Rate Of Change In Discharge Research Articles

A geometric approach to quantifying the neuromodulatory effects of persistent inward currents on individual motor unit discharge patterns

Objective. All motor commands flow through motoneurons, which entrain control of their innervated muscle fibers, forming a motor unit (MU). Owing to the high fidelity of action potentials within MUs, their discharge profiles detail the organization of ionotropic excitatory/inhibitory as well as metabotropic neuromodulatory commands to motoneurons. Neuromodulatory inputs (e.g. norepinephrine, serotonin) enhance motoneuron excitability and facilitate persistent inward currents (PICs). PICs introduce quantifiable properties in MU discharge profiles by augmenting depolarizing currents upon activation (i.e. PIC amplification) and facilitating discharge at lower levels of excitatory input than required for recruitment (i.e. PIC prolongation). Approach. Here, we introduce a novel geometric approach to estimate neuromodulatory and inhibitory contributions to MU discharge by exploiting discharge non-linearities introduced by PIC amplification during time-varying linear tasks. In specific, we quantify the deviation from linear discharge (‘brace height’) and the rate of change in discharge (i.e. acceleration slope, attenuation slope, angle). We further characterize these metrics on a simulated motoneuron pool with known excitatory, inhibitory, and neuromodulatory inputs and on human MUs (number of MUs; Tibialis Anterior: 1448, Medial Gastrocnemius: 2100, Soleus: 1062, First Dorsal Interosseus: 2296). Main results. In the simulated motor pool, we found brace height and attenuation slope to consistently indicate changes in neuromodulation and the pattern of inhibition (excitation–inhibition coupling), respectively, whereas the paired MU analysis (ΔF) was dependent on both neuromodulation and inhibition pattern. Furthermore, we provide estimates of these metrics in human MUs and show comparable variability in ΔF and brace height measures for MUs matched across multiple trials. Significance. Spanning both datasets, we found brace height quantification to provide an intuitive method for achieving graded estimates of neuromodulatory and inhibitory drive to individual MUs. This complements common techniques and provides an avenue for decoupling changes in the level of neuromodulatory and pattern of inhibitory motor commands.

Streamflow Recession Analysis Using Water Height

AbstractRecession analysis is widely used for characterizing aquifer and basin properties based on the falling limb of the hydrograph. However, recession analysis using streamflow discharge requires a relationship (the rating curve) between simultaneous measurements of water height, h, and discharge, Q, across a wide range of flows, which is expensive to obtain, and changes in time. We leverage the relationship between h and Q (typical power law) to perform recession analysis using h directly, thus permitting identification of transient flow regimes, where only h is available. Recession analysis evaluates the rate of change in discharge, −dQ/dt, as a function of discharge, Q, in a bilogarithmic plot where the slope, b, contains information about aquifer characteristics. While values of b are not conserved when replacing Q with h, we find that the variability in values of b within and between events is captured in recession analysis for both Q and h. For example, when considering individual recessions from a large number of watersheds, a change from a smaller b at high discharge/stage to a larger b at lower discharge/stage occurs in most watersheds and suggests a transition to a more long‐lasting, and less drought‐sensitive, baseflow regime. With the advent of low‐cost reliable pressure loggers, as well as satellites that provide global reporting of river stage, recession analysis using water height expands the number of river systems where recession analysis can be conducted and provides the potential for insights into the variability of watershed drainage characteristics without the need for a discharge record.

Recession analysis revisited: impacts of climate on parameter estimation

Abstract. Recession analysis is a classical method in hydrology to assess watersheds' hydrological properties by means of the receding limb of a hydrograph, frequently expressed as the rate of change in discharge (-dQ/dt) against discharge (Q). This relationship is often assumed to take the form of a power law -dQ/dt=aQb, where a and b are recession parameters. Recent studies have highlighted major differences in the estimation of the recession parameters depending on the method, casting doubt on our ability to properly evaluate and compare hydrological properties across watersheds based on recession analysis of -dQ/dt vs. Q. This study shows that estimation based on collective recessions as an average watershed response is strongly affected by the distributions of event inter-arrival time, magnitudes, and antecedent conditions, implying that the resulting recession parameters do not represent watershed properties as much as they represent the climate. The main outcome from this work highlights that proper evaluation of watershed properties is only ensured by considering independent individual recession events. While average properties can be assessed by considering the average (or median) values of a and b, their variabilities provide critical insight into the sensitivity of a watershed to the initial conditions involved prior to each recharge event.

Geographical patterns of flow-regime alteration by flood-control dams in Japan

Natural variability in water flow is an inherent feature of river ecosystems, but many rivers in the world have been dammed, altering the flow regime and leading to ecosystem degradation. Dam reoperation to maintain environmental flows has been proposed for ecosystem and biodiversity improvement. Reoperation requires an understanding of flow alteration due to dam operations. However, knowledge of natural flow regimes and their degree of alteration remain poor in Japan. The Japanese islands extend from the sub-Arctic to the subtropics with four seasons and thus are considered to show high spatial and temporal variation in flow regime and alterations caused by those variations. We examined the spatial and temporal dependency of flow alteration by flood-control dams in Japan. We confirmed that flood-control dams reduced the rate of change in discharge and peak discharge and that such dams fulfilled their primary role of preventing flood disaster by reducing and delaying flooding. However, other flow characteristics, such as high- and low-flow frequency and duration, were also altered. We demonstrated that the magnitude, frequency, duration, and seasonality of high and low flows in undammed flow regimes differed with latitude and that discharge alteration was spatially and temporally dependent, presumably because dam operation responded to the inherent differences in seasonal flow variability at different latitudes.

Examining individual recession events instead of a data cloud: Using a modified interpretation of dQ/dt–Q streamflow recession in glaciated watersheds to better inform models of low flow

Summary To examine stream recession rates, hydrologists have plotted the rate of change in discharge (dQ/dt) versus the mean discharge (Q). Such plots typically result in a large cloud of data points where the slope of the lower bound of the cloud is often used to infer aquifer hydraulic properties as informed by certain interpretations of the Boussinesq Equation. For seven watersheds in New York State, USA ranging from 100 km2 to 6415 km2, we distinguish data points in the dQ/dt–Q plot belonging to individual recession events instead of looking at the entire data cloud. The recession curve of individual events consistently shifts upward during the summer and late fall (relative to spring and late fall curves) and much of the scatter in the data cloud appears to be due to seasonal variations in recession. We speculate that these seasonal variations in recession rate may be due to variations in watershed evapotranspiration (ET). Additionally, most individual recession events have slopes of approximately two when plotted as log dQ/dt versus log Q. Application of the Boussinesq Equation to watershed-scale recession date predicts slopes shifting from 3 to 3/2 as recession progresses, thus the observed slope of two casts doubt on whether it is appropriate to apply hydraulic aquifer theory to these types of watersheds to infer aquifer properties or predict low flows. As a further validation of the hydrologic information content of individual recession curves, the individual recession curves from time periods with minimal ET (early spring and late fall) were used to establish storage–discharge functions for two of the smaller watersheds. With these storage–discharge functions, a simple hydrologic model could reasonably simulate time series with minimal calibration (Nash–Sutcliffe R2 of 0.71 and 0.67 on log transformed discharge). Overall, this paper suggests that the analysis of individual event recession curves (particularly when compared among watersheds and seasons) can be a valuable tool for gaining insights into hydrological processes at the scale of large watersheds and can justify alternatives to current low flow models.

Modelling the effect of time‐dependent river dune evolution on bed roughness and stage

AbstractThis paper presents an approach to incorporate time‐dependent dune evolution in the determination of bed roughness coefficients applied in hydraulic models. Dune roughness is calculated by using the process‐based dune evolution model of Paarlberg et al. (2009) and the empirical dune roughness predictor of Van Rijn (1984). The approach is illustrated by applying it to a river of simple geometry in the 1‐D hydraulic model SOBEK for two different flood wave shapes. Calculated dune heights clearly show a dependency on rate of change in discharge with time: dunes grow to larger heights for a flood wave with a smaller rate of change. Bed roughness coefficients computed using the new approach can be up to 10% higher than roughness coefficients based on calibration, with the largest differences at low flows. As a result of this larger bed roughness, computed water depths can be up to 15% larger at low flow. The new approach helps to reduce uncertainties in bed roughness coefficients of flow models, especially for river systems with strong variations in discharge with time. Copyright © 2010 John Wiley & Sons, Ltd.

Hydrological impacts of land use/land cover change in a large river basin in central–northern Thailand

AbstractThe purpose of this study is to determine the hydrological impacts of land use/land cover (LULC) change in the Yom watershed in central–northern Thailand over a 15‐year period using an integration of remote sensing, Geographic Information System, statistical methods, and hydrological modelling. The LULC changes showed an expansion of urban areas by 132% (from 210 km2 in 1990 to 488 km2 in 2006). The Yom River's daily discharge long‐term trend significantly increased at most of the measurement stations (p value < 0.05), and the rate of increase in discharge at areas downstream of the rapid urbanisation was significantly greater than that at areas upstream. There were no significant long‐term trends in precipitation characteristics in the basin, except for one station. The rate of change in discharge after changes in LULC showed a systematic increase over a range from 0.0039 to 0.0180 m3 s−1 day−1 over a 15‐year period, with the increase in urbanised area spanning a range from 81 to 149% in two flood‐prone provinces. A rainfall‐runoff model simulated a small increase (∼10%) in peak flows. The coupling of surface observations, remote sensing, and rainfall‐runoff modeling demonstrated the impacts of changes in LULC on peak river discharge, hence flooding behaviour, of a major river in central–northern Thailand. Copyright © 2010 Royal Meteorological Society

Influence of hydrologic attributes on brown trout recruitment in low-latitude range margins

Factors controlling brown trout Salmo trutta recruitment in Mediterranean areas are largely unknown, despite the relevance this may have for fisheries management. The effect of hydrological variability on survival of young brown trout was studied during seven consecutive years in five resident populations from the southern range of the species distribution. Recruit density at the end of summer varied markedly among year-classes and rivers during the study period. Previous work showed that egg density the previous fall did not account for more than 50% of the observed variation in recruitment density. Thus, we expected that climatic patterns, as determinants of discharge and water temperature, would play a role in the control of young trout abundance. We tested this by analyzing the effects of flow variation and predictability on young trout survival during the spawning to emergence and the summer drought periods. Both hatching and emergence times and length of hatching and emergence periods were similar between years within each river but varied considerably among populations, due to differences in water temperature. Interannual variation in flow attributes during spawning to emergence and summer drought affected juvenile survival in all populations, once the effect of endogenous factors was removed. Survival rate was significantly related to the timing, magnitude and duration of extreme water conditions, and to the rate of change in discharge during hatching and emergence times in most rivers. The magnitude and duration of low flows during summer drought appeared to be a critical factor for survival of young trout. Our findings suggest that density-independent factors, i.e., hydrological variability, play a central role in the population dynamics of brown trout in populations from low-latitude range margins. Reported effects of hydrologic attributes on trout survival are likely to be increasingly important if, as predicted, climate change leads to greater extremes and variability of flow regimes.

Reply to comment on ‘C.‐P. Tung, N.‐M. Hong, C.‐H. Chen, and Y.‐C. Tan. 2004. Regional daily baseflow prediction. Hydrological Processes 18: 2147–2164’

AbstractThe recession analysis introduced by Brutsaert and Nieber (1977) has been applied in many studies. Tung et al. (2004) stated that using time‐averaged flows to estimate coefficients for recession equations may result in bias. The reasons include improper time interval to estimate averaged flows and the coefficient a in the recession analysis depends on the initial water table. The latter implies that the coefficient a may be different for different recession events. Rupp and Woods (2008) commented that the bias can be made negligible by using time intervals that are appropriate to the time rate of change in discharge. However, the bias of estimating coefficient a can still be expected if flows from different recession events are used on a log‐log plot. It desires attention even if appropriate time interval is considered. Copyright © 2008 John Wiley & Sons, Ltd.

The influence of lee sediment behind large bed elements on bedload transport rates in supply-limited channels

A coarse surface layer can help to limit bedload transport rates in channels with cobble and gravel beds. In these systems, periodic boulder-sized clasts often exist with small deposits of fine material in the lee of these large bed elements. A combined field and flume study was conducted to investigate the potential impact of lee deposits with distinctly finer sediment-sizes behind boulders on bedload transport rates. Detailed sediment characterizations were performed on surface, subsurface, and lee sediments in two coarse-bedded Connecticut channels. Bedload measurements also were conducted in a series of flows that approached the bankfull level in these two systems to determine transport rates and the size distribution of bedload material. A 6-m long, 0.5-m wide flume was used to model these systems with fine sediment passing over a fixed bed of sediment particles with uniform-sized, large bed elements. Sediment distributions of the lee deposits in the two Connecticut channels indicate that lee deposits may be produced from winnowing of sediments from the surface layer. Lee deposits also exhibit sediment distributions similar to bedload sediment distributions from low to near-bankfull flow in one of the two channels. Bedload sediments in the second channel were finer than lee deposits, presumably from selective entrainment of fines. Flume experiments demonstrate that bedload transport rates are lower for periods of steady flow relative to periods that include either an increase or decrease in discharge. The results show that lee sediments establish a metastable deposit behind each obstruction for a given discharge. Either increases or decreases in discharge disrupt this temporary stability and increase sediment delivery to the main flow. The study suggests that the influence of the rate of change in discharge may be as important as the absolute magnitude of discharge on sediment transport rates at moderate and low discharges in sediment-limited systems with large bed elements.

Comment on ‘C.‐P. Tung, N.‐M. Hong, C.‐H. Chen and Y.‐C. Tan, Regional daily baseflow prediction. Hydrological Processes, 18(2004) 2147–2164’

AbstractThere are both practical and theoretical issues to consider when doing recession analyses of the type introduced by Brutsaert and Nieber (1977). Tung et al. (2004) point out a practical issue, which is the error introduced by using time‐averaged values of discharge. The issue, however, is probably not serious for many practical applications and the error can be made negligible by using time intervals that are appropriate to the time rate of change in discharge. Copyright © 2007 John Wiley & Sons, Ltd.

Discharge and hydraulic interactions in contrasting channel morphologies and their influence on site utilization by spawning Atlantic salmon (Salmo salar)

Six study sites were selected to represent the range of channel morphologies, extending from dynamic pool–riffle to transitional step–pool/plane bed reach types, used by spawning Atlantic salmon (Salmo salar) in a small upland Scottish stream. The hydraulic functioning of reaches over the range of discharges used by spawning fish was characterized, and the influence of hydraulic heterogeneity and rates of change in discharge on the frequency of spawning was assessed. Relationships between discharge and depths and velocities differed significantly between sites; thus, hydraulic responses to changes in discharge were different. The range of discharges used for spawning differed between sites, although optimum discharges were similar. Integration of hydraulic information with microhabitat suitability predicted that spawning conditions should occur at discharges higher than those utilized by fish. There was no evidence that hydraulically heterogeneous sites were used more frequently than homogeneous ones. Rather, data suggest that the frequency of utilization of sites was governed principally by the availability of suitable sediment. Flow stability was important for spawning, with periods of rapidly varying discharge avoided. It is suggested that the rate of change in discharge should be considered more explicitly when assessing environmental flow needs.

Information, artifacts, and noise in d Q/d t − Q recession analysis

The plotting of the time rate of change in discharge d Q/d t 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 Δ t over which the recession slope d Q/d t is approximated is held constant. It is shown here this that leads to upper and lower envelopes in graphs of log(−d Q/d t) 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 d Q/d t 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 Δ t for each observation in time is properly scaled to the observed drop in discharge Δ Q. It is shown, with examples, how the new method can succeed in exposing the underlying relationship between d Q/d t and Q where the standard method fails.

Flow-variation-paced sampling: a method for automatic sampling of streamflow during peak runoff periods

Automated sampling of streamflow water in small watersheds is usually controlled by a flow-paced algorithm (i.e. sampling rate is proportional to discharge, ls−1). However, this sampling method typically takes too few samples during runoff peaks (the critical periods for assessment of suspended solids losses) and too many samples during periods of basal or near-basal discharge (increasing the likelihood that there will be no sample bottles left when an important event occurs). We describe a sampling algorithm designed to overcome these problems: specifically, sampling rate is made proportional to the absolute rate of change in discharge (ls−2). We call this approach “flow-variation-paced (FVP) sampling”, and have developed a simple device for its implementation. This device has proved reliable in field trials. Furthermore, simulated sampling studies using data from a small agricultural watershed in northwest Spain indicate that estimation of suspended solids losses on the basis of FVP sampling is considerably more accurate than estimation on the basis of conventional flow-paced sampling.

Flood behaviour of the Burdekin River, tropical north Queensland, Australia

Abstract Strongly seasonal rainfall in north Queensland, Australia, causes extremely variable fluvial discharge, and tropical cyclones commonly produce high-magnitude, short-duration floods. In the Burdekin River catchment (129 500 km 2 of eastern Queensland), rapid runoff and channel floodplain configuration lead to very fast flood-wave speeds (up to 4.34 m s −1 calculated). The large catchment and varying tropical cyclone paths result in extreme variations in flood history at different sites. Changes in channel conditions (bed elevation, vegetation, bedforms, sediment surface character) in successive events, combined with complex rainfall patterns and highly unsteady flow, make flood estimates extremely difficult. Because of the short duration of flow events and very rapid rate of change in discharge during individual events, sediment transport rate, bedforms, and bed elevation change continuously. For most of the year the channel is occupied by an underfit stream, but this small perennial stream does not significantly rework the deposits or change channel form before the next major discharge event. Consequently, there is little channel form recovery between major discharge events. Successive events have very variable size and consequently the bedforms and channel morphology are normally out of equilibrium with the flow, and record the result of the most recent major events. High-magnitude floods transport coarse sediment onto the floodplain and the short duration of flooding and rapid runoff results in relatively low preservation of mud in the channel or overbank environment. The Holocene flood deposits include thick, coarse sand and medium sand units and generally thin, fine-grained units.