Showing papers on "Streamflow published in 1998"

Design of Total Runoff Integrating Pathways (TRIP)—A Global River Channel Network

Abstract: As a first step toward designing a comprehensive model for validating land surface hydrology and river flow in Earth system models, a global river channel network has been prepared at 18 latitude 3 18 longitude resolution. The end product is the Total Runoff Integrating Pathways (TRIP) network. The aim of TRIP is to provide information of lateral water movement over land following the paths of river channels. Flow directions were deter- mined from vector data of river channels and river pathways available in two recent atlases; however, an automatic procedure using a digital elevation map of the corresponding horizontal resolution was used as a first guess. In this way, a template to convert the river discharge data into mean runoff per unit area of the basin has been obtained. One hundred eighty major rivers are identified and adequately resolved; they cover 63% of land, excluding Ant- arctica and Greenland. Most of the river basin sizes are well within a 20% difference of published values, with a root-mean-square error of approximately 10%. Furthermore, drainage areas for more than 400 gauging stations were delineated. Obviously, the stream lengths in TRIP are shorter than the natural lengths published as data. This is caused by the meandering of rivers in the

A spatial assessment of hydrologic alteration within a river network

Abstract: Maintaining natural hydrologic variability is essential in conserving native riverine biota and river ecosystem integrity. Hydrologic variation plays a major role in structuring the biotic diversity within river ecosystems as it controls key habitat conditions within the river channel, the floodplain, and hyporheic (stream-influenced ground water) zones. Alterations in streamflow regimes may modify many of these habitat attributes and impair ecosystem connectivity. We demonstrate use of the ‘Range of Variability Approach’ for assessing hydrologic alteration at available streamgauge sites throughout a river basin. We then illustrate a technique for spatially mapping the degree of hydrologic alteration for river reaches at and between streamgauge sites. Such maps can be used to assess the loss of natural hydrologic variation at a river basin scale, thereby facilitating river restoration planning. © 1998 John Wiley & Sons, Ltd.

Interaction between stream temperature, streamflow, and groundwater exchanges in alpine streams

Abstract: Four alpine streams were monitored to continuously collect stream temperature and streamflow for periods ranging from a week to a year. In a small stream in the Colorado Rockies, diurnal variations in both stream temperature and streamflow were significantly greater in losing reaches than in gaining reaches, with minimum streamflow losses occurring early in the day and maximum losses occurring early in the evening. Using measured stream temperature changes, diurnal streambed infiltration rates were predicted to increase as much as 35% during the day (based on a heat and water transport groundwater model), while the measured increase in streamflow loss was 40%. For two large streams in the Sierra Nevada Mountains, annual stream temperature variations ranged from 0° to 25°C. In summer months, diurnal stream temperature variations were 30–40% of annual stream temperature variations, owing to reduced streamflows and increased atmospheric heating. Previous reports document that one Sierra stream site generally gains groundwater during low flows, while the second Sierra stream site may lose water during low flows. For August the diurnal streamflow variation was 11% at the gaining stream site and 30% at the losing stream site. On the basis of measured diurnal stream temperature variations, streambed infiltration rates were predicted to vary diurnally as much as 20% at the losing stream site. Analysis of results suggests that evapotranspiration losses determined diurnal streamflow variations in the gaining reaches, while in the losing reaches, evapotranspiration losses were compounded by diurnal variations in streambed infiltration. Diurnal variations in stream temperature were reduced in the gaining reaches as a result of discharging groundwater of relatively constant temperature. For the Sierra sites, comparison of results with those from a small tributary demonstrated that stream temperature patterns were useful in delineating discharges of bank storage following dam releases. Direct coupling may have occurred between streamflow and stream temperature for losing stream reaches, such that reduced streamflows facilitated increased afternoon stream temperatures and increased afternoon stream temperatures induced increased streambed losses, leading to even greater increases in both stream temperature and streamflow losses.

Stream flow characterization and feature detection using a discrete wavelet transform

Abstract: An exploration of the wavelet transform as applied to daily river discharge records demonstrates its strong potential for quantifying stream flow variability. Both periodic and non-periodic features are detected equally, and their locations in time preserved. Wavelet scalograms often reveal structures that are obscure in raw discharge data. Integration of transform magnitude vectors over time yields wavelet spectra that reflect the characteristic time-scales of a river's flow, which in turn are controlled by the hydroclimatic regime. For example, snowmelt rivers in Colorado possess maximum wavelet spectral energy at time-scales on the order of 4 months owing to sustained high summer flows; Hawaiian streams display high energies at time-scales of a few days, reflecting the domination of brief rainstorm events. Wavelet spectral analyses of daily discharge records for 91 rivers in the US and on tropical islands indicate that this is a simple and robust way to characterize stream flow variability. Wavelet spectral shape is controlled by the distribution of event time-scales, which in turn reflects the timing, variability and often the mechanism of water delivery to the river. Five hydroclimatic regions, listed here in order of decreasing seasonality and increasing pulsatory nature, are described from the wavelet spectral analysis: (a) western snowmelt, (b) north-eastern snowmelt, (c) mid-central humid, (d) south-western arid and (e) ‘rainstorm island’. Spectral shape is qualitatively diagnostic for three of these regions. While more work is needed to establish the use of wavelets for hydrograph analysis, our results suggest that river flows may be effectively classified into distinct hydroclimatic categories using this approach. © 1998 John Wiley & Sons, Ltd.

Interannual and Decadal Cycles in River Flows of Southeastern South America

Abstract: The time series of annual streamflow of four rivers in southeastern and south-central South America (the Negro, Paraguay, Parana, and Uruguay Rivers) for the period 1911–93 are analyzed. Application of the multitaper method shows that the following features are significant at the 95% level: 1) a nonlinear trend, 2) a near-decadal component, and 3) interannual peaks with ENSO timescales. The trend and near-decadal components are most marked in the two more central rivers, the Paraguay and Parana, with ENSO timescale variability most pronounced in the Negro and Uruguay rivers in the southeast. Composites of SST are made for each of the statistically significant oscillatory components of river flow, by reconstructing each component using singular spectrum analysis. These composites confirm the influence of ENSO on the streamflow variability of the Negro and Uruguay Rivers, with El Nino associated with enhanced streamflow. On the decadal timescale, high river runoff is associated with anomalously coo...

Establishment of woody riparian vegetation in relation to annual patterns of streamflow, Bill Williams River, Arizona

Abstract: Previous studies have revealed the close coupling of components of annual streamflow hydrographs and the germination and establishment ofPopulus species. Key hydrograph components include the timing and magnitude of flood peaks, the rate of decline of the recession limb, and the magnitude of base flows. In this paper, we retrospectively examine establishment of four woody riparian species along the Bill Williams River, Arizona, USA, in the context of annual patterns of streamflow for the years 1993–1995. The four species examined were the nativePopulus fremontii, Salix gooddingii, andBaccharis salicifolia and the exoticTamarix ramosissima. We modeled locations suitable for germination of each species along eight study transects by combining historic discharge data, calculated stage-discharge relationships, and seed-dispersal timing observations. This germination model was, a highly significant predictor of seedling establishment. Where germination was predicted to occur, we compared values of several environmental variables in quadrats where we observed successful establishment with quadrats where establishment was unsuccessful. The basal area of mature woody vegetation, the maximum annual, depth to ground water, and the maximum rate of water-table decline were the variables that best discriminated between quadrats with and without seedlings. The results of this study suggest that the basic components of models that relate establishment ofPopulus spp. to annual patterns of streamflow may also be applicable to other woody riparian species. Reach-to-reach variation in stage-discharge relationships can influence model parameters, however, and should be considered if results such as ours are to be used in efforts to prescribe reservoir releases to promote establishment of native riparian vegetation.

Application of a GIS-based distributed hydrology model for prediction of forest harvest effects on peak stream flow in the Pacific Northwest

Abstract: Spatially distributed rainfall–runoff models, made feasible by the widespread availability of land surface characteristics data (especially digital topography), and the evolution of high power desktop workstations, are particularly useful for assessment of the hydrological effects of land surface change. Three examples are provided of the use of the Distributed Hydrology-Soil–Vegetation Model (DHSVM) to assess the hydrological effects of logging in the Pacific Northwest. DHSVM provides a dynamic representation of the spatial distribution of soil moisture, snow cover, evapotranspiration and runoff production, at the scale of digital topographic data (typically 30–100 m). Among the hydrological concerns that have been raised related to forest harvest in the Pacific Northwest are increases in flood peaks owing to enhanced rain-on-snow and spring radiation melt response, and the effects of forest roads. The first example is for two rain-on-snow floods in the North Fork Snoqualmie River during November 1990 and December 1989. Predicted maximum vegetation sensitivities (the difference between predicted peaks for all mature vegetation compared with all clear-cut) showed a 31% increase in the peak runoff for the 1989 event and a 10% increase for the larger 1990 event. The main reason for the difference in response can be traced to less antecedent low elevation snow during the 1990 event. The second example is spring snowmelt runoff for the Little Naches River, Washington, which drains the east slopes of the Washington Cascades. Analysis of spring snowmelt peak runoff during May 1993 and April 1994 showed that, for current vegetation relative to all mature vegetation, increases in peak spring stream flow of only about 3% should have occurred over the entire basin. However, much larger increases (up to 30%) would occur for a maximum possible harvest scenario, and in a small headwaters catchment, whose higher elevation leads to greater snow coverage (and, hence, sensitivity to vegetation change) during the period of maximum runoff. The third example, Hard and Ware Creeks, Washington, illustrates the effects of forest roads in two heavily logged small catchments on the western slopes of the Cascades. Use of DHSVM's road runoff algorithm shows increases in peak runoff for the five largest events in 1992 (average observed stream flow of 2·1 m3 s−1) averaging 17·4% for Hard Creek and 16·2% for Ware Creek, with a maximum percentage increase (for the largest event, in Hard Creek) of 27%. © 1998 John Wiley & Sons, Ltd.

Effect of groundwater springs on NO3− concentrations during summer in Catskill Mountain streams

Abstract: Groundwater and stream water data collected at three headwater catchments in the Neversink River watershed indicate that base flow is sustained by groundwater from two sources: a shallow flow system within the till and soil and a deep flow system within bedrock fractures and bedding planes that discharges as perennial springs. Data from eight wells finished near the till/bedrock interface indicate that saturated conditions are not maintained in the shallow flow system during most summers. In contrast, the discharge of a perennial spring remained constant during two summer rainstorms, providing evidence that the deep flow system is disconnected from the shallow flow system in summer. Discharge from perennial springs was the principal source of streamflow in a headwater reach during low flow. Mean NO3− concentrations were 20–25 μmol L−1 in five perennial springs during the summer but only 5–10 μmol L−1 in shallow groundwater. Thus the deep flow system does not reflect typical NO3− concentrations in the soil during summer. A hydrologic budget at a headwater drainage reveals that March and late fall are the principal groundwater recharge periods. Residence time modeling based on analyses of 18O and 35S indicates that groundwater in the deep flow system is 6–22 months old. These data indicate that summer base flow largely originates from previous dormant seasons when available soil NO3− is greater. In these Catskill watersheds, high base flow concentrations of NO3− during summer do not provide sufficient evidence that the atmospheric N deposition rate exceeds the demand of terrestrial vegetation.

Trends in streamflow and rainfall in tropical South America : Amazonia, eastern Brazil, and northwestern Peru

Abstract: Long hydrological records, from the Amazon Basin, northeastern Brazil, and northwestern Peru spanning most of this century, are examined for trends in rainfall (three wettest months) and runoff (three months of highest flow) or stage, where no rating curves exist. Trends are tested for significance using the Mann-Kendall statistic. In basins where large soil, aquifer, or man-made reservoirs give rise to appreciable over-year storage, flows and water levels may be serially correlated. Where serial correlation exists, the usual statistical tests (linear regression, t-test, and Mann-Kendall) will overestimate the significance of trends, showing significance where none exists. Analysis for trend therefore requires particular care when data are serially correlated, and to avoid misleading results, additional supportive evidence must be sought. For example, rainfall records within the same river basin can be checked for trends; serial correlation in rainfall records, in particular, is less likely to be present, so the validity of any trends in rainfall is less open to question. Strong negative trends were found in flow data from the coast of northern Peru and the Sao Francisco River, while positive significant trends were detected in the Parnaiba River basin. No significant trends were found in the discharge or stage records from Amazonia, while rainfall in northeastern Brazil shows a slow increase over long periods. In the Parnaiba and in some rivers of northern Peru unusually large discharges at the beginning or end of the records seem to account for the direction and significance of trends.

Chapter 10 – Oxygen and Hydrogen Isotopes in Rainfall-Runoff Studies

Abstract: Publisher Summary This chapter provides an overview of traditional hydrograph separation applications on storm event time-scales, and discusses the requirements for successful separation and the results of several isotopic hydrograph separation studies. It also presents other frameworks for application of isotope data on storm-event and longer time-scales, and the findings from a number of studies in which oxygen and/or hydrogen isotopes were used to separate storm streamflow into pre-event and event water. Stable isotopes of oxygen and hydrogen have proven to be useful tools in determining the contribution of rainfall to stormflow, the residence time of water on catchments, and other aspects of watershed hydrology. The separation of contributions from event and pre-event waters to stormflow adds a constraint on streamflow generation that physical (hydrometric) measurements never could. The large contribution of pre-event water to storm streamflow is entirely consistent with the importance of subsurface stormflow as documented by hydrometric studies on forested catchments before isotopes became widely used. Pre-event water usually makes up the bulk of stormflow through some combination of mixing and displacement, even discharging to streams through macro-pores and soil pipes. The isotopes move as the water moves and do not fractionate between the time the water reaches the ground and the time the water exits the catchment as streamflow.

Field study and simulation of diurnal temperature effects on infiltration and variably saturated flow beneath an ephemeral stream

Abstract: Two experiments were performed to investigate flow beneath an ephemeral stream and to estimate streambed infiltration rates. Discharge and stream-area measurements were used to determine infiltration rates. Stream and subsurface temperatures were used to interpret subsurface flow through variably saturated sediments beneath the stream. Spatial variations in subsurface temperatures suggest that flow beneath the streambed is dependent on the orientation of the stream in the canyon and the layering of the sediments. Streamflow and infiltration rates vary diurnally: Streamflow is lowest in late afternoon when stream temperature is greatest and highest in early morning when stream temperature is least. The lower afternoon Streamflow is attributed to increased infiltration rates; evapotranspiration is insufficient to account for the decreased Streamflow. The increased infiltration rates are attributed to viscosity effects on hydraulic conductivity from increased stream temperatures. The first set of field data was used to calibrate a two-dimensional variably saturated flow model that includes heat transport. The model was calibrated to (1) temperature fluctuations in the subsurface and (2) infiltration rates determined from measured Streamflow losses. The second set of field data was to evaluate the ability to predict infiltration rates on the basis of temperature measurements alone. Results indicate that the variably saturated subsurface flow depends on downcanyon layering of the sediments. They also support the field observations in indicating that diurnal changes in infiltration can be explained by temperature dependence of hydraulic conductivity. Over the range of temperatures and flows monitored, diurnal stream temperature changes can be used to estimate streambed infiltration rates. It is often impractical to maintain equipment for determining infiltration rates by traditional means; however, once a model is calibrated using both infiltration and temperature data, only relatively inexpensive temperature monitoring can later yield infiltration rates that are within the correct order of magnitude.

Seasonal streamflow forecasting in eastern Australia and the El Niño–Southern Oscillation

Abstract: Previous studies have identified a strong link between climate variability in Australia and the El Nino–Southern Oscillation (ENSO). This paper describes the development and use of a seasonal streamflow forecast model based on an optimal linear combination of forecasts derived from climatology, persistence, the Southern Oscillation index (SOI), and equatorial Pacific sea surface temperatures (SST). The model builds on the work of the Australian Bureau of Meteorology and that of other researchers who have investigated southeast Australian rivers. The model is tested using 66 years of unimpaired streamflow data from 10 eastern Australian catchments. Results from testing the model further support the ENSO-hydroclimate link, showing that eastern Australia generally receives below normal streamflow during El Nino conditions and above normal streamflow during La Nina conditions. In southeast Australia the SOI is a better predictor for July–September and October–December streamflow and the SST a better predictor of January–March and April–June streamflow. For many of the seasons and stations, the skill associated with the cross-validation forecast is better than that drawn from the baseline condition of climatology.

A Recent Increasing Trend in the Streamflow of Rivers in Southeastern South America

Abstract: This paper examines the records of streamflow during the period 1901–95 corresponding to four major rivers in southeastern South America: Uruguay, Negro, Parana, and Paraguay. The emphasis is on the detection of long-term trends in the records. The authors demonstrate that the 30-yr running averaged streamflows increased after the mid-1960s at a rate that is approximately linear but not the same in all rivers. There seems to be a tendency toward leveling off in the most recent values. The increased streamflow is consistent with a significant decrease in the amplitude of the seasonal cycle in all rivers, except in the Negro River. An analysis of the sea surface temperature in the eastern equatorial Pacific Ocean suggests that an important component of such an increase in streamflows is consistent with a large-scale and low-frequency variability of the climate system.

A linked global model of terrestrial hydrologic processes: Simulation of modern rivers, lakes, and wetlands

Abstract: A terrain-based hydrologic model is developed to simulate rivers, lakes, and wetlands on the continental scale as a linked dynamical system. This surface water area model (SWAM) is an extension of earlier work [Coe, 1997] and is based on a linear reservoir model. The model requires, as input, estimates of runoff, precipitation, and evaporation from either observations or climate simulations. The model develops its own river transport directions based on elevation. The river discharge is calculated at each grid cell as the accumulated flow of water across the land surface. Lake and wetland area and volume are calculated as a function of the local precipitation minus evaporation, the streamflow into and out of the grid cells, and the potential for storage of water on the surface as derived from 5′ × 5′ resolution digital terrain models. SWAM is applied on a 5′ × 5′ spatial resolution to simulate present-day surface waters and river transport for all continents (except Antarctica and Greenland). The model simulates the discharge of the 27 major rivers of the world in fair agreement with the observations; 12 of the rivers have simulated discharge within ±20% of the observational estimates. The discharge from rivers in arid and semi-arid climates is generally overestimated probably due to underestimated evaporation from wetlands, irrigated croplands, and reservoirs within the river basins. The modern simulated lake area (about 3% of the land area) is larger than the observed area (about 2% of the land area). Wetlands are poorly simulated by the model due to the coarse vertical and horizontal resolution of the digital terrain models. The model simulates the potential for increased surface water (up to 7.5% of the global land area) and river basin area in semi-arid and arid regions where closed basins exist in the present day climate which illustrates the utility of SWAM for climate change experiments. While higher resolution and more accurate digital terrain models are needed to improve these surface water simulations (particularly for wetlands), these preliminary results indicate that current digital terrain models are adequate for including lakes and rivers as interactive components in the surface hydrology parameterizations of climate models and for studying feedbacks between lakes and climate.

Palaeohydrological variation in a tropical river catchment: a reconstruction using fluorescent bands in corals of the Great Barrier Reef, Australia

Abstract: Massive, long-lived corals in inshore waters of the Great Barrier Reef contain yellow-green fluorescent bands. These bands are due to terrestrial humic and fulvic compounds incorporated into the coral skeleton during high river flow events. Fluorescence measurements are presented for two colonies of Porites spp. from locations in the path of the Burdekin River floodwaters the major river in north Queensland draining into the Coral Sea. The records extend from AD 1737 to 1980 and 1644 to 1986, respectively. The two independent coral records show a high degree of similarity. The two series are combined and used to reconstruct Burdekin River runoff for the period AD 1644 to 1980. The regression model accounts for 83% of the annual (water year) variability of Burdekin River flow and is verified over independent data. The 337-year reconstruction thus increases by threefold the length of record for considering interannual to decadal climate variations in northeast Australia. Instrumental and reconstructed Burde...

Trends in hydrological parameters of a southern Brazilian watershed and its relation to human induced changes

Abstract: The Piracicaba river basin is a subtropical watershed located in the southeastern region of Brazil. With an area of 12 400 km2, the basin is a typical example of new landscape resulting from development in tropical and sub-tropical regions: establishment of intensive industrial and agricultural processes were followed by significant population growth and water management. This scenario has led to significant increase in water demand and decrease in water quality. The main objective of this study is the detection of changes in the patterns of flow and precipitation in the basin, and its possible relation to man-induced changes. Statistical analyses were performed on records of precipitation, evapotranspiration and streamflow, from 1947 to 1991. Precipitation and evapotranspiration totals showed significant increasing trends for the entire basin. From eight streamflow gauge stations, half showed significant decreasing trend. The most probable cause of such trends is the export of water from the basin to the metropolitan region of Sao Paulo city.

Geomorphology and endangered fish habitats of the upper Colorado River 1. Historic changes in streamflow, sediment load, and channel morphology

Abstract: The hydrologic, geomorphic, and ecologic effects of reservoir operations are thought to be key factors in the decline of native fishes in the upper Colorado River basin. The present paper examines the extent to which changes in streamflow and sediment loads have affected alluvial reaches of the Colorado River near Grand Junction, Colorado. The analysis shows that since 1950, annual peak discharges of the Colorado River and its major tributary, the Gunnison River, have decreased by 29–38%. The total volume of runoff delivered to the study area has not changed significantly over the period of record, but the annual hydrograph has been modified greatly by reductions in peak flows and augmentation of base flows. Annual suspended sediment loads of the Colorado River and Gunnison River have likewise decreased. This was particularly apparent during the period from 1964 to 1978, when annual sediment loads were 40–65% less than the long-term average. Analysis of aerial photographs indicates that between 1937 and 1993 the main channel of the Colorado River has narrowed by an average of 20 m and about 1/4 of the area formed by side channels and backwaters has been lost.

Consequences of the 1993 Mississippi River flood in the Gulf of Mexico

Abstract: Seasonally severe hypoxia (≤2 mg O2 l−1) occurs in waters below the pycnocline on the northern Gulf of Mexico inner continental shelf in May through September over extensive areas (up to 18 000 km2). Spatial and temporal variability in the distribution of hypoxic water masses is related, in part, to the amplitude and phasing of freshwater discharge from the Mississippi and Atchafalaya Rivers, circulation patterns, nutrient flux and a close coupling with net productivity. The Mississippi River flood in 1993 and sustained freshwater inputs to the Gulf of Mexico occurred during mid-summer through early autumn when long-term mean flows (1930–1995) are normally lowest. Long-term studies of the Louisiana shelf hypoxic zone provided a natural experiment to examine the effects of extreme high river flow on the adjacent continental shelf. Oxygen levels in bottom waters were severely reduced in July, August and September compared to long-term averages (1985–1992). Also, the areal extent of the bottom-water hypoxia in mid-summer 1993 was approximately twice as large as the average area mapped in the previous 8 years during mid-summer shelfwide surveys. Contributing to increased severity and areal extent of hypoxia in 1993 were reduced surface water salinities, increased strength of the pycnocline, five to ten times higher nutrient concentrations, greater phytoplankton biomass, an order of magnitude greater abundance of phytoplankton, mostly small, coccoid cyanobacteria, and a shift in diatom community dynamics. An equally extensive hypoxic zone in mid-summer of 1994, when riverine fluxes of freshwater and nutrients were ‘normal’, suggests some residual effects of the 1993 summer flooding. © 1998 John Wiley & Sons, Ltd.

Evidence of climate change effects on the hydrology of streams in south-central bc

Abstract: This study is a selected search of streamflow records in south-central British Columbia for changes that may be associated with climate change. A force analysis approach was used to identify watersheds and segments of hydrologic records which were most likely to be responsive to changing climate. Initially three watersheds were selected and an additional three were added to study the effects of drainage area and land use intervention. It was found that spring runoff starts earlier, late summer – early fall flows are lower, and early winter flows are higher with a warmer climate. These changes were found to be statistically significant and are consistent with the hydrological impacts currently expected with global climate change.

Hydrological Effects of Land-Use Change in a Zero-Order Catchment

Abstract: Hydrologic modeling and relatively simple monitoring were used to estimate the hydrologic balance for two geographically close and, in the undisturbed state, hydrologically similar, zero-order basins: one undeveloped forest and the other suburban. Continuous precipitation and streamflow were measured in each basin; the model was used to estimate time series of evapotranspiration and ground-water recharge over a 4-yr period. The suburban catchment was denuded of forest cover, soil thickness was reduced, and 30% of the area was covered with impervious surfaces. The amount of annual precipitation that becomes runoff ranged from 12-30% in the forested catchment and 44 to 48% in the suburban catchment where runoff from pervious areas accounts for 40–60% of the annual total. The peak flow rate per unit area for an approximate 24-in, 50-yr rainfall was more than 10 times higher from the pervious area at the suburban site than at the forested site. These findings emphasize the need to consider surface flow from all sources in the catchment when considering mitigation measures.

Quantifying the effects of stream discharge on summer river temperature

Abstract: Control of summer river temperature is needed for maintaining water temperature standards to protect aquatic biota and wildlife habitats. Given the fact that instream discharge, among meteorological and hydrological factors, may be the only one that can be practically managed, is it feasible to moderate summer river temperature through reservoir and streamflow regulations? An analysis is conducted to quantify the effects of the magnitude of instream flow on summer river temperature with weather as a reference. Relationships between water temperature and river discharge or flow depth are developed using a simplified model and adopting the concept of equilibrium temperature and bulk surface heat exchange coefficient. The relationships are validated against continuous 5-year field measurements at the central Platte River, Nebraska, USA. It was found that the variation of daily maximum water temperature with flow was stronger than that of daily mean. A critical discharge was obtained, which divides d...

Simulating Climate Change Effects in a Minnesota Agricultural Watershed

Abstract: The effect of climate change on quality and quantity of runoff from a northern, agricultural watershed was simulated using the Soil and Water Assessment Tool, 1996 Version (SWAT96) SWAT`s snow evaporation submodel was modified SWAT was calibrated using water quality and quantity data measured in the Cottonwood River near New ULM, MN The standard errors after calibration were 331 mm, 157 kg/d, 752 kg/d, 3744 kg/d, and 85 t/d for mean monthly streamflow, P yield, ammonia (NH{sub 3})/organic N yield, nitrate (NO{sub 3}) yield, and sediment yield, respectively The standard error for monthly streamflow was 962 mm SWAT96 was then used to simulate the effect on the Cottonwood River watershed of a 2xCO{sub 2} climate scenario, obtained from the Canadian Climate Center`s global circulation model Assuming land cover and land management remained constant, SWAT96 projected a decrease in mean annual streamflow, P yield, NH{sub 3}/organic N yield, NO{sub 3}/nitrate (NO{sub 2}) yield, and sediment yield Mean monthly values changed significantly for many months of the year under the 2xCO{sub 2} climate scenario The standard errors in SWATs baseline simulations, however, were too high for the simulated climate change effects to be measurable for NO{sub 3}/NO{sub 2} and sediment yields Themore » model assumptions and calibration methods used to obtain the accuracy required for simulating the effects of climate change lead to the conclusions that land use/land cover and land management practices are likely to have a greater impact on water quality than climate change and that SWAT must be calibrated to be used for climate change analysis« less

Tracing Hydrologic Pathways Using Chloride at the Panola Mountain Research Watershed, Georgia, USA

Abstract: An analysis of chloride (Cl−) concentrations and fluxes at the 41 ha Panola Mountain Research Watershed indicates that Cl− may be used effectively to differentiate “new” and “old” water flow through the hillslope and their respective contributions to streamwater. Rainfall and throughfall, the “new” water inputs, are marked by low Cl− concentrations ( 30 µeg L−1). Timing of soil water transport is not sufficiently rapid to suggest that soil water from this hillslope site (20 m from the stream) contributes to streamwater during individual rainstorms. The source of streamflow, therefore, must be a combination of channel interception, overland flow and soil water from near-channel areas, and runoff from a 3 ha bedrock outcrop in the headwaters. Groundwater contribution to streamflow was estimated using CF concentrations of throughfall and groundwater as the two end members for a two-component hydrograph separation. For the study period, groundwater contributed 79% of the streamflow and from 1985 to 1995, contributed 75% of the streamflow. Rainfall was the source of 45% of the Ct flux from the watershed in the long term; the remaining Cl− is hypothesized to be derived from dry deposition, consistent with the enrichment noted for throughfall. At peak flow during individual rainstorms, “new” water can contribute 95% of the runoff.

Snowmelt-dominated systems

Abstract: Publisher Summary The temporary storage of precipitation in snowpack and the subsequent melting greatly influences the hydrologic regime. During the period of snow storage, there will be little or no water input to the ground. The groundwater reservoir will gradually decline by draining to the stream, whose discharge recedes in proportion to the falling groundwater level and flow. During snowmelt, the groundwater reservoir recovers and stream discharge may reach its annual peak by contributions from groundwater as well as overland flow. This chapter presents and discusses findings of isotope studies in catchments where snowmelt accounts for an important part of the total water input, with the focus on isotopic and hydrologic conditions related to meltwater input. Isotope studies have made a considerable contribution to our knowledge of catchment flow processes. The importance of direct measurements of the isotope content of the water input to the ground, that is, the snowpack drainage, must be emphasized in studies of snowmelt runoff. Other methodological problems concern the spatial variability of the isotope content of the pre-event water contributing to streamflow, and how to handle temporal variability of the isotope content of the water input. When it comes to snowmelt infiltration and runoff, it can be noted that no studies have been found where isotopes have been used in connection with measurements of soil frost and related analysis of the water flow.