Quasi‐equilibrium conditions of urban gravel‐bed stream channels in southern Ontario,Canada

Urban gravel‐bed stream channels in southern Ontario, Canada identified to be in a state of quasi‐equilibrium have been studied over the past 15 years and compared against rural gravel bed stream channels of the same hydrophysiographic region. Bankfull width and depth versus bankfull discharge were not found to increase as a function of increasing urbanization as has been found in many other studies. The observed annual frequency of bankfull discharge was typically less than a 1‐year return period with many sites ranging between 2 and 18 bankfull events per year with higher intensity and shorter duration urban flood responses, which further identified significant limitations in using annual peak discharge methods for predicting morphological forming flows in urban watersheds. The cumulative volume of bankfull and larger flood events from the urban stream channels were very similar to the same annual event volumes in the rural comparison study reaches. Bed material supply was found to decrease with increasing urbanization and the reduction in bed material supply appears to be off‐set by the smaller bankfull channel width, depth and access to floodplains during large flood events. Field evidence may also suggest a even greater reduction in channel width trajectory, relative to the rural setting, with expansive floodplains to maintain quasi‐equilibrium conditions as bed material supply continues to decrease with increased anthropogenic activity. Copyright © 2010 John Wiley & Sons, Ltd.     

Downstream Regime Relations for Single‐Thread Channels

New empirically derived downstream hydraulic geometry relations are developed for single‐thread gravel/cobble‐bed and sand‐bed channels using the independent variables bankfull discharge, channel slope, and median bed grain size. Differences in channel response to the controlling variables are observed between gravel/cobble‐bed and sand‐bed channels. It is found that the inclusion of channel slope into regime relations is necessary for accurate channel geometry predictions and that bed grain size becomes an unnecessary variable. Accuracy of predictions is superior to many existing relations and comparable with those that already include slope as an independent variable. Variability of prediction errors is comparable with existing relations. Applications and implications of the new relations are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Tradeoffs associated with sediment‐maintenance flushing flows: a simulation approach to exploring non‐inferior options

Sediment‐maintenance flushing flows designed to mimic the action of natural floods in removing the accumulated fine sediments from the channel and loosening the gravel bed have been increasingly proposed as an effective alternative in dam management and a required component of riverine restoration programmes. However, reservoir releases are generally associated with financial and environmental costs, thus it is highly desirable to specify flushing flows as accurately as possible. In this paper we present a simulation approach to evaluating flushing flows and exploring the tradeoffs associated with non‐inferior flushing options. A two‐fraction sediment routing model is used to simulate the gravel‐sand bed response to flushing flows. The results reveal that the sand cleansing effect propagates from upstream to downstream and from surface to subsurface. Under a steady gravel supply from upstream, an equilibrium state of gravel transport and bed degradation is eventually reached in the simulation reach. The flushing flow and sediment transport system investigated in this study involves a transient state variable (bed sand content), a decision variable (flushing flow discharge), a flushing goal (ultimate bed sand content), and three outcomes to be minimized (flushing duration, released water volume, and total gravel loss). A series of numerical simulations are carried out with a range of flows and pre‐flushing bed sediment conditions. The results reveal that the flushing efficiency is higher for the larger flow. However, for flows greater than ～100 m³/s the flushing duration is less sensitive to the flow discharge, thus the system may be simplified as a bi‐objective one. The gravel loss and water volume are two conflicting outcomes within the non‐inferior flow region. Under a worse bed sediment condition, the feasible flushing options are constrained in a narrower range and also associated with higher costs. The tradeoffs between the conflicting outcomes are quantitatively displayed with the transformed feasible solutions in the objective space. We provide here a general and practical approach permitting a quantitative evaluation of the different flushing options that is appropriate to the level of data typically available. Copyright © 2004 John Wiley & Sons, Ltd.     

Estimating channel‐forming discharge in urban watercourses

Several methods of estimating channel‐forming discharge were conducted on 12 quasi‐stable urban stream channels ranging from 9 to 99% urban land use to test their applicability in the urban condition. Bankfull stage was identified at a series of locations along each study reach and it was found that the most consistent observations of bankfull discharge occurred during flood conditions where bankfull stage was identified at the top of point bars along the convex arc of bends. The largest errors in estimation occurred at gauge stations where cross‐sectional geometry had been altered to conform to bridges or culverts rather than the channel morphology. Independent evaluations of channel forming discharge were conducted by 11 practitioners ranging from 10 years to 43 years of experience with similar findings and errors. Various methods of relating frequency return periods were evaluated using annual peak series discharge observations and continuous 15‐min systematic discharge records using partial duration series analysis. Bankfull discharge was observed to occur more than once a year in all of the urban streams studied and often averaged from 4 to 8 bankfull discharge or larger events per year. In one particular case in a single given year 18 events exceeding bankfull discharge were observed. No specific correlations were identified between frequency return periods and land use change. However, based upon the findings of this study, the applicability of employing annual series peak discharge data to evaluate bankfull frequency return in urban stream channels is highly discouraged. Copyright © 2010 John Wiley & Sons, Ltd.     

EVALUATING SHALLOW‐WATER BATHYMETRY FROM THROUGH‐WATER TERRESTRIAL LASER SCANNING UNDER A RANGE OF HYDRAULIC AND PHYSICAL WATER QUALITY CONDITIONS

The fine‐scale structure of the water–sediment boundary in fluvial environments is dynamic and complex, influencing near‐bed flows, sediment transport and instream ecology. However, accurate high‐resolution surveying of marginally or partially inundated areas of river channels is problematic. Previous work has shown that terrestrial laser scanning (TLS) through relatively shallow‐water columns using standard green‐wavelength equipment introduces errors of <5 mm in a static, clear water column. This paper presents seven laboratory and field tests of through‐water TLS under variable flow velocities, depths, suspended sediment concentrations, water colour levels and scan ranges. Flow velocity decreased point accuracy only for supercritical flows, whereas point density decreased as a function of both water depth and suspended sediment concentration. A similar point return threshold was observed for water colour variations with no grains in suspension. Conversely, point precision and accuracy were a function of suspended sediment concentration alone (a threshold of 0.11 g L^?1 was observed). Field tests showed larger errors (<10 mm) and lower point precisions. A clear‐water depth‐penetration limit of 0.68 m was identified. Fluvial bathymetry acquired from through‐water TLS is presented for a gravel/boulder bed reach. Despite observed limits, these experiments demonstrate that our approach provides centimetre‐resolution bathymetry and sub‐aerial survey in an integrated dataset without the need for the following: (i) additional financial resources; (ii) concurrent depth measurements; or (iii) extra field effort for bathymetry acquisition, thereby enabling regular surveys to characterize the fine‐scale structure of channel beds and to constrain the geomorphic effect of individual flood events. Copyright © 2013 John Wiley & Sons, Ltd.     

Advantages of a mobile LSPIV method for measuring flood discharges and improving stage–discharge curves

This paper investigates the potential of fast flood discharge measurements conducted with a mobile LSPIV device. LSPIV discharge measurements were performed during two hydrological events on the Arc River, a gravel-bed river in the French Alps: a flood greater than the 10-year return period flood in May, 2008, and a reservoir flushing release in June, 2009. The mobile LSPIV device consists of a telescopic mast with a remotely controlled platform equipped with a video camera. The digital video camera acquired sequences of images of the surface flow velocities. Ground Reference Points (GRPs) were positioned using a total station, for further geometrical correction of the images. During the flood peak, surface flow velocities up to 7 m/s and large floating objects prevented any kind of intrusive flow measurements. For the computation of discharge, the velocity coefficient was derived from available vertical velocity profiles measured by current meter. The obtained value range (0.72–0.79) is consistent with previous observations at this site and smaller than the usual default value (0.85) or values observed for deeper river sections (0.90 typically). Practical recommendations are drawn. Estimating stream discharge in high flow conditions from LSPIV measurements entails a complex measurement process since many parameters (water level, surface velocities, bathymetry, velocity coefficient, etc.) are affected by uncertainties and can change during the experiment. Sensitivity tests, comparisons and theoretical considerations are reported to assess the dominant sources of error in such measurements. The multiplicative error induced by the velocity coefficient was confirmed to be a major source of error compared with estimated errors due to water level uncertainty, free-surface deformations, number of image pairs, absence or presence of artificial tracers, and cross-section bathymetry profiles. All these errors are estimated to range from 1% to 5% whereas the velocity coefficient variability may be 10%–15% according to the site and the flow characteristics. The analysis of 36 LSPIV sequences during both events allowed the assessment of the flood discharges with an overall uncertainty less than 10%. A simple hydraulic law based on the geometry of the three sills of the Pontamafrey gauging station was proposed instead of the existing curve that is fitted on available gauging data. The high flow LSPIV discharge measurements indicated that this new curve is more accurate for high discharges since they are evenly distributed in a ±10% interval around it. These results demonstrate the interest of the remote stream gauging techniques together with hydraulic analysis for improving stage–discharge relationships and reducing uncertainties associated with fast flood discharges.     

河流水面成像测速方法的比测试验研究

大尺度粒子图像测速（LSPIV）是一种新兴的非接触式瞬时全场流速测量技术。以LSPIV为基本原理,针对现场条件下特有的水流示踪物、复杂的光学成像环境及受限的测点布设方式,通过对流场图像采集、水面背景抑制、运动矢量估计、时均流场重建、水面流场定标及断面流量估计等技术方法的集成创新,建立一套完整的河流水面成像测速（RSIV）工作模式。为评价RSIV的性能并提出研究需求,在现场开展与流速仪法和雷达法的比测试验。结果表明,RSIV法的时均流速测量精度可以达到0.5 mm/s以内,相比流速仪法具有更高的时空分辨率。当流速系数和断面划分方式选择合适时,流量估计值和雷达法的一致性较好。试验初步验证河流水面成像测速方法用于河流流速、流量测量的可行性。     

Rapid Response of a Sand‐Dominated River to Installation and Removal of a Temporary Run‐of‐the‐River Dam

Run‐of‐the‐river dams (RORDs) comprise the vast majority of dams on river systems and are commonly removed as a part of stream restoration strategies. Although these dams are routinely removed, few studies have documented the geomorphological responses of sand‐bed rivers to the removal of RORDs. We examined the response of a large sand‐bed river located in South‐Central Kansas, USA, to the installation and removal of a dam that is installed annually for seasonal recreational purposes. Channel adjustments were tracked using cross‐sections sampled over the course of 7 months as the dam was installed and subsequently removed. Multivariate spatiotemporal analysis revealed emergence of channel stability when the dam was in place for most cross‐sections, except for those immediately adjacent to or at great distances from the dam. Our results provide an approximation for how sand‐bed rivers respond to RORD construction and removal and are useful for guiding management decisions involving preservation or restoration of connectivity. Results of this study suggest that sand‐bed rivers are resilient and recover quickly when transient RORDs are removed. Copyright © 2014 John Wiley & Sons, Ltd.     

A GIS‐based approach to mapping probabilities of river bank erosion: regulated River Tummel,Scotland

This study explores the use of Geographic Information Systems (GIS) techniques for mapping river channel planform change and bank erosion probability. The method used is primarily based on an approach developed by Graf (Graf, W.L. 1984. ‘A probabilistic approach to the spatial assessment of river channel instability’, Water Resour. Res., 20 (7), 953–962), which proposed that bank erosion probability could be determined for any given cell on a floodplain by taking into account (i) its distance laterally and in the upstream direction to the active river channel, and (ii) a value representing flood magnitudes for the given period. In this study, Graf's method is refined by using a GIS approach and by incorporating the influence of geomorphic variables, such as river bank morphology, sediment type and floodplain vegetation, on bank erosion rates. In addition, the technique is applied to a wandering gravel‐bed river of roughly 80 m width, representing a different type and size of river to that used in Graf's study. Thus, the wider applicability of the technique is tested. In addition, the analysis here covers only a short time scale (1988–1994) compared with that used by Graf. The high temporal resolution of this study is enabled by the use of aerial photography and also by the substantial channel changes that occurred within this time period as a result of several high magnitude flood events. The results of the study indicate the usefulness and validity of the approach, particularly with regard to floodplain erosion hazard mapping and the assessment of the effects of altered flood regimes and land use. Copyright © 2000 John Wiley & Sons, Ltd.     

Refinement of the wetted perimeter breakpoint method for setting cease‐to‐pump limits or minimum environmental flows

Analysis of inflections or breakpoints apparent in relationships between measures of wetted perimeter and discharge can be used to assist in the determination of minimum environmental flows for perennial rivers. This paper suggests refinements and provides an example application of the wetted perimeter method for the determination of cease‐to‐pump limits in a perennial, unregulated gravel‐bed river subject to increasing levels of surface water extraction. HEC‐GeoRAS modelling outputs of riffle wetted area are used to illustrate that the magnitude of the discharge selected to represent 100% habitat availability is of crucial importance to the breakpoint method. Because of the dependence of the technique on this assumption, we suggest that it is prudent to use an upper and lower limiting discharge based on an assessment of the degree of flow variability to develop a flow range around the zone of diminishing return in the wetted perimeter to discharge relationship. For rivers exhibiting a low degree of flow variability, the mean and median daily flows are likely to provide appropriate discharges for representation of 100% habitat availability. For perennial rivers with a higher degree of flow variability and considerable differences between the mean and median daily flows we suggest use of the 50th and 80th flow duration percentiles. Wetted perimeter breakpoint results are also influenced by the degree to which areas of non‐riffle habitat are included in the analysis. Inclusion of excessive pool areas can lead to significant reductions in resultant recommendations for cease‐to‐pump limits or minimum environmental flows. Integration of hydraulic model outputs with GIS for wetted perimeter analysis of riffles provides a useful, rapid, field‐based approach that can assist with determination of cease‐to‐pump limits or minimum environmental flows in gravel‐bed rivers. However, care is needed in its application and interpretation as the technique is prone to numerous subjective choices that have a substantial influence on results. Copyright © 2004 John Wiley & Sons, Ltd.     

浅谈雷达测流技术在美国的发展

随着光学、计算机技术等各相关技术领域的飞速发展,雷达技术、声学技术等非接触式流量测量技术有了突破性的发展。简要说明了非接触式测流技术的优点,叙述了采用雷达技术进行明渠流量测量的方法,重点介绍了美国地理调查局(USGS)应用雷达技术进行非接触式明渠流量测量的监测系统,此系统对我国研究非接触式明渠流量测流方法有着很好的参考和借鉴价值。     

Change detection of gravel mining on riverbeds from the multi‐temporal and high‐spatial‐resolution formosat‐2 imagery

Gravel mining from river channels is conducted in many countries around the world, yet ground‐based monitoring of these activities requires considerable manpower and is not very effective. Therefore, innovative and effective approaches to monitoring gravel mining are urgently required. Deployed as a high spatial resolution sensor in a daily revisit orbit, Formosat‐2 has proved to be an ideal satellite for site surveillance. Using one known event of gravel mining in the Tseng‐Wen River, Taiwan, between March 2004 and March 2005, we analysed nine Formosat‐2 images taken during this period to summarize three characteristics of gravel mining in the images. Based on these characteristics, a standard procedure for processing Formosat‐2 imagery to detect gravel mining is proposed. This procedure is validated against ground truthing collected by an unmanned helicopter flying at low altitude. The evolution of this gravel‐mining event in the Tseng‐Wen River is described by processing all historical Formosat‐2 imagery using the proposed procedure. This standard procedure has been successfully incorporated into the Formosat‐2 automatic image processing system and has been used to monitor gravel mining on a daily‐basis. Copyright © 2008 John Wiley & Sons, Ltd.     

雷达波流速仪在中小河流流量测验中的应用分析

针对目前大部分中小河流仍采用转子式流速仪或浮标法测流, ADCP 在大洪水和有漂浮物无法入水测验的问题,提出应用雷达波流速仪在中小河流进行流量测验.雷达波流速仪即电波流速仪,有多种类型,如无线遥控雷达波数字化测流系统、在线遥控多探头雷达波测流系统、缆道雷达波测流设备和手持电(雷达)波流速仪等.其中“无线遥控雷达波数字化测流系统”是新研制的雷达波测流系统,详细分析测验原理、性能特点,为推广使用,在山西省,黄河中游局,湖南常德、张家界等水文测站严格测试下,通过不同河流和环境进行多次比测,测验成果的各项参数齐全,可直接录入数据库,各项指标均符合《水文测验规范》要求,施工和安装简便,随时可投入使用,且能在最短的时间内能够测得准、报得出,可以成为中小河流流量自动测验的主要测具     

基于垂线流速模型的雷达法断面流量测流精度分析

利用雷达多普勒流速仪进行测流是目前成本较低的实时自动测流方法。传统的雷达多普勒流速仪获得断面单条垂线上的表面流速,一般采用代表流速法建模计算断面流量,导致水位变幅剧烈的断面测流误差较大。本文基于表面流速数据的垂线法测流模型,采用雷达式二合一传感器获得断面的垂线表面流速和水深实测数据计算断面流量,并以新田水文站断面测流为例,与缆道流速仪法的测流数据结果进行对比验证。结果表明垂线平均流速相对误差在 5%以内的合格率达到 75%,断面平均流速相对误差和断面流量相对误差在 5%以内的合格率均达到 67%,故仅需布设两个雷达测速仪即可达到相对误差小于 5%的高精度测流,在自动测流站中有较好的应用。     

HIGH‐FLOW GRAVEL INJECTION FOR CONSTRUCTING DESIGNED IN‐CHANNEL FEATURES

A planned gravel bar was dynamically constructed at a river rehabilitation project site through a combination of mechanical channel reconfiguration and high‐flow gravel injection. Mechanical alterations intended to promote deposition in a target area were followed by the injection of 1570 m³ of gravel and small cobble 400 m upstream during a high‐flow dam release. This dynamic bar construction proved successful in that bed elevations increased locally by more than 1 m in the target area and a new alternate bar sequence was created nearby. Morphodynamic modelling used to plan the injection correctly identified general areas prone to deposition or scour, but did not correctly predict the magnitudes of change or resolve features at the scale of individual alternate bars. A flow perturbation induced by a constructed meander bend just upstream from the injection point may have contributed to alternate bar development. Despite the observed bar development, sediment budget calculations indicate that the quantity of gravel stored in the target reach remained constant, perhaps because of an interruption in the delivery of bed material from upstream. The estimated gravel load over the release increased steadily in the downstream direction and, at the downstream study area boundary, had attained a magnitude 4.6 times larger than the quantity of injected gravel. These results demonstrate that bedload entrainment from the channel perimeter dominated the gravel supply to downstream reaches and suggest that the gravel injection had little effect on geomorphic adjustments downstream from its target area. Copyright © 2013 John Wiley & Sons, Ltd.     

Bryophytes as a special mesohabitat for meiofauna in a rip‐rapped channel

Rock rip‐rap is commonly used by river engineers for bank stabilization. However, there is a general lack of information on invertebrate communities inhabiting these structures. This study examines the permanent and temporary meiofauna dwelling in dense clumps of an aquatic moss Fontinalis antipyretica growing on rock rip‐rap along a side channel of the Morava river, Czech Republic. We estimated the amount of fine particulate matter (total trapped matter, TM) trapped in the moss as both a habitat and food source for meiofauna. Total mean numbers of the moss‐dwelling meiofauna per 10 g dry weight of moss and 1 m² of the bottom area were 253 917 ± 178 335 (mean ± SD) and 7 160 461 ± 5 029 047 individuals, respectively, during October 1999–November 2000. Out of 20 operational taxonomic units, Bdelloidea was the dominant group with about 76% of the total meiofauna numbers followed by Monogononta (11.23%), Nematoda (6.38%), Chironomidae (4.08%) and Oligochaeta (1.06%). Coarse trapped matter (500–1000 µm) contributed about 4% to the total, medium TM (100–500 µm) around 14% and the finest TM (30–100 µm) 82%. Organic matter (OM) forms 10% of the total TM. The seasonal variations in TM, OM and mineral matter and their size fractions have significantly correlated (Spearman rank correlation coefficient, P < 0.05 or 0.01) with densities of Oligochaeta, Hydrachnidia, Cladocera, Harpacticoida, nauplii of Copepoda, Chironomidae. In regulated channels, rock rip‐rap overgrown by aquatic bryophytes is desirable because it increases the spatial diversity of habitats and supports considerably higher numbers of meiofauna compared to the gravel bed and may substantially contribute to the stream metabolism. Copyright © 2002 John Wiley & Sons, Ltd.     

长江防洪有关水文问题探讨

探讨长江洪水的水文计算问题，建议舍弃水文系列中的不可靠的历史洪水与推算系列，直接采用１９４６ 年以来实测系列推算频率洪水；建议从可能的暴雨分布推算可能的洪水组合，由频率法与成因法联合确定设防洪水．１９９８ 年洪水流量不太大，洪量也与１９３１，１９５４ 年大体同一等级，推断只是由于河床沙砾卵石含量增大，河床粗化面不易冲刷，从而导致１９９８ 年洪水位最高、历时最长的一次特大洪水；建议水文部门进行全河段淤积、河床质组成的探测与水位流量关系变化的研究分析．     

Modelling reach‐scale variability in sediment mobility: An approach for within‐reach prioritization of river rehabilitation works

Many Australian river ecosystems have been, and continue to be, adversely affected by increased channel dimensions and sediment supplies occurring in the period since European settlement. One of the key aims of river rehabilitation in these rivers is to help reduce sediment yield by preventing ongoing bank erosion and remobilization of instream bed material stores. While various tools have been developed to help identify sediment sources at the catchment scale, this is often at a resolution that is too coarse to be translated directly to on‐ground rehabilitation works, as most riverworks programs are designed and implemented at the reach or within‐reach scale. This paper provides a method of prioritizing rehabilitation at the within‐reach scale by using a high‐resolution reach‐scale modelling approach to examine the relative entrainment potential of sediment stores. The method has been developed for a 10 km reach of the upper Hunter River, NSW, Australia. Shear stress distribution is examined using the widely available model HEC‐RAS, and incorporating a detailed, LiDAR‐derived, representation of the in‐channel vegetation into a spatially distributed Manning's roughness layer. At the geomorphic unit scale, the results highlight that the elevated ‘bench’ units, which represent significant stores of sand and silt, are much more vulnerable to remobilization than the lower elevation gravel bar units. At the sub‐reach scale (500–2000 m) shear stresses are greatest in the most confined sections. While instream geomorphic heterogeneity has been significantly reduced in these locations, ongoing erosion is limited by bedrock and buried coarse gravel terrace material in the bed and banks. These results highlight the need for targeted rehabilitation strategies that account for within‐reach variability in entrainment potential as well as on‐the‐ground knowledge of sediment supply and geological controls. Copyright © 2010 John Wiley & Sons, Ltd.     

Combining remote sensing with physical flow laws to estimate river channel geometry

A reliable representation of river terrains is essential to river research. Field surveys of river channel geometry are time‐consuming, costly, and logistically constrained and thus would encounter difficulties to achieve sufficient spatial coverage, resolution, and frequency of resurvey. This paper aims to demonstrate an efficient approach to building a river terrain model (RTM), the emphasis being on how to combine bathymetry and topography derived from satellite images captured at different flow stages. A method for calculating the difference between high and low stages (DHLS) based on the uniform‐flow theory is proposed. Calculations are carried out for a 13‐km long meandering section of the gravel‐bed Goulais River in Canada, which features pools and riffles, alternating point bars, and midchannel bars. A RTM for this complex section has been successfully produced. It consists of three data components: bathymetry at low stage, topography at high stage, and DHLS. The results capture realistic characteristics, including thalweg shift, steep outer banks, and gradual inner banks. They also show realistic longitudinal and lateral locations of pools and riffles. To illustrate potential applications of RTM, this paper has computed extreme bed shear stresses at bankfull discharge through hydrodynamics simulations of depth‐averaged flow in the river section and further estimated bed‐sediment grain‐size distributions. The estimates compare well with field measurements. The DHLS can vary significantly along a river channel. The proposed method for determining it is not site‐specific, and hence applicable to other rivers. The novelty of the methodology discussed lies in combining remote sensing techniques with physical flow laws.     

Water quality response to a pulsed‐flow event on the Mokelumne river,California

Controlled water releases from reservoirs (i.e. artificial floods) are used as a management technique to remove fine sediments and detrital materials from spawning gravels, mobilize gravel bars and clear encroaching brush from stream banks. The effects of a managed release event on water quality were investigated on the lower Mokelumne River in the western Sierra Nevada, California. The managed release was characterized by an increase in flow over a 4‐day period (from 11 to 57 m³ s⁻¹). Automatic pump samplers were used to collect samples for water quality from 0.7, 16.4, 37.4 and 54.4 km below Camanche Dam. These sampling sites provided water quality data for three distinct stream reaches: a gravel and sand‐textured substrate reach (0.7–16.4 km), a reach characterized by lentic conditions associated with a small reservoir (16.4–37.4 km), and fine sand and silt‐textured substrate reach (37.4–54.4 km). Water samples were analysed for total suspended solids (TSS), total nitrogen, ammonium (NH₄‐N), nitrate (NO₃‐N), total phosphorus, soluble reactive phosphorus (SRP), dissolved organic carbon (DOC), foecal coliforms and E. coli. Chemographs for all constituents exhibited spikes in concentration with each increase in streamflow for the rising limb. Fluxes of TSS, total P and total N released from the 0.7 to 16.4 km reach were 322, 0.32 and 0.70 Mg, respectively. The small reservoir acted as a sink for particulate materials retaining about 50% of TSS, 48% of total P and 43% of total N. However, the reservoir acted as a source of dissolved nutrients (NO₃‐N = 0.28 Mg and SRP = 0.055 Mg). The stream reach below the reservoir (37.4 to 54.4 km) was a source of particulate materials, dissolved nutrients and bacteria, possibly due to agricultural and urban inputs. Copyright © 2007 John Wiley & Sons, Ltd.