Discharge Relationship Research Articles

Research on stage–discharge relationship model based on random forest algorithm

Hydrological simulations and predictions are vital aspects of hydrological change research. Accurate predictions of hydrological factors such as stage and discharge are essential for water resources planning, reservoir dispatching and operation, shipping management and flood control. River discharge forecasting during flood seasons is an important issue in water resources planning and management. To improve the calibration accuracy and stability of the stage–discharge relationship model, the feasibility of integrated algorithms for studying the stage–discharge relationship was explored. A random forest (RF) algorithm based on a neural network (NN) was developed using a framework of integrated algorithms. First, the Levenberg–Marquardt (LM) algorithm was used to optimise the weight updating process of a back-propagation (BP) NN and improve the convergence speed. Then, the LM-BP algorithm was used as a decision tree to build an RF algorithm. The model was tested using hydrological data from Hongqi station on the Dadu River in China in the flood season. Results for the classical model, BP NN model, LM-BP NN model and optimised algorithm model were evaluated based on the mean absolute error (MAE), mean square error (MSE) and mean absolute percentage error (MAPE). The performance indicators showed that the optimised algorithm model (MAE = 3.13 m3/s, MSE = 19.28 m3/s and MAPE = 1.8%) was superior to the other models and showed high accuracy and good stability in flood-season flow forecasting.

River adjustments in response to human activities: A case study of the lower Beijiang River, China

AbstractIntensive human activity has caused significant changes in the river morphology and hydrological characteristics of the Pearl River Delta. Particularly, in‐channel mining and dam construction have induced remarkable levels of downward riverbed incision. Although strict control measures have been implemented for in‐channel sand mining, it remains unclear how the river has evolved since the abandonment of high‐intensity mining and its impact on flow diversion at the downstream confluence. This study presents the hydrological and morphological adjustments in the lower Beijiang River, the second largest tributary of the Pearl River, under the impacts of human interventions. A hydrodynamic model was developed to reveal the impacts of riverbed deformation on the flow diversion ratio at Sixianjiao, the confluence of the Beijaing River and the Xijiang River. The results showed that construction of cascade reservoirs upstream reach did not strongly influence run‐off, whereas incoming sediment loads were decreased. Because of upstream damming and in‐channel sand mining, a dramatic downward incision was observed in the lower Beijiang River, with a degradation volume of approximately 239.8 million m3 from 1999 to 2012. Particularly, in the upper reach, the incision depth was typically larger than 8 m. Riverbed incision caused continuous changes in the water stage–discharge relationship, and discharge increased remarkably under the same water level at the three hydrometric stations. During 2012–2020, because in‐channel sand mining was strictly controlled, rapid degradation was alleviated, deposition occurred in some cross‐sections and the deformation volume decreased by approximately 90% compared to that in the last period. A fast downward incision induced a change in flow exchange between the two rivers, and the flow diversion ratio of the Beijiang River increased from an average of 17% before 1998 to more than 21%.

Catchment concentration–discharge relationships across temporal scales: A review

AbstractProcesses that drive variability in catchment solute sourcing, transformation, and transport can be investigated using concentration–discharge (C–Q) relationships. These relationships reflect catchment and in‐stream processes operating across nested temporal scales, incorporating both short and long‐term patterns. Scientists can therefore leverage catchment‐scale C–Q datasets to identify and distinguish among the underlying meteorological, biological, and geological processes that drive solute export patterns from catchments and influence the shape of their respective C–Q relationships. We have synthesized current knowledge regarding the influence of biological, geological, and meteorological processes on C–Q patterns for various solute types across diel to decadal time scales. We identify cross‐scale linkages and tools researchers can use to explore these interactions across time scales. Finally, we identify knowledge gaps in our understanding of C–Q temporal dynamics as reflections of catchment and in‐stream processes. We also lay the foundation for developing an integrated approach to investigate cross‐scale linkages in the temporal dynamics of C–Q relationships, reflecting catchment biogeochemical processes and the effects of environmental change on water quality.This article is categorized under: Science of Water > Hydrological Processes Science of Water > Water Quality Science of Water > Water and Environmental Change

Advancing Discharge Ratings: A Novel Approach Based on Observed and Derivable GIS Factors in Alluvial Systems

Depth–discharge rating is required at gauged and ungauged locations for hydrologic modeling of alluvial systems to evaluate streamflow and manage regional water resources. Spanning low to high-flow conditions, manual field measurements are used to develop discharge ratings at gauged locations, producing continuous flow data from automated water depth measurements. The discharge rating is dependent on channel geometry, stream slope, vegetation, roughness coefficient, sediment load, and bank stability. To construct discharge ratings for many locations within larger model domains (hundreds to thousands of km2), intensive GIS and manual (spreadsheet) data manipulation are often required. In this analysis, available USGS gauging stations and readily available GIS coverages were used to learn and implement a novel method to characterize the depth–discharge relationships for hydrologic modeling of larger or complex areas using commonly available data and normalization techniques. The improved procedure simply uses drainage area, channel slope, and channel width, readily derivable GIS data, to develop discharge ratings for gauged and ungauged sections. The discharge rating curves for 70 USGS streamflow gauges were reproduced using the procedure. Then, the produced and observed discharge rating curves were compared to evaluate the accuracy of the method. In the analysis of streamflow depth predictions, the average Root Mean Squared Error was recorded at approximately 0.38 m (≈1.24 ft), with an interquartile range between 0.21 m and 0.49 m. The Mean Error remained centered around 0 m, with interquartile values ranging from −0.24 m to 0.24 m.

Calibrating Complexity: A Comprehensive Approach to Developing Stage–Storage–Discharge Relationships for Geographically Isolated Wetlands (GIWs) in W-C Florida

Geographically isolated wetlands (GIWs) play a critical role in regional hydrology, streamflow, groundwater recharge, evapotranspiration, and water quality. Despite their importance, research on quantifying discharges from these wetlands remains scarce. This study focuses on the hydrological characterization of GIWs in W-C Florida, a region where they cover a significant proportion of the land surface. The paper introduces a new procedure for developing Stage–Storage–Discharge (rating) characteristics essential for deterministic hydrological modeling in larger geographic areas. The approach synthesizes and extends previous research methodologies and offers simplified key modeling coefficients (m and n), which act as intelligent calibration knobs. These coefficients, when coupled with easily derivable physical attributes such as areas, slopes, and elevations, allow for the accurate simulation of downstream discharge timings and magnitudes, including flood behavior. The proposed method was tested using observational data from well-calibrated models. The results indicated a relative error of −7.2% for stage–storage and 15% for stage–discharge. GIS-based techniques were evaluated against surveyed data, and the results showed an accuracy of 0.16 m (0.52 ft) in estimating both the invert elevation and the maximum depth of GIWs. This effort will ultimately contribute to a better understanding and management of these critical ecosystems.

Stage discharge relations of a trapezoidal broad-crested weir pierced by a circular culvert

The present work focusses on the stage discharge relationship of a trapezoidal broad-crested weir pierced by a circular shape culvert at its base. The objective is to evaluate the relevance of the experimental and of the predictive superposition approaches for this hydraulic structure frequently encountered at the outlet of flood prevention basins, combining a flow through the culvert and a flow over the weir. The “experimental” superposition consists of the linear sum of the experimental relations of both elementary structures. Compared to the stage discharge relation of the complete structure, this sum performs well with a difference in discharge that does not exceed 15 %. The sum of discharges through both elementary structures slightly exceeds the discharge through the complete structure for an upstream head slightly above the weir crest elevation; it slightly underestimates this discharge for a larger upstream head, as already reported in the literature. The “predictive” superposition approach consists in predicting the stage discharge relation of the hydraulic structure using the sum of the stage discharge relations, available in the literature, for the elementary structures. The predictive superposition proves to be highly accurate for our combined hydraulic structure, especially for flow conditions with an incoming head high enough, for which the flow over the weir dominates.

Study on coupling of typical elements in surface water and groundwater in the middle reaches of the Yangtze River, China

Understanding the coupling relationship of typical elements between surface water (SW) and groundwater (GW) is helpful to the prevention of regional water environment pollution. In this study, the coupling of typical elements (C, N, P) of SW and GW in the middle reaches of the Yangtze River was comprehensively analyzed using multiple statistics and hydrogeochemical modeling methods. SW chemical characteristics was found similar with that of GW in the middle reaches of the Yangtze River with cluster analysis, and all sampling points was divided into two principal components based on principal component analysis. One principal component was more affected by the water-carbonate mineral interaction, the other one was greatly affected by anthropogenic activities. More interestingly, no fixed replenishment and discharge relationship was found between SW and GW in different seasons, which laid a foundation for the coupling of typical elements between SW and GW. Cl- in SW and GW had the same major source. In addition, almost identical water-carbonate reactions was found occurred in phreatic water (PGW) and confined water (CGW). As a link between SW and CGW, PGW may accept the supplies of the two waters at the same time, resulting the concentrations of δD, Cl-, DOC and HCO3– in PGW ranking between SW and CGW. Furthermore, Nitrogen and phosphorus were found to migrate between SW and GW, and a potential ammonium source in shallow aquitard which generated a large amount of ammonium. The coupling effect of nitrogen source input and transformation occurred in the process of nitrogen coupling between SW and GW, which increased the ecological risk of water environment. This study provided a scientific basis for the control of SW-GW pollution in the middle reaches of the Yangtze River, and supported the security of the water ecological environment in the Yangtze River Basin.

Upland Hillslope Groundwater Subsidy Affects Low‐Flow Storage–Discharge Relationship

AbstractLarge‐scale cross‐site scientific synthesis on low‐flow storage–discharge relation can promote developing transferable hypotheses on the interactions among critical zone attributes and on how such interactions affect catchments’ water vulnerabilities. This study leverages cross‐site empirical and theoretical analyses and develops a similarity index, based on the interactions among critical zone attributes, to help determine the less‐explored influence of upland hillslope groundwater subsidy on storage–discharge relation. We show that an increase in the relative extent of upland hillslope groundwater subsidy to low‐flow discharge, occurring through deep slow low‐moving (e.g., bedrock) storage unit, leads to (a) an increase in the nonlinearity of low‐flow discharge sensitivity to storage (β1) and (b) an increase in the convexity of low‐flow storage–discharge relation. Our findings also raise new hypotheses on the applicability of Boussinesq‐based hydraulic groundwater theory at low‐flow condition. Empirical results show that in a portion of our study catchments, particularly in those with a relatively small extent of upland hillslope groundwater subsidy, the theory’s proposed range of nonlinearity sufficiently explains the nonlinearity of low‐flow storage–discharge relation. However, in catchments with a strong influence of upland hillslope groundwater subsidy through deep slow‐moving storage unit, the current state of hydraulic groundwater theory, using one single (non)linear representative storage unit, may not be sufficient to explain the large nonlinearity and convexity of low‐flow storage–discharge relation (or the long tail of hydrograph late recession). Considering β1 informs the low‐flow vulnerability of catchments, the findings of this study deepen and generalize our understanding of where low‐flow discharge is vulnerable to storage’s change.

HARP: A suite of parameters to describe the hysteresis of streamflow and water quality constituents

Hysteresis occurs in ecological systems when there are internal dynamics that produce variable responses to an external stimuli or stressors. Understanding and quantifying hysteresis is important to inform understanding of system behaviour, support modelling, and provide comparisons within and between systems. We introduce a new tool, HARP (Hysteresis Area, Residual and Peaks) to describe and quantify hysteresis. HARP quantifies the key features of stream discharge–constituent concentration relationships, including the magnitude of the hysteresis (deviation from linearity), phase shifts in the system (end-state deviation from the pre-event state), and the timing of the turning points in the relationship of discharge and concentration. HARP is suitable to use on complex discharge–concentration data, including figure-eight loops, and supports statistical analysis to quantify the characteristics of independent events. The HARP metrics are introduced using discharge–water quality constituent concentration data, but are equally applicable to any system with properties of hysteresis. HARP provides a tool to develop quantitative observations of stream hydrological processes into quantitative enumeration statistics that facilitate comparisons of events and streams.

Quantitative Evaluation of Suspended Solid Runoff from Large-Scale Landslide Areas Presumed to Be the Source of Turbid Water

In the uppermost stream of the Mimikawa River, in northern Miyazaki Prefecture, the contribution to river turbidity of a huge, collapsed slope alternating sandstone and mudstone layers was qualitatively shown in our previous study. In this study, the water level and turbidity were continuously observed, to obtain a quantitative estimation of this contribution. The conversion equation from the water level to the flow rate is required, but field measurements during the flooding term in the mountainous site are difficult. In this study, a high-resolution survey was conducted, and the relationship was determined via a small-scale hydraulic model shaped using a 3D printer from the survey results, to determine the relationship between the water level and the flow rate. The flow rate time series was reproduced with the distributed runoff model that is verified with the flow rate converted from the water level. The flow rate and turbidity load time series were also estimated from the long-term rainfall. The area of the bare soil surface of each small basin was obtained via satellite image analysis, and the soil yield from each surface condition was calculated. Furthermore, the amount of turbidity produced upstream of Kamishiiba Dam was calculated for each small basin. It was estimated that 24% of the turbidity was generated from the small basin covering 5.7% of the total catchment area. This study showed that it is possible to verify the hydrological model by obtaining the water-level–discharge relationship, even in the mountains, where it is difficult to observe the discharge on-site, via small-scale hydraulic model experiments.

A sand tank experimental study of distribution, migration and transformation mechanism of iron and phosphorus species under redox fluctuation in a simulated riparian zone

The coupling transformation of iron (Fe) and phosphorous (P) in riparian zones is significant to their biogeochemical cycle in the interaction between surface water and groundwater systems. However, the spatiotemporal distribution and biochemical transformation within the river bank media are not well elucidated in the literature. In this study, we used a sand tank experiment to investigate the migration and transformation of iron and phosphorus under redox fluctuation forced by the variability in river stage in the riparian zone. Results show that there is a significant positive correlation between the trend of iron/aluminum coupled phosphorus (Fe/Al coupled P) and amorphous total iron (TFe). Additionally, more attention should be paid to the effect of dissolved organic carbon (DOC) rather than dissolved oxygen on the redox condition in the underground environment. For example, with the organic carbon decreasing, the inverse crystalline transformation process of Fe species (i.e. conversion of high crystalline Fe species into the low ones) gradually changes to the crystallization process, resulting in the immobilization and release of the aqueous phosphorus (PO43–). Furthermore, due to the adsorption and oxidation process, the migration of aqueous iron (Fe2+) was seriously inhibited, while the distribution and transformation of solid Fe species was similar at different locations. On the other hand, PO43− was observed to accumulate in the transition area of the riparian zone, and was hard to migrate through the river regardless of the recharge or discharge relationship between the river and the groundwater. Overall, this study elucidates the distribution, migration and transformation mechanism of Fe and P in a typical fine sandy riparian zone, and first provides theoretical support for tracing and controlling the source of phosphorus pollution in riparian aquifers.

Isotope Ratio – Discharge Relationships of Solutes Derived From Weathering Reactions

To date, the vast majority of studies seeking to link discharge to solute concentrations have been based on representations of fluid age distributions in watersheds that are time-invariant. As increasingly detailed spatial and temporal datasets become available for weathering-derived riverine solute concentrations, the capacity to link this mass flux to transient routing of reactive fluids through Critical Zone environments is vital to quantitative interpretation. Relationships between fluid age distributions and the stable isotope ratios of these geogenic solutes are even less developed, yet these signatures are vital to parsing the suite of water-rock-life interactions that create concentration-discharge relationships. Here we offer the first merging of a hydrological model featuring time-variant fluid age distributions with a geochemical model for isotopically fractionating weathering reactions. Using SiO2(aq) and the corresponding silicon isotope ratio δ30Si as an example, we show that the stable isotope signatures of riverine solutes produced by weathering reactions reflect a component of the fluid age distribution that is unique to the corresponding solute concentrations. This distinct sensitivity is the result of a stronger link between isotope ratios and the age distribution parameters describing a given watershed. This novel modeling framework is used to provide a quantitative basis for the interpretation of SiO2(aq) and δ30Si in six low-order streams spread across a diversity of climates, geologies, and ecosystems. To our knowledge, this is the first forward and process-based model to describe the isotopic signatures of solutes derived from weathering reactions in watersheds subject to time-varying discharge.

Composite Factors during Snowmelt Erosion of Farmland in Black Soil Region of Northeast China: Temperature, Snowmelt Runoff, Thaw Depths and Contour Ridge Culture

Snowmelt erosion could cause serious damage to soil quality and agricultural production conditions of slope farmland in the black soil region of northeast China. Contour ridge tillage is a traditional and effective measure to mitigate soil loss on slope farmland. However, the characteristics and influence factors of snowmelt erosion of slope farmland with contour ridge culture and the effect of this measure on the snowmelt process have not been comprehensively investigated, especially at the field scale. To bridge the gap, in situ observation was conducted on the snowmelt erosion process of a typical farmland in Baiquan County, Heilongjiang Province, China. The results revealed that during the snowmelt erosion period, the average daily snowmelt runoff volume and sediment concentration exhibited a trend of first increase and then a subsequent decrease. In the early stage, although the sediment concentration was large, limited discharge and soil thaw depths led to minimal soil loss. In the following stage, due to increased runoff and thaw depths, 94% of the total soil loss amount was obtained with an obvious erosion path formed. For each event, when soil thaw depths were shallow, sediment concentration had a high and early peak, whereas a reverse trend was observed when thaw depths increased. The hysteresis relationship of discharge–sediment indicated that the location where snowmelt erosion primarily occurred would change, under the influence of variations in runoff, freeze and thaw action, thaw depths, and micro-topography. The results could provide a guide in the control of soil erosion in seasonal snowmelt-erosion-prone areas.

Estimating uncertainty in streamflow and solute fluxes at the Hubbard Brook Experimental Forest, New Hampshire, USA

AbstractStream fluxes are commonly reported without a complete accounting for uncertainty in the estimates, which makes it difficult to evaluate the significance of findings or to identify where to direct efforts to improve monitoring programs. At the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, USA, stream flow has been monitored continuously and solute concentrations have been sampled approximately weekly in small, gaged headwater streams since 1963, yet comprehensive uncertainty analyses have not been reported. We propagated uncertainty in the stage height–discharge relationship, watershed area, analytical chemistry, the concentration–discharge relationship used to interpolate solute concentrations, and the streamflow gap‐filling procedure to estimate uncertainty for both streamflow and solute fluxes for a recent 6‐year period (2013–2018) using a Monte Carlo approach. As a percentage of solute fluxes, uncertainty was highest for NH4+ (34%), total dissolved nitrogen (8.8%), NO3− (8.1%), and K+ (7.4%), and lowest for dissolved organic carbon (3.7%), SO42− (4.0%), and Mg2+ (4.4%). In units of flux, uncertainties were highest for solutes in highest concentration (Si, DOC, SO42−, and Na+) and lowest for those lowest in concentration (H+ and NH4+). Laboratory analysis of solute concentration was a greater source of uncertainty than streamflow for solute flux, with the exception of DOC. Our results suggest that uncertainty in solute fluxes could be reduced with more precise measurements of solute concentrations. Additionally, more discharge measurements during high flows are needed to better characterize the stage‐discharge relationship. Quantifying uncertainty in streamflow and element export is important because it allows for determination of significance of differences in fluxes, which can be used to assess watershed response to disturbance and environmental change.

Quantification of Discharge‐Specific Effects on Dissolved Organic Matter Export From Major Arctic Rivers From 1982 Through 2019

AbstractLong‐term increases in Arctic river discharge have been well documented, and observations in the six largest Arctic rivers show strong positive correlations between dissolved organic carbon (DOC) concentration, river discharge, and chromophoric dissolved organic matter (CDOM) content. Here, observations of DOC and CDOM collected from 2009 to 2019 by the Arctic Great Rivers Observatory were used to estimate chromophoric DOC (CDOC) concentrations in the Kolyma, Lena, Mackenzie, Ob', Yenisey, and Yukon Rivers. All rivers except the Mackenzie showed significant positive correlations between annual watershed runoff and the proportion of the DOC that is chromophoric. Historical estimates of DOC and CDOC export were calculated for 1982–2019 by extrapolating the DOC and CDOC concentration—discharge relationships from 2009 to 2019 as a hindcast modeled estimate. For the six rivers combined, modeled DOC and CDOC exports increased, but CDOC increased faster than total DOC. The Lena and Ob' Rivers showed significant increases in DOC export individually, with annual trends of 39.1 and 20.4 Gg C yr−1 respectively. November–April (winter) DOC and CDOC exports increased in all rivers but the Yenisey, with the hindcast winter Kolyma export increasing by more than 20% per decade. There were no significant trends in discharge or associated DOC and CDOC fluxes during the observational period from 2009 to 2019; only when hindcasted values driven by changes in river discharge were analyzed did trends in DOC and CDOC emerge. This demonstrates how shifting seasonal distributions and increases in discharge can drive changes in DOC and CDOC concentrations and exports independent of other environmental factors.

Research and Application of the Calculation Method of River Roughness Coefficient with Vegetation

The roughness coefficient is a comprehensive parameter reflecting river resistance, which is widely used in the planning and design of river regulation and flood control projects. In recent years, as the upstream water conservancy and hydro-power projects have been put into operation, the frequency of low flow in the middle and lower reaches has increased, and the frequency of flood flow has decreased. All kinds of vegetation in the river floodplain grow luxuriantly, which causes a change in the river resistance and roughness coefficient. The present study was carried out with theoretical analysis and laboratory tests. A formula for the roughness coefficient calculation was derived based on the momentum equilibrium equation and momentum exchange between the vegetation layer and upper layer. The relationship between the depth-averaged velocity within the vegetation layer and depth-averaged velocity of the whole flow was analyzed. The reliability of the formula was verified by a large amount of previous experimental data. Based on the derived formula, the variation law of the roughness coefficient with vegetation density, vegetation height, and water depth were obtained. For the emerged vegetation flow, the Manning coefficient tended to increase with the increase in the vegetation density and water depth. For the submerged vegetation flow, the Manning coefficient showed a trend of decreasing with the increase in the water depth and increased with the increase in the vegetation height. Finally, the derived formula was applied in the Yueyang reach of the Yangtze River and the Duliujian River. The study can be applied in the fields of water level-flow discharge relationship analysis and the water surface line calculation of vegetated rivers.

Steady Flow through Gated Circular Culverts: Hydraulic Operation and Experiments

Culverts are ubiquitous hydraulic structures used in cross-drainage and agricultural water systems, especially at farm outlets in irrigation systems. Gate control adds hydraulic complexity to culvert water flow, yet it has hardly been studied. This study has two objectives: (1) to classify the operational conditions of gated culverts, and (2) to establish an experimental data set for analyzing discharge relationships based on that classification. A theoretical inlet–outlet control–based classification resulted in 22 inlet control and 19 outlet control cases, organized in 4 inlet and 5 outlet control groups. A total of 230 laboratory tests were conducted. The laboratory setup reproduced the conditions of inlet submerged with outlet in free surface (one of four inlet control groups) and all conditions except inlet in free surface with outlet submerged (four of five outlet control groups) of the inlet and outlet control groups, respectively. Comparison with existing classification schemes for gated culverts confirmed the suitability of the proposed scheme and provided further insight into flow classification. The discharge grouped by narrow ranges of gate openings was found to follow a power-law relationship of head with an exponent between 0 and 1. Flow transition regions between groups of conditions were examined, suggesting parabolic transition curves. The gate opening was found to be the dominant variable, resulting in a direct proportional effect on discharge, i.e., data corresponding to greater gate openings enveloped those with smaller openings. The slope’s influence could not be discerned within the slope range tested. Discharge estimation based on a dimensionless, empirical model produced reasonable results, although its case-dependent nature requires further research to develop operational hydraulic models for determining discharge through gated culverts. Application of the proposed classification scheme could help develop these hydraulic tools with sufficient accuracy.

Modelling and Numerical Simulation Approaches to the Stage–Discharge Relationships of the Lansheng Bridge

In recent years, extreme rainfall events with short delays and heavy rainfall have often occurred due to severe climate change. In 2015, Typhoon Soudelor caused a short-delayed heavy rainfall event in Nanshih River, which caused damage to a section of the Lansheng Bridge discharge station. The section was relocated upstream to rebuild the discharge station in 2019. However, the new discharge station cannot measure high flow due to the bridge structure. The flow observation range of Lansheng Bridge is therefore limited to normal flow, making it impossible to accurately estimate the flow during high-water stages. The purpose of this study is to use the past flow data of Nanshih River to estimate the flow rate under different return periods using frequency analysis. We used a Digital Elevation Model (DEM) to map the river’s topography, and used the 3D hydraulic calculations of the FLOW-3D model to estimate the water stage and discharge of the Lansheng Bridge. We then verified the accuracy of the model with the measured flow and water stage, and finally used the water stage and discharge data obtained from numerical simulation to construct the stage–discharge rating curve of the Lansheng Bridge. In addition to preventing flood disasters, this study approach can provide reliable data for use in water conservation. It may also be utilized to overcome the problem of measuring and estimating high flow during typhoon floods.

Laboratory Study of the Hydraulic Performance of the A-Type Triangular Piano Key Weir

A piano key weir (PKW), a new type of weir aiming to increase the discharge capacity of an existing dam, was recently designed. Despite a large body of research in this field, only a few studies were conducted on A-type triangular piano key weirs (TPKW) in straight channels. In this context, this present research sought to study the flow regime, stage–discharge relationship, and discharge coefficient. Experiments were carried out using nine TPKW models and three linear weirs (LW) as the control weirs. The results indicated that the triangular piano key weirs are capable of passing a higher discharge in similar laboratory conditions compared to linear key weirs due to their longer length. For a given h/P ratio (h is the water head over the weir crest, and P is the weir height) and constant length (Le), an increase in the weir height from 0.07 m to 0.15 m decreases the discharge coefficient by approximately 20%. From sensitivity analysis, the most influential parameters for the tested TPKW models are the h/Le dimensionless ratio, followed by the P/Le and Fr. Moreover, the discharge coefficient has a reverse trend when the dimensionless parameters h/P, h/Le, and Froude number are increased. However, with decreasing h/Le, the discharge coefficient of TPKW tends to that of a broad-crested weir because of local submergence. It is expected that the results obtained will be a reference for researchers who work in this field.

Review of hydraulic performance of open‐channel flow‐measuring flumes

The review explored various flumes used for open channel flow measurement and provided insight into operational concepts, discharge measurement, range of flow, head loss requirements, degree of accuracy and submergence, advantages, and limitations for use. The reviewed flumes included; Parshall flumes, Montana flumes, Cutthroat flumes, H-flumes, Trapezoidal flumes, Replogle-Bos-Clemmens (RBC) flumes, Palmer-Bowlus flumes and Central Baffle flumes (CBF). Based on the stage and discharge relationship, the reviewed flumes have a reasonable accuracy of ± 10 % over a wide range of flows. RBC flumes are the most accurate flumes (± 2 %). For flows that deal with a lot of sediments, most flumes have self-cleaning capability except for Palmer-Bowlus flumes and Central Baffle flumes. H-flumes have low resistance to submergence. The submergence transition for H-flumes is only 25-30 %. RBC flumes and Palmer-Bowlus flumes have the highest submergence (90 %). CBF and Palmer-Bowlus flumes need to be improved in order to have self-cleaning capability. Submerged flow corrections need to be developed and published for Palmer-Bowlus flumes and RBC flumes. The reviewed flumes effectively operate with a minimal head loss. The review has provided an insight on selection of an appropriate type of flume for flow measurement in open channels.