Recurrence Interval Discharge Research Articles

Geomorphological change detection of an urban meander loop caused by an extreme flood using remote sensing and bathymetry measurements (a case study of Karoon River, Iran)

Flooding and flood inundation are key hydrological characteristics of meander Loop Rivers. However, the effects of extreme floods on river morphology and spatial patterns of erosion and deposition are poorly understood. A detailed geomorphologic change detection and sediment/erosion process caused by an extreme flood (more than 100-year recurrence interval discharge) on 14 Apr 2016 was surveyed for a single urban meander loop of the Karoon River, Iran. The studied meander loop is located next to the city of the Ahavz and has a centerline length of about 14 km. The bathymetry in 8892 stable points was measured, also the detailed bathymetry layers for before (8 Apr 2016) and after (24 Apr 2016) the extreme flood event were compared. Geomorphological change detection (GCD) results show that in the studied reach about 106 ha of bank erosion was detected, with a total volume of approximately 450,600 m3. Furthermore, total volume of surface lowering and the total volume of surface rising volumes that were obtained were 95421.6 m3 and 98619.0 m3, respectively. The talweg length of the studied meander loop decreased about 126 m, and the average depth decreased from 3.71 m to 3.14 m after the flood event. Channel widening as a consequence of the extreme flood was found to be about 21 m (17%). The findings of this study indicate that extreme floods play an important role in the sediment budget and morphological evolution of meandering rivers.

Predicting Hydrologic Function With Aquatic Gene Fragments

AbstractRecent advances in microbiology techniques, such as genetic sequencing, allow for rapid and cost‐effective collection of large quantities of genetic information carried within water samples. Here we posit that the unique composition of aquatic DNA material within a water sample contains relevant information about hydrologic function at multiple temporal scales. In this study, machine learning was used to develop discharge prediction models trained on the relative abundance of bacterial taxa classified into operational taxonomic units (OTUs) based on 16S rRNA gene sequences from six large arctic rivers. We term this approach “genohydrology,” and show that OTU relative abundances can be used to predict river discharge at monthly and longer timescales. Based on a single DNA sample from each river, the average Nash‐Sutcliffe efficiency (NSE) for predicted mean monthly discharge values throughout the year was 0.84, while the NSE for predicted discharge values across different return intervals was 0.67. These are considerable improvements over predictions based only on the area‐scaled mean specific discharge of five similar rivers, which had average NSE values of 0.64 and −0.32 for seasonal and recurrence interval discharge values, respectively. The genohydrology approach demonstrates that genetic diversity within the aquatic microbiome is a large and underutilized data resource with benefits for prediction of hydrologic function.

Streambed scour of salmon spawning habitat in a regulated river influenced by management of peak discharge

Abstract In the Pacific Northwest of the United States, salmon eggs incubating within streambed gravels are susceptible to scour during floods. The threat to egg‐to‐fry survival by streambed scour is mitigated, in part, by the adaptation of salmon to bury their eggs below the typical depth of scour. In regulated rivers globally, we suggest that water managers consider the effect of dam operations on scour and its impacts on species dependent on benthic habitats. We instrumented salmon‐spawning habitat with accelerometer scour monitors (ASMs) at 73 locations in 11 reaches of the Cedar River in western Washington State of the United States from Autumn 2013 through the Spring of 2014. The timing of scour was related to the discharge measured at a nearby gage and compared to previously published ASM data at 26 locations in two reaches of the Cedar River collected between Autumn 2010 and Spring 2011. Thirteen percent of the recovered ASMs recorded scour during a peak‐discharge event in March 2014 (2‐to 3‐year recurrence interval) compared to 71% of the recovered ASMs during a higher peak‐discharge event in January 2011 (10‐year recurrence interval). Of the 23 locations where ASMs recorded scour during the 2011 and 2014 deployments, 35% had scour when the discharge was ≤87.3 m3/s (3,082 ft3/s) (2‐year recurrence interval discharge) with 13% recording scour at or below the 62.3 m3/s (2,200 ft3/s) operational threshold for peak‐discharge management during the incubation of salmon eggs. Scour to the depth of salmon egg pockets was limited during peak discharges with frequent (1.25‐year or less) recurrence intervals, which managers can regulate through dam operations on the Cedar River. Pairing novel measurements of the timing of streambed scour with discharge data allows the development of peak‐discharge management strategies that protect salmon eggs incubating within streambed gravels during floods.

Full Spectrum Analytical Channel Design with the Capacity/Supply Ratio (CSR)

Analytical channel design tools have not advanced appreciably in the last decades, and continue to produce designs based upon a single representative discharge that may not lead to overall sediment continuity. It is beneficial for designers to know when a simplified design may be problematic and to efficiently produce alternative designs that approximate sediment balance over the entire flow regime. The Capacity/Supply Ratio (CSR) approach—an extension of the Copeland method of analytical channel design for sand channels—balances the sediment transport capacity of a design reach with the sediment supply of a stable upstream reach over the entire flow duration curve (FDC) rather than just a single discharge. Although CSR has a stronger physical basis than previous analytical channel design approaches, it has not been adopted in practice because it can be a cumbersome and time-consuming iterative analysis without the use of software. We investigate eighteen sand-bed rivers in a comparison of designs based on the CSR approach and five single-discharge metrics: the effective discharge (Qeff) or discharge that transports the most sediment over time; the 1.5-year recurrence interval discharge (Q1.5); the bankfull discharge (Qbf); and the discharges associated with 50th (Qs50) and 75th (Qs75) percentiles of the cumulative sediment yield curve. To facilitate this analysis, we developed a novel design tool using the Visual Basic for Applications (VBA) programming language in Excel® to produce stable channel slope/width combinations based on the CSR methodology for both sand- and gravel-bed streams. The CSR Stable Channel Design Tool’s (CSR Tool) code structure was based on Copeland’s method in SAM and HEC-RAS (Hydrologic Engineering Center’s River Analysis System) and was tested with a single discharge to verify outputs. The Qs50 and Qs75 single-discharge designs match the CSR output most closely, followed by the Qbf, Qeff, and Q1.5. The Qeff proved to be the most inconsistent design metric because it can be highly dependent on the binning procedure used in the effectiveness analysis. Furthermore, we found that the more rigorous physical basis of the CSR analysis is potentially most important in designing “labile” channels with highly erodible substrate, high perennial flow “flashiness”, low width-to-depth ratio, and high incoming sediment load. The CSR Tool provides a resource for river restoration practitioners to efficiently utilize design techniques that can promote sediment balance in dynamic fluvial systems.

A combined field, laboratory and numerical study of the forces applied to, and the potential for removal of, bar top vegetation in a braided river

AbstractVegetation can have an important role in controlling channel planform, through its effects on channel roughness, and root‐reinforcement of bank and bar materials. Along the Platte River in central Nebraska, USA, The Platte River Recovery Implementation Program (PRRIP) has been tasked with managing the planform of the river to benefit endangered species. To investigate the potential use of planned short duration high flow (SDHF) events to manage bar vegetation, this study combined several approaches to determine whether flows of up to 227 m3s−1 through the central Platte River, could remove cottonwood, Phragmites and reed canarygrass stands of various ages and densities from in‐channel bars. First, fieldwork was carried out to measure the uprooting resistance, and resistance to bending for each species. Second, a set of flume experiments was carried out to measure the forces exerted on the three species of interest under different flow conditions. Finally, a numerical study comparing drag forces (driving) measured in the flume study, with uprooting forces (resisting) measured in the field, was carried out for each species to determine the likelihood of plant removal by SDHF events. Results showed that plants with more than a year of root growth, likely cannot be removed through drag and local scour alone, even at the 100‐year recurrence interval discharge. At most, a few cottonwood seedlings could be removed from bars through drag, scour and undercutting, where rooting depths are still small. The results presented here help us further understand the positive feedbacks that lead to the creation of permanent, vegetated bars rather than mobile braided channels. As such, the findings could help inform management decisions for other braided rivers, and the combined field, flume and modeling techniques used in this study could be applied to other fluvial systems where vegetation and planform dynamics are of interest. Copyright © 2016 John Wiley & Sons, Ltd.

The frequency of channel-forming discharges in a tributary of Upper Big Walnut Creek, Ohio

Understanding floodplain hydrology is necessary to interpret water quality and properly identify and predict the effectiveness of conservation practices in headwater watersheds. The goal of this study was to determine the frequency and magnitude of out-of-bank and channel-forming discharges in Sugar Creek, a tributary of the Upper Big Walnut Creek, in Ohio. To address this goal, a stream geomorphology study was conducted, measured discharge data at a downstream location were used to develop a calibrated discharge versus recurrence interval relationship, and the Hydrologic Engineering Center9s Hydrologic Modeling System (HEC-HMS) and River Analysis System (HEC-RAS) simulation models were used to develop out-of-bank discharge recurrence interval relationships for selected locations along Sugar Creek. Much of Sugar Creek was in dynamic equilibrium and had an extensive floodplain with entrenchment ratios ranging from 2 to 18. At the eight locations studied, two experienced bankfull or larger discharges an average of 12 times per year, with an approximate 0.2-year recurrence interval. Seventy-five percent of the locations experienced bankfull or larger discharges an average of at least 3 times per year, with an approximate 0.8-year recurrence interval. All of the locations experienced out-of-bank discharges an average of at least once per year, with the 2-year recurrence interval discharge. The annual out-of-bank discharges at each location ranged from 0.4% to 13% of the average annual flow volume. Based on the results, we recommended that research be conducted in the Sugar Creek Watershed to quantify the water quality benefits of a system in dynamic equilibrium and a well-attached, active floodplain.

Politicians and geomorphological blunders. Some examples relating to rivers and coasts from Queensland, Australia

Geomorphologists have an important role to not just understand and interpret the nature of processes operating within the physical landscape, but also to communicate this information to those who can use it to benefit society. Policy makers and legislators often develop documents relating to the management and use of landforms and landscapes that contain little or no input from geomorphologists, which can and do have undesirable consequences for governments, communities and the natural environment. Examples relating to rivers and coasts from Queensland, Australia highlight inadequacies in policies and legislation because of a lack of input from geomorphologists. In one instance the definition of a stream channel has been reinterpreted by the legal system because of a poorly developed definition within the legislation. The outcome is a legal definition of a stream channel based on the Q3 month flow (3-month average recurrence interval discharge or flow). In another instance, people and property are being placed at risk from coastal erosion and impact from tropical cyclone generated marine inundations (waves and surge) because a lack of understanding of geomorphic processes operating along the coast has been inscribed into policies and legislation. These are examples from one region but similar situations will exist elsewhere globally. Both politicians and geomorphologists have a role to communicate better with each other about these matters. Geomorphologists in particular need to be more proactive in advising politicians on issues in which they have expertise.

청미천 구하도 복원 설계를 위한 하도형성유량 산정

구하도 및 폐천복원은 하천에서의 이수와 치수적인 기능뿐만 아니라 환경 및 생태 서식처 기능을 강화하고 개선하기 위한 여러 방법들 중 하나이며 이러한 구하도를 복원하기 위해서는 주수로와의 하도 안정성을 고려하여 횡단면 형태를 결정하고 하도선형을 설계하게 된다. 이러한 하도설계시 기준이 되는 유량이 반드시 필요하며 이 기준유량을 하도형성유량 또는 지배유량이라고 한다. 일반적으로 하도형성유량을 산정하는 방법으로는 만제유량, 특정 재현기간별 유량, 유효유량을 계산하여 결정하는 방법이 있다. 본 연구에서는 구하도 복원 사업이 시행되는 청미천 구간에 대해 만제유량, 특정 재현기간별 유량, 유효유량을 산정하여 상호 관계를 분석하고 과거의 하상변동 특성 자료와 비교하여 연관성을 평가하였다. 청미천 구하도 복원구간의 만제유량은 HEC-RAS 자료를 이용하여 만제수위에 해당되는 유량으로 산정하였으며 488 <TEX>$m^3/s$</TEX>인 것으로 나타났고 이는 1.5년과 2년 빈도 사이의 유량에 포함되는 것으로 나타났다. 또한 유사량 자료와 과거 일유량 자료를 이용하여 계산된 유효유량은 만제유량보다 큰 값을 갖는 것으로 나타났다. 과거 측량자료 분석에 의하면 청미천의 대상구간 하도는 1994년에 비해 2008년 현재 하도가 침식된 것으로 나타났으며 이는 유효유량을 소통시킬 수 있는 형태로 하도가 진화하고 있다는 것을 의미하며 곧 하천이 안정한 상태로 변화하고 있다는 것을 의미한다. The abandoned channel restoration is one of methods to enhance the environmental function and ecological habitat as well as the functions of water-utilization and flood control. The channel-forming or dominant discharge must be evaluated and defined to design the cross-sectional and plane geometries of the stable and equilibrium channel for the abandoned channel restoration project. In general, bankfull discharge, specified recurrence interval discharge, and effective discharge have been used to decide the channel-forming discharge. In this study, bankfull discharge, specified recurrence interval discharge, and effective discharge were calculated and compared for the abandoned channel restoration site of Cheongmi Stream and their relations to historical bed changes were analyzed. The bankfull discharge, 488 <TEX>$m^3/s$</TEX>, of the abandoned channel restoration site of Cheongmi Stream was calculated using HEC-RAS data and ranged between 1.5-year and 2-year recurrence discharges. Also, the effective discharge evaluated with the sediment rating curve and mean daily discharge data is greater than the bankfull discharge. According to the survey data of 1994 and 2008, the bed elevation of the study reach was decreased over time. It is indicated that the channel bed is changing to the stable condition to allow the effective discharge.