Amount Of Streamflow Research Articles

A Stable Isotopic Investigation of a Polar Desert Hydrologic System, McMurdo Dry Valleys, Antarctica

The hydrologic system of the coastal McMurdo Dry Valleys, Antarctica, is defined by snow accumulation, glacier melt, stream flow, and retention in closed-basin, ice-covered lakes. During the austral summers from 1993–1996 and 1999–2000 to 2002–2003, fresh snow, snow pits, glacier ice, stream water, and lake waters were sampled for the stable isotopes deuterium (D) and 18O in order to resolve sources of meltwater and the interactions among the various hydrologic reservoirs in the dry valleys. This data set provides a survey of the distribution of natural water isotope abundances within the well-defined dry valley hydrologic system in Taylor Valley, which extends 20 km inland from McMurdo Sound. The three major Taylor Valley lakes are not connected to one another hydrologically, and their levels are maintained by glacial meltwater inflow and perennial ice-cover sublimation. At the valley scale, glacial ice, snow, stream, and lake waters become more depleted in δD with increasing distance from McMurdo Sound (further inland). Snow pack in glacial accumulation zones is heterogeneous, likely a result of varying storm sources (continental versus coastal), and, in general, snow pits, fresh snow samples, and glacier ice are more depleted than stream waters. Within the lake basins, glacial ice source waters are depleted by as much as 111‰ δD and 20‰ δ18O compared to lake waters. These results demonstrate the importance of in-stream fractionation at the valley scale. In-stream enrichment occurs through direct evaporation fractionation from the channel and hyporheic exchange with isotopically enriched waters in the near-stream subsurface during transport from the glacial source to lake. Furthermore, the results show that lake waters directly reflect their glacial ice sources, despite fractionation during stream transport. Inter-annual comparisons of lake profiles suggest that lake waters are directly influenced by the isotopic composition and amount of stream flow during a season.

Modelling the hydrologic effects of land-use and climate changes

Climate and land use affect water quantity and quality; however, the complex relations of climate and land use regarding flow and instream nutrient levels have yet to be elucidated. This study aims to assess the hydrologic effects of different land-use and climatic regimes in the Lower Great Miami River Basin. The modelling results from BASINS showed that, as expected, agricultural lands and the wettest scenario yielded the highest amount of streamflow, fecal coliform, and nutrient loadings. But, it was the dry scenario (+2°C, -20% precipitation of the current average climatic conditions in SW Ohio), instead of the driest scenario (+4°C, -20% precipitation), that produced the highest daily nutrient concentrations. When the future land-use and climate scenarios were coupled, the worst situation was found under the current land use and the wettest condition. Hence, a change in land-use pattern may help to alleviate the adverse hydrologic impacts of climate change.

The zone of vegetation influence on baseflow revealed by diel patterns of streamflow and vegetation water use in a headwater basin

AbstractWater use by vegetation can be closely linked to streamflow patterns on a variety of time scales. However, many of the details of these linkages are poorly understood. We compared diel (24 h) patterns of transpirational water use with streamflow patterns in a small headwater basin that displays a marked diel variation during summer months. The study site was in western Oregon. Our objectives were to: (1) determine the phase shift, i.e. the time lag between maximum transpiration and minimum streamflow, and the strength of the correlation at that time lag; (2) determine the amount of streamflow that is ‘missing’ during each diel cycle (i.e. the difference between base flow, defined by the daily maxima, and actual flow) and use it to estimate the zone, or area, of vegetation that influences daily streamflow patterns; (3) test and refine a conceptual model of how the coupling between vegetation water use and streamflow changes over the period of summer drought in this basin. We found that vegetation water use in the summer is coupled to streamflow over time scales of 4 to 8 h, and water‐use‐related fluctuations accounted for 1 to 6% of summer base flow. Direct evaporation from the channel was an order of magnitude less than the diel streamflow decrease. Transpiration within only 0·1 to 0·3% of the basin area accounted for the diel variation in streamflow. As the basin drained further through the summer, the coupling between vegetation and streamflow was diminished and occurred at longer time scales, and the zone of vegetation influence became smaller. This pattern is in accordance with our conceptual model, which attributes the summer decline in the strength of the vegetation–streamflow coupling to the increasing depth of plant‐available water in the soil profile. Although this study is preliminary, we believe it is an important first step in describing better the coupling of vegetation water use to streamflow. Copyright © 2002 John Wiley & Sons, Ltd.

SENSITIVITY OF AQUATIC ECOSYSTEMS TO CLIMATIC AND ANTHROPOGENIC CHANGES: THE BASIN AND RANGE, AMERICAN SOUTHWEST AND MEXICO

Variability and unpredictability are characteristics of the aquatic ecosystems, hydrological patterns and climate of the largely dryland region that encompasses the Basin and Range, American Southwest and western Mexico. Neither hydrological nor climatological models for the region are sufficiently developed to describe the magnitude or direction of change in response to increased carbon dioxide; thus, an attempt to predict specific responses of aquatic ecosystems is premature. Instead, we focus on the sensitivity of rivers, streams, springs, wetlands, reservoirs, and lakes of the region to potential changes in climate, especially those inducing a change in hydrological patterns such as amount, timing and predictability of stream flow. The major sensitivities of aquatic ecosystems are their permanence and even existence in the face of potential reduced net basin supply of water, stability of geomorphological structure and riparian ecotones with alterations in disturbance regimes, and water quality changes resulting from a modified water balance. In all of these respects, aquatic ecosystems of the region are also sensitive to the extensive modifications imposed by human use of water resources, which underscores the difficulty of separating this type of anthropogenic change from climate change. We advocate a focus in future research on reconstruction and analysis of past climates and associated ecosystem characteristics, long-term studies to discriminate directional change vs. year to year variability (including evidence of aquatic ecosystem responses or sensitivity to extremes), and studies of ecosystems affected by human activity.

Nutrient budgets in a dry heathland watershed in northeastern Spain

Dissolved nutrient inputs in bulk precipitation and outputs in streamwater were measured during 3 years of contrasting hydrological conditions in a 6.3-ha, grazed heathland watershed on schists in the Montseny mountains (NE Spain), drained by an intermittent stream. On average, 39% of the precipitation became streamflow. Bulk precipitation delivered positive net alkalinity (mean 0.22 keq/ha/yr), sulphate input was moderate (9.0 kg SO4-S/ha/yr), and the mean input of inorganic N was not exceptionally high (6.6 kg/ha/yr). Ion concentrations were relatively low in streamwater; S042- was the dominant anion. Most concentrations in streamwater varied seasonally, with maxima in late summer or early autumn and minima in spring. This pattern probably resulted from increased availability of ions for leaching due to decomposition of organic matter and chemical weathering during the warm period. Nitrate concentrations were relatively high in winter and dropped sharply in early spring, probably because of biological uptake. Annual element outputs in streamwater varied between years and seemed to be controlled by both the amount of annual streamflow and its seasonal distribution. Annual inputs exceeded outputs for dissolved inorganic N. The watershed accumulated H+ and Ca2+, had net losses of Na+ and Mg2+, and was close to steady state for K+, S042-, C1- and alkalinity. The chloride budgets gave no evidence of substantial dry deposition in this system. The cationic denudation rate was negative (-0.14 keq/ha/yr) because Ca2+ retention was higher than net exports of Na+ and Mg2+ from silicate weathering. Low nutrient export and little production of alkalinity suggest that this watershed has a low buffering capacity.

Potential for enhancing riparian habitats in the southwestern United States with watershed practices

Numerous watershed practices currently being implemented for erosion control and water augmentation purposes have improved hydrologic conditions in southwestern streams and enhanced establishment of riparian vegetation. This paper summarizes some potential opportunities for better managing existing riparian ecosystems, or for creating hydrologic regimes favoring re-establishment of new riparian communities in the southwestern United States. Generally, management opportunities exist where either the amount of water or duration of streamflow can be increased, or both. Various-sized channel structures, ranging from small gully check dams to large flood-control structures, have been used successfully for both stabilizing erodible channels and lengthening streamflow duration. These channel structures trap sediment in upstream deposits which store water and release it slowly over time, thereby producing perennial flow in previously ephemeral streams. In addition to providing a more favorable hydrologic regime, the deposited sediment also provides a nutrient-rich medium which further favors plant establishment and growth. The amount and duration of streamflow through a riparian zone can also be increased by manipulating upslope vegetation where deep-rooted plants are replaced with shallower-rooted species using less water. Case studies documenting these different watershed practices and the resulting riparian communities are discussed.

Hydrologic influences on the potential benefits of basinwide groundwater management

The potential benefits of basinwide groundwater management in agricultural areas are analyzed with an optimization model. The model incorporates functions to compute spatial and temporal groundwater responses to hydraulic stresses, net agricultural revenues as a function of water use, and groundwater recharge from individual stream reaches. Stream recharge is computed on the basis of both groundwater elevations and the amount of streamflow. The model can be run either to maximize basinwide net revenue over a planning period or to simulate private optimization by individual agricultural sectors. The effects of several hydrologic factors on the benefits of basinwide groundwater management are estimated by comparing model results for conditions in the Salinas Valley in California prior to reservoir construction with a number of other hydrologic scenarios. Results indicate that basinwide groundwater management and reservoir operation may be close substitutes for each other under certain conditions, that an interesting relationship appears to exist between the potential benefits of groundwater management and the annual amount of streamflow available for recharge, and that consideration of stochastic variations in streamflow is unnecessary in the analysis of systems relying primarily on groundwater. A framework is also presented for identifying strategies that meet environmental constraints while minimizing the revenue losses to current water users. For all scenarios considered, basinwide groundwater management generates larger revenues than private optimization while using considerably less water.

The importance of groundwater in the transportation of allochthonous dissolved organic matter to the streams draining a small mountain basin

The importance of groundwater in the dissolved organic matter (DOM) budget of small upland streams is not well understood. This paper is concerned with the amount of streamflow which can be attributed to groundwater, the organic chemistry of rainwater, streamwater, and groundwater, and the rate of transfer of DOM in groundwater to the streams of a small mountain catchment basin in Alberta. Using naturally occurring isotopes (18O and tritium) groundwater is concluded to be the largest contributor to stream discharge throughout the year. This means that most of the water which reaches the stream must pass through the soil column and be exposed to microbial attack. Groundwater in the Marmot Basin spends an average of about ten years in the ground before being discharged into streams. In this area it appears that the majority of DOM from forest productivity is consumed in the soil and only small amounts of refractory by-products reach the stream. This is in keeping with the finding of Fisher & Likens (1973) that 99% of forest productivity is consumed terrestrially. It is probable that bacteria in stream sediments are capable of taking up refractory compounds which deep soil bacteria can not. Increases in DOM concentration in streams are not usually observed during storm runoff because of the ability of bacteria to take up groundwater DOM and because most of stream discharge is groundwater low in DOM being flushed into the channel even during snowmelt and rainfall events.

A STOCHASTIC DYNAMIC PROGRAMMING MODEL FOR THE OPTIMUM OPERATION OF A MULTI‐PURPOSE RESERVOIR1

ABSTRACT: The main objective of this paper is to present a stockastic dynamic programming model useful in determining the optimal operating policy of a single multipurpose surface reservoir. It is the unreliability of forecasting the amount of future streamflow which makes the problem of a reservoir operation a stochastic process. In this paper the stochastic nature of the streamflow is taken into account by considering the correlation between the streamflows of each pair of consecutive time intervals. This interdependence is used to calculate the probability of transition from a given state and stage to its succeeding ones. A dynamic programming model with a physical equation and a stochastic recursive equation is developed to find the optimum operational policy. For illustrative purposes, the model is applied to a real surface water reservoir system.

Economic Evaluation of Some Watershed Management Alternatives on Forest Land in West Virginia

Timber and water research conducted at the Fernow Experimental Forest provides a 10‐year record of timber growth and streamflow increases. An approach for evaluating streamflow increases in terms of timber growth forgone is modeled. Light cutting (up to one‐fourth of the timber volume) slightly increased the value of timber growth as well as the amount of streamflow. Cutting one‐third to one‐half of the merchantable volume sacrificed timber regrowth for streamflow gain. Cutting one‐half to three‐fourths of the timber volume resulted in small streamflow increases for large sacrifices of timber regrowth. Cutting three‐fourths or more of the forest vegetation provided major increases in streamflow but no return from timber during the 10‐year period of regrowth. Average annual water costs ranged from 0 to $1.30 per thousand gallons. Although these water costs may be invalid outside the Fernow Experimental Forest, they nevertheless suggest a magnitude for water costs under similar forest conditions.