collection were grouped into three central themes: (1) streambank erosion monitoring, (2) streambank erodibility characterization, and (3) streambank erosion loading. In this article, key findings within each of these central themes are summarized, emphasizing the significant contributions of each study. Likewise, perspectives on future research directions are discussed, outlining important challenges that remain to be addressed. Overall, the studies in this special collection are unified in their overarching goal of improving quantitative and predictive understanding of streambank erosion phenomena

Comparison of three regionalization techniques for predicting streamflow in ungaged watersheds in Nebraska, USA using SWAT model

This study compared three approaches, regional averaging, nearest neighbor, and donor techniques, to regionalize parameters in the Soil and Water Assessment Tool (SWAT) on eleven watersheds located in the Dissected Plains, Plains, and Rolling Hills Landforms in the eastern portion of the State of Nebraska, USA. Within the Rolling Hills Landform, three watersheds were randomly selected as calibration watersheds while two were randomly selected as validation watersheds. Two watersheds were randomly selected as calibration watersheds while one was randomly selected as a validation watershed within each of the Dissected Plains and Plains Landforms. The seven calibration watersheds were used to provide the necessary calibrated parameter sets to execute each of the regional approaches, while the four validation watersheds were used to assess the impact of applying each of these approaches to an uncalibrated watershed. Percent Bias (PBIAS) and the Nash Sutcliffe Coefficient of Efficiency (NSE) were used to assess model performance. Test results of this study show that all three methods performed poorly, since the majority of watersheds among each method tested exhibited PBIAS values greater than ±25% and/or NSE values less than 0.50, which were considered to be unsatisfactory in terms of model performance. The average regionalization, nearest neighbor and donor methods resulted in only four (two calibration and two validation), zero and one satisfactory set of simulated watershed results, respectively. The findings from this study indicate that although each watershed was successfully calibrated with NSE values ranging from 0.51 to 0.84, none of the three regionalization methods provided suitable calibration data sets to define parameter values for performing satisfactory simulations on ungaged watersheds across the eastern Nebraska landscape

Comparison of three regionalization techniques for predicting streamflow in ungaged watersheds in Nebraska, USA using SWAT model

This study compared three approaches, regional averaging, nearest neighbor, and donor techniques, to regionalize parameters in the Soil and Water Assessment Tool (SWAT) on eleven watersheds located in the Dissected Plains, Plains, and Rolling Hills Landforms in the eastern portion of the State of Nebraska, USA. Within the Rolling Hills Landform, three watersheds were randomly selected as calibration watersheds while two were randomly selected as validation watersheds. Two watersheds were randomly selected as calibration watersheds while one was randomly selected as a validation watershed within each of the Dissected Plains and Plains Landforms. The seven calibration watersheds were used to provide the necessary calibrated parameter sets to execute each of the regional approaches, while the four validation watersheds were used to assess the impact of applying each of these approaches to an uncalibrated watershed. Percent Bias (PBIAS) and the Nash Sutcliffe Coefficient of Efficiency (NSE) were used to assess model performance. Test results of this study show that all three methods performed poorly, since the majority of watersheds among each method tested exhibited PBIAS values greater than ±25% and/or NSE values less than 0.50, which were considered to be unsatisfactory in terms of model performance. The average regionalization, nearest neighbor and donor methods resulted in only four (two calibration and two validation), zero and one satisfactory set of simulated watershed results, respectively. The findings from this study indicate that although each watershed was successfully calibrated with NSE values ranging from 0.51 to 0.84, none of the three regionalization methods provided suitable calibration data sets to define parameter values for performing satisfactory simulations on ungaged watersheds across the eastern Nebraska landscape

Geostatistical features of streambed vertical hydraulic conductivities in Frenchman Creek Watershed in Western Nebraska

This study evaluated the spatial variability of streambed vertical hydraulic conductivity (Kv) in different stream morphologies in the Frenchman Creek Watershed, Western Nebraska, using different variogram models. Streambed Kv values were determined in situ using permeameter tests at 10 sites in Frenchman, Stinking Water and Spring Creeks during the dry season at baseflow conditions. Measurements were taken both in straight and meandering stream channels during a 5 day period at similar flow conditions. Each test site comprised of at least three transects and each transect comprised of at least three Kv measurements. Linear, Gaussian, exponential and spherical variogram models were used with Kriging gridding method for the 10 sites. As a goodness-of-fit statistic for the variogram models, cross-validation results showed differences in the median absolute deviation and the standard deviation of the cross-validation residuals. Results show that using the geometric means of the 10 sites for gridding performs better than using either all the Kv values from the 93 permeameter tests or 10 Kv values from the middle transects and centre permeameters. Incorporating both the spatial variability and the uncertainty involved in the measurement at a reach segment can yield more accurate grid results that can be useful in calibrating Kv at watershed or sub-watershed scales in distributed hydrological models

Pesticide occurrence and persistence entering recreational lakes in watersheds of varying land uses

Currently little is known of newer pesticide classes and their occurrence and persistence in recreational lakes. Therefore, the objectives of this study were to (1) assess average pesticide concentrations and loadings entering recreational lakes in three mixed land use watersheds throughout the growing season, (2) evaluate pesticide persistence longitudinally within the lakes, and (3) perform an ecotoxicity assessment. Six sampling campaigns were conducted at three lakes from April through October 2018 to measure the occurrence and persistence during pre, middle, and post growing season. Polar organic chemical integrative samplers (POCIS) were placed in streams near lake inlets and monthly samples were collected for analysis of twelve pesticides. Additional monthly grab water samples were taken at each POCIS location and at the midpoint and outlet of each lake. All pesticide samples were analyzed using liquid chromatography/tandem mass spectrometry (LC/MS/MS) and individual pesticide loading rates were determined. Occurrence and persistence of specific pesticides were significantly different between lakes in varying watershed land uses. Specifically, the recreational lake receiving predominately urban runoff had the highest load of pesticides, likely in the form of biocides, entering the waterbody. Concentrations of imidacloprid exceeded acute and chronic invertebrate levels for 11% and 61% of the sampling periods, respectively, with the recreational lake receiving predominately urban runoff having the most occurrences. Findings from this study are critical for preventing and mitigating potential effects of pesticides, specifically applied as biocides in urban landscapes, from entering and persisting in recreational lakes

The assessment of water resources in ungauged catchments in Rwanda

Study region: Rwanda is a landlocked country in Africa with precipitation ranging from 800 mm yr−1 in the east to 1500 mm yr−1 in high-altitude regions in the north and west. Study focus: Streamflow estimation is an important task that is required in water resource assessments due to its importance in planning, decision-making and economic development. In this study, streamflow characteristics of ungauged catchments in Rwanda were calculated using a regionalization approach based on climate similarity and stepwise multiple-regression analysis. One climatic homogeneous region was identified and datasets of nine gauged stations and general available catchment characteristics were used to develop non-transformed and log-transformed regression models. New hydrological insights for the region: Results of this study show that climate, physiography and land cover strongly influence the hydrology of catchments in Rwanda. Using leave-one-out crossvalidation, the log-transformed models were found to predict the flow parameters more suitably. These models can be used for estimating the flow parameters in ungauged catchments in Rwanda and the methodology can be applied in any other region, as long as sufficient and good quality streamflow data is available

ISOTOPIC COMPOSITION OF GROUNDWATER AND PRECIPITATION IN NEBRASKA, USA

Groundwater is vital worldwide for water supply, agriculture and industry. Nearly 60% of all water use in Nebraska is from groundwater. Over 90% of groundwater is used for irrigation in Nebraska, which has the largest area of irrigated land in the United States. Many Nebraskans depend on groundwater for drinking water, both from private wells and municipal wells. The sustainability of groundwater resources is dependent on groundwater recharge. The recharge processes, as well as climatic patterns, influence the stable isotope signatures. Based on weekly samples collected at two monitoring stations managed by the National Atmospheric Deposition Program (NADP), Harvey (2001) and Harvey and Welker (2000) presented an overview of isotopic composition of precipitation in Nebraska. Two stations, located in Mead and North Platte (Figure 1), were monitored from 1992-1994 and 1989-1994, respectively. This data illustrated patterns in the isotopic composition of precipitation, both spatially and seasonally. To better understand the recharge processes, over 789 groundwater samples were collected across Nebraska in 2011 and their isotopic signatures analyzed. While other studies have evaluated isotope ratios (seasonal ratios) (Jasechko et al., 2017; Sanchéz-Murillo and Birkel., 2016), in this study we compared the precipitation signals. The objective of this study was to investigate recharge characteristics based on stable isotope signatures of groundwater and comparisons of the isotopic composition of groundwater and precipitation across Nebraska

The combined impact of redcedar encroachment and climate change on water resources in the Nebraska Sand Hills

The Nebraska Sand Hills (NSH) is considered a major recharge zone for the High Plains Aquifer in the central United States. The uncontrolled expansion of the eastern redcedar (Juniperus Virginiana) under climate warming is posing threats to surface water and groundwater resources. The combined impact of land use and climate change on the water balance in the Upper Middle Loup River watershed (4,954 km2) in the NSH was evaluated by simulating different combination of model scenarios using the Soil Water Assessment Tool (SWAT) model. A total of 222 climate models were ranked according to the aridity index and three models representing wet, median (most likely), and dry conditions were selected. Additionally, the impacts of carbon dioxide (CO2) emissions on root water uptake were simulated. Four plausible redcedar encroachment scenarios, namely 0.5% (no encroachment), 2.4, 4.6, and 11.9%, were considered in the numerical simulations. We, therefore, built: i) the historical scenario (2000–2019) with the current climate and redcedar cover leading to baseline results; ii) the most-likely future scenario (2020–2099) with projected climate (50th percentile of aridity index distribution) and redcedar encroachment that was estimated by using a combination of neural network and Markov-chain cellular automata model; iii) 16 future scenarios (2020–2099) with different combinationsof extreme climate (5th and 95th percentiles of aridity index distribution) and four hypothetical encroachment scenarios (0.5, 2.4, 4.6, and 11.9%). The most-likely climate projection indicates that a warming pattern will be expected with a 4.1◦C increase in average over the 100-year period, and this will be associated with lower-than-normal precipitation (P). Nevertheless, the concurrent increase in temperature and CO2 concentration is likely to induce stomata closure by reducing potential (ETp) and actual (ETa) evapotranspiration losses. Projected P and ETa are expected to decrease by 10 and 14% while recharge (R) and discharge (D) are expected to increase by 38 and 30% for the period 2020-2050. For the period 2051-2099, the projected P and ETa are expected to decrease by 8 and 32% while R and D are expected to increase by 140.2 and 40%. Finally, a sensitivity analysis of 16 combined climate and land use scenarios is presented and discussed. The scenario modeling approach presented in this paper can support decision-making by stakeholders for optimal management of water resources

A biological and chemical approach to restoring water quality: A case study in an urban eutrophic pond

Efforts to improve water quality of eutrophic ponds often involve implementing changes to watershed management practices to reduce external nutrient loads. While this is required for long-term recovery and prevention, eutrophic conditions are often sustained through the recycling of internal nutrients already present within the waterbody. In particular, internal phosphorus bound to organic material and adsorbed to sediment has the potential to delay lake recovery for decades. Thus, pond and watershed management techniques are needed that not only reduce external nutrient loading but also mitigate the effects of internal nutrients already present. Therefore, our objective was to demonstrate a biological and chemical approach to remove and sequester nutrients present and entering an urban retention pond. A novel biological and chemical management technique was designed by constructing a 37 m2 (6.1 m × 6.1 m) floating treatment wetland coupled with a slow-release lanthanum composite inserted inside an airlift pump. The floating treatment wetland promoted microbial denitrification and plant uptake of nitrogen and phosphorus, while the airlift pump slowly released lanthanum to the water column over the growing season to reduce soluble reactive phosphorus. The design was tested at the microcosm and field scales, where nitrate-N and phosphate-P removal from the water column was significant (α = 0.05) at the microcosm scale and observed at the field scale. Two seasons of field sampling showed both nitrate-N and phosphate-P concentrations were reduced from 50 μg L–1 in 2020 to \u3c10 μg L–1 in 2021. Load calculations of incoming nitrate-N and phosphate-P entering the retention pond from the surrounding watershed indicate the presented biological-chemical treatment is sustainable and will minimize the effects of nutrient loading from nonpoint source pollution