Investigating the linkage between streamflow recession rates and channel network contraction in a mesoscale catchment in New York state

The rate of recession (dQ/dt) in a given time interval has long been plotted in log–log space against the concurrent mean discharge (Q_avg). Recent interpretations of these dQ/dt–Q_avg plots have sought to look at curves for individual events instead of the data cloud from all the data points together. These individual recession curves have been observed to have near‐constant slope but to have varying intercepts, features hypothesized to possibly be explained by the nature of the contraction of the active channel network during recession. For a steep, 150‐ha forested catchment in central New York state with an 8.8‐km channel network, changes in the active channel network were mapped between April and November 2013. Streamflow recession occurred in a matter of days, but changes in the active channel network occurred over a matter of weeks. Thus, in this catchment, it does not appear that channel contraction directly controls recession. Additionally, field observations indicate that dry down did not occur in a spatially organized, sequential way such that the upper end of higher‐order streams dried first. Instead, the location of groundwater seeps, in part, controlled the active portion of the channel network. Consistent with the presence of different types of flow contributing zones, the paper presents a conceptual model that consists of multiple parallel reservoirs of varying drainage rate and varying degrees of recharge at different times of the year. This conceptual model is able to reproduce a slope of 2 and a seasonal shift in intercept typical of individual recession curves. Copyright © 2015 John Wiley & Sons, Ltd.     

How well can the subsurface storage–discharge relation be interpreted and predicted using the geometric factors in headwater areas?

Headwater storage–discharge (S–Q) remains one of the least understood processes, and there is renewed interest in the S–Q relation. How well can the S–Q relation be interpreted mechanistically using geometric factors? In this paper, the hillslope storage Boussinesq and hillslope storage kinematic wave equation were adopted to guide the theoretical derivations. Analytical solutions were derived based on the hsKW equation for nine idealized hillslope aquifers, which were subdivided into two groups, i.e. hillslope aquifers with exponential hillslope width function (C1) and hillslope aquifers with Gaussian hillslope width function (C2). We found that analytical expressions of the S–Q relation can be derived for C1 hillslope aquifers. For more compound hillslope aquifers, i.e. C2, no explicit S–Q relation can be obtained. The whole subsurface recession after a rainstorm is simulated by applying the initial saturation condition. We found that the simulated S–Q processes can be characterized by a two‐phase recession, i.e. quick and slow recession. The time (t_b) at the dividing point of the quick and slow recessions depends on the geometric factors, such as the plan and profile curvature. In the quick recession for C1, many of the S–Q curves can be described as linear or quasi‐linear functions, which indicate that linear reservoir models can be applied approximately for recession simulations. However, during the slow recession phase of C1 and during the whole recession of C2, the S–Q relations are highly non‐linear. Finally, we compared the hillslope storage kinematic wave and hillslope storage Boussinesq models for simulating subsurface water recession after a rainstorm event in a real‐world headwater catchment (G5) in China. Through comparison of the recession slope curves, we found that the simulated results of the models employing the Gaussian hillslope width function match the observed hydrograph. The results indicated that appropriate organization of the hillslope geometric factors enhances our ability to make S–Q predictions. Copyright © 2016 John Wiley & Sons, Ltd.     

Nonlinear baseflow recession analysis in watersheds with intermittent streamflow

Abstract

Discharge in most rivers consists mainly of baseflow exfiltrating from shallow groundwater reservoirs, while surface or other direct flows cease soon after rain storms or snowmelt. Analysis of observed baseflow recessions of two rivers in Turkey with intermittent flows and different geographical and climatic characteristics yielded nonlinear storage–outflow relationships of the highly seasonal aquifers. Baseflow separation was carried out using a nonlinear reservoir algorithm. Baseflow seasonality is related to the hydro-climatic conditions influencing groundwater recharge and evapotranspiration of groundwater. As intermittent streams generally have zero flows in the dry season, calibration of recession parameters is in many cases a complicated task.

Citation Aksoy, H. & Wittenberg, H. (2011) Nonlinear baseflow recession analysis in watersheds with intermittent streamflow. Hydrol. Sci. J. 56(2), 226–237.     

Information,artifacts, and noise in dQ/dt − Q recession analysis

The plotting of the time rate of change in discharge dQ/dt versus discharge Q has become a widely used tool for analyzing recession data since Brutseart and Nieber [Water Resour Res 13 (1977) 637–643] proposed the method. Typically the time increment Δt over which the recession slope dQ/dt is approximated is held constant. It is shown here this that leads to upper and lower envelopes in graphs of log(−dQ/dt) versus log(Q) that have been observed in previous studies but are artifacts. The use of constant time increments also limits accurate representation of the recession relationship to the portion of the hydrograph for which the chosen time increment is appropriate. Where dQ/dt varies by orders of magnitude during recession, this may exclude much of the hydrograph from analysis. In response, a new method is proposed in which Δt for each observation in time is properly scaled to the observed drop in discharge ΔQ. It is shown, with examples, how the new method can succeed in exposing the underlying relationship between dQ/dt and Q where the standard method fails.     

Trend analyses with river sediment rating curves

Sediment rating curves, which are fitted relationships between river discharge (Q) and suspended‐sediment concentration (C), are commonly used to assess patterns and trends in river water quality. In many of these studies, it is assumed that rating curves have a power‐law form (i.e. C = aQ^b, where a and b are fitted parameters). Two fundamental questions about the utility of these techniques are assessed in this paper: (i) how well to the parameters, a and b, characterize trends in the data, and (ii) are trends in rating curves diagnostic of changes to river water or sediment discharge? As noted in previous research, the offset parameter, a, is not an independent variable for most rivers but rather strongly dependent on b and Q. Here, it is shown that a is a poor metric for trends in the vertical offset of a rating curve, and a new parameter, â, as determined by the discharge‐normalized power function [C = â (Q/Q_GM)^b], where Q_GM is the geometric mean of the Q‐values sampled, provides a better characterization of trends. However, these techniques must be applied carefully, because curvature in the relationship between log(Q) and log(C), which exists for many rivers, can produce false trends in â and b. Also, it is shown that trends in â and b are not uniquely diagnostic of river water or sediment supply conditions. For example, an increase in â can be caused by an increase in sediment supply, a decrease in water supply or a combination of these conditions. Large changes in water and sediment supplies can occur without any change in the parameters, â and b. Thus, trend analyses using sediment rating curves must include additional assessments of the time‐dependent rates and trends of river water, sediment concentrations and sediment discharge. Published 2014. This article is a U.S. Government work and is in the public domain in the USA. Hydrological Processes published by John Wiley & Sons Ltd.     

Analysis of the nonlinear storage–discharge relation for hillslopes through 2D numerical modelling

Storage–discharge curves are widely used in several hydrological applications concerning flow and solute transport in small catchments. This article analyzes the relation Q(S) (where Q is the discharge and S is the saturated storage in the hillslope), as a function of some simple structural parameters. The relation Q(S) is evaluated through two‐dimensional numerical simulations and makes use of dimensionless quantities. The method lies in between simple analytical approaches, like those based on the Boussinesq formulation, and more complex distributed models. After the numerical solution of the dimensionless Richards equation, simple analytical relations for Q(S) are determined in dimensionless form, as a function of a few relevant physical parameters. It was found that the storage–discharge curve can be well approximated by a power law function Q/(LK_s) = a(S/(L²(? ? θ_r)))^b, where L is the length of the hillslope, K_s the saturated conductivity, ? ? θ_r the effective porosity, and a, b two coefficients which mainly depend on the slope. The results confirm the validity of the widely used power law assumption for Q(S). Similar relations can be obtained by performing a standard recession curve analysis. Although simplified, the results obtained in the present work may serve as a preliminary tool for assessing the storage–discharge relation in hillslopes. Copyright © 2012 John Wiley & Sons, Ltd.     

Field application of a numerical method for the derivation of baseflow recession constant

In an earlier paper (Bako and Hunt, 1988), a method for the derivation of the baseflow recession constant (K) using one-way analysis of variance was presented. This paper presents the results of the field application of this method. The K values obtained by using the numerical equation of Bako and Hunt (1988) were inserted in the exponential recession equation (Barnes, 1939) to generate a series of baseflows. The fit between the model and the historical flows was found to be greater than 99 per cent thus confirming the applicability of the numerical method under field situation. The main advantage of this technique is its amenability for computerized application thus making it relatively faster than any of the existing techniques of fitting the recession equation. For this reason, the subjectivity inherent in most of the existing techniques is eliminated and a measure of procedural consistency can be guaranteed. Consistency is necessary if intercatchment comparison or interpolation of K values is to be meaningful.     

Impact of forest degradation on streamflow regime and runoff response to rainfall in the Garhwal Himalaya,Northwest India

Baseflows have declined for decades in the Lesser Himalaya but the causes are still debated. This paper compares variations in streamflow response over three years for two similar headwater catchments in northwest India with largely undisturbed (Arnigad) and highly degraded (Bansigad) oak forest. Hydrograph analysis suggested no catchment leakage, thereby allowing meaningful comparisons. The mean annual runoff coefficient for Arnigad was 54% (range 44–61%) against 62% (53–69%) at Bansigad. Despite greater total runoff Q_t (by 250 mm year^–1), baseflow at Bansigad ceased by March, but was perennial at Arnigad (making up 90% of Q_t vs. 51% at Bansigad). Arnigad storm flows, Q_s, were modest (8–11% of Q_t) and occurred mostly during monsoons (78–98%), while Q_s at Bansigad was 49% of Q_t and occurred also during post-monsoon seasons. Our results underscore the importance of maintaining soil water retention capacity after forest removal to maintain baseflow levels.

EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR D. Gerten     

Estimation of baseflow nitrate loads by a recursive tracing source algorithm in a rainy agricultural watershed

Baseflow has become an important source of nitrate nonpoint source pollution in many intensive agricultural watersheds. Uncertainties in baseflow nutrient load separation are caused by the effects of hydrometeorological factors on both baseflow recession and baseflow nutrient load recession. These uncertainties have not been addressed well in the existing separating algorithms, which are based on simple baseflow rate–load relationships. In the present study, a recursive tracing source algorithm (RTSA) was developed based on a nonlinear reservoir algorithm and hydrometeorology-corrected baseflow nutrient load recession parameter. This approach was used to reduce the uncertainty of baseflow nitrate load estimation caused by variations in different load recessions under varying climate conditions. RTSA validation in a typical rainy agricultural watershed yielded Nash–Sutcliffe efficiency, root mean square error-observation standard deviation ratio, and R² values of 0.91, 0.30, and 0.91, respectively. The baseflow nitrate–nitrogen (N─NO₃^–) loads from 2003 to 2012 in the Changle River watershed of eastern China were estimated with the RTSA. The results indicated that baseflow nitrate export accounted for 62.0% of the mean total annual N─NO₃^– loads (18.0 kg/ha). The total baseflow N─NO₃^– export was highest in spring (3.6 kg/ha), followed by summer (3.2 kg/ha), winter (2.3 kg/ha), and autumn (2.1 kg/ha). The contribution of baseflow to total nitrate in the stream decreased in the order of winter (69.88%) >spring (66.59%) >autumn (60.36%) >summer (54.04%). The monthly baseflow N─NO₃^– loads and flow-weighted concentrations greatly increased during the research period (Mann–Kendall test, Z_s > 2.56, p < .01). Without proper countermeasures, baseflow nitrate may represent a serious long-term risk for water surfaces in the future.     

Increased flexibility in base flow modelling using a power law transmissivity profile

The hydrological catchment model known as TOPMODEL, in its original and most widely‐used form, assumed that subsurface transmissivity decreases exponentially as subsurface water storage decreases. It has been shown that this leads to recession curves of discharge Q that take the form ? dQ/dt = aQ^b, where a is a constant and b = 2. In order to reproduce a wider range of recession, or base flow, behaviour, a power function for transmissivity was subsequently incorporated into TOPMODEL as an alternative to the exponential function. This was claimed to extend the realistic values of b to range from 1 to 2, inclusive. We show here that the power transmissivity function can also generate values of b > 2 without making unrealistic assumptions (beyond those arguably made in the original TOPMODEL), thus generating recession curves consistent with catchments showing prolonged base flow. Furthermore, the power transmissivity function can generate recession curves that steepen with time (b < 1). Copyright © 2007 John Wiley & Sons, Ltd.     

Estimation of baseflow residence times in watersheds from the runoff hydrograph recession: method and application in the Neversink watershed,Catskill Mountains,New York

A method for estimation of mean baseflow residence time in watersheds from hydrograph runoff recession characteristics was developed. Runoff recession characteristics were computed for the period 1993–96 in the 2 km² Winnisook watershed, Catskill Mountains, southeastern New York, and were used to derive mean values of subsurface hydraulic conductivity and the storage coefficient. These values were then used to estimate the mean baseflow residence time from an expression of the soil contact time, based on watershed soil and topographic characteristics. For comparison, mean baseflow residence times were calculated for the same period of time through the traditional convolution integral approach, which relates rainfall δ¹⁸O to δ¹⁸O values in streamflow. Our computed mean baseflow residence time was 9 months by both methods. These results indicate that baseflow residence time can be calculated accurately using recession analysis, and the method is less expensive than using environmental and/or artificial tracers. Published in 2002 by John Wiley & Sons, Ltd.     

Application of a conceptual method for separating runoff components in daily hydrographs in Kimakia forest catchments,Kenya

This paper highlights the use of a conceptual method for separating runoff components in daily hydrographs, contrary to the traditionally used graphical method of separation. In the conceptual method, the components, viz. surface flow, interflow and baseflow, are regarded as high, medium and low frequency signals and their separation is done using the principle of a recursive digital filter commonly used in signal analysis and processing. It requires estimates of the direct runoff (β_d) and surface runoff (β_s) filter parameters which are obtained by a least‐squares procedure involving baseflow and interflow indices based on graphical and recursive digital filter estimation techniques. The method thus circumvents the subjective element associated with the graphical procedure of hydrograph separation, in which case the eye approximation and/or one's skill at plotting is the prime basis for the whole analysis. The analysis based on three forest catchments in Kimakia, Kenya, East Africa, revealed that β_d=K_b and β_s=K_i , where K_b and K_i are the baseflow and interflow recession constants. Copyright © 1999 John Wiley & Sons, Ltd.     

Shift from transport limited to supply limited sediment concentrations with the progression of monsoon rains in the Upper Blue Nile Basin

Long‐term erosion monitoring data in the Ethiopian highlands are only available from the Soil Conservation Research Program (SCRP) watersheds including the Anjeni watershed. The 113 ha Anjeni watershed was established in 1984 and fanya juu terraces were installed in 1986. Runoff and erosion data are available from three different plot sizes and at the watershed outlet. The objective of this study was to investigate how erosion processes and sediment rating parameters vary with plot size and the progression of the rainy monsoon phase. We analyzed runoff and sediment loss data from 40 plots and the watershed outlet. The dataset included erosion data from 24 newly constructed plots (3 m length) during the rainy monsoon phase of 2012 and 2013, and 16 long‐term plots (with 12, 16, 22, and 24% slopes and 3, 15 and 30 m lengths) and the watershed outlet during the period between 1986 to 1990. Sediment concentration (C) was fitted to runoff (Q) using a power regression equation (C = aQ^b). Sediment concentration and yield increased with increasing plot length from 3 m to 15 m, but sediment yield decreased as plot length increased to 30 m.The coefficients (a and b) were affected by plot size and the progression of the rainy monsoon phase. As plot size increases, the a value increased, while the b value decreased. Greater a values were observed during the beginning of the monsoon phase, while values of b were greater towards the end of the monsoon phase. Overall findings suggest that erosion from cultivated fields is primarily controlled by transport limitations at the beginning of the monsoon phase, while towards the end of the monsoon phase, as surface covers emerge, sediment availability will be reduced, and thus sediment source would be a limitation. Copyright © 2016 John Wiley & Sons, Ltd.     

Statutes and Bye-laws of the International Association of Hydrological Sciences

Abstract

A baseflow recession constant, which can be derived from a simple exponential equation, is used to characterize the behaviour of low flows. Its derivation and quantification is important to the water industry. The use of a computer statistical package that speeds up its derivation has been tried and found to be more effective than the present tedious manual and subjective techniques. It is therefore advocated in this paper.     

A comparison of techniques for hydrograph recession analysis

A comparison between commonly used techniques for hydrograph recession analysis, namely the semi‐logarithmic plot of a single recession segment, the master recession and a relatively new approach based on wavelet transform was carried out. These methods were applied to a number of flood hydrograph events of two catchments in West Java, Indonesia. The results show that all the methods tested produce reasonable and comparable results. However, problems arise in the semi‐logarithmic plot and the master recession, i.e. determining the recession parameter K is not an easy task especially where the plotted data on a semi‐logarithmic plot is not a linear but a curved line. On a curved line, the end of direct flow or starting point of baseflow is not clear and it is quite difficult to identify. Hence, the best line as a basis for computing the recession parameter K becomes uncertain. The wavelet transform approach, however, produces promising results and minimizes a number of problems associated with hydrograph recession analysis. The end of direct flow and the location of the baseflow component are easily determined through the wavelet maps. Copyright © 2004 John Wiley & Sons, Ltd.     

Study of dynamic behaviour of recession curves

Since Brutsaert and Neiber (1977), recession curves are widely used to analyse subsurface systems of river basins by expressing ? dQ/dt as a function of Q, which typically take a power law form: ? dQ/dt = kQ^α, where Q is the discharge at a basin outlet at time t. Traditionally recession flows are modelled by single reservoir models that assume a unique relationship between ? dQ/dt and Q for a basin. However, recent observations indicate that ? dQ/dt ‐ Q relationship of a basin varies greatly across recession events, indicating the limitation of such models. In this study, the dynamic relationship between ? dQ/dt and Q of a basin is investigated through the geomorphological recession flow model which models recession flows by considering the temporal evolution of its active drainage network (the part of the stream network of the basin draining water at time t). Two primary factors responsible for the dynamic relationship are identified: (i) degree of aquifer recharge (ii) spatial variation of rainfall. Degree of aquifer recharge, which is likely to be controlled by (effective) rainfall patterns, influences the power law coefficient, k. It is found that k has correlation with past average streamflow, which confirms the notion that dynamic ? dQ/dt ‐ Q relationship is caused by the degree of aquifer recharge. Spatial variation of rainfall is found to have control on both the exponent, α, and the power law coefficient, k. It is noticed that that even with same α and k, recession curves can be different, possibly due to their different (recession) peak values. This may also happen due to spatial variation of rainfall. Copyright © 2012 John Wiley & Sons, Ltd.     

A wind tunnel investigation of the influences of fetch length on the flux profile of a sand cloud blowing over a gravel surface

Wind tunnel tests were conducted to examine the fetch effect of a gravel surface on the ?ux pro?le of the sand cloud blowing over it using typical dune sand. The results suggest that the ?ux pro?le of blown sand over a gravel surface differs from that over a sandy surface and is characterized by a peak ?ux at a height above the surface while that over a sandy surface decreases exponentially with height. The ?ux pro?le of a sand cloud over a gravel surface can be expressed by a Gaussian peak function: q = a + b exp (?0·5((h ? c)/d)²), where q is the sand transport rate at height h, and a, b, c and d are regression coef?cients. The signi?cance of the coef?cients in the function could be de?ned in accordance with the fetch length of the gravel surface and wind velocity. Coef?cient c represents the peak ?ux height and increases with both wind velocity and fetch length, implying that the peak ?ux height is related to the bounce height of the particles in the blowing sand cloud. Coef?cient d shows a tendency to increase with both wind velocity and fetch length. The sum of a and b, representing the peak ?ux, increases with wind velocity but decreases with fetch length. The average saltation height derived from the cumulative percentage curve shows a tendency to increase with both the fetch length and wind velocity. For any fetch length of a gravel surface the sand transport equation is expressed as Q = C(1 ? U_t/U)(ρ/g)U³, where Q is the sand transport rate, U is the wind velocity, U_t is the threshold velocity measured at the same height as U, g is the gravitational acceleration, ρ is the air density, C is a proportionality coef?cient that decreases with the fetch length of the gravel surface. At a given wind velocity, the sand transport rate over a gravel surface is only 52–68 per cent of that over a sandy surface. The ?ux rate in true creep over a gravel surface increases with wind velocity but decreases with the fetch length, whereas the creep proportion (the ratio of creep ?ux to the sand transport rate) decreases with both the wind velocity and fetch length. Two‐variable (including fetch length and wind velocity) equations were developed to predict the peak ?ux height, average saltation height and transport rate. Copyright © 2004 John Wiley & Sons, Ltd.     

A method to assess annual average renewable groundwater reserves for large regions in Spain

Abstract

This paper proposes a method for assessing the renewable groundwater reserves of large regions for an average year, based on the integration of the recession curves for their basins' springs or the natural baseflow of their rivers. In this method, the hydrodynamic volumes (or renewable reserves), were estimated from the baseflow. It was assumed that the flow was the same as the natural recharge, and the recession coefficients were derived from the hydrogeological parameters and geometric characteristics of the aquifers and adjusted to fit the recession curves at gauging stations. The method was applied to all the aquifers of Spain, which have a total renewable groundwater reserve of 86 118 hm³—four times the mean annual recharge. However, the spatial distribution of these reserves is highly variable; 18.6% of the country's aquifers contain 94.7% of the entire reserve.

Citation Sanz, E. & Recio, B. (2010) A method to assess annual average renewable groundwater reserves for large regions in Spain. Hydrol. Sci. J. 56(1), 99–107.     

Scaling of Canadian low flows

Scaling properties of Canadian low flows, namely annual minimum mean 1-, 5- and 7-day flows, are evaluated across Canada and in its sub-climatic regions. Across the entire country, the log relationship between the kth product moments (PMs, E[Q_i^k]) of low flows and drainage area (A_i) can be represented by: ln(E[Q_i^k])=a_k+b_kln(A_i)and b_k=k, with = 0.86, 0.94 and 0.93 for annual minimum mean 1-, 5- and 7-day flows, respectively. The log linear relationships between the kth probability weighted moments (PWMs, ) and A_i are ln()=c_k+Hln(A_i), in which H is constant and is independent of k. The values of H are 0.87, 0.97, and 0.96 for annual minimum mean 1-, 5- and 7-day flows, respectively, which are almost the same as the values. The coefficients of variation (Cv) are almost independent of drainage area. These results demonstrate that Canadian low flows generally exhibit simple scaling and drainage area alone describes most of the variability in the moments of the low flows. Low flows in each of the sub-climatic regions also obey a simple scaling law. The values of , H and Cv are different in each region, which may stem from physiographical and climatological differences among these regions. The finding lays a basis for applying the index flood method to conduct regional low flow frequency analysis as simple scaling is equivalent to the index flood method.Acknowledgements The authors thank Prof. Thian Yew Gan of University of Alberta, Canada for providing additional pristine data sites for regions 4 and 10. A constructive comments provided by an anonymous reviewer improved the quality of the paper.     

Some aspects of the hydrology of one-day annual minimum low flows of malawian rivers

Five aspects of the hydrology of one-day annual minimum flows Q_IM, have been studied using data from twelve catchments in Malawi. Results indicate that the log-normal distribution can be fitted to all twelve catchments. Four of the rivers studied are intermittent. Application of statistical methods developed in meterology to the dichotomous-transformed data of these catchments revealed that two are ‘flow-dominant’ and the other two are ‘dry-dominant’. Another catchment is entirely dominated by a hydraulic gradient towards the Shire River and Elphant Marsh and so dries up every dry season for considerable periods of time despite the relatively high rainfall in the catchment. Q_IM, t-days after the date of occurrence of Q_IM(May), can be better estimated from simple regression than from an empirically determined recession constant.