Streamflow Generation Mechanisms Research Articles

Interpreting streamflow generation mechanisms from integrated surface-subsurface flow models of a riparian wetland and catchment

[1] The understanding of streamflow generation processes is vitally important in the management of water resources. In the absence of the data required to achieve this, Integrated Surface-Subsurface Hydrological Models (ISSHM) can be used to assist with the development of this understanding. However, the standard outputs from these models only enable elicitation of information about hydrological drivers and hydrological responses that occur at the same time. This generally limits the applicability of ISSHMs for the purposes of obtaining an improved understanding of streamflow generation processes to catchment areas that do not exhibit significant storage, travel times or flow depletion mechanisms. In order to overcome this limitation, a previously published Hydraulic Mixing-Cell (HMC) method is improved so that it can be used to follow surface water derived from direct rainfall and groundwater discharge to the stream and adjacent overland flow areas. The developed approach was applied to virtual experiments (based on the Lehstenbach catchment in southeastern Germany), which are composed of two ISSHMs of contrasting scales: (1) a riparian wetland of area 210 m2 and (2) a catchment of area 4.2 km2. For the two models, analysis of modeling results for a large storm event showed complex spatiotemporal variability in streamflow generation and surface water-groundwater interaction. Further analysis with the HMC method elucidated in-stream and overland flow generation mechanisms. This study showed within a modeling framework that identification and quantification of in-stream and overland flow generation better informed understanding of catchment functioning through decomposition of streamflow hydrographs, and analysis of spatiotemporal variability of flow generation mechanisms.

Streamflow generation in a large, alpine watershed in the southern Rocky Mountains of Colorado: Is streamflow generation simply the aggregation of hillslope runoff responses?

Spatial and temporal trends in stream chemistry were investigated in a large (1600 km2) alpine watershed in the southern Rocky Mountains of Colorado to help understand mechanisms of streamflow generation. We observed linear increases of concentrations of chemical constituents in streamflow as accumulated drainage area increased along the main channel of Saguache Creek. We tested two conceptual models of streamflow generation against our stream chemistry observations. One model is essentially two‐dimensional and treats streamflow generation at the large watershed scale as the aggregation of runoff responses from individual hillslopes, primarily surface and shallow subsurface flow paths. Alternatively, a fully three‐dimensional conceptual model treats streamflow generation as being controlled by a distribution of large‐scale groundwater flow paths as well as surface and shallow subsurface flow paths. The structure and magnitude of groundwater contributions in streamflow as a function of increasing scale provided a key distinction between these two conceptual models. End‐member mixing analysis and measurements of hydraulic head gradients in streambeds were used to quantify basin‐scale groundwater contributions to streamflow with increasing spatial scale in the Saguache Creek watershed. Our data show that groundwater contributions are important in streamflow generation at all scales and, more importantly, that groundwater contributions to streamflow do increase with increasing watershed scale. These results favor the three‐dimensional conceptual model in which long groundwater flow paths provide a streamflow generation process at large scales that is not operative at smaller scales. This finding indicates that large watersheds may be more than simply the aggregation of hillslopes and small catchments.

A hydraulic mixing-cell method to quantify the groundwater component of streamflow within spatially distributed fully integrated surface water–groundwater flow models

The complexity of available hydrological models continues to increase, with fully integrated surface water–groundwater flow and transport models now available. Nevertheless, an accurate quantification of streamflow generation mechanisms within these models is not yet possible. For example, such models do not report the groundwater component of streamflow at a particular point along the stream. Instead, the groundwater component of streamflow is approximated either from tracer transport simulations or by the sum of exchange fluxes between the surface and the subsurface along the river. In this study, a hydraulic mixing-cell (HMC) method is developed and tested that allows to accurately determine the groundwater component of streamflow by using only the flow solution from fully integrated surface water–groundwater flow models. By using the HMC method, the groundwater component of streamflow can be extracted accurately at any point along a stream provided the subsurface/surface exchanges along the stream are calculated by the model. A key advantage of the HMC method is that only hydraulic information is used, thus the simulation of tracer transport is not required. Two numerical experiments are presented, the first to test the HMC method and the second to demonstrate that it quantifies the groundwater component of streamflow accurately.

How do streamflow generation mechanisms affect watershed hypsometry?

AbstractSeveral studies have shown that the dominant streamflow generation mechanism in a river basin can leave distinct geomorphological signatures in basin topography. In particular, it has been suggested previously that basins generated by groundwater discharge tend to have a larger hypsometric integral than surface runoff basins because fluvial erosion is more focused in the valleys where groundwater discharge tends to occur. In this analysis, we aim to clarify this relationship by developing an alternative method to quantify the effects of streamflow generation mechanisms on basin hypsometry and by using a numerical model that can generate streamflow by different processes to evaluate the sensitivity of the results to the hydrological and geomorphological properties of the basin. The model results suggest that the hypsometric characteristics that are usually associated with groundwater discharge basins, such as a larger hypsometric integral, occur primarily when drainage networks are still advancing in the watershed. During later stages of development, an additional factor such as lithological controls or a distinct geomorphological process would be needed to preserve these features. The model results also show that the hypsometric effects are stronger when the parameters of the fluvial erosion process promote the influence of small discharge rates. Copyright © 2007 John Wiley & Sons, Ltd.

Simulating hydrological response for the R‐5 catchment: comparison of two models and the impact of the roads

AbstractIn this paper the performance of two hydrological‐response models is evaluated and compared based upon simulations for a single rainfall–runoff event. The two models are QPBRRM, a relatively simple model of Horton overland flow, and InHM, a comprehensive physics‐based model of each of the known streamflow generation mechanisms. The rainfall–runoff event focused upon in this study is from the small rangeland catchment in Oklahoma known as R‐5. When calibrated, both QPBRRM and InHM are shown to effectively simulate the R‐5 event. The calibration procedures used in this study for QPBRRM and InHM were quite different. The calibration of QPBRRM was a curve fitting exercise, whereas the calibration of InHM was based upon an internally valid estimate of the continuous head field. In this study QPBRRM did not perform well outside of the calibrated range. The impact of the roads cutting across the R‐5 catchment is simulated with InHM and discussed for the first time in the study reported here. The relative merits of QPBRRM and InHM are each discussed. Copyright © 2002 John Wiley & Sons, Ltd.

Impacts of Vegetative Practices on Suspended Sediment from Watersheds of Arizona

Effects of vegetative practices on suspended sediment discharge from ponderosa pine forests and pinon-juniper woodlands in north-central Arizona are examined. Sediment-rating curves were developed to analyze the impacts. Disturbance from vegetative practices generally increased suspended sediment transport above those of control (reference) watersheds. Completely cleared and strip-cut ponderosa pine watersheds produced higher sediment concentrations than did a control watershed. Likewise, cabled and herbicide-treated pinon-juniper watersheds yielded higher sediment-laden streamflows than did a control. Sediment transport regimes are also related to streamflow-generation mechanisms and hydrograph stages. Although about 85% of the data analyzed represented snowmelt-runoff events in both vegetative types, derivation of sediment-rating curves based on streamflow-generation mechanisms improved the sensitivity of the analysis. Sediment data collected during rising and falling hydrograph stages varied between th...

Nitrogen Dynamics in Stream and Soil Waters

The mountainous riparian corridor performs important hydrologic functions including nutrient transfers between the terrestrial (upslope) and aquatic (stream) ecosystems. Nitrate-nitrogen and ammonium-nitrogen concentrations were determined on water samples collected in 1993 and 1994 from a montane riparian zone in Northern Colorado. Soil water samples were collected from the riparian corridor and upslope systems, under both losing (summer reservoir releases) and gaining (spring snowmelt runoff) streamflow conditions. Statistical analyses using least square means contrasts were made to identify spatial and temporal differences between: 1) the upslope system and the riparian corridor, 2) the upslope system and the stream, and 3) the riparian corridor and the stream. The Sheep Creek riparian corridor may serve as a sink for nitrate-nitrogen in both gaining and losing streamflow conditions, and as a source for ammonium nitrogen in gaining streamflow conditions. The length of the source or sink period is relatively short and is not meant to suggest differences in site productivity. Streamflow generation mechanisms help determine if the riparian corridor is a nutrient sink or source.

Abflußereignisse, eine skalenabhängige multiple Antwort von Einzugsgebieten auf Niederschläge

Die Untersuchungen im kleinsten der untersuchten Einzugsgebiete, dem Kartelbornsbach, haben gezeigt, daß es ein typisches Grundmuster sommerlicher Hochwasserreaktionen gibt. Abweichungen von diesem Schema gehen auf die Höhe der Niederschläge, die Dauer des Niederschlagsereignisses und in Ausnahmefällen auch auf die Vorfeuchte des Bodens zurück. Die Ergebnisse zeigen außerdem, daß das Einzugsgebiet des Kartelbornsbaches als Blocksystem betrachtet werden kann, dessen räumliche Differenzierung zwar für das Grundmuster der Reaktion, nicht aber für etwaige Unterschiede zwischen den Hochwasserreaktionen verantwortlich ist. Es ist ein entscheidender Vorteil kleiner Einzugsgebiete, daß sich in ihnen ein typisches Verhalten mit vertretbarem Aufwand untersuchen und erkennen läßt. Mit zunehmender Größe der Einzugsgebiete werden auch die Abweichungen von einem Grundmuster aufgrund des zunehmenden Einflusses der räumlichen Verteilung der Niederschläge und Liefergebiete sowie der unterschiedlichen Reisezeiten der Fließkomponenten größer. Flood Events, a Multiple Basin Response to Precipitation Events at Different Scales Results in the small catchment of the Kartelbornsbach have shown that summer events lead to typical types of flood waves that can be classified according to their response patterns. Differences to this pattern are due to the precipitation amount and duration and in some times to the pre-event moisture of the soil. The results show further that the Kartelbornsbach catchment can be considered as a block system where spatial differences are responsible for the basic pattern of the reaction but not for differences between flood events. Small catchments are excellent tools for relatively inexpensive hydrological and hydrochemical research on streamflow generation mechanisms. With increasing size of the basin the response becomes less clear, because the spatial distribution of rainfall and the distance of delivering areas from the sampling station mask or modify the type of response. Although the main flow components may not change, there is a considerable shift in the composition of water quality, because the increase of travel time does not affect all flow components at the same rate.

Monitoring the effects of timber harvest on annual water yield

Paired catchment studies have been used as a method to assess the effects of vegetation removal (timber harvesting) on streamflow responses including lowflows and peakflows, but particularly annual water yield. Paired catchment studies in the United States reporting on the effects of timber harvesting on annual water yields were compiled. In general, changes in annual water yield from forest cover reduction (or catchment area harvested) of less than 20% could not be determined by hydrometric or streamflow measurement methods. The catchment studies were discriminated by hydrologic region, defined by temperature and precipitation regimes. This regionalization suggested that as little as 15% of the catchment area (or basal area) could be harvested for a measurable increase in annual water yield at the catchment level in the Rocky Mountain region as compared with 50% in the Central Plains, although system responses are variable. Given changing world-wide objectives for forest land management, hydrologists will be asked to develop monitoring programs to assess the effects of multiple and temporally and spatially distributed land use activities on water resources. Less catchment area will be disturbed, thus monitoring programs must be carefully designed to obtain useful information. The concept of hydrologic recovery, i.e. return to pretreatment condition tends to be based on annual water yield, but also needs the evaluation of streamflow generation and routing mechanisms including lowflows and peakflows when compared with the pretreatment condition.

Water yield issues in the jarrah forest of south-western Australia

The jarrah forest of south-western Australia produces little streamflow from moderate rainfall. Water yield from water supply catchments for Perth, Western Australia, are low, averaging 71 mm (7% of annual rainfall). The low water yields are attributed to the large soil water storage available for continuous use by the forest vegetation. A number of water yield studies in south-western Australia have examined the impact on water yield of land use practices including clearing for agricultural development, forest harvesting and regeneration, forest thinning and bauxite mining. A permanent reduction in forest cover by clearing for agriculture led to permanent increases of water yield of approximately 28% of annual rainfall in a high rainfall catchment. Thinning of a high rainfall catchment led to an increase in water yield of 20% of annual rainfall. However, it is not clear for how long the increased water yield will persist. Forest harvesting and regeneration have led to water yield increases of 16% of annual rainfall. The subsequent recovery of vegetation cover has led to water yields returning to pre-disturbance levels after an estimated 12–15 years. Bauxite mining of a high rainfall catchment led to a water yield increase of 8% of annual rainfall, followed by a return to pre-disturbance water yield after 12 years. The magnitude of specific streamflow generation mechanisms in small catchments subject to forest disturbance vary considerably, typically in a number of distinct stages. The presence of a permanent groundwater discharge area was shown to be instrumental in determining the magnitude of the streamflow response after forest disturbance. The long-term prognosis for water yield from areas subject to forest thinning, harvesting and regeneration, and bauxite mining are uncertain, owing to the complex interrelationship between vegetation cover, tree height and age, and catchment evapotranspiration. Management of the forest for water yield needs to acknowledge this complexity and evaluate forest management strategies both at the large catchment scale and at long time-scales. The extensive network of small catchment experiments, regional studies, process studies and catchment modelling at both the small and large scale, which are carried out in the jarrah forest, are all considered as integral components of the research to develop these management strategies to optimise water yield from the jarrah forest, without forfeiting other forest values.

SEDIMENT RATING CURVES FOR A CLEARCUT PONDEROSA PINE WATERSHED IN NORTHERN ARIZONA1

ABSTRACT: Data from a 455‐acre clearcut ponderosa pine forest watershed in northern Arizona were used to identify relationships between suspended sediment concentration and streamflow discharge. Sediment rating curves were derived by geometric least‐squares regression using 515 paired suspended sediment concentration and streamflow discharge measurements obtained from 1974 through 1982. Scatter about the straight line relationship was found when all available pairs of suspended‐sediment‐concentration and streamflow measurements were used together. The effect of some of the variation was offset by subdividing the data set on the basis of streamflow generation mechanisms. Improved descriptive power also was achieved when separate rising‐ and falling‐stage data sets were considered in deriving the sediment rating curves. Most noticeable was the improvements within low‐intensity, frontal rainfall events. There was no significant improvement in descriptive power when separate rising‐ and falling‐stage data sets were considered in deriving the sediment rating curves for snowmelt‐runoff events. Higher suspended sediment concentrations were observed during the rising stage of hydrographs than for similar flows on the falling stage, mainly for winter‐rainfall with insignificant snow accumulation on the ground and rain‐on‐snow events.

Mechanisms Affecting Streamflow and Stream Water Quality: An Approach via Stable Isotope, Hydrogeochemical,and Time Series Analysis

Stable isotope (deuterium) and hydrogeochemical (chloride, nitrate) data in rainfall, streamflow and deep and shallow groundwaters have been applied to develop an understanding of the mechanisms of streamflow generation and nutrient discharge from a 27 km2 rural catchment near Perth, Western Australia. Intensive sampling of the stable isotopic composition of rainfall, groundwater and streamflow during the winter flow periods of 1987 and 1988 identified several significant rainfall events that were up to 90‰ depleted in deuterium relative to deep and shallow groundwaters in the catchment. Isotopic responses in streamflow to the depleted rainfall could be discerned on three time scales: (1) the rainfall events themselves (i.e., 1 to 2 days); (2) isotopic relaxation periods lasting up to 6 weeks as streamflow δ values slowly returned to their preevent values; and (3) a longer seasonal scale response of 2 to 3 months caused by a seasonal isotopic trend in rainfall composition and an increase in the proportion of groundwater in streamflow toward the end of the flow period. The sharp isotopic responses in streamflow observed in this study were in marked contrast to the attenuated responses observed in a previous study on a 1 km2 catchment under native forest in the same region. This contrast reflects the different roles of the shallow groundwater system in streamflow generation between the two catchments under different land use. Kalman filtering techniques were applied to investigate the numerical functions linking rainfall amount and streamflow volume and their respective stable isotopic compositions. The purpose of the numerical analysis was to estimate the average lag between rainfall and streamflow, thereby quantifying the time scales of streamflow generation. Analysis of streamflow water quality has been shown that the bulk of nutrients and solutes are discharged from the catchment at the onset of flow, in response to the first major rainfall events of the winter period. Integration of the isotopic, hydrogeochemical and numerical analysis presents a consistent view that surface and subsurface storm flow are important streamflow generating mechanisms over the time scale of a rainfall event. Postevent periods of isotopic relaxation in streamflow are due to discharge of groundwater to streamflow from an ephemeral perched aquifer. There is evidence for an increasing component of deep groundwater in streamflow as streamflow declines toward the end of the flow period in October and November.

Field studies of the effects of the capillary fringe on streamflow generation

Two field experiments were conducted to investigate the effect of the capillary fringe on surface water-groundwater interactions and on streamflow generation in a shallow water-table aquifer. The results from both experiments showed that the water-table adjacent to the stream, where the capillary fringe extended to or close to ground surface, responded rapidly to the precipitation events due to the initially low storage capacity of the medium. This rapid and large response led to the development of a water-table mound on both sides of the stream and flow nets showed that the mound resulted in the discharge of pre-event water through the seepage faces that developed on both sides of the stream. Furthermore, the mound contributed to the discharge of event water in that precipitation falling on the seepage faces was transported directly to the stream as overland flow. A further contribution of event water to the stream occurred as surface runoff from areas upslope of the seepage faces, where the pressure head was zero, but the rainfall rate exceeded the infiltration capacity of the soil. Under the conditions of the study, the results support the commonly recognized mechanisms of streamflow generation, including the partial area, variable-source-area overland flow, and variable-source-area subsurface flow concepts. The relative contribution of these mechanisms to stormflow appeared to be determined by the response of the capillary fringe. The amount of pre-event water in the discharge determined by the tracer method of hydrograph separation showed good agreement with the instantaneous pre-event discharge hydrograph determined from flow nets.

Analysis of streamflow generation following deforestation in southwest Western Australia

The clearing of native vegetation and establishement of agricultural plants on a small catchment in southwest Western Australia resulted in a large streamflow increase (∼30% rainfall yr −1). This increase was brought about by a decrease in transpiration and interception loss. Streamflow increased markedly in the first year after clearing (∼10% rainfall) and continued to increase at a slower rate for a further five years, when a new streamflow equilibrium was reached. Explanations of the time trend of streamflow increase were sought in terms of streamflow generation mechanisms. The initial increase in streamflow was attributed to the impact of the immediate decrease in interception loss (∼13% of rainfall). The subsequent linear increase in streamflow was closely correlated with the expansion of the groundwater discharge area, and the cessation of streamflow increase was considered to result from the attainment of a new groundwater recharge-discharge equilibrium. Evidence from other catchments which have undergone forest reduction show that the permanent groundwater system is instrumental in controlling the streamflow response following forest reduction.

The generation and quality of streamflow on inactive uranium tailings near Elliot Lake, Ontario

This study was undertaken to investigate the physical and chemical interactions between groundwater and surface water in an area of inactive uranium mill tailings near Elliot Lake, Ontario. The study area had a shallow water table and was drained by a single channel. Streamflow chemistry and discharge and the hydraulic response of the groundwater system were monitored for several runoff events during the period of September 1981 through May 1982. The hydrographs measured for each event were separated into groundwater and surface-water components using the mass-balance technique with Cl − and 18O as conservative tracers. The mechanisms of streamflow generation and their effect on runoff quality were evaluated on the basis of the hydrograph separations, the observed groundwater response, and the characteristics of the precipitation events. The results indicate that groundwater constitutes a significant amount of the stormflow generated in the study area. The magnitude of this contribution was dependent upon the intensity and duration of rainfall and on the initial depth to the water table. The capillary fringe played an important role in the processes of streamflow generation, both in causing a large water-table rise which increased groundwater flow to the stream, and in forming an expanding seepage face which enhanced overland flow. During runoff events the stream contained high concentrations of several dissolved inorganic species. The groundwater contribution was a major source of these constituents. The findings of this study indicate that groundwater can be a major component of streamflow during runoff events in inactive tailings areas, and as a result, can have a major influence on runoff quality. The groundwater contribution to streamflow represents an important pathway of contaminant migration to the biosphere which can be anticipated to persist for long periods of time.

The mechanisms of catchment flow processes using natural variations in deuterium and oxygen-18

Stable isotope compositions and chloride concentrations in rainfall, deep and shallow groundwaters and streamflow have been used to investigate the flow processes through a small catchment in southwest Western Australia. In addition to the stable isotope and chloride data, daily rainfall, streamflow rate, streamflow chloride concentrations and shallow and deep groundwater hydrographs were used in an integrated approach to determine the mechanisms of streamflow generation. The range in δ 18O and δ 2H of rainfall events incident to the catchment during 1985 was 9.0 and 60‰, respectively, and was large enough to be useful in tracing flows generated from them through the catchment. During the season, four separate rainfall events were analysed using stream hydrograph separation methods based on δ 18O, δ 2H and chloride. Results showed that between 60 and 95% of the streamflow generated from the respective events had originated from pre-event shallow groundwater within the catchment. The seasonal pattern in the streamflow isotopic composition during 1985 was also analysed. Most significant rainfall events during the season generated an almost immediate response in the streamflow isotopic composition. The response to individual rainfall events was strongest early in the season but diminished as the season progressed. This attenuation with time indicated isotopic mixing and dilution of individual rainfall events with the increasing storage of shallow groundwater as the season progressed. Kalman filtering methods were used to investigate the function linking rainfall volume and streamflow and also the average time lag between rain and flow, using δ values in rainfall as time markers. The analysis showed a range of “ages” for the streamflow from about 20 to about 50 days lag after rainfall, tending to decrease after rainfall events and then increase again. The estimated value of the lag was always significantly greater than zero. Deep and shallow groundwaters in the 1985 season were readily distinguished from each other in δ 18O- δ 2H space. Streamflow isotopic composition matched that of the shallow groundwater system for almost the entire season. Thus the isotopic evidence was in accord with chemical evidence that streamflow originated primarily from preceding rainfall after a comparatively short residence time in the shallow groundwater system.

Streamflow generation

During the past 10 years under the impetus of the International Hydrological Decade there has been a burst of research activity aimed at obtaining better insight into the mechanisms of streamflow generation. The research has focused on an examination of the ways in which water moves from hillslopes into small stream channels during and between rainfall events in upstream tributary basins. The research has been of two types: field measurements in representative experimental drainage basins and theoretical studies using mathematical models of hydrologic processes, carried out with the aid of a digital computer. The field studies have identified the sources of lateral inflow to streams as overland flow, subsurface storm flow, and groundwater flow. They have also proven that most overland flow is generated either on small upland partial areas that are more or less fixed in size and that are controlled by the distribution of soil types or on expanding and contracting ‘variable source areas’ that are adjacent to streams and that are controlled by the topographic and hydrogeologic configuration of the hillslopes. They have shown qualitatively that the relative importance of the different processes depends on such controls as climate, geology, topography, soil characteristics, vegetation, and land use. This variety of field conditions coupled with the complexity of the processes themselves has hindered the growth of generalized interpretations based solely on the field evidence, and hydrologists have increasingly turned to mathematical modeling to isolate the various components of the system. Physically based mathematical models, in the form of boundary value problems based on the partial differential equations of flow, are now available for all the processes involved in streamflow generation. The concepts of open channel hydraulics form the basis for models of flow in a stream channel and for overland flow. The concept of saturated and unsaturated porous media flow has been brought to bear on models of infiltration, subsurface storm flow, and groundwater flow. Applications of these models at field sites and for series of hypothetical cases have identified the physical parameters that control the various observed mechanisms of downslope water movement and for some environments have determined the necessary conditions for the dominance of one mechanism over the others.