Showing papers on "Streamflow published in 1995"

Continuous-time water and sediment-routing model for large basins

Abstract: Simulation models are needed to evaluate the impact of changes in land use and agricultural management on streamflow and sediment yields from watersheds and river basins. Current agricultural-management models are limited by spatial scale, and river-basin models do not simulate land use and management adequately to evaluate management strategies. A model called ROTO (routing outputs to the outlet) was developed to estimate water and sediment yield on large basins (several thousand square miles). ROTO is a continuous model operating on a daily time step that accepts inputs from continuous-time soil-water balance models. Components for water and sediment movement in channels and reservoirs are developed within a comprehensive basin-scale agricultural management model. The model is validated on three different spatial scales: the small watershed, watershed, and river basin. At the small watershed scale, ARS station G (17.7 kg 2 ) at Riesel, Texas, is used for validation of water and sediment yields. White Ro...

Flow duration curves II : a review of applications in water resources planning

Abstract: A streamflow duration curve illustrates the relationship between the frequency and magnitude of streamflow. Flow duration curves have a long history in the field of water-resource engineering and have been used to solve problems in water-quality management, hydropower, instream flow methodologies, water-use planning, flood control, and river and reservoir sedimentation, and for scientific comparisons of streamflow characteristics across watersheds. This paper reviews traditional applications and provides extensions to some new applications, including water allocation, wasteload allocation, river and wetland inundation mapping, and the economic selection of a water-resource project.

Neural-Network Models of Rainfall-Runoff Process

Abstract: Spatially distributed rainfall patterns can now be detected using a variety of remote–sensing techniques ranging from weather radar to various satellite–based sensors. Conversion of the remote–sensed signal into rainfall rates, and hence into runoff for a given river basin, is a complex and difficult process using traditional approaches. Neural–network models hold the possibility of circumventing these difficulties by training the network to map rainfall patterns into various measures of runoff that may be of interest. To investigate the potential of this approach, a very simple 5 × 5 grid cell synthetic watershed is used to generate runoff from stochastically generated rainfall patterns. A back–propagation neural network is trained to predict the peak discharge and the time of peak resulting from a single rainfall pattern. Additionally, the neural network is trained to map a time series of three rainfall patterns into a continuum of discharges over future time by using a discrete Fourier series fit to the runoff hydrograph.

Scale and the Nature of Spatial Variability: Field Examples Having Implications for Hydrologic Modeling

Abstract: In this paper we examine how the nature of spatial variability affects hydrologic response over a range of scales using five field studies as examples. The nature of variability was characterized as either stochastic, when random, or deterministic, when due to known, nonrandom sources. We have emphasized how that characterization may change with the scale of hydrologic model. The five field examples, along with corresponding sources of variability, were (1) infiltration and surface runoff affected by shrub canopy, (2) groundwater recharge affected by soil depth, (3) groundwater recharge and streamflow affected by small-scale topography, (4) frozen soil runoff affected by elevation, and (5) snowfall distribution affected by large-scale topography. In each example there was a scale, the deterministic length scale, over which the hydrologic response was strongly dependent upon the specific, location-dependent ecosystem properties. Smaller-scale variability may be represented as either stochastic or homogeneous with nonspatial data. In addition, changes in scale or location sometimes resulted in the introduction of larger-scale sources of variability that subsume smaller-scale sources. Thus recognition of the nature and sources of variability can reduce data requirements by focusing on important sources of variability and using nonspatial data to characterize variability at scales smaller than the deterministic length scale. All the sources of variability described are present in the same watershed and affect hydrologic response simultaneously. Physically based models should therefore utilize both spatial and stochastic data where scale appropriate. Other implications for physically based modeling are that modeling algorithms should reflect larger-scale variability which generally has greater impact and that model and measurement grids should be consistent with the nature of variability.

Tree-ring reconstruction of upper Gila River discharge

Abstract: Effective planning for use of water resources requires accurate information on hydrologic variability induced by climatic fluctuations. Tree-ring analysis is one method of extending our knowledge of hydrologic variability beyond the relatively short period covered by gaged streamflow records. In this paper, a network of recently developed tree-ring chronologies is used to reconstruct annual river discharge in the upper Gila River drainage in southeastern Arizona and southwestern Arizona since A.D. 1663. The need for data on hydrologic variability for this semi-arid basin is accentuated because water supply is inadequate to meet current demand. A reconstruction based on multiple linear regression (R2=0.66) indicates that 20th century is unusual for clustering of high-discharge years (early 1900s), severity of multiyear drought (1950s), and amplification of low-frequency discharge variations. Periods of low discharge recur at irregular intervals averaging about 20 years. Comparison with other tree-ring reconstructions shows that these low-flow periods are synchronous from the Gila Basin to the southern part of the Upper Colorado River Basin.

SCS Runoff Equation Revisited for Variable-Source Runoff Areas

Abstract: Simple methods for predicting runoff from watersheds are important in engineering practice, particularly in flood forecasting and water-balance calculation. In this paper, we illustrate that the of...

Runoff Production in a Forested, Shallow Soil, Canadian Shield Basin

Abstract: Storm flow in forested basins on the Canadian Shield is largely supplied by subsurface water; however, mechanisms by which this water reaches the stream remain unclear. Side slope contributions to storm flow were studied using throughflow trenches on slopes in a headwater basin near Dorset, Ontario. Discharge, soil water content, and chemical and isotopic signatures of subsurface water were monitored at each site. Four hypotheses were tested: (1) most flow occurs at the soil-bedrock interface on shield slopes with thin soil; (2) a significant fraction of event water moves vertically to bedrock via preferential flow pathways and laterally over the bedrock surface; (3) relative preevent water contribution to subsurface flow on shield slopes is a function of soil thickness; and (4) a significant portion of event water flux in storm flow from forested basins with shallow soil cover is supplied from side slopes via subsurface flow along the soil-bedrock interface. Hypothesis 1 was confirmed from hydrometric observations during spring and fall rainstorms. Hypotheses 2 and 3 were supported by temporal trends in dissolved organic carbon and 18O in flow at the soil-bedrock interface and by isotopic hydrograph separations (IHSs) of hillslope runoff. Comparison with the streamflow IHS indicated that event water flux from the basin in excess of that attributable to direct precipitation onto near-channel saturated areas could be supplied by flow along the bedrock surface (hypothesis 4). Flow at the soil-bedrock interface on side slopes also contributed ∼25% of preevent water flux from the basin. Much of the event water component of basin storm flow may travel considerable distances via subsurface routes and is not necessarily contributed by surface runoff processes (Horton flow or saturation overland flow). Therefore the assumption that event water undergoes little interaction with the soil during its passage downslope may be unwarranted here.

Geomorphic response to river flow regulation: Case studies and time-scales

Abstract: River regulation imposes primary changes on flow and sediment transfer, the principal factors governing the alluvial channel regime. In this study, the effect of flow regulation is isolated from sediment delivery. Peace River (Q = 1080m3 s-', increasing to 21 10 m3 s-' downstream) was regulated in 1967 for hydropower. The gravel-bed reach immediately downstream from the dam has become stable. Gravel accumulates at major tributary junctions, so the river profile is becoming stepped. Further downstream, the river has a sand bed. It can still transport sand, so morphological changes along the channel include both aggradation and channel narrowing by lateral accretation. In the gravel-bed Kemano River (Q = 150m3 s-I), the addition of water by diversion from another river caused degradation when additional bed material was entrained below the inflow point. However, the effect became evident only after many years, when a competent flood occurred. The short-term response was channel widening. The time-scale for the response depends on the size of the river and the nature and seventy of regulation. In both rivers, significant adjustment will require centuries and will intimately involve the riparian forest.

SOCRATES: A system for scheduling hydroelectric generation under uncertainty

Abstract: The Pacific Gas and Electric Company, the largest investor-owned energy utility in the United States, obtains a significant fraction of its electric energy and capacity from hydrogeneration. Although hydro provides valuable flexibility, it is subject to usage limits and must be carefully scheduled. In addition, the amount of energy available from hydro varies widely from year to year, depending on precipitation and streamflows. Optimal scheduling of hydrogeneration, in coordination with other energy sources, is a stochastic problem of practical significance to PG&E. SOCRATES is a system for the optimal scheduling of PG&E's various energy sources over a one- to two-year horizon. This paper concentrates on the component of SOCRATES that schedules hydro. The core is a stochastic optimization model, solved using Benders decomposition. Additional components are streamflow forecasting models and a database containing hydrological information. The stochastic hydro scheduling module of SOCRATES is undergoing testing in the user's environment, and we expect PG&E hydrologists and hydro schedulers to place progressively more reliance upon it.

Flooding Hydrology and Mixture Dynamics of Lake Water Derived from Multiple Sources in an Amazon Floodplain Lake

Abstract: The temporal dynamics in the lake water mixture derived from river flooding, local rainfall and runoff, exchange with an adjacent lake, groundwater exchange, and evaporation was computed from detailed measurements over an annual cycle for a permanent lake on the central Amazon floodplain. River water invaded the lake at the start of rising water, but by mid-rising water, lake water steadily flowed out from the lake and into the river, while river levels continued to rise. Despite a relatively low ratio of catchment area to water surface area, the lake exported to the river three times the amount of water originally received from the river. The lake water mixture was dominated by river water early during the water year, increasing to 70% of the mixture. When lake water began flowing out from the lake, the river water fraction was steadily diluted as runoff became dominant. By the end of the water year, runoff contributed 57% of the total water input, river inflow 21%, rainfall 11%, inflow from an adjacent lake 6%, and seepage inflow 4%. However, local runoff, river inflow, and lake water carried over between water years have the potential for considerable interannual variation. The finding that runoff from relatively small local catchments can be sufficiently large to prevent flood waters from entering the lakes during periods of rising water may critically limit our ability to characterize the long-term frequency and duration of flooding in lakes on the floodplains of large rivers in the wet tropics.

Alternative River Management Using a Linked GIS-Hydrology Model

Abstract: A geographic information system (GIS)-hydrologic model link was used to aid in forming input files for the hydrologic model, SWAT (Soil and Water Assessment Tool) The link and SWAT prediction of streamflow volume were then tested for the Lower Colorado River basin of Texas With no calibration, simulated monthly streamflow volume along the river was underestimated for the extreme events, but the relationship was significant (R2 = 075) Model results also suggest that urbanization further upstream can significantly affect streamflow downstream The system is general enough to be applicable to other river systems

Estimation of discharge from braided glacial rivers using ERS 1 synthetic aperture radar: first results

Abstract: Using multitemporal ERS 1 synthetic aperture radar (SAR) satellite imagery and simultaneous ground measurements of streamflow, a strong correlation (R2 = 0.89) was found between water surface area and discharge for a braided glacial river in British Columbia, Canada. Satellite-derived effective width (We) was found to vary with discharge (Q) as We = 27.5Q0.42, where We is defined as the total water surface area within a 10 km × 3 km control section, divided by the section length. This “area/discharge rating curve” yields instantaneous discharge estimates with a mean error of ±275 m3/s for ground-measured flows that ranged from 242 to 6350 m3/s.

Variations and change in south American streamflow

Abstract: Long-term hydroclimatological records in tropical South America have been analyzed in order to determine whether or not there have been significant changes in the hydrological cycle. Streamflow data from several rivers in Peru, Brazil, Argentina and Venezuela, as well as rainfall in Northeast Brazil have been used here for the study of long-term and interannual variations on hydrological conditions in different regions of South America. The Mann-Kendall statistical test is applied to the historical streamflow annual series in order to detect trends or changes in the mean. The Studentt-test is also applied to study the relationship between interannual variability and the magnitude of change and length of data required to identify a statistically significant trend.

Multicriterion Validation of a Semidistributed Conceptual Model of the Water Cycle in the Fecht Catchment (Vosges Massif, France)

Abstract: Model validation is still a crucial issue in hydrology. It is usually limited to comparing simulated and measured streamflows, while many other fluxes and storages are also simulated. This is especially true for spatially distributed models, for which multivariable and multiscale validation procedures are needed. Such an approach has been tested on the Fecht research basin (Vosges Massif, France) over a 5-year period, using the semidistributed conceptual MC model, whose physical soundness has been improved. The catchment discretization into land units was based on simple physiographic criteria, which were statistically validated. Water balance parameters were derived from measured soil water retention, without any calibration. Catchment streamflow was used to calibrate water transfer parameters over a single year and validate the model. Two subcatchments were used for the internal validation, and two neighboring nested catchments were used for the regional transposition of both the model and its distributed parameterization. At the mesh scale (250 to 1000 m), snowpack and soil water storages and contribution to streamflow were validated by using measurements from two small catchments. Despite the very limited calibration, the results were generally satisfactory. Nash-Sutclifife efficiencies on daily streamflow varied from 0.92 in calibration to 0.89 in validation and 0.71 in transposition. The results of the simulated patterns of fluxes and storages can therefore be considered with some confidence.

Chemical fingerprints of hydrological compartments and flow paths at La Cuenca, Western Amazonia

Abstract: A forested first-order catchment in western Amazonia was monitored for 2 years to determine the chemical fingerprints of precipitation, throughfall, overland flow, pipe flow, soil water, groundwater, and streamflow. We used five tracers (hydrogen, calcium, magnesium, potassium, and silica) to distinguish “fast” flow paths mainly influenced by the biological subsystem from “slow” flow paths in the geochemical subsystem. The former comprise throughfall, overland flow, and pipe flow and are characterized by a high potassium/silica ratio; the latter are represented by soil water and groundwater, which have a low potassium/silica ratio. Soil water and groundwater differ with respect to calcium and magnesium. The groundwater-controlled streamflow chemistry is strongly modified by contributions from fast flow paths during precipitation events. The high potassium/silica ratio of these flow paths suggests that the storm flow response at La Cuenca is dominated by event water.

Impacts of a severe sustained drought on Colorado River water resources

Abstract: The impacts of a severe sustained drought on Colorado River system water resources were investigated by simulating the physical and institutional constraints within the Colorado River Basin and testing the response of the system to different hydrologic scenarios. Simulations using Hydrosphere's Colorado River Model compared a 38-year severe sustained drought derived from 500 years of reconstructed streamflows for the Colorado River basin with a 38-year streamflow trace extracted from the recent historic record. The impacts of the severe drought on streamflows, water allocation, storage, hydropower generation, and salinity were assessed. Estimated deliveries to consumptive uses in the Upper Basin states of Colorado, Utah, Wyoming, New Mexico, and northern Arizona were heavily affected by the severe drought, while the Lower Basin states of California, Nevada, and Arizona suffered only slight shortages. Upper Basin reservoirs and streamflows were also more heavily affected than those in the Lower Basin by the severe drought. System-wide, total hydropower generation was 84 percent less in the drought scenario than in the historical stream-flow scenario. Annual, flow-weighted salinity below Lake Mead exceeded 1200 ppm for six years during the deepest portion of the severe drought. The salinity levels in the historical hydrology scenario never exceeded 1100 ppm.

Concentrations and Export of Solutes from Six Mountain Streams in Northwestern Costa Rica

Abstract: Streamwater chemistry in six streams draining adjacent, undisturbed catchments of volcanic origin in northwestern Costa Rica was monitored between 1990 and 1993. The catchments ranged from 0.36 to 3.2 km 2 in area, and from 600 to 1300 m in elevation. Rainfall averaged 2.4 m/yr at 600 m but was unmeasured and probably much greater at higher elevations. Runoff among the catchments ranged from 1.4 to 4.3 m/yr, with approximately 84% occurring during the May-December rainy season. Within individual streams, concentrations of NO 3 - , total dissolved phosphorus (TDP), and dissolved organic carbon (DOC) increased with streamflow while Ca 2+ , Mg 2+ , and Na + decreased with streamflow. K + showed little response to streamflow. Among streams, flow-weighted mean concentrations of NO 3 - (0.12-0.30 mg/L), DOC (0.63-1.79 mg/L), and TDP (0.008-0.029 mg/L) were intercorrelated and varied inversely with annual runoff. DOC concentra...

A field demonstration of the effect on streamflow of clearing invasive pine and wattle trees from a riparian zone.

Abstract: SYNOPSIS Two portable weirs were used to quantify changes in streamflow following clearfelling of a dense stand of self-sown Pinus patula and Acacia mearnsii along a riparian zone on Kalmoesfontein, a SAPPI forest plantation south-east of Lydenburg, Eastern Transvaal. The weirs were set up at positions 500 m apart on the same stream, and used to monitor streamflow levels before and after the clearing of all trees between the weirs to an average distance of 25 m from the stream. Analysis of streamflow data revealed that the clearing operation resulted in a 120% increase in streamflow at the lower weir, equivalent to 30,5 m3 of water per day. Streamflow at the lower weir was less than at the upper weir before clearfelling, but equalled that at the upper weir after clearfelling. This demonstrates that the intervening trees were responsible for the initial difference in streamflow. Two further lines of evidence point to the adjacent trees exerting a strong influence on streamflow. Firstly, a clear daily fluct...

Modeling Climate Change in the Absence of Climate Change Data. Editorial Comment

Abstract: Practitioners of climate change prediction base many of their future climate scenarios on General Circulation Models (GCM's), each model with differing assumptions and parameter requirements. For representing the atmosphere, GCM's typically contain equations for calculating motion of particles, thermodynamics and radiation, and continuity of water vapor. Hydrology and heat balance are usually included for continents, and sea ice and heat balance are included for oceans. The current issue of this journal contains a paper by Van Blarcum et al. (1995) that predicts runoff from nine high-latitude rivers under a doubled CO2 atmosphere. The paper is important since river flow is an indicator variable for climate change. The authors show that precipitation will increase under the imposed perturbations and that owing to higher temperatures earlier in the year that cause the snow pack to melt sooner, runoff will also increase. They base their simulations on output from a GCM coupled with an interesting water routing scheme they have devised. Climate change models have been linked to other models to predict deforestation.

The role of individual terrain units in the water balance of wetland tundra

Abstract: The water balance of a High Subarctic wetland was measured in a newly established research basin near Churchill, Manitoba, Canada. Measurements spanned the growing season from early June through to the end of August 1991. The watershed was instrumented such that the water budget could be monitored over each of the dominant terrain unlts. The study basin has 5 major terrain types consisting of sedge-dominated wetland, upland lichen-heath, tundra lakes and ponds, willowbirch wetland, and open spruce forest, in decreasing order of coverage. These terrain units, and the ecosystem as a whole, are representative of coastal wetlands underlain by permafrost in the Hudson Bay Lowland. Runoff and thus streamflow were closely tied to the moisture status of the peatlands and to the depth of the active layer. During 2 unusually dry periods, the peatlands remained wet, which indicates a lack of water mobility when the water table drops below the surface of the wetland. Streamflow response to rainfall during these periods was small in comparison to early summer when the frost table was near the surface, or to wet periods when the water table rose above the surface. Energy balance measurements showed the lakes and ponds to have about 15 % higher net radiation than wetlands and 29% greater than upland lichen-heath. From 9 to 18% of net radiation was used in thawing and heating the ground whereas the latent heat flux for the various terrain types utilized from 49 to 83 % of net radiation. Even with unusually large rainfalls that occurred in July, evaporation exceeded precipitation over the course of the summer. Despite this, runoff was high and required a large negative change in groundwater storage to account for it. The lichen-heath and ponds exhibited the greatest change in water storage. The drainage of water from the uplands to the lowlands maintained the soil moisture of the peatlands and contributed to streamflow. Each terraln type had a characteristic water balance due to differences in one or more of the hydrologic variables (evapotranspiration, runoff and storage). This has important lrnplications concerning the impact on the water balance of a change in surface cover brought about by a change in climate.

Hydroclimatology of Continental Watersheds: 1. Temporal Analyses

Abstract: The linkage between meteorology/climate and hydrology of temperate latitude catchments on daily to decade time scales is studied. Detailed hydrology is provided by a hydrologic catchment model, adapted from the operational streamflow forecast model of the National Weather Service River Forecast System. The model is tuned to respond to observed daily precipitation and potential evaporation input. Results from the Bird Creek basin with outlet near Sperry, Oklahoma, and from the Boone River basin with outlet at Webster City, Iowa, indicate that the model quite accurately simulates the observed daily discharge over 40 years at each of the two 2000-km2 basins. Daily cross-correlations between observed and simulated basin outflows were better than 0.8 for both basins over a 40-year historical period. Soil moisture variability over a period of four decades is studied, and an assessment of temporal and spatial (as related to the separation distance of the two basins) scales present in the estimated soil moisture record is made. Negative soil water anomalies have larger magnitudes than positive anomalies, and comparison of the simulated soil water records of the two basins indicates spatial scales of variability that in several cases are as long as the interbasin distance. The temporal scales of soil water content are considerably longer than those of the forcing atmospheric variables for all seasons and both basins. Timescales of upper and total soil water content anomalies are typically 1 and 3 months, respectively. Linkage between the hydrologic components and both local and regional-to-hemispheric atmospheric variability is studied, both for atmosphere forcing hydrology and ydrology forcing atmosphere. For both basins, cross- correlation analysis shows that local precipitation strongly forces soil water in the upper soil layers with a 10-day lag. There is no evidence of soil water feedback to local precipitation. However, significant cross-correlation values are obtained for upper soil water leading daily maximum temperature with 5–10 day lags, especially during periods of extremely high or low soil water content. Complementary results of a spatial hydroclimatic analysis are presented in a companion paper (Cayan and Georgakakos, this issue).

Hydrologic scenarios for severe sustained drought in the southwestern united states

Abstract: This paper considers the risk of drought and develops drought scenarios for use in the study of severe sustained drought in the Southwestern United States. The focus is on the Colorado River Basin and regions to which Colorado River water is exported, especially southern California, which depends on water from the Colorado River. Drought scenarios are developed using estimates of unimpaired historic streamflow as well as reconstructions of streamflow based on tree ring widths. Drought scenarios in the Colorado River Basin are defined on the basis of annual flow at Lees Ferry. The risk, in terms of return period, of the drought scenarios developed, is assessed using stochastic models.

The channel-geometry method: Guidelines and applications

Abstract: All river engineering schemes require flood discharge estimates as part of the design and appraisal process. Unfortunately, continuous measurement of flood discharges is limited to those river sites with instrumented gauging stations, which constitute only a small proportion of channel reaches where information is required. Therefore, considerable research effort has been devoted to the development of reliable indirect techniques of flood discharge estimation. Research on the interrelationship of stream channel geometry and river discharge has provided the basis for an indirect method of flood estimation – the channel-geometry method – which employs river channel dimensions alone to estimate discharge characteristics at ungauged river sites. Channel-geometry equations are developed empirically by relating streamflow data from gauging stations and channel dimensions measured from natural river reaches in the vicinity of the gauge, and take the form of power function relations. Once regional channel-geometry equations have been defined, a channel width or channel capacity measurement is the only variable needed to estimate the flood flow characteristics at a specified river site. The method is useful as an alternative to traditional catchment-based approaches or as a rapid reconnaissance technique. In addition to the application for flood discharge prediction, channel-geometry equations could prove helpful in the management of river channels, first, by providing a basis for assessing local deviations in the channel form–discharge relation, deviations which could be employed as indicators of the sensitivity of particular stretches of river channel to change, and secondly, in the computation of natural channel dimensions for use in river channel design and river restoration.

Global-Warming Effects on New York Streamflows

Abstract: Impacts of global warming on streamflows were estimated for four large watersheds in New York State using a daily streamflow model. Three different 100-yr daily weather sequences were input to the model. The first was produced using statistics of current (1961–90) weather records. The second and third sequences were based on modifications of these historic statistics according to the monthly mean temperature and precipitation changes associated with a doubling of atmospheric CO 2 as predicted by two different general circulation models. For 2 × CO 2 conditions, mean annual water balances for all four watersheds indicated modest (1–9%) decreases in precipitation, but much larger (16–42%) decreases in streamflow due to increases in evapotranspiration. Winter flows generally increased, but flows in the remaining seasons often decreased. Monthly streamflow changes varied considerably among watersheds, and we could not attribute these changes to specific differences in land uses or soils.