On the hydrological difference between catchments above and below the intermittent-persistent snow transition

Because of the importance of snow for river discharge in mountain regions, hydrological research often focuses on seasonally snow-covered zones. However, in many basins the majority of the land surface area is intermittently snow-covered. Discharge monitoring in these areas is less common, so their contributions to downstream rivers remain largely unknown. We evaluated hydrological differences between three intermittently snow-covered (mean annual Jan 1–Jul 3 snow persistence <60%) and two seasonally snow-covered headwater catchments in the Colorado Front Range. We compared water balance variables to evaluate how and why discharge differs between the snow zones and estimated the relative contributions from each snow zone to regional river discharge. We focused on water years 2016–2019 and used a combination of in situ sensors and regional climate datasets. Annual discharge from the intermittent snow zone was low for all three catchments (10–77 mm), despite covering a wide range in annual snow persistence (25%–64%), whereas annual discharge from the seasonal snow zone was up to 73 times higher. Soil moisture in the seasonal snow zone was above field capacity for longer periods of time than in the intermittent snow zone, and the intermittent snow zone was uniquely subject to soil freezing (up to 102 days per year). For most of the year, potential evapotranspiration exceeded rainfall and snowmelt inputs in the intermittent snow zone, but was lower than rainfall and snowmelt inputs in the seasonal snow zone. This is likely a primary driver of the differences in soil moisture and discharge for catchments with a seasonal versus intermittent snow cover. Despite the large difference in discharge between these two snow zones, the intermittent snow zone contributed about a quarter of the discharge in the regional river, highlighting the importance of studying discharge generation across all elevations.     

Effects of geological structures on rainfall-runoff responses in headwater catchments in a sedimentary rock mountain

Clarifying rainfall-runoff responses in mountainous areas is essential for disaster prediction as well as water resource management. Although runoff is considered to be significantly affected by topography, some previous studies have reported that geological structures also have significant effects on rainfall-runoff characteristics. Particularly in headwater catchments located in sedimentary rock mountains, dips and strikes may significantly affect rainwater discharge. In this study, the effects of geological structures on rainfall-runoff characteristics were investigated based on observed discharge hydrographs from 12 catchments, which lie radially from the summit of a sedimentary rock mountain. The results obtained were as follows: (1) Even though the topographic wetness index (TWI) distributions of the 12 catchments were similar, there were significant differences in their runoff characteristics; (2) Catchments with average flow direction oriented towards the strike direction (strike-oriented catchments) are characterized by large baseflows; (3) Catchments with average flow direction oriented towards the opposite dip direction (opposite dip-oriented catchments) are steep, and this results in quick storm runoff generation; (4) Catchments with average flow direction oriented toward the dip direction (dip-oriented catchments) are gentle, and this results in delayed storm runoff generation. It was presumed that in strike-oriented catchments, large quantities of groundwater flowing along the bedding planes owing to hydraulic anisotropy, exfiltrate and sustain the large amount of the observed baseflow, that is, in strike-oriented catchments, runoff is directly controlled by geological structures. Conversely, in opposite dip-oriented and dip-oriented catchments, runoff is indirectly controlled by geological structures, that is, geological structures affect slope gradients, which result in differences in storm runoff generation. Thus, this study clearly illustrates that geological structures significantly affect rainfall-runoff responses in headwater catchments located in sedimentary rock mountains.     

应用综合震源机制解法对辽宁及邻区现今构造应力场的初步分析

根据辽宁测震台网最近10年记录到的6245次天然地震,28698个P波初动极性数据,在考虑不同震中距数据权重的同时给出辽宁及相邻地区0.25°×0.25°的精细构造应力场,并结合构造背景对反演结果进行分析.总体来看,反演得到的主压应力轴方位以NE、NEE向为主,倾伏角较小;主张应力轴方位以NW、NNW向为主,局部有近N...     

Modelling the effects of land‐use change on water and salt delivery from a catchment affected by dryland salinity in south‐east Australia

A comprehensive framework for the assessment of water and salt balance for large catchments affected by dryland salinity is applied to the Boorowa River catchment (1550 km²), located in south‐eastern Australia. The framework comprised two models, each focusing on a different aspect and operating on a different scale. A quasi‐physical semi‐distributed model CATSALT was used to estimate runoff and salt fluxes from different source areas within the catchment. The effects of land use, climate, topography, soils and geology are included. A groundwater model FLOWTUBE was used to estimate the long‐term effects of land‐use change on groundwater discharge. Unlike conventional salinity studies that focus on groundwater alone, this study makes use of a new approach to explore surface and groundwater interactions with salt stores and the stream. Land‐use change scenarios based on increased perennial pasture and tree‐cover content of the vegetation, aimed at high leakage and saline discharge areas, are investigated. Likely downstream impacts of the reduction in flow and salt export are estimated. The water balance model was able to simulate both the daily observed stream flow and salt load at the catchment outlet for high and low flow conditions satisfactorily. Mean leakage rate of about 23·2 mm year^?1 under current land use for the Boorowa catchment was estimated. The corresponding mean runoff and salt export from the catchment were 89 382 ML year^?1 and 38 938 t year^?1, respectively. Investigation of various land‐use change scenarios indicates that changing annual pastures and cropping areas to perennial pastures is not likely to result in substantial improvement of water quality in the Boorowa River. A land‐use change of about 20% tree‐cover, specifically targeting high recharge and the saline discharge areas, would be needed to decrease stream salinity by 150 µS cm^?1 from its current level. Stream salinity reductions of about 20 µS cm^?1 in the main Lachlan River downstream of the confluence of the Boorowa River is predicted. The FLOWTUBE modelling within the Boorowa River catchment indicated that discharge areas under increased recharge conditions could re‐equilibrate in around 20 years for the catchment, and around 15 years for individual hillslopes. Copyright © 2004 John Wiley & Sons, Ltd.     

The assumption of uniform specific discharge: unsafe at any time?

Nearby catchments in the same landscape are often assumed to have similar specific discharge (runoff per unit catchment area). Five years of streamflow from 14 nested catchments in a 68 km² landscape was used to test this assumption, with the hypothesis that the spatial variability in specific discharge is smaller than the uncertainties in the measurement. The median spatial variability of specific discharge, defined as subcatchment deviation from the catchment outlet, was 33% at the daily scale. This declined to 24% at a monthly scale and 19% at an annual scale. These specific discharge differences are on the same order of magnitude as predicted for major land‐use conversions or a century of climate change. Spatial variability remained when considering uncertainties in specific discharge, and systematic seasonal patterns in specific discharge variation further provide confidence that these differences are more than just errors in the analysis of catchment area, rainfall variability or gauging. Assuming similar specific discharge in nearby catchments can thus lead to spurious conclusions about the effects of disturbance on hydrological and biogeochemical processes. Copyright © 2016 John Wiley & Sons, Ltd.     

Structural controls on groundwater flow and groundwater salinity in the Spicers Creek catchment,Central West region,New South Wales

Saline seepage zone development, and hence the onset of dryland salinity, is a major environmental problem occurring within the Spicers Creek catchment. The primary objective of this paper was to identify previously unmapped faults and show the correlation between these faults and groundwater salinization. As identified from this study, there is a close association between geological structural features and the formation of saline seepage zones. The most saline groundwaters in the catchment were encountered where two geological structures join and form a fault intersection. These saline groundwaters are found at various depths within the fractured aquifers, and changes in groundwater chemistry in the aquifers are associated with the presence of fault zones. ¹⁸O and δ²H stable isotopes, together with ⁸⁷Sr/⁸⁶Sr isotopic ratios, indicate that groundwaters within the fault zones are enriched in ¹⁸O and have a strontium signature similar to seawater. This study identifies several geological structures in the Spicers Creek catchment and demonstrates that groundwaters with the highest salinity arise where fault intersections occur. The results of this study may be used to interpret further the mechanisms leading to seepage zone formation in dryland salinity‐affected catchments located throughout the Central West region of New South Wales, Australia. Copyright © 2006 John Wiley & Sons, Ltd.     

On the contribution of groundwater to streamflow in laterite catchments of the Darling Range,south-western Australia

In deeply weathered laterite catchments of the Darling Range in south-western Australia, the direct contribution (i.e., discharge) of permanent groundwater to streamflow has long been considered as minor. Instead, downslope shallow throughflow was thought to dominate, generating more than 90% of streamflow. We used a chemical hydrograph separation approach to estimate annual groundwater discharge for three catchments over periods of up to 39 years, and found that direct groundwater contributions to streamflow were far more variable across catchments and through time than has previously been acknowledged. The estimated proportion of annual streamflow sourced directly from groundwater ranged from 0 to 93% and was related linearly to the size of the groundwater discharge area in the catchment valley floor. In contrast, contributions from shallow sources including shallow throughflow varied primarily and linearly with annual rainfall. However, the response to rainfall was “amplified” in a predictable way by the size of the groundwater discharge area, consistent with the variable source area concept. We derived a functional relationship between catchment annual rainfall-runoff ratio and groundwater discharge area and successfully applied this to a further four catchments, inferring that the results were broadly applicable across the Darling Range. The implications for an improved understanding of streamflow generating processes in the study region, and for laterite catchments generally, are discussed.     

Influence of lowland aquifers and anthropogenic impacts on the isotope hydrology of contrasting mesoscale catchments

We examined the isotope hydrology of eight, contrasting mesoscale (104–488 km²) catchments characterized by a systematic change in the relative importance of upland and lowland areas that reflects the relative distribution of metamorphic and sedimentary rocks. Precipitation and stream water were monitored over a 12‐month period, and stable isotopes were used to examine spatial variations in the hydrometric and tracer dynamics of the catchments. Isotopic tracers were used to examine the temporal dynamics of different runoff sources, and geochemical tracers (alkalinity) were used to identify the geographic sources of runoff. Input–output relationships of isotopic tracers were explored using a gamma function to fit a transit time distribution, which was used to test the hypothesis that the length of mean transit times increased systematically with the cover of sandstone aquifers in the catchments. However, in three catchments, the increased influence of anthropogenic factors, notably reservoir storage, urban runoff and agricultural abstraction for irrigation, prevented reliable transit time estimation. For sites where tentative mean transit time estimates were possible, these varied from around 1.6 years in upland catchments dominated by metamorphic rocks (>75%) and responsive soils to around 4 years in catchments with 34% sandstone cover and freely draining soils. These preliminary results were consistent with inferences of geochemical tracers on the increased role of sedimentary aquifers as runoff sources in lowland areas, but observation from a larger number of sites is needed to confirm this. Copyright © 2012 John Wiley & Sons, Ltd.     

漾濞MS6.4地震长周期强地震动的有限差分初步模拟

根据我国川滇地区的地质地貌特征、前人地质资料和2021年漾濞M_S6.4地震的震源参数初步反演结果,建立三维速度结构模型,采用三维有限差分法对漾濞地震的长周期地震动进行研究.对实际地震烈度和模拟烈度进行对比,同时在区域附近布置了36个观测点,给出其中6个观测点的三分量速度时程,并给出所有观测点阻尼比为5%的速度反应谱,结果表明:(1)模拟的速度峰值已超过25 cm/s,与实际漾濞地区附近的烈度为8度吻合;(2)受断层滑动分布影响,速度水平分量在西北方向分布范围更广,衰减速度明显慢于东南方向,并且在极震区,东北—西南方向的地震动衰减也较慢.方向性效应对峰值大小及其分布范围的影响显著;(3)观测点速度反应谱的特征周期分布在1~3 s范围内,可能会因为共振效应对区域附近的大型建筑物产生较为严重的破坏.需要对漾濞地震进行进一步研究,以期对漾濞地震的长周期地震动有更为细致的认识.     

Spatial variability in specific discharge and streamwater chemistry during low flows: Results from snapshot sampling campaigns in eleven Swiss catchments

Catchments consist of distinct landforms that affect the storage and release of subsurface water. Certain landforms may be the main contributors to streamflow during extended dry periods, and these may vary for different catchments in a given region. We present a unique dataset from snapshot field campaigns during low‐flow conditions in 11 catchments across Switzerland to illustrate this. The catchments differed in size (10 to 110 km²), varied from predominantly agricultural lowlands to Alpine areas, and covered a range of physical characteristics. During each snapshot campaign, we jointly measured streamflow and collected water samples for the analysis of major ions and stable water isotopes. For every sampling location (basin), we determined several landscape characteristics from national geo‐datasets, including drainage area, elevation, slope, flowpath length, dominant land use, and geological and geomorphological characteristics, such as the lithology and fraction of quaternary deposits. The results demonstrate very large spatial variability in specific low‐flow discharge and water chemistry: Neighboring sampling locations could differ significantly in their specific discharge, isotopic composition, and ion concentrations, indicating that different sources contribute to streamflow during extended dry periods. However, none of the landscape characteristics that we analysed could explain the spatial variability in specific discharge or streamwater chemistry in multiple catchments. This suggests that local features determine the spatial differences in discharge and water chemistry during low‐flow conditions and that this variability cannot be assessed a priori from available geodata and statistical relations to landscape characteristics. The results furthermore suggest that measurements at the catchment outlet during low‐flow conditions do not reflect the heterogeneity of the different source areas in the catchment that contribute to streamflow.     

Testing a 1-D analytical salt intrusion model and its predictive equations in Malaysian estuaries

Abstract

Little is known about the salt intrusion behaviour in Malaysian estuaries. Study of salt intrusion generally requires large amounts of data, especially if 2-D or 3-D numerical models are used; thus, in data-poor environments, 1-D analytical models are more appropriate. A fully analytical 1-D salt intrusion model, which is simple to implement and requires minimal data, was tested in six previously unsurveyed Malaysian estuaries (Kurau, Perak, Bernam, Selangor, Muar and Endau). The required data can be collected during a single day of observations. Site measurements were conducted during the dry season (June–August 2012 and February–March 2013) near spring tide. Data on cross-sections (by echo-sounding), water levels (by pressure loggers) and salinity (by moving boat) were collected as model input. A good fit was demonstrated between the simulated and observed salinity distribution for all six estuaries. Additionally, the two calibration parameters (the Van der Burgh coefficient and the boundary condition for the dispersion) were compared with the existing predictive equations. Since gauging stations were only present in some nested catchments in the drainage basins, the river discharge had to be up-scaled to represent the total discharge contribution of the catchments. However, the correspondence between the calibration coefficients and the predictive equations was good, particularly in view of the uncertainty in the river discharge data used. This confirms that the predictive salt intrusion model is valid for the cases studied in Malaysia. The model provides a reliable, predictive tool, which the water authority of Malaysia can use for making decisions on water abstraction or dredging.

Editor D. Koutsoyiannis; Associate editor A. Fiori     

Effects of instream processes,discharge, and land cover on nitrogen export from southern Appalachian Mountain catchments

Catchments with minimal disturbance usually have low dissolved inorganic nitrogen (DIN) export, but disturbances and anthropogenic inputs result in elevated DIN concentration and export and eutrophication of downstream ecosystems. We studied streams in the southern Appalachian Mountains, USA, an area dominated by hardwood deciduous forest but with areas of valley agriculture and increasing residential development. We collected weekly grab samples and storm samples from nine small catchments and three river sites. Most discharge occurred at baseflow, with baseflow indices ranging from 69% to 95%. We identified three seasonal patterns of baseflow DIN concentration. Streams in mostly forested catchments had low DIN with bimodal peaks, and summer peaks were greater than winter peaks. Streams with more agriculture and development also had bimodal peaks; however, winter peaks were the highest. In streams draining catchments with more residential development, DIN concentration had a single peak, greatest in winter and lowest in summer. Three methods for estimating DIN export produced consistent results. Annual DIN export ranged from less than 200 g ha^?1 year^?1 for the less disturbed catchments to over 2,000 g ha^?1 year^?1 in the catchments with the least forest area. Land cover was a strong predictor of DIN concentration but less significant for predicting DIN export. The two forested reference catchments appeared supply limited, the most residential catchment appeared transport limited, and export for the other catchments was significantly related to discharge. In all streams, baseflow DIN export exceeded stormflow export. Morphological and climatological variation among watersheds created complexities unexplainable by land cover. Nevertheless, regression models developed using land cover data from the small catchments reasonably predicted concentration and export for receiving rivers. Our results illustrate the complexity of mechanisms involved in DIN export in a region with a mosaic of climate, geology, topography, soils, vegetation, and past and present land use.     

Quantifying the effects of Eucalyptus plantations and management on water resources at plot and catchment scales

Our aim was to quantify the effects of forest plantation and management (clear cut or 30% partial harvest) in relation to pasture, on catchment discharge in southeast Rio Grande do Sul state, Brazil. A paired‐catchment approach was implemented in two regions (Eldorado do Sul and São Gabriel municipalities) where discharge was measured for 4 years at three catchments in each region, two of which were predominantly eucalypt plantation (mainly Eucalyptus saligna, rotation of approximately 7–9 years) with native forest and grass in streamside zones. The third catchment was covered with grazed pasture. Weather, soils, canopy interception, groundwater level, tree growth, and leaf area index were also measured. The 3‐PG process‐based forest productivity model was adapted to predict spatial daily plantation and pasture water balance including precipitation interception, soil evaporation, transpiration, soil moisture, drainage, discharge, and monthly plantation growth. The TOPMODEL framework was used to simulate water pools and fluxes in the catchments. Discharge was higher under pasture than pre‐harvesting plantation and increased for 1–2 years after complete plantation harvest; this change was less pronounced in the catchments under partial harvest. The ratio of discharge to precipitation before harvesting varied from 7% to 13% in the eucalypt catchments and 28% to 29% under pasture. The ratio increases to 23–24% after total harvest, and to 17% after partial harvesting. The ratio under pasture also increases during this period (to 32–44%) owing to increased precipitation. The baseflow, in relation to total discharge, varied from 28% to 62% under Eucalyptus and from 38% to 43% in the pasture catchments. Hence, eucalypt plantations in these regions can be expected to influence discharge regimes when compared with pasture land use, and modelling suggests that partial harvesting would moderate the magnitude of discharge variation compared with a full catchment plantation harvesting. The model efficiency coefficient (Nash–Sutcliffe model efficiency coefficient) varied from 0.665 to 0.799 for the total period of the study. Simulation of alternative harvesting scenarios suggested that at least 20% of the catchment planted area must be harvested to increase discharge. This model could be a useful practical tool in various plantation forestry contexts around the world. Copyright © 2016 John Wiley & Sons, Ltd.     

Application of the Takagi–Sugeno fuzzy system for combination forecasting of river flow in semiarid mountain regions

Because of high spatial heterogeneity and the degree of uncertainty about hydrological processes in large‐scale catchments of semiarid mountain areas, satisfactory forecasting of daily discharge is seldom available using a single model in many practical cases. In this paper the Takagi–Sugeno fuzzy system (TS) and the simple average method (SAM) are applied to combine forecasts of three individual models, namely, the simple linear model (SLM), the seasonally based linear perturbation model (LPM) and the nearest neighbour linear perturbation model (NNLPM) for modelling daily discharge, and the performance of modelling results is compared in five catchments of semiarid areas. It is found that the TS combination model gives good predictions. The results confirm that better prediction accuracy can be obtained by combining the forecasts of different models with the Takagi–Sugeno fuzzy system in semi‐arid mountain areas. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrical earth resistivity surveying for delineating the characteristics of ground water in a semi‐arid region in the Khanasser Valley,northern Syria

A resistivity survey is conducted in Khanasser Valley, a semi‐arid region in northern Syria, to delineate the characteristics of ground water affected by the salt‐water intrusion related to Al‐Jaboul Sabkha. Existing wells were used to measure salinity and conductivity of water samplings. Vertical electrical sounding was carried out near the existing wells. The combination of resistivity and hydrogeological data enables the establishment of empirical relationships between earth resistivity, water resistivity, and the amount of total dissolved solids. These relationships are then used in order to derive salinity maps for electrode spacings of 70, 100, and 150 m. The distribution of fresh, brackish and salt‐water zones and their variations in space along two longitudinal profiles (LP1 and LP2) are established through converting subsurface depth–resistivity models into different ground‐water areas. The constructed ground‐water area maps allow interfaces between different water zones to be determined. Copyright © 2006 John Wiley & Sons, Ltd.     

Catchment chemostasis revisited: Water quality responds differently to variations in weather and climate

Solute concentrations in streamflow typically vary systematically with stream discharge, and the resulting concentration–discharge relationships are important signatures of catchment biogeochemical processes. Solutes derived from mineral weathering often exhibit decreasing concentrations with increasing flows, suggesting dilution of a kinetically limited weathering flux by a variable flux of water. However, previous work showed that concentration–discharge relationships of weathering‐derived solutes in 59 headwater catchments were much weaker than this simple dilution model would predict. Instead, catchments behaved as chemostats, with rates of solute production and/or mobilization that were nearly proportional to water fluxes, on both event and interannual timescales. Here, we re‐examine these findings using data for a wider range of solutes from 2,186 catchments, ranging from ~10 to >1,000,000 km² in drainage area and spanning a wide range of lithologic and climatic settings. Concentration–discharge relationships among this much larger set of larger catchments are broadly consistent with the previously described chemostatic behaviour, at least on event and interannual timescales for weathering‐derived solutes. Among these same catchments, however, site‐to‐site variations in mean concentrations of weathering‐derived solutes exhibit strong negative correlations with long‐term average precipitation and discharge, reflecting strong climatic control on long‐term leaching of the critical zone. We use multiple regression of site characteristics including discharge to identify potential controls on long‐term mean concentrations and find that lithologic and land cover controls are significant predictors for many analytes. The picture that emerges is one in which, on event and interannual timescales, weathering‐derived stream solute concentrations are chemostatically buffered by groundwater storage and fast chemical reactions, but each catchment's chemostatic “set point” reflects site‐to‐site differences in climatically driven evolution of the critical zone. In contrast to these weathering products, some nutrients and particulates are often near‐chemostatic across all timescales, and their long‐term mean concentrations correlate more strongly with land use than climatic characteristics.     

Near-surface study of a hot spring site in Fiji

A geophysical investigation of a hot spring system located in Rabulu, Fiji, was carried out from October 2014 to March 2015. The investigation covered a survey area of 6075 m². Self-potential (SP), ground temperature and soil carbon dioxide (CO₂) concentrations were measured and investigated for their distribution characteristics and inter-linkages. Results indicated obvious anomalous zone at the hot spring discharge site. The SP profile analysis highlighted thermal water upwelling zones and elevation-driven subsurface groundwater pathways. Measurement of subsurface temperatures up to 1 m depths revealed increasing temperatures, indicating potentially high thermal gradients in the area. Surface soil CO₂ distributions also agreed with SP and ground temperature results. The overall result of the study demonstrated that synchronised measurements of SP, ground temperature and soil CO₂ can be instrumental in identifying anomalous zones near the hot spring sites. Other parameters such as spring water temperature, discharge rate and energy flux estimates from the spring were calculated and analysed. The high-dense multi-parameter data coverage allowed interpretation of geothermal features at a scale never conducted in Fiji before. The near-surface investigations reported in this study corroborate previously suggested steady geothermal activity in the region, deserving further detailed investigation.     

On the relationships between catchment scale and streamwater mean residence time

The relationship between streamwater mean residence time (MRT) and landscape characteristics is poorly understood. We used tritium (³H) to define our MRT. We tested the hypothesis that baseflow water MRT increases with increasing absolute catchment size at the Maimai catchments. These catchments are simple hydrologic systems relative to many catchments around the world, with uniformly wet climatic conditions, little seasonality, uniform and nearly impermeable bedrock, steep short hillslopes, shallow soils, and well‐characterized hillslope and catchment hydrology. As a result, this is a relatively simple system and an ideal location for new MRT‐related hypothesis testing. Whilst hydrologists have used ³H to estimate water age since the 1960s nuclear testing spike, atmospheric ³H levels have now approached near background levels and are often complicated by contamination from the nuclear industry. We present results for ³H sampled from our set of nested catchments in nuclear‐industry‐free New Zealand. Because of high precision analysis, near‐natural atmospheric ³H levels, and well‐characterized rainfall ³H inputs, we were able to estimate the age of young (i.e. less than 3 years old) waters. Our results showed no correlation between MRT and catchment size. However, MRT was correlated to the median sub‐catchment size of the sampled watersheds, as shown by landscape analysis of catchment area accumulation patterns. These preliminary findings suggest that landscape organization, rather than total area, is a first‐order control on MRT and points the way forward for more detailed analysis of how landscape organization affects catchment runoff characteristics. Copyright © 2003 John Wiley & Sons, Ltd.     

Channel precipitation dynamics in a forested Pennsylvania headwater catchment (USA)

Seasonal and event variations in stream channel area and the contributions of channel precipitation to stream flow were studied on a 106‐ha forested headwater catchment in central Pennsylvania. Variations in stream velocity, flowing stream surface width and widths of near‐stream saturated areas were periodically monitored at 61 channel transects over a two‐year period. The area of flowing stream surface and near‐stream saturated zones combined, ranged from 0·07% of basin area during summer low flows to 0·60% of total basin area during peak storm flows. Near‐stream saturated zones generally represented about half of the total channel area available to intercept throughfall and generate channel precipitation. Contributions of routed channel precipitation from the flowing stream surface and near‐stream zones, calculated using the Penn State Runoff Model (PSRM, v. 95), represented from 1·1 to 6·4% of total stream flow and 2·5–29% of total storm flow (stream flow–antecedent baseflow) during the six events. Areas of near‐stream saturated zones contributed 35–52% of the computed channel precipitation during the six events. Channel precipitation contributed a higher percentage of stream flow for events with low antecedent baseflow when storm flow generated by subsurface sources was relatively low. Expansion of channel area and consequent increases in volumes of channel precipitation with flow increases during events was non‐linear, with greater rates of change occurring at lower than at higher discharge rates. Copyright © 1999 John Wiley & Sons, Ltd.