River Gauging Stations Research Articles

Significant lateral inputs of fresh groundwater into a stratified tropical estuary: Evidence from radon and radium isotopes

River discharges are usually gauged at sites farther upstream than estuarine tidal reaches. As a result, global estimates of river water and nutrient fluxes to the ocean are likely underestimated as they often neglect groundwater discharge occurring in estuaries downstream of river gauging stations. We used radon and radium isotopes as tracers of groundwater discharge into the Sebastian River Estuary, a gaining stream in Florida, USA. We developed a spatially-distributed mass balance model that accounts for radon sources and sinks in waters above and below the estuarine pycnocline. Radium isotopes ( 224Ra, 223Ra, and 226Ra) were not enriched in groundwater relative to surface water and thus had limited usefulness as tracers at this specific site. The detection of fresh groundwater just beneath the sediment:water interface overlain by brackish bottom water implies that fresh groundwater dominates over saline groundwater in this salt wedge estuary. Lateral groundwater inputs from sandy banks into waters above the estuarine pycnocline were about 6-fold higher than inputs into waters below the pycnocline. Groundwater discharge rates into the surface layer of the estuary estimated from a radon mass balance ranged from 5 to 18 m 3/s (or 18 to 62 cm/day if uniformly distributed throughout the entire estuary area). The fluxes into the bottom layer ranged from 0.8 to 1.1 m 3/s (or 2.8 to 3.9 cm/day). These groundwater inputs augmented river discharges gauged upstream of the estuary tidal reaches by about 260% during the dry period and 135% during the wet period. As nutrient and other dissolved species are often highly enriched in groundwaters, groundwater probably controls surface water quality in this and other Florida estuaries.

Generation of synthetic seasonal hydrographs for a large river basin

Summary This paper describes a methodology for the generation of synthetic seasonal stage hydrographs with a number of flood waves for a large braided river basin based on statistical analysis of the historical stage records. The synthetic seasonal hydrographs in a river is required for different purposes such as assessing the hydraulic performances of various river training structures, morphological predictions, environmental impact analysis. The typical stage hydrograph of such a river has two components: flood waves and seasonal (monsoonal) response. Using historical stage records, flood waves in a seasonal stage record were identified and their characteristics were approximated using Maxwell distribution. The extracted characteristics of flood waves such as time of occurrence and successive flood lifts were analysed with various probability distribution function to find out their best distribution. The frequency analysis of the annual maximum flood lift was carried out. Beside this, seasonal responses were also approximated using Maxwell distribution. A relationship between the seasonal lift and total monsoonal rainfall was established. For a given total seasonal rainfall and return period of annual maximum flood wave lift, synthetic seasonal hydrograph is generated by superimposing both seasonal response and flood waves. The generated hydrographs are evaluated by comparing the cumulative frequency function of river stage and relative frequency of daily stage changes (rise/fall) for three seasons with different flood wave return periods, at two river gauging stations for the river Brahmaputra, India.

Regionalisation of low flow frequency curves for the Peninsular Malaysia

SUMMARY Regional maps and equations for the magnitude and frequency of 1, 7 and 30-day low flows were derived and are presented in this paper. The river gauging stations of neighbouring catchments that produced similar low flow frequency curves were grouped together. As such, the Peninsular Malaysia was divided into seven low flow regions. Regional equations were developed using the multivariate regression technique. An empirical relationship was developed for mean annual minimum flow as a function of catchment area, mean annual rainfall and mean annual evaporation. The regional equations exhibited good coefficient of determination ( R 2 > 0.90). Three low flow frequency curves showing the low, mean and high limits for each region were proposed based on a graphical best-fit technique. Knowing the catchment area, mean annual rainfall and evaporation in the region, design low flows of different durations can be easily estimated for the ungauged catchments. This procedure is expected to overcome the problem of data unavailability in estimating low flows in the Peninsular Malaysia.

2005 drought event in the Amazon River basin as measured by GRACE and estimated by climate models

Satellite gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) provide new quantitative measures of the 2005 extreme drought event in the Amazon river basin, regarded as the worst in over a century. GRACE measures a significant decrease in terrestrial water storage (TWS) in the central Amazon basin in the summer of 2005, relative to the average of the 5 other summer periods in the GRACE era. In contrast, data‐assimilating climate and land surface models significantly underestimate the drought intensity. GRACE measurements are consistent with accumulated precipitation data from satellite remote sensing and are also supported by in situ water‐level data from river gauge stations. This study demonstrates the unique potential of satellite gravity measurements in monitoring large‐scale severe drought and flooding events and in evaluating advanced climate and land surface models.

The sharp decrease in suspended sediment supply from China's rivers to the sea: anthropogenic and natural causes

Based on data from river gauging stations, the multi-year variations in suspended sediment flux (SSF) from China's nine major rivers to the sea were examined. The decadal SSF decreased by 70.2%: from 1.81 Gt/year for 1954–1963 to 0.54 Gt/year for 1996–2005. The decrease in SSF was more dramatic in the arid northern region than in the wet southern region; from north to south, the SSF decreased by 84% in the Yellow River, 42% in the Yangtze River, and 22% in the Pearl River. Dam construction was the principal cause for the decrease in SSF. At present, approximately 2 Gt/year of sediment is trapped in the reservoirs within the nine river basins. Reduced precipitation and increased water extraction and sand mining have also played a role in the decrease in SSF. Although water and sediment conservation programmes have not counteracted the influence of deforestation, they have enhanced the decrease in SSF in recent years. It is concluded that human activity has become a governing factor on riverine sediment delivery to the sea in China.

Hydrologic Regionalization of Watersheds in Turkey

Hydrologic regionalization can be employed for importing data from gauged sites to ungauged sites. A number of techniques have been developed for hydrologic regionalization. This study presents an approach that combines three regionalization techniques in order to obtain homogeneous regions and compute streamflow at desired ungauged sites. First, an agglomerative hierarchical clustering algorithm is used to determine the number of homogeneous regions. Second, homogeneous regions are defined by the k -means partitioning method. Third, the flow duration curve (FDC) method is used to compute streamflow discharge at desired ungauged sites in homogeneous regions. The combined approach was then applied to 26 river basins in Turkey having 1,410 river gauging stations, where homogeneous regions were identified and streamflow discharge was calculated at ungauged sites. At many of the unguaged sites, small hydropower projects are being planned for development. It was found that these 1,410 river gauging stations (2...

An integrated model for the assessment of global water resources – Part 1: Model description and input meteorological forcing

Abstract. To assess global water availability and use at a subannual timescale, an integrated global water resources model was developed consisting of six modules: land surface hydrology, river routing, crop growth, reservoir operation, environmental flow requirement estimation, and anthropogenic water withdrawal. The model simulates both natural and anthropogenic water flow globally (excluding Antarctica) on a daily basis at a spatial resolution of 1°×1° (longitude and latitude). This first part of the two-feature report describes the six modules and the input meteorological forcing. The input meteorological forcing was provided by the second Global Soil Wetness Project (GSWP2), an international land surface modeling project. Several reported shortcomings of the forcing component were improved. The land surface hydrology module was developed based on a bucket type model that simulates energy and water balance on land surfaces. The crop growth module is a relatively simple model based on concepts of heat unit theory, potential biomass, and a harvest index. In the reservoir operation module, 452 major reservoirs with >1 km3 each of storage capacity store and release water according to their own rules of operation. Operating rules were determined for each reservoir by an algorithm that used currently available global data such as reservoir storage capacity, intended purposes, simulated inflow, and water demand in the lower reaches. The environmental flow requirement module was newly developed based on case studies from around the world. Simulated runoff was compared and validated with observation-based global runoff data sets and observed streamflow records at 32 major river gauging stations around the world. Mean annual runoff agreed well with earlier studies at global and continental scales, and in individual basins, the mean bias was less than ±20% in 14 of the 32 river basins and less than ±50% in 24 basins. The error in the peak was less than ±1 mo in 19 of the 27 basins and less than ±2 mo in 25 basins. The performance was similar to the best available precedent studies with closure of energy and water. The input meteorological forcing component and the integrated model provide a framework with which to assess global water resources, with the potential application to investigate the subannual variability in water resources.

Regionalization of the Upper Tana Basin of Kenya Using Stream Flow Records

In this study, the upper Tana basin of Kenya was delineated into homogenous hydrological zones based on monthly stream flow records from several river gauge stations in the basin using the empirical orthogonal function analysis technique. Results indicate the study basin to be grouped into four homogenous hydrological zones that seemed to reflect the drainage, geological and climatic patterns of the catchments of the basin. The identified zones would be useful and crucial to understanding the physical and dynamic processes governing hydrology and water use such as hydroelectric power, storage and irrigation potential and other land use characteristics in the different catchments of the basin.

Estimation of total sediment load concentration obtained by experimental study using artificial neural networks

Estimation of sediment concentration in rivers is very important for water resources projects planning and managements. The sediment concentration is generally determined from the direct measurement of sediment concentration of river or from sediment transport equations. Direct measurement is very expensive and cannot be conducted for all river gauge stations. However, sediment transport equations do not agree with each other and require many detailed data on the flow and sediment characteristics. The main purpose of the study is to establish an effective model which includes nonlinear relations between dependent (total sediment load concentration) and independent (bed slope, flow discharge, and sediment particle size) variables. In the present study, by performing 60 experiments for various independent data, dependent variables were obtained, because of the complexity of the phenomena, as a soft computing method artificial neural networks (ANNs) which is the powerful tool for input–output mapping is used. However, ANN model was compared with total sediment transport equations. The results show that ANN model is found to be significantly superior to total sediment transport equations.

A two‐dimensional hydrodynamic model for flood inundation simulation: a case study in the lower Mekong river basin

AbstractThe lower Mekong basin is frequently affected by floods. Prolonged floods disrupt daily activities and cause huge socio‐economic damage almost every year. An advanced flood warning system could provide achievable non‐structural measures for reducing such damages. With a view to developing an advanced flood warning system, a distributed hydrodynamic modelling approach has been adopted for simulating a flood inundation phenomenon in the lower Mekong basin. A modelling system with a one‐dimensional (1‐D) river flow model and a two‐dimensional (2‐D) surface flow model has been used for simulating flood inundation. In the model, exchange of flows between the river and surface floodplain is calculated through established links, which determine the overflow from river nodes to surface grids or vice versa. These occur due to overtopping or failure of the levee when water height surpasses levee height. The model has incorporated detailed information about urban terrain features like embankments, roads, bridges, culverts, etc. in the simulation. A geographical information system (GIS)‐based comprehensive raster database of different spatial data layers is prepared and used in the model development. An explicit solution scheme is used for numerical computation, which considerably reduces the run time and makes the model suitable for use as a flood warning system in a large river basin. The model simulated results in the lower Mekong basin have shown close alignment with the observed data in terms of water level and discharge in various river gauging stations and flood extents in the floodplain and from the results it can be inferred that the model can predict the magnitude and duration of flood inundation to a reasonable level of accuracy. Copyright © 2007 John Wiley & Sons, Ltd.

Rainfall and streamflow response to El Niño Southern Oscillation: a case study in a semiarid catchment, Australia

This paper aims to compare the shift in frequency distribution and skill of seasonal climate forecasting of both streamflow and rainfall in eastern Australia based on the Southern Oscillation Index (SOI) Phase system. Recent advances in seasonal forecasting of climate variables have highlighted opportunities for improving decision making in natural resources management. Forecasting of rainfall probabilities for different regions in Australia is available, but the use of similar forecasts for water resource supply has not been developed. The use of streamflow forecasts may provide better information for decision-making in irrigation supply and flow management for improved ecological outcomes. To examine the relative efficacy of seasonal forecasting of streamflow and rainfall, the shift in probability distributions and the forecast skill were evaluated using the Wilcoxon rank-sum test and the linear error in probability space (LEPS) skill score, respectively, at three river gauging stations in the Border Rivers Catchment of the Murray-Darling Basin in eastern Australia. A comparison of rainfall and streamflow distributions confirms higher statistical significance in the shift of streamflow distribution than that in rainfall distribution. Moreover, streamflow distribution showed greater skill of forecasting with 0–3 month lead time, compared to rainfall distribution.

Hydrogeological Changes Related to the Umbria?Marche Earthquake of 26 September 1997 (Central Italy)

Evidences of variations of the hydrologic regime have been observed after the Umbria–Marche seismic sequence, started on September 26th 1997, at the boundary between Umbria and Marche regions, central Italy. In order to quantify the hydrological variations, several data regarding groundwater level, spring discharge and river flow rates, have been collected from local authorities and mineral water companies. They allowed to confine the area affected by anomalies and to quantify the hydrological variations by a comparison with the average yearly regime, estimated from the data referring to previous years. An attempt to identify precursor phenomena has also been carried out. The results of the analysis sustain the close connection of two water reservoirs, the Umbria–Marche ridge and the Valnerina unit, that have both been affected by changes of the hydrologic regime. Two of the river gauge stations registered anomalies several months before the crisis started, acting as earthquake precursors.

Selenium in the Blackfoot, Salt, and Bear River Watersheds

Nine stream sites in the Blackfoot River, Salt River, and Bear River watersheds in southeast Idaho, USA were sampled in May 2001 for water, surficial sediment, aquatic plants, aquatic invertebrates, and fish. Selenium was measured in these aquatic ecosystem components, and a hazard assessment was performed on the data. Water quality characteristics such as pH, hardness, and specific conductance were relatively uniform among the nine sites. Of the aquatic components assessed, water was the least contaminated with selenium because measured concentrations were below the national water quality criterion of 5 microg/L at eight of the nine sites. In contrast, selenium was elevated in sediment, aquatic plants, aquatic invertebrates, and fish from several sites, suggesting deposition in sediments and food web cycling through plants and invertebrates. Selenium was elevated to concentrations of concern in fish at eight sites (> 4 microg/g in whole body). A hazard assessment of selenium in the aquatic environment suggested a moderate hazard at upper Angus Creek (UAC) and Smoky Creek (SC), and high hazard at Little Blackfoot River (LiB), Blackfoot River gaging station (BGS), State Land Creek (SLC), upper (UGC) and lower Georgetown Creek (LGC), Deer Creek (DC), and Crow Creek (CC). The results of this study indicate that selenium concentrations from the phosphate mining area of southeast Idaho were sufficiently eleated in several ecosystem components to cause adverse effects to aquatic resources in southeastern Idaho.

Changes in the timing of high river flows in New England over the 20th Century

The annual timing of river flows is a good indicator of climate-related changes, or lack of changes, for rivers with long-term data that drain unregulated basins with stable land use. Changes in the timing of annual winter/spring (January 1 to May 31) and fall (October 1 to December 31) center of volume dates were analyzed for 27 rural, unregulated river gaging stations in New England, USA with an average of 68 years of record. The center of volume date is the date by which half of the total volume of water for a given period of time flows past a river gaging station, and is a measure of the timing of the bulk of flow within the time period. Winter/spring center of volume (WSCV) dates have become significantly earlier ( p<0.1) at all 11 river gaging stations in areas of New England where snowmelt runoff has the most effect on spring river flows. Most of this change has occurred in the last 30 years with dates advancing by 1–2 weeks. WSCV dates were correlated with March through April air temperatures ( r=−0.72) and with January precipitation ( r=−0.37). Three of 16 river gaging stations in the remainder of New England had significantly earlier WSCV dates. Four out of 27 river gaging stations had significantly earlier fall center of volume dates in New England. Changes in the timing of winter/spring and fall peak flow dates were consistent with the changes in the respective center of volume dates, given the greater variability in the peak flow dates. Changes in the WSCV dates over the last 30 years are consistent with previous studies of New England last-frost dates, lilac bloom dates, lake ice-out dates, and spring air temperatures. This suggests that these New England spring geophysical and biological changes all were caused by a common mechanism, temperature increases.

A suspended sediment yield predictive equation for river basins in the South Western river basin system of Ghana

An empirical equation that can be used for estimating the suspended sediment yields of river drainage basins without sediment data has been established for basins in the sub-tropical forest Southwestern river basin system of Ghana. The power law equation relates mean annual specific suspended sediment yield (t km-2 yr-1) of the drain-age basin to the basin area (km2) and the mean daily stream discharge (m3/s) of the river at the outlet of the draiinage basin. Values of the parameters of the equation were computed from the least squares linear regression fit to the logarithmic transforms of observed mean annual specific suspended sediment yield, mean daily stream discharge and basin area data at selected river gauging stations in the basin system. The equation was found to fit the observed data very well with a high coefficient of multiple determination, R2 of 0.95. The fit was found to be better than those relating mean annual specific suspended sediment yield to basin area or runoff only. Since many stream gauging stations in the country have no records on fluvial sediment, the empirical equation can be used to obtain preliminary estimates of expected sediment load of streams for engineering design of hydraulic structures such as reservoirs. Journal of Applied Science and Technology (JAST) , Vol. 5, Nos. 1 & 2, 2000, pp. 108 - 113

The relationship between climate and streamflow in the Namoi Basin

The Namoi River Basin (42 000 km 2) is located in the Murray-Darling Basin, west of the Great Australian Dividing Range in northeast New South Wales (NSW), and includes some of the most fertile agricultural lands in Australia. One of the environmental concerns for this basin is erosion and its effects on downstream water quality. Models that relate climate, land use, and these concerns require measurements of climate (rainfall and temperature) and streamflow. These measurements were examined as a preliminary to the modelling. The residual mass technique was used to examine the temporal variation of annual rainfalls over the approximately 100 years of available data, and significant spatial variations were found in annual rainfall trends over the catchment. Streamflow was examined at key river gauging stations. The impact of recent large-scale irrigation operations was clearly observed. The impact of changing land use and land management on runoff ratios was examined for eight subcatchments. Temperature variations were examined for the four major towns in the catchment. The duration of the temperature data is too short to make any comments about long-term trends. Significant variations were observed in an east to west direction.

Characterisation of the Flow Regime of Ewaso Ngiro North River

AbstractThis study aimed at characterising the river flow regime using statistical and probability methods. Streamflow data for Archers Post river gauging station for the period 1960 to 1998 were u...

Baseflow recession and recharge as nonlinear storage processes

Discharge in many rivers is often fed by outflow from a shallow groundwater reservoir. It is becoming clear that the outflow from this aquifer is not linearly proportional to storage as is commonly assumed in many algorithms. Numerical analysis of flow recession curves from about 100 river gauging stations instead reveals a nonlinear relationship between baseflow, Q, and storage, S, for which the equation S=aQb was adopted. Values of the exponent b are found by calibration to be between 0 and 1 but with a high concentration around 0·5, which is in accordance with the findings of other studies and theoretical approaches yielding b=0·5 for unconfined aquifers and relating the coefficient a to catchment properties, primarily area and shape of basin, pore volume and transmissivity. This non-linear reservoir function is proposed as a more realistic alternative to the linear reservoir function. The relatively fast response of groundwater flow to rainfall is mainly a result of the increase of hydraulic head of the groundwater reservoir accelerating the exfiltration of ‘old’, pre-event water into the river bed. As fissure and pore volumes communicate hydraulically, it appears physically reasonable to model the system by one non-linear reservoir for catchments, or parts of them, instead of applying independent parallel linear reservoirs. The non-linear reservoir algorithms are supported by an analytical derivation. They are extended for the automatic separation of baseflow from a time-series of daily discharge in rivers and the computation of storage and effective recharge of groundwater in river basins by inverse nonlinear reservoir routing. The time-series obtained allow the identification and quantification of long-term changes to the water balance. Relationships between computed groundwater storage and observed groundwater level can also be established. Copyright © 1999 John Wiley & Sons, Ltd.

Hysteresis Sensitive Neural Network for Modeling Rating Curves

Hysteresis is sometimes exhibited in rating curves representing the stage-discharge relationships at stream gauging locations. In practice, this creates a problem for hydrologists and makes the deduction of discharges, from regularly measured stages, rather difficult. Different approaches have been proposed for modeling such rating curves. A commonly used approach in the Nile river gauging stations is to develop two rating curves for the rising and falling phases of flood waves. However, this approach involves subjective judgment and may produce separation in the deduced discharge hydrograph. This paper proposes an artificial neural network methodology for providing a more accurate and practical solution to this problem. The aim of the study is to investigate the potential of employing neural networks for modeling stage-discharge relationships at specific stream locations. A simple three-layer back propagation neural network is introduced for developing rating curves at two Nile gauging stations. The proposed technique avoids drawbacks in current practice such as subjectivity in classifying observations into falling and rising sets, and separation in the deduced discharge hydrograph.

Regional hydrochemical modelling by delineation of chemical hydrological response units (CHRUs) within a GIS: An approach of observing man-made impacts in the Broel River catchment (Germany)

Abstract Characterizing and modelling hydrochemical catchment dynamics implies dealing with the challenges of upscaling point measurements to a regional, spatial distribution and with the regional spatial dynamics of nonpoint sources and their relation to catchment management. These two challenges can be met by applying the concept of ‘chemical response units (CHRUs)’ and using GIS-analysis to delineate their spatial distribution. CHRUs can be defined as areas having similar hydrochemical dynamics dependent on their landuse management. This concept was applied to the mesoscale catchment of the Broel River (A = 216km 2 ) in the middle-mountain range of the Rheinische Schiefergebirge in Germany. The catchment is underlayn by impermeable Devonian shale where losses of water due to deep percolation are negligible. The climate is oceanic and mean annual rainfall ranges between 950 and 1100 mm. The landuse pattern of the catchment was mapped in the field and digitized with the aid of a GIS-system. About 34% is covered by coniferous and deciduous forest, 11% — impervious, 52% — range land and the remaining 3% — agriculture. The catchment was instrumented to capture atmospheric dry and wet deposition as bulk samples, and two river gauging stations were equipped with instruments for continuous logging of electrical conductivity EC (mS/m) and water temperature. Additionally, water samples were taken in two-week intervals for complete anorganic analysis. An intensive questionary of farmers regarding their fertilizing practices was carried out and trade figures of fertilizers, sold to the farming community, were supplied by local traders to estimate chemical-fertilizer input. Data from neighbouring forested test catchments were used to evaluate the salt contribution from forested areas. The database also included other physiographic factors like soils and topography and GIS-overlay analysis was used to delineate specific CHRUs. Their hydrochemical dynamics is strongly characterized by landuse and atmospheric deposition. The annual chemical balances of the Broel catchment were calculated using these CHRUs and the results compared with the measured output at the two gauging stations. First, results from these balance calculations showed deviations associated with undetected point sources but also good fits during periods with unique hydrological conditions. In summary, the concept of CHRUs proved to be a practical method for the evaluation of the chemical dynamics of the heterogeneous mesoscale Broel River catchment. Future research is directed at combining the CHRU-concept with a hydrological model like MMS/PRMS, WASNOD&STOMOD or APEX, and thereby interfacing the hydrochemical and the hydrological dynamics, on a basin-scale.