Showing papers on "Streamflow published in 1990"

A rationale for old water discharge through macropores in a steep, humid catchment.

Abstract: Simultaneous observations of rapid preferential flow through macropores and isotopically “Old” water displacement remain unresolved in the Maimai (M8) catchment. Continuous, three-dimensional soil moisture energy conditions were monitored in two discrete catchment positions for a series of storm events in 1987. Tensiometric response was related to the soil water characteristic curve, hillslope throughflow, and total catchment runoff. For events yielding ≪2 mm hr−1 peak runoff, near-stream valley bottom groundwater systems discharged water volumes sufficient to account for storm period streamflow. This process was assisted by regular low ( 2 mm hr−1 peak storm flow, hillslope hollow drainage into steeply sloping first-order channels dominated old water production and most of the catchment storm flow. Highly transient macropore-driven processes of crack infiltration (bypass flow), slope water table development, and lateral pipe flow enabled large volumes of stored water to be delivered to the first-order channel bank at the appropriate time to satisfy catchment storm flow volumes and water isotopic and chemical composition.

Runoff generation in a sandy area—the nizzana sands, Western Negev, Israel

Abstract: This paper presents the results of sprinkling experiments conducted over the lower part of vegetated and crusted linear dunes as well as over flat playa surfaces that appear in the interdune corridors. Data obtained show that these two surface units respond quickly to rainstorms. Runoff generation can be expected for any storm exceeding 2-3 mm and runoff coefficients are high. When the topsoil algal crust, 1 to 2 mm thick, is removed from the surface of the dune, infiltration increases drastically and eliminates any possibility of runoff generation under present-day rainfall conditions. This data may be of great help in the understanding of the geomorphology and sedimentary sequence of the corridors separting linear dunes.

Logging effects on streamflow: Storm runoff at Caspar Creek in northwestern California

Abstract: The effects of road building and selective tractor harvesting on storm runoff were assessed for a small (424 ha) coastal watershed in northern California. Road building alone did not significantly affect the storm runoff. After road building and logging, lag time was decreased approximately 1.5 hours, and the very small storm volumes (less than 1209 m3) and storm peaks (less than 566 L/s) were increased by about 132 and 111%, respectively. Storm volumes and peaks of large storms (occurring less frequently than eight times a year) were not significantly increased by either roads or logging, even though more than 15% of the watershed was compacted in roads, skid trails, and landings. Although a decrease in lag time showed that the average storm hydrograph was shifted forward in time, only the small storm hydrographs were changed in shape. We speculate that the rate of delivery of water to the stream channel during large channel-forming flows was governed by infiltration and subsurface flow rates on the 85% of the watershed that was unaffected by roads, landings, or skid trails. From these findings we conclude that, in a rain-dominated hydrologic environment, logging and forest road construction (as carried out in this study) are not likely to change the flow regime of a stream adversely.

Naturally Occurring Radon 222 as a Tracer for Streamflow Generation: Steady State Methodology and Field Example

Abstract: This paper presents a quantitative framework for the use of naturally occurring 222Rn as a hydrologic flow path tracer under conditions of steady streamflow. The methodology consists of two distinct parts, the first of which is the determination of R¯q, the average 222Rn content of the water feeding a given stream reach. R¯q is determined by measuring the concentrations of 222Rn and two injected tracers (one conservative, the other volatile) in the stream water and solving a mass balance equation for 222Rn around the reach of interest. The second part of the methodology involves using R¯q values to determine the sources of stream inflow (and, implicitly, the flow paths important in streamflow generation). One means of accomplishing this, simple “geographic source” separations, is presented here. Both parts of the methodology were illustrated with a field experiment at the Bickford watershed in central Massachusetts. The injected tracers used were NaCl (conservative) and propane (volatile). The value of R¯q (700 disintegrations per minute (dpm)/L) was found to be closer to the 222Rn content of vadose zone water (500 dpm/L) than to that of saturated zone water (2000 dpm/L), suggesting that lateral unsaturated flow was important in supplying base flow at the study site.

Logging effects on streamflow: Water yield and summer low flows at Caspar Creek in northwestern California

Abstract: Streamflow data for a 21-year period were analyzed to determine the effects of selective tractor harvesting of second-growth Douglas fir and redwood forest on the volume, timing, and duration of low flows and annual water yield in northwestern California. The flow response to logging was highly variable. Some of this variability was correlated with antecedent precipitation conditions. Statistically significant increases in streamflow were detected for both the annual period and the low-flow season. Relative increases in water yield were greater for the summer low-flow period than for annual flows, but these summer flow increases generally disappeared within 5 years.

Groundwater contribution to the nutrient budget of Tomales Bay, California

Abstract: Tomales Bay, a graben structure along the San Andreas Fault, was selected for modeling ecosystem nutrient dynamics because of its linear, one-dimensional morphology and relatively pristine state Groundwater is a potentially important term in the nutrient budget The geologic complexities created by the San Anreas Fault, however, complicate the hydrogeology and require the area to be subdivided into three regions: granite to the west, Franciscan Formation to the east, and alluvial fill in the trough Nutrient concentrations in the groundwater were determined through extensive well sampling; groundwater discharge was estimated using both Darcy's Law calculations and a soil moisture budget Results indicate that groundwater discharge is of the same order of magnitude as summer streamflow into the Bay, while being significantly less than other freshwater inputs in winter Dissolved nutrient (phosphate, nitrate + nitrite, ammonium, silica and DIC) concentrations in groundwater were consistently higher (by as much as an order of magnitude) than in surface water discharges During the summer months, groundwater flow contributes about as much nutrient load to the bay as does streamflow During the winter, the groundwater contribution to nutrient loading is about 20% of the streamflow contribution Our findings indicate that groundwater is a significant component of terrestrial nutrient and freshwater loading to Tomales Bay, particularly so during the summer months However, neither groundwater nor streamflow nutrient fluxes are large in comparison to the mixing flux at the bay mouth or the flux of N2 gas across the air-water interface

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

Abstract: 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.

The identification of runoff‐production mechanisms using environmental isotopes in a tussock grassland catchment, eastern otago, New Zealand

Abstract: A previous hydrometric study of runoff production in tussock grassland drainage basins in Otago (45°50′S, 169°45′E), New Zealand, revealed a marked change of slope in storm hydrograph recessions. An environmental isotope study was initiated to investigate the runoff mechanisms operating and to test specific hypotheses to explain this break in the hydrograph recession. The results indicated that for quickflow volumes in excess of 10mm, the first part of the storm hydrograph can be attributed to two separate sources, namely, ‘old’ water from a shallow, unconfined groundwater reservoir and ‘new’ water from saturation overland flow on the lower wetlands of concave slopes. Despite the extensive area of wetlands, ‘old’ water runoff from the unconfined groundwater reservoir is delivered more rapidly to the stream than ‘new’ water from saturation overland flow. Substantial surface storage in the wetlands has first to be exceeded before rain becomes a significant part of stream discharge. For quickflow volumes less than 10mm, only ‘old’ water from groundwater contributes to the first part of the hydrograph recession. This means that only the largest 7 per cent of storms (in terms of quickflow volume) generate quickflow containing significant amounts of ‘new water’. The second part of the recession of the storm hydrograph consists of ‘old’ water derived from a remarkably well-mixed shallow unconfined groundwater body.

An assessment of a conceptual rainfall‐runoff model's ability to represent the dynamics of small hypothetical catchments: 1. Models, model properties, and experimental design

Abstract: A set of tests is proposed to determine the reliability of soil moisture accounting rainfall-runoff models for prediction beyond the calibration experience and for extreme event forecasts under dry and wet antecedent conditions. The tests are developed for small (less than 0.5 km2) hypothetical hillslope catchments whose hydrologic response to rainfall and evapotranspiration (ET) fluxes is modeled with an accurate physically based model (S-H) developed by Smith and Hebbert (1983). The tests are based on the assumption that the climatic and resulting S-;H streamflow time series are error free. The conceptual model explored is a modified version of the Sacramento model (used by the U.S. National Weather Service) reprogrammed for inputs at various time increments as small as 1 min. A Nelder and Mead (1965) direct search optimization scheme is also included in this modified model (denoted SMA) to assist in model calibration. The set of tests is designed to illuminate differences in modeled ET fluxes, streamflow time series, and the relative amounts of Hortonian and saturated overland flow and subsurface flow under a wide variety of climate and hillslope combinations. The test scheme ensures that the conceptual model is tested for a number of hydrodynamic conditions where flow responses range from primarily surface, to primarily subsurface, to relatively even amounts of surface and subsurface flow for humid and subhumid environments. It also provides direct comparisons of the physical (hillslope catchments) and conceptual model storages, and explicit evaluation of the combined influence of conceptual model structure and calibration errors. Specific model structure differences between S-H and SMA are detailed to elucidate any differences between model responses reported in the companion paper. Hydrologic responses are evaluated with statistical measures and graphical comparisons for time increments ranging from minutes to years.

Hydrology and water quantity control

Abstract: Meteorology and the hydrologic cycle precipitation infiltration and evapotranspiration streamflow measurements hydrographs synthetic hydrographs flow routing probability and statistics for hydrologic processes groundwater hydrology volume/peak discharge management.

Characterization and simulation of rainfall-runoff relations for headwater basins in western King and Snohomish Counties, Washington

Abstract: The characteristics of rainfall-runoff relations were hypothesized for the study area as a whole by using existing information. In undisturbed areas, shallow-subsurface flow from hillslopes mantled with glacial till, groundwater flow from glacial outwash deposits, and saturation overland flow from depressions, stream bottoms, and till-capped hilltops are the important runoff mechanisms. In disturbed, primarily urban areas, Horton overland flow, which is runoff generated from rain falling at a greater rate than the infiltration rate of the soil, is a significant mechanism, along with overland flow from impervious surfaces. These hypothesized characteristics were incorporated into the Hydrologic Simulation Program-FORTRAN (HSPF) simulation model, and the model was calibrated concurrently at 21 stream-gage sites in the study area with hydrologic data from the 1985-86 water years. The calibration resulted in 12 sets of generalized HSPF parameters, one set for each land-segment type with a unique hydrologic response. The generalized parameters can be used with HSPF to simulate runoff from most headwater basins within the study area. The average standard errors of estimate for calibrated streamflow simulation at all 21 sites were 7.9 percent for annual runoff, 11.2 percent for winter runoff, 13.1 percent for spring runoff, 40.1 percent for summer runoff, 21.7 percent for storm peak discharge, 21.4 percent for storm runoff volume, and 42.3 percent for all daily mean discharges. High flows were simulated more accurately than were low flows. The simulation errors were not large enough to reject the hypothesized rainfall-runoff relations.

Effects of CO2-induoed climatic changes on soowpack and streamflow

Abstract: Atmospheric concentrations of carbon dioxide (CO2) may double during the next century, causing changes in the Earth's climate. Warming of up to 4°C, slight cooling, and 10% changes in precipitation have been projected. Researchers have studied the possible impacts these changes may have on various aspects of the hydrological cycle, but little emphasis has been placed on snow accumulation and melt. In this study, the effects of climatic change on streamflow from a snowmelt-dominated basin in southwestern Montana, USA, are investigated. The National Weather Service River Forecast System model (NWSRFS) was first calibrated using data for the 1973–1984 period. Daily temperature and precipitation values were then changed, and the model ran again to assess the effects on snowpack and streamflow of some possible climatic changes. Results indicate that streamflow may vary by from −22 to +45% depending on the combination of climatic changes imposed.

Climatic influences on streamflow variability: A comparison between southeastern Australia and southeastern United States of America

Abstract: Differences in runoff and rainfall variability between southeastern Australia and southeastern United States have been examined, using various standard techniques such as principal component and spectral analyses, and examination of the quick and base flow components of runoff It is shown that the higher runoff variability in Australia can be partly explained by the large-scale circulation and rainfall patterns associated with the Southern Oscillation which are unlike those in the southeastern United States Whereas the Southern Oscillation signal is easily detectible in the southeast Australian rainfall and runoff data, it is, with the exception of several small areas, absent in the southeastern United States data In the case of this particular comparison, the differences in runoff variability between the two selected regions were found to be largest in winter and spring months and smallest in summer

Hydrologic modeling Of New England river basins using radar rainfall data

Abstract: Quantitative weather radar measurements of rainfall provide the input to a hydrologic forecast model designed to use the full spatial resolution of the radar data. The gridded model, which incorporates a detailed map of the stream network, is based on a simple kinematic representation of the river basin response. Only two parameters control the shape of the hydrograph: the velocity characteristic of subsurface flow to the nearest stream, and the streamflow velocity itself. Comparisons are made between model hydrograph forecasts and observed streamflow records for the Souhegan (440 km2), and the Squannacook (160 km2) river basins. A single Z-R relation was used for all storms (Z = 230R1.4), except for one case with strong convection (Z = 400R1.3). A linear scaling of the volume of the radar-derived storm rainfall produces reasonable agreement between the predicted and observed hydrographs. The volume scale factor, which varies from 20% or less in the summer to 100% in the spring, is consistent with the climatological mean monthly rainfall-runoff ratio. In the two basins studied, for hydrograph peaks of moderate amplitude, overland flow and other quickflow components of the hydrograph are not generally observed. The hillslope response is modeled by a single characteristic subsurface flow velocity (2 × 10−3 m s−1), with a streamflow velocity of 0.6 m s−1 in the Souhegan, (0.3 m s−1 in the Squannacook). The results suggest that models which utilize the basin geometry and rainfall data to a maximum, but which otherwise contain few parameters, can be very successful.

Impact of climatic variability and change on river flow regimes in the UK

Abstract: The objectives of this report are to examine past variability in river flow regimes, concentrating in particular on recent years, and to consider the possible consequences of future climate change for river flow regimes in the United Kingdom. The geological and climatic characteristics of a catchment determine how variations in rainfall from year to year impact upon river flow variability. In general terms, the drier the catchment (as indexed by the proportion of rainfall which runs off from a basin) and the lower the base flow component, the greater the variation in flow regime between years. There is some evidence that years containing similar hydrological characteristics tend to cluster: wet winters tend to follow wet winters, for example. There is no conclusive evidence, however, that 'recent' years (excluding 1989 and 1990) have seen an unusually large number of extreme events, although the test used is rather conservative and the period defined as 'recent' influences the results. Annual and seasonal runoff totals during the 1980s were generally higher than in previous decades, and there are some indications that year-to-year variability was also higher. Data from 1989 and 1990 were not included in the analysis. Future changes in UK flow regimes depend very significantly on assumed changes in evapotranspiration and, particularly, precipitation, which are currently very difficult to predict. The study therefore examined the sensitivity of river flow regimes to a range of feasible climate change scenarios, biased towards generally wetter conditions but assuming both wetter and drier summers. Simple regression-type relationships were considered, but most of the analyses used monthly water balance models applied at a range of representative sites. Changes in average annual runoff under a given climate change scenario were found to depend strongly on catchment dryness. If potential evapotranspiration is assumed to remain constant, for example, a 10% increase in annual rainfall could produce up to 30% extra runoff in south east England, whilst in more humid western regions it would result in only an additional 12 to 15%. Increases in average annual rainfall of between 8 and 10% would be required to offset the effects of 15% higher potential evapotranspiration. The effect of drier summers on summer river flows depends upon the current summer water balance and catchment geology: the greatest relative reductions are expected in responsive catchments which currently have a close balance between rainfall and potential evapotranspiration. In catchments with a large groundwater storage, delayed drainage of additional winter rainfall may mitigate the effects of drier, warmer summers.

Groundwater and Wetland Contributions to Stream Acidification: An Isotopic Analysis

Abstract: Stream water pH may be influenced by (1) the flow paths and (2) the residence time of water that contributes to streamflow, when these hydrologic factors interact with the biogeochemical processes that neutralize H+ ions in the catchment. This paper presents measures of the volumes of groundwater contributing to streamflow, the groundwater residence times, and the sources of stream water acidity found during spring runoff in three basins on the Canadian Shield. Isotopic hydrograph separations were used to estimate the relative contributions of groundwater to spring runoff. The contributions of old (premelt) groundwater to spring runoff were greater (60%) in a well-buffered, third-order basin than in a more acidic first-order basin (49%). Using a simple mixing model, a larger groundwater reservoir (420 mm unit depth) and longer residence time (162 days) were estimated in the third-order basin. The lowest stream pH (4.8) was observed in a second-order basin with a wetland that collects drainage from about 79% of the basin. In this basin the principal source of H+ ions was the conifer-sphagnum wetland. We conclude that the hypotheses that the pH of these streams was proportional to (1) a fraction of streamflow contributed by groundwater or (2) the residence time of water in a basin are rejected. More attention must be focused upon the source of acidity generated in wetlands, since these are ubiquitous in small basins.

Marginal Economic Value of Streamflow: A Case Study for the Colorado River Basin

Abstract: The marginal economic value of streamflow leaving forested areas in the Colorado River Basin was estimated by determining the impact on water use of a small change in streamflow and then applying economic value estimates to the water use changes. The effect on water use of a change in streamflow was estimated with a network flow model that simulated salinity levels and the routing of flow to consumptive uses and hydroelectric dams throughout the Basin. The results show that, under current water management institutions, the marginal value of streamflow in the Colorado River Basin is largely determined by nonconsumptive water uses, principally energy production, rather than by consumptive agricultural or municipal uses. The analysis demonstrates the importance of a systems framework in estimating the marginal value of streamflow.

Reference manual for generation and analysis of Habitat Time Series: version II

Abstract: : The premise of time series analysis is that the instream physical habitat at a given time and place can be calculated as a function of the streamflow using the equation HA(t) = PH(Q(t)) where PH( ) is the physical habitat-versus-streamflow function for a given life stage and species of aquatic organism or river activity; Q(t) is the streamflow at time t; and HA(t) is the habitat area for time t. The physical habitat represents the space in a river that can be used as habitat by a given species and life stage of fish. The assumptions and calculation procedures used to determine the physical habitat are described in Stainaker (1979). The Time Series Library (TSLIB) of programs has been developed to analyze the pattern of time-varying events. The TSLIB system can be considered a decision support system with the decision being quantification of an instream flow need, an instream flow water right, or a minimum flow requirement for operation of a water resource project. The general concept of a decision support system using TSLIB is shown in Fig. 1.1; the objective is to choose between water resource management alternatives or to modify the operation of an existing water resource system.

A review of techniques used by Canada and other northern countries for measurement and computation of streamflow under ice conditions

Abstract: In Canada, Water Survey of Canada, a division of the Water Resources Branch of Environment Canada, is responsible for the collection and processing of data from more than 3,300 active streamflow, water level and sediment data gauging stations. Because of the climatic conditions prevalent in Canada, an important part of the monitoring program is conducted under winter ice conditions. The determination of daily streamflow records during the winter period is important for several practical purposes, in particular for water power development. Essential to the computation of daily discharge records, are reliable streamflow measurements. However, discharge measurements under ice conditions are generally difficult to obtain because of severe weather conditions, hazardous field conditions, and ill-adapted field measurement techniques. In this paper, the field methods and instruments, and computational methods used by Water Survey of Canada for streamflow measurement and computation under ice conditions are reviewed. Factors affecting the accuracy of discharge measurements performed under ice conditions are discussed. Newly developed instruments for use under ice conditions are described and their advantages discussed. A comparison between techniques used by Canada and other northern countries is also given. Areas of research and investigations for improvement in the overall quality of data are suggested.