Unit Drainage Area Research Articles

A groundwater security model based on hydraulic turnover times and flow compartments

Starting with a log-linear relationship between groundwater discharge per unit drainage area (Q/Ab), hydraulic turnover time (t) and aquifer mobile storage (z), this study builds a groundwater security method at catchment scale. The method embeds previously published approaches to calculate Q/Ab, t and z, and relies solely on stream flow discharges and watershed areas. The ability to build a method on a couple of variables is remarkable. The method recasts the calculated variables as aquifer security indicators (SQ, St and Sz), relating SQ with yield capacity, St with self-depuration capacity and Sz with resilience. Groundwater security is the weighted product of SQ, St and Sz. The method is validated with stream flow discharges and drainage areas concerning 294 hydrometric stations and their watersheds, located in continental Portugal. The results revealed a majority of moderately to highly secure watersheds, especially as regards St (> 62%), while 7–10% were classified as very highly secured in general (SQ-St-Sz). The least secured basins are located in the more arid regions of continental Portugal (Northeast and south regions), as expected. The method can be easily transposed to any other region worldwide, with the necessary adaptions to regional climate, geological and topographic settings.• Compile stream flow discharge data and organize them as natural logarithms and logarithmic variations as function of time, to estimate Q, t and z;• Recast the Q, t and z values as SQ, St and Sz ratings, respectively, using the appropriate reclassification scales, and estimate watershed security levels, namely average security or customized (weighted) securities that highlight the contributions of Q/Ab (watershed yield), t (aquifer's self-depuration capacity) or z (aquifer's resilience);• Use the results to draw illustrative diagrams and spatial distribution maps.

Sediment Production in French Alpine Rivers

AbstractGlobal compilations of river sediment loads show that mountainous areas produce a high proportion of the sediment transported to the oceans. However, because of the effort involved in measuring sediment fluxes in mountain river systems, the loads of these rivers are generally unknown. Here, we present estimates of contemporary sediment loads of 16 gravel bed rivers draining the Ecrins‐Pelvoux Massif in southeast France. Sediment production in this part of the Alps is relatively high and many river segments are either wandering or braided. We model sediment fluxes and annual sediment yields by coupling hydraulic‐based relations for sediment transport with hydrologic‐based relations for flow frequency. Bed load fluxes are modeled for a range of discharges using a function that relates transport rates to excess shear stress. Fluxes are then weighted by the frequency of individual discharges and summed to get the annual bed load for each site. The suspended load is estimated empirically as a fraction of the bed load. Results suggest that bed load fluxes at channel‐forming flows scale almost linearly with downstream increases in discharge. In addition, it appears that annual sediment loads (bed load + suspended load) scale linearly with drainage area. A complementary relation for specific sediment yield suggests that the load per unit drainage area is constant across the range of basins studied. The modeled sediment yields are comparable to previous field‐based estimates of modern sediment yields, and generally lower than estimates developed from analyses of cosmogenic radionuclides.

Inventory of riverine dissolved organic carbon in the Bohai Rim

Riverine carbon (C) composition and export are closely related to changes in the coastal environment and climate. Excessive C inputs from rivers to seas and their subsequent decomposition could result in harmful algal blooms and ecosystem degradation in the coastal sea. In this study, we explored the C transportation and composition in the 24 major rivers of the Bohai Sea (BS) Rim based on the investigation of dissolved organic carbon (DOC), carbon stable isotopes (δ13CDOC) and chromophoric dissolved organic matter (CDOM). The results showed that the riverine DOC concentrations were high (10.6 ± 6.04 mg/L) in the BS Rim compared with the DOC levels in the main rivers in Eastern China (4.98 ± 2.45 mg/L). The δ13CDOC ranged from −28.29‰ to −25.32‰ in the rivers of the BS Rim, suggesting that the DOC mainly originated from riverine plankton, soil organic matter mainly induced by C3 plants, and sewage. The excitation-emission matrix fluorescence spectroscopy of the CDOM indicated that a soluble, microbial by product-like material accounted for the largest proportion (approximately 40%) of CDOM in these rivers and that CDOM mainly originated from autochthonous riverine sources with high protein-like components. The rivers in the BS Rim transported approximately 0.55 Tg C of DOC to the BS each year, with more than 70% of reactive C based on the CDOM composition. The DOC yields in terms of unit drainage area transported from the small rivers to the BS were higher compared to those of the larger rivers in the world, which indicated that the small rivers in the Bohai Rim could be an important source of the C in the BS. This study would enrich our understanding of environmental evolution in coastal areas with numerous small rivers.

Model estimated baseflow for streams with endangered Atlantic Salmon in Maine,USA

AbstractWe present a regression model for estimating mean August baseflow per square kilometer of drainage area to help resource managers assess relative amounts of baseflow in Maine streams with Atlantic Salmon habitat. The model was derived from mean August baseflows computed at 31 USGS streamflow gages in Maine. We use an ordinary least squares regression model to estimate mean August baseflow per unit drainage area from two explanatory variables: percentage of the basin underlain by sand and gravel aquifers and mean July precipitation in the basin. This model provides the ability to estimate mean August baseflow in cubic meters per second per square kilometer of basin area on user‐selected, ungaged sites throughout Maine south of 46° 21′55″ N latitude. The model has an adjusted R2of 0.78 and a mean 95% prediction interval of plus or minus 0.002 cubic meters per second per square kilometer. A map of the Narraguagus watershed in eastern coastal Maine shows reaches color coded by relative amounts of baseflow predicted by the model as an example of how this method could be applied throughout Maine. The map can be used to identify reaches with relatively higher amounts of baseflow during summer low flows for habitat conservation and restoration work. These areas have the potential to be high‐quality habitat for Atlantic salmon and other cold‐water fish because baseflows are known to moderate stream temperatures in summer low‐flow periods.

Geological Effects on the Scaling Relationships of Groundwater Contributions in Forested Watersheds

AbstractThe scaling relationships of groundwater contributions have been examined in previous studies, but whether these findings are site‐specific or applicable to other watersheds remains unclear. Here, we illustrate how scaling relationships differ between watersheds with different geology. We investigated the spatial distributions of the specific discharge (discharge per unit drainage area) and chemical compositions of stream and spring water during baseflow periods in three Cretaceous to Eocene sedimentary watersheds and three Neogene volcanic watersheds in the Ishikari River basin, Japan. End‐member mixing analysis was used to separate stream water into shallow and deep groundwater. The specific discharge of stream water only significantly increased with drainage area for two of the volcanic study sites. Conversely, the ratio of deep groundwater to stream water only significantly increased with drainage area for two of the sedimentary study sites. The specific discharge of deep groundwater increased with area in both volcanic and sedimentary sites, but the specific discharge of shallow groundwater only increased with area for the volcanic sites. These findings indicate that the shallow groundwater flow played a crucial role in making geology‐dependent differences in scaling relationships. The geological effects on shallow groundwater flow were likely characterized by the spatial distribution of highly permeable bedrock layer. This geological control provides a useful framework for generalizing knowledge about the scaling relationships of groundwater contributions.

Brahmaputra river in India: An analytical study with special reference to its erosion.

The complex and unique riverbank erosion characteristics of the Brahmaputra River in India, the fourth largest river in the world in terms of average discharge at the mouth and second only to the Yellow River in China in the amount of sediment transported per unit drainage area, is highlighted with illustrations of the severity of erosion caused at various bank locations. First, the source and the entire course of the river are described. Riverbank erosion mechanisms and existing erosion control measures and their effectiveness in the Assam reach of the Brahmaputra River are described. As part of a joint effort for the first time between U.S. and Indian (local) investigators to understand and find solutions to this mega unique problem of the Brahmaputra River, a set of recommendations, including a phase-wise multiple solutions to the acute and potential riverbank erosion sites along this large river, is forwarded for discussion and getting feed back from international experts.

Combining observations of channel network contraction and spatial discharge variation to inform spatial controls on baseflow in Birch Creek, Catskill Mountains, USA

Study regionThis study was carried out in the 32km2 Birch Creek watershed in the Catskill Mountains of New York State. Birch Creek is situated within the Hudson River Basin. Study focusVery few studies have paired measurements of changes in the extent of the actively flowing channel network with measurements of small scale flow variations. In this study, we map changes in a 23.5km active channel network and concurrently take periodic measurements of discharge at 31 sub-channels (with drainage areas ranging from 0.04 to 11.5km2) in order to better understand the spatial distribution of baseflow generation over time within the catchment. New hydrological insightsFor the 31 different sub-channels, baseflow discharge per unit drainage area and per unit stream length were highly variable, even during periods of higher moisture storage when all channels were active. Simple mapping of the active channels would not have recognized these sizable spatial differences in discharge contribution. Previous studies of hydrologic scaling in the Catskills have noted the likelihood of heterogeneity in discharge below a threshold of approximately 3–8km2. This study provides direct documentation of such heterogeneity at smaller spatial scales. When considering perennial and ephemeral streams, such heterogeneity was not well explained by standard topographic, geologic, or meteorological factors. We suggest the heterogeneity may arise from difficult to map fine-scale variations in subsurface properties.

Bankfull Regional Curves for the Alleghany Plateau/Valley and Ridge, Piedmont, and Coastal Plain Regions of Maryland

AbstractRegional curves are empirical relationships that can help identify the bankfull stage in ungaged watersheds and aid in designing the riffle dimension in stream restoration projects. Bankfull regional curves were developed from gage stations with drainage areas less than 102 mi2 (264.2 km2) for the Alleghany Plateau/Valley and Ridge (AP/VR), Piedmont, and Coastal Plain regions of Maryland. The AP/VR regions were combined into one region for this project. These curves relate bankfull discharge, cross‐sectional area, width, and mean depth to drainage area within the same hydro‐physiographic region (region with similar rainfall/runoff relationship). The bankfull discharge curve for the Coastal Plain region was further subdivided into the Western Coastal Plain (WCP) and Eastern Coastal Plain (ECP) region due to differences in topography and runoff. Results show that the Maryland Piedmont yields the highest bankfull discharge rate per unit drainage area, followed by the AP/VR, WCP, and ECP. Likewise, the Coastal Plain and AP/VR streams have less bankfull cross‐sectional area per unit drainage area than the Piedmont. The average bankfull discharge return interval across the three hydro‐physiographic regions was 1.4 years. The Maryland regional curves were compared to other curves in the eastern United States. The average bankfull discharge return interval for the other studies ranged from 1.1 to 1.8 years.

On the impact of urbanization on flood hydrology of small ungauged basins: the case study of the Tiber river tributary network within the city of Rome

AbstractThe small ungauged basins of the highly urbanized area of the city of Rome are often the subject of critical flood conditions for the significant human‐made transformations. In this work the EBA4SUB framework, implementing the hydrogeomorphic width function instantaneous unit hydrograph rainfall run‐off model, and using digital elevation model, land use and synthetic precipitation as main input information, is applied for evaluating extreme hydrologic forcing conditions at the basic scale. The goal is to understand the rationale behind the observed increasing frequency of local urban inundations that are also observed in the uplands. Results present the impact of urbanization expressed by both the run‐off coefficient, the artificial drainage, impacted by paved surfaces and a dramatic number of river–road intersections (i.e. culverts), and the upstream to downstream non‐natural scaling behaviour of hydrologic parameters and in particular the peak discharge per unit drainage area.

A Methodology to Reduce Uncertainties in the High-Flow Portion of a Rating Curve

<abstract> <bold><sc>Abstract.</sc></bold> Streamflow monitoring typically relies on the establishment of a rating curve that describes the relationship between stage and streamflow. This rating curve is based on direct and indirect measurements of discharge at various stages and application of open-channel hydraulics principles. Potential measurement errors increase with out-of-bank flow conditions because of difficulties in measuring flow velocity and flow depth during increased stages. With increasing frequency of large rain events attributed to climate change, it becomes critical to have an accurate rating curve for flood flows. This article presents techniques that, when used concurrently, can help identify errors and reduce uncertainty in the rating curve. They include commonly used techniques such as comparison of mean annual discharge per unit drainage area with those from nearby watersheds having similar characteristics. In addition, new techniques are proposed based on the hydrologic budget of a storm event and the analysis of the change in flow relative to time and stage. The methodology was tested using flow data from the 72 km² Goodwater Creek Experimental Watershed in northeast Missouri. Results showed that the original rating curve overestimated flow values by 30% for out-of-bank conditions. A revised rating curve was proposed based on channel conveyance. This revised rating curve satisfied the requirements of water balance and change in flow relative to time and stage. The resulting annual flows were reduced by up to 30%, better matching those of nearby watersheds. These techniques are useful for retrospective analysis of flow data series and for identifying rating curve inconsistencies.

A Methodology to Reduce Uncertainties in the High-Flow Portion of a Rating Curve

Abstract. Streamflow monitoring typically relies on the establishment of a rating curve that describes the relationship between stage and streamflow. This rating curve is based on direct and indirect measurements of discharge at various stages and application of open-channel hydraulics principles. Potential measurement errors increase with out-of-bank flow conditions because of difficulties in measuring flow velocity and flow depth during increased stages. With increasing frequency of large rain events attributed to climate change, it becomes critical to have an accurate rating curve for flood flows. This article presents techniques that, when used concurrently, can help identify errors and reduce uncertainty in the rating curve. They include commonly used techniques such as comparison of mean annual discharge per unit drainage area with those from nearby watersheds having similar characteristics. In addition, new techniques are proposed based on the hydrologic budget of a storm event and the analysis of the change in flow relative to time and stage. The methodology was tested using flow data from the 72 km2 Goodwater Creek Experimental Watershed in northeast Missouri. Results showed that the original rating curve overestimated flow values by 30% for out-of-bank conditions. A revised rating curve was proposed based on channel conveyance. This revised rating curve satisfied the requirements of water balance and change in flow relative to time and stage. The resulting annual flows were reduced by up to 30%, better matching those of nearby watersheds. These techniques are useful for retrospective analysis of flow data series and for identifying rating curve inconsistencies.

Erratum1“Evidence for Changing Flood Risk in New England Since the Late 20th Century”2

The correct units for the “Magnitude” column in Table 1 are cms/km2 (cms is cubic meters per second, m3/s). Related text in the first paragraph on p. 284 should be similarly corrected to read: “… trend magnitude per unit drainage area (cms/km2) for the study gages …” and “… show larger magnitude trends (>0.100 cms/km2).” The legends for Figures 4A and 4B should show solid filled triangle symbols for the “1940-1970 floods” and “1941-1970 floods”, respectively, to properly correspond with the plots. These changes correct presentation errors that occurred in the production phase and do not affect the study results or interpretations.

Linking runoff response to burn severity after a wildfire

AbstractExtreme floods often follow wildfire in mountainous watersheds. However, a quantitative relation between the runoff response and burn severity at the watershed scale has not been established. Runoff response was measured as the runoff coefficient C, which is equal to the peak discharge per unit drainage area divided by the average maximum 30 min rainfall intensity during each rain storm. The magnitude of the burn severity was expressed as the change in the normalized burn ratio. A new burn severity variable, hydraulic functional connectivity Φ was developed and incorporates both the magnitude of the burn severity and the spatial sequence of the burn severity along hillslope flow paths. The runoff response and the burn severity were measured in seven subwatersheds (0·24 to 0·85 km2) in the upper part of Rendija Canyon burned by the 2000 Cerro Grande Fire near Los Alamos, New Mexico, USA.A rainfall–discharge relation was determined for four of the subwatersheds with nearly the same burn severity. The peak discharge per unit drainage area $Q_{\rm u}^{\rm peak}$ was a linear function of the maximum 30 min rainfall intensity I30. This function predicted a rainfall intensity threshold of 8·5 mm h−1 below which no runoff was generated. The runoff coefficient $C = Q_{\rm u}^{\rm peak}/I_{30}$ was a linear function of the mean hydraulic functional connectivity of the subwatersheds. Moreover, the variability of the mean hydraulic functional connectivity was related to the variability of the mean runoff coefficient, and this relation provides physical insight into why the runoff response from the same subwatershed can vary for different rainstorms with the same rainfall intensity. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Geomorphic effectiveness of extraordinary floods on three large rivers of the Indian Peninsula

The efficacy of extreme events is directly linked to the flood power and the total energy expended. The geomorphic effectiveness of floods is evaluated in terms of the distribution of stream power per unit boundary area ( ω) over time, for three very large floods of the 20th Century in the Indian Peninsula. These floods stand out as outliers when compared with the peak floods per unit drainage area recorded elsewhere in the world. We used flood hydrographs and at-a-station hydraulic geometry equations, computed for the same gauging site or a nearby site, to construct approximately stream-power curves and to estimate the total energy expended by each flood. Critical unit stream power values necessary to entrain cobbles and boulders were estimated on the basis of empirical relationships for coarse sediment transport developed by Williams [Williams, G.P., 1983. Paleohydrological methods and some examples from Swedish fluvial environments. I. Cobble and boulder deposits. Geografiska Annaler 65A, 227–243.] in order to determine the geomorphological effectiveness of the floods. The estimates indicate that the minimum power per unit area values for all three floods were sufficiently high, and stream energy was above the threshold of boulder movement (90 W m − 2 ) for several tens of hours. The peak unit stream power values and the total energy expended during each flood were in the range of 290–325 W m − 2 and 65–160 × 10 6 J respectively. The average and peak flood powers were found to be higher or comparable to those estimated for extreme palaeo or modern floods on low-gradient, alluvial rivers.

Impact of Flood Disasters on Taiwan in the Last Quarter Century

The increasing natural disasters, especially floods during the last quarter century, are raising the economic losses in Taiwan. The most severe hazard in Taiwan is flooding induced by typhoons and storms in summer and autumn. By comparing the rivers around the world, the ones in Taiwan have the steepest slopes, the largest discharge per unit drainage area, and the shortest time of concentrations. Rapid urbanization without proper land uses managements usually worsen the flood problems. Consequently, flood hazards mitigation has become the most essential task for Taiwan to deal with. Although the government keeps improving flood defense structures, the flood damage grows continuously. In this article, possible flood mitigation strategies are identified for coping with complex environmental and social decisions with flood risk involved.

Effect of hydraulic radius on long-term drainage capacity of geosynthetics drains

The results of the long-term drainage capacity of four types of prefabricated vertical drains (PVDs) and three types of prefabricated horizontal drains (PHDs), and as well of the transmissivity of a dual function (reinforcement and drainage) geotextile (DFG) are presented. PVD, PHD and DFG are together called geosynthetics drains in this study. A method of calculating the hydraulic radius ( R) (cross-sectional area divided by the perimeter of a drainage channel) of PVDs and PHDs by considering the deformation of the filter (under confinement) is proposed. Based on the limited test data, it is found that the rate of water flow per unit drainage area, q, increases with the hydraulic radius of the drainage channel, thereby q is approximately proportional to R 1.2 and R 1.7 for elapsed times of 1 and 3 months, respectively. Including the results of the DFG ( R-value is close to zero), the drainage capacity ratio ( r), defined as the value at time t divided by the corresponding initial value ( t=0) increases almost linearly with the R-value. It is recommended to employ geosynthetics drains with a larger R-value, i.e. a stiff filter, a strong core, and large and square-shaped drainage channels.

Classification of reaches in the Missouri and lower Yellowstone Rivers based on flow characteristics

AbstractSeveral aspects of flow have been shown to be important determinants of biological community structure and function in streams, yet direct application of this approach to large rivers has been limited. Using a multivariate approach, we grouped flow gauges into hydrologically similar units in the Missouri and lower Yellowstone Rivers and developed a model based on flow variability parameters that could be used to test hypotheses about the role of flow in determining aquatic community structure. This model could also be used for future comparisons as the hydrological regime changes. A suite of hydrological parameters for the recent, post‐impoundment period (1 October 1966–30 September 1996) for each of 15 gauges along the Missouri and lower Yellowstone Rivers were initially used. Preliminary graphical exploration identified five variables for use in further multivariate analyses. Six hydrologically distinct units composed of gauges exhibiting similar flow characteristics were then identified using cluster analysis. Discriminant analyses identified the three most influential variables as flow per unit drainage area, coefficient of variation of mean annual flow, and flow constancy. One surprising result was the relative similarity of flow regimes between the two uppermost and three lowermost gauges, despite large differences in magnitude of flow and separation by roughly 3000 km. Our results synthesize, simplify and interpret the complex changes in flow occurring along the Missouri and lower Yellowstone Rivers, and provide an objective grouping for future tests of how these changes may affect biological communities. Copyright © 2002 John Wiley &amp; Sons, Ltd.

GIS-based statistical and fractal/multifractal analysis of surface stream patterns in the Oak Ridges Moraine

Conventional quantities (stream length, number of streams, bifurcation ratio, density of streams per unit drainage area, elevation difference, slope, and perimeter and area of drainage basins) were extracted for approximately 322 drainage basins from a DEM of the Oak Ridges Moraine area, southern Ontario. These values were mapped and analyzed using statistical and multifractal approaches and GIS to characterize the stream networks and drainage basin systems. Useful measures for characterizing drainage basins in the area included, slope, stream densities, ratio of perimeter and area, and ratio of stream lengths. The distinct patterns identified on the basis of these parameters and on the combined indexes generated by using multivariate statistical analysis were compared with other datasets (geology, bedrock topography, and drift thickness). The associations illustrate the relationship between stream patterns and geological and geomorphological factors. The stream networks in the area as a whole have statistical space-filling properties or are free of geological constraints; however, the variance of individual drainage basins can be characterized by a combined principal component consisting of several quantities. Geological and hydrological interpretations suggest that geological structures, bedrock topography, drift thickness, lithology and slope of drainage basins are the main geological and geomorphological factors influencing the evolution of streams in the area. The results obtained on the basis of stream and drainage basin analysis may provide information for an improved understanding of hydrological characteristics in the area. As an example, the drainage basins along the Niagara Escarpment and on the south side of the Oak Ridges Moraine show distinct patterns with relatively high stream densities and steeper slopes, which may be one of the reasons why these basins have relatively high baseflow compared to basins elsewhere. In addition, high baseflow may have partly induced a relatively high stream density.

IDENTIFICATION OF CHANGES IN STREAMFLOW CHARACTERISTICS1

ABSTRACT: A set of procedures for identifying changes in selected streamflow characteristics at sites having long‐term continuous streamflow records is illustrated by using streamflow data from the Waccamaw River at Freeland, North Carolina for the 55‐year period of 1940–1994. Data were evaluated and compared to streamflow in the adjacent Lumber River Basin to determine if changes in streamflow characteristics in the Waccamaw River were localized and possibly the result of some human activity, or consistent with regional variations. Following 1963, droughts in the Waccamaw Basin seem to have been less severe than in the Lumber Basin, and the annual one‐, seven‐, and 30‐day low flows exhibited a slightly increasing trend in the Waccamaw River. Mean daily flows in the Waccamaw River at the 90 percent exceedance level (low flows) during 1985–194, a relatively dry period, were very nearly equal to flows at the same exceedance level for 1970–1979, which represents the 10‐year period between 1940 and 1994 with the highest flows. Prior to the 1980s, flows per unit drainage area in the Waccamaw Basin were generally less than those in the Lumber Basin, but after 1980, the opposite was true. The ratio of base flow to runoff in the Waccamaw River may have changed relative to that in the Lumber River in the late 1970s. There was greater variability in Waccamaw River streamflow than in Lumber River flow, and flow variability in the Waccamaw River may have increased slightly during 1985–1994.

Runoff Scaling in Large Rivers of the World

Runoff and precipitation scaling with respect to drainage area is analyzed for large river basins of the world, those with mean annual runoff in excess of 10 k3/yr. The usefulness of the specific runoff (runoff per unit drainage area, m/yr) to categorize runoff scaling laws across the complete spectrum of climatic and hydrologic conditions is evaluated. It is found that (1) runoff scales with drainage are in those river basins with specific runoff in excess of 0.15 m/yr (r2 = 0.88); (2) runoff scaling with drainage area shows remarkably high statistical correlation (r2= 0.97) in river basins with specific runoff equal to or larger than 1.0 m/yr; (3) runoff does not Inc.rease with Inc.reasing drainage area in river basins with specific runoff below 0.15 m/yr, where no discernible statistical association was found between runoff and drainage area; and (4) precipitation depth (m/yr) is inversely proportional to drainage area raised to a fractional exponent in river basins with specific runoff in excess of 0.15 m/yr.