Slope Recession Research Articles

Prediction of seaward slope recession in berm breakwaters using M5' machine learning approach

In the design process of berm breakwaters, their front slope recession has an inevitable rule in large number of model tests, and this parameter being studied. This research draws its data from Moghim’s and Shekari’s experiment results. These experiments consist of two different 2D model tests in two wave flumes, in which the berm recession to different sea state and structural parameters have been studied. Irregular waves with a JONSWAP spectrum were used in both test series. A total of 412 test results were used to cover the impact of sea state conditions such as wave height, wave period, storm duration and water depth at the toe of the structure, and structural parameters such as berm elevation from still water level, berm width and stone diameter on berm recession parameters. In this paper, a new set of equations for berm recession is derived using the M5' model tree as a machine learning approach. A comparison is made between the estimations by the new formula and the formulae recently given by other researchers to show the preference of new M5' approach.

SOME CHARACTERISTICS OF STEPPED SLOPES: RESULTS OF KINEMATIC MODELLING

Kinematic model of slope development includes terms concerning slope recession, slope flattening and tectonic movements. Different types of tectonic movements and base level reaction were used. The modelling shows that the preservation of characteristic features of slope profile (memory of relief) depends on the ratio between the different slope processes intensity: the more the contribution of arid-type processes (sheet erosion, deflation) and the less the contribution of humid-type ones (ground's viscous flow) - the longer existence of characteristic details of the slope profile. Intermittent tectonic uprise leads to formation of the horizontal steps sequence (piedmont benchland) of different modes depending of base level conditions and tectonic movements character.

청미천 유역 내 산림사면에서 단면선에 따른 토양수분특성의 공간적 계절적 변동

사면스케일에서 토양수분의 시공간적 분포를 이해하기 위해서는 사면의 단면선(Transect line)에 따른 토양수분 분포 및 변동에 대해 기본적인 해석과 이해가 선행되어야 한다. 이에 단면선에 따라 설계된 여러 토양수분 측정지점으로부터 토양수분 자료에 대해 토양수분 특성인자를 고려하여 토양수분의 특성변동에 대해 이해하고자 하였다. 또한 사면의 위치 및 지형 그리고 토성의 공간적 분포의 토양수분 특성에 대한 영향도 분석하였다. 연구 사면에서 깊은 토양 층에서 평균적 토양수분의 공간적 분포는 지표 층에서의 공간적 분포 경향과는 많이 달랐으며, 사면의 지형 및 위치 그리고 토성의 공간적 분포는 토양수분의 시공간적 분포특징에 큰 영향을 주는 것으로 나타났다. 특히 상부흐름의 기여가 상당한 측정지점에서는 토양수분 변동의 안정화가 진행이 되는 것으로 나타나, 수문학적 경계(hydrologic Threshold)에 대한 추가 연구가 진행되어야 할 것으로 보인다. 또한 토양수분의 불균질한 공간적 경향은 우선적 흐름의 영향과 관련이 있다고 보여진다. Soil moisture is critical for understanding the spatial-temporal variability of hydrologic processes. The distributions of soil moisture have been explored along transect line in hillslope hydrology. In this study, we measured several soil moistures along transect lines during ten-month period at a hillslope located the Cheong-mi catchment. The soil moisture properties were expressed by simple statistical methods (average, standard deviation, and recession slope) and analyzed in terms of soil depths and transects from the seasonal context. Supplementary studies were also performed about the effect of location, topography and soil texture to the soil moisture responses. The spatial distributions of average soil moisture at deep soil layer were distinguished from those at near surface due to the possibility of expected factors such as subsurface lateral flow from upslope, preferential flow and existence of bedrock. The soil moistures in combined line affected from significant contribution of upper transect line were relatively higher(wetter), low variability compared to those in other transect lines and seemed to be under stabilization process. There are confirmed heterogeneity of soil moisture variation related with preferential flow and significant influence of soil texture for soil moisture properties in upslope.

Estimation of pumpage and recharge in alluvial fan topography under multiple irrigation practices

► Estimate small-scale temporal variation in pumpage and recharge on a monthly scale. ► Identify flow amount in a groundwater system under multiple irrigation practices. ► Can estimate illegal pumpage for irrigation or non-irrigation use. ► Recharge sources can be individually identified as rainfall, river, boundary inflow, and irrigation. ► Semi-arid multiple irrigation region shows huge temporal variation in groundwater budget. In this study, we estimate small-scale temporal variations in groundwater pumpage and recharge in alluvial fan topography. We study these variations on a monthly scale using groundwater storage hydrograph and isotope analysis along with area rainfall hydrographs and data of historical irrigation pumpage variations. We consider multiple irrigation practices whose effect was measured only on an annual basis in mostly previous studies. In previous studies, pumpage for non-irrigation or irrigation purposes was regarded as known but illegal pumping was not accounted for. Also, recharge sources include rainfall, rivers, boundary inflow, and groundwater-irrigation, which have not been individually accounted for in previous studies. Pumpage can be estimated from the pumping rate and the number of pumping days. In alluvial fan topography, the actual pumping rate, including that because of illegal wells, can be deduced from the recession slope of the groundwater hydrograph. The annual pumping rate of non-irrigation pumping is assumed to be constant, and can be estimated as the slope of the groundwater hydrograph over consecutive non-rainy days during the non-irrigation periods of the dry season. For cases where there are multiple irrigation practices, the temporal distribution of the irrigation pumping rate can be estimated from the slope of the groundwater hydrograph and also from records provided by the Irrigation Association. In this study, we regard recharge as the difference between inflow and loss. Different types of inflow can be inferred from the storage hydrograph in rainy or non-rainy days, and the loss can then be obtained by using the groundwater balance equation. The isotope mass balance equation is then used to quantify various sources of recharge. In this study, we apply the proposed methodology to the Cho-Shui River alluvial fan, Taiwan. The results show that the proposed methodology can overcome previous restrictions of groundwater hydrograph and isotope analyses to effectively and rationally estimate monthly variations in pumpage and recharge, thus making it possible to research fine flow mechanisms within a multi-layer groundwater system.

Surface geomorphology of Jupiter Family Comets: A geologic process perspective

Recent spacecraft encounters with Jupiter Family Comets have revealed markedly diverse surface morphologies: Wild 2 is dominated by steep-walled and flat-floored depressions, Tempel 1 is relatively smooth and exhibits evidence for flows and layering, while Hartley 2 is bi-lobed with knobby terrain at its ends and a much smoother terrain in its middle. This diversity of surface morphologies has been interpreted as an evolutionary sequence (Belton, M.J.S. [2010]. Icarus 210, 881–897) where Jupiter Family Comets evolve from Wild 2 morphology, then to Tempel 1 morphology, and finally to Hartley 2 morphology. We propose instead that the diversity of surface morphology reflects geologic processing with diverse outcomes. In addition to impact cratering, we consider surface modification driven by the cometary activity which is responsible for gas and dust production. We consider eolian erosion that may be driven by the outflow of cometary vapor, making use of information from wind tunnel experiments and in situ studies of eolian erosion on Mars. We adopt the model of van der Waals cohesion recently proposed by Scheeres et al. (Scheeres, D., Hartzell, C., Sanchez, P., Swift, M. [2010]. Icarus 210, 968–984) and find that the average CO2 vapor outflow flux at Hartley 2 of 0.95×1017cm−2s−1 implies wind speeds sufficient to mobilize particles of 10cm size even close to the icy reservoirs where the vapor is evolved, below the surface. We suggest that particles are mobilized and entrained in flows within sub-surface outflow channels, emerging to be readily lifted into the coma, and fragmenting in the process. Although water production from Hartley 2 is greater, most of it is evolved in the coma from icy particles and does not contribute to eolian erosion of the nucleus. On the other hand, the much lower vapor outflow flux at Tempel 1 of 4×1014cm−2s−1 is insufficient, in the present model, to mobilize particles but is consistent with generating repeated fluidization episodes. The Wild 2 case is intermediate, with average outflow flux 7×1016cm−2s−1 which would be, in our model, sufficient to support eolian erosion. The steep-walled, flat-floor depressions on Wild 2 may have originated as impact features but have been subsequently modified by eolian erosion causing slope recession. We do not have definitive evidence to discriminate between an evolutionary sequence and diverse geologic outcomes, but we suggest future in situ observations at comets that may do so.

Ecosystem processes at the watershed scale: Hydrologic vegetation gradient as an indicator for lateral hydrologic connectivity of headwater catchments

Lateral water flow in catchments can produce important patterns in water and nutrient fluxes and stores and also influences the long‐term spatial development of forest ecosystems. Specifically, patterns of vegetation type and density along hydrologic flow paths can represent a signal of the redistribution of water and nitrogen mediated by lateral hydrologic flow. This study explores the use of emergent vegetation patterns to infer ecohydrologic processes and feedbacks in forested headwater catchments. We suggest a hydrologic gradient of vegetation density as an indicator of lateral connectivity within headwater catchments. We define the hydrologic vegetation gradient (HVG) as the increase of normalized difference vegetation index per unit increase of the topographic wetness index. HVG are estimated in different headwater catchments in the Coweeta Hydrologic Laboratory using summer IKONOS imagery. We use recession slope analysis with gauge data and a distributed ecohydrological model to characterize the patterns of seasonal flow regimes within the catchments. Correlations between HVG, catchment runoff, early recession parameters, and model parameters show the interactive role of vegetation and lateral hydrologic connectivity of systems in addition to climatic and geomorphic controls. This suggests that HVG effectively represents the level of partitioning between localized water use and lateral water flow along hydrologic flow paths, especially during the growing season. It also presents the potential to use simple remotely sensed hydrologic vegetation gradients as an indicator of lateral hydrologic connectivity to extrapolate recession behavior and key model parameters of distributed hydrological models for ungauged headwater catchments.

Effects of irrigation withdrawals on streamflows in a karst environment: lower Flint River Basin, Georgia, USA

AbstractExtensive implementation of centre pivot irrigation systems occurred between 1970 and 1980 in the lower Flint River Basin (FRB) of southwestern Georgia, USA. Groundwater within this karstic system is in direct hydraulic connection with regional streams, many of which are incised through the overburden into underlying limestone. We used long‐term U.S. Geological Survey gaging station data to evaluate multiple flow metrics of two tributaries (Ichawaynochaway Creek and Spring Creek) in the lower FRB to determine the extent of changes in stream behaviour since irrigation practices intensified. We compared pre‐ and post‐irrigation flow duration curves, 1‐, 7‐, and 14‐day minimum flows, and 8‐day (seasonal) and annual baseflow recession slopes, in addition to evaluating regional climate data to determine whether significant differences existed between the pre‐ and post‐irrigation periods. Our results showed significant changes in low‐flow durations in the post‐irrigation record for both gages, including a decrease by an order of magnitude for 98% exceedance flows at Spring Creek. Both gages indicated significant reductions in 1‐, 7‐, and 14‐day low flows. Eight‐day baseflow recession curves (within early summer months) and annual baseflow recession curves became significantly steeper during the post‐irrigation period for Ichawaynochaway Creek. We also found that a significant relationship existed between winter and summer minimum flows in both streams in the pre‐irrigation period which was disrupted in post‐irrigation years. Regional climate data for the study period revealed no significant changes in rainfall totals or frequency of drought; however, there was evidence for a shift in seasonal rainfall patterns. Copyright © 2011 John Wiley & Sons, Ltd.

On the base flow recession at the Panola Mountain Research Watershed, Georgia, United States

There are two types of nonlinearity for recession slope curves: (1) the data cloud of observed ln(–dQ/dt) versus ln(Q) along a straight line where the slope is not equal to 1, and (2) the data cloud of observed ln(–dQ/dt) versus ln(Q) is concave or convex. From the 0.1 ha hillslope, the 10 ha headwater subwatershed, and the 41 ha watershed at the Panola Mountain Research Watershed (PMRW), the observed ln(–dQ/dt) versus ln(Q) changes from convex to concave. This has been explained by the spatial heterogeneity of recession properties and nonlinearity of hillslope hydraulics. Hillslope bedrock leakage and return flow to the perennial riparian zone aquifer are important factors affecting the ln(–dQ/dt) versus ln(Q) relations, and an assessment of this mechanism for explaining the observed base flow recessions at the PMRW is the sole focus of this research. As a result, the lower envelope and the upper envelope should be used to estimate the recession parameters for the 0.1 ha hillslope and the 41 ha watershed, respectively, and the recession at the 10 ha watershed is a mixture of them. Based on the recession analysis, the leakage to the bedrock on the hillslope and return flow to the perennial stream riparian groundwater can be estimated, and the estimation can be verified by other studies.

Recession slope curve analysis under human interferences

To study the base flow recession at the watershed scale, the log-scale plot of − dQ/ dt ∼ Q proposed by Brutsaert and Nieber [10] has been used to estimate the recession parameters, i.e., the slope and interception of the theoretical recession slope curve. The lower envelope or the best fit in some studies is usually used to determine the recession slope curve for natural watersheds. However, human interferences exist in most watersheds around the world. This paper discusses the impact of human interferences, which include groundwater pumping, water diversion and return flow, on the determination of the recession slope curve and the cloud shape of the data points of − dQ/ dt ∼ Q. First, values of − dQ/ dt generated for hypothetical watersheds are analyzed. Then real data for three watersheds in Illinois is analyzed to verify the hypothetical analysis. The placement of the recession slope curve depends on the coexistence and relative amount of the evapotranspiration, groundwater pumping or even water diversion if it exists, and the return flow. When the water consumption rate is small, the recession slope curve can even be located at the upper envelope of the cloud of points representing historical data. These results suggest that the use of the lower envelope as a guideline for estimating recession parameters for watersheds subject to human interferences can result in biased estimates.

Comparative study of climate and human impacts on seasonal baseflow in urban and agricultural watersheds

This study explores the long‐term trends of low flow magnitude and the slopes and shapes of the recession curves during winter and summer seasons under climatic and human factors. Four watersheds in the American Midwest are selected for the analysis, including two urban watersheds (Salt Creek and Des Plaines) and two agricultural watersheds (Embarras and Kankakee). The results show that the long‐term baseflow recession slope trends in all the watersheds are primarily induced by human interferences. In the urban watersheds, the recession slopes decrease over time in both winter and summer due to effluent discharges. In the Kankakee watershed with irrigation, the recession slopes decrease in winter but increase in summer, and the opposite winter and summer trends are caused by the seasonal water use regime of irrigated agriculture. In the Embarras watershed with rainfed agriculture, the recession slopes decrease over time in winter but display no change in summer. Sources of water withdrawal (groundwater versus surface water) also have different impacts on the recession process. This long‐term analysis of recession rates, in conjunction with the changes in low flow magnitude, offers valuable insight on human interferences to hydrologic processes. Beyond the specific case studies, this paper documents how a scientific approach based on existing streamflow observation can be applied to improving our understanding of the impact of human and climatic influences on baseflow and low flow processes.

A new formula for front slope recession of berm breakwaters

The front slope stability of breakwaters with a homogeneous berm was studied in a large number of two dimensional model tests at Aalborg University, Denmark. The results are presented together with a new formula for prediction of the berm recession which is the most important parameter for describing the reshaping. The formula has also been calibrated and validated against model test data from other researchers. The significance of the new design formula is that it predicts berm recession much better than the existing methods, especially in case of more stable structures.

Power law catchment‐scale recessions arising from heterogeneous linear small‐scale dynamics

Power law recession behavior has typically been attributed to the hydraulics of subsurface flows in the landscape (e.g., the Boussinesq equation). Many catchments exhibit enormous heterogeneity in their characteristics, such as the permeability of soils, hillslope length and gradient, and soil mantle thickness. In the paper we demonstrate using a simple linear flow model that the between‐hillslope heterogeneity alone can give rise to observed apparently nonlinear recession slope curves. The degree of nonlinearity (represented by the exponent fitted to the recession slope curve) is shown to increase with the degree of heterogeneity of catchment hydraulic properties. In sufficiently heterogeneous catchments, the recession is also sensitive to the history of recharge events, tending to increase when the past events have built up a storage of water in the ‘slow’ parts of the catchment. The models based on the catchment heterogeneity were fitted to data from the Panola Mountain Research watershed, yielding a good fit, and allowing us to infer how the heterogeneity in catchment properties varies with scale. The range of exponents explained by this theory overlaps with the range explained by the hydraulics of subsurface flow, which raises doubts about our ability to extract catchment hydraulic parameters on the basis of recession curves so long as the heterogeneity is not accounted for. In general the results presented here have enabled us to show how the heterogeneity of landscape characteristics is upscaled and manifested in the apparent nonlinear relationship at the catchment scale.

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.

A lumped‐parameter model of groundwater influx to a mine adit in mountainous terrain

Acidic and metal‐laden drainage from the portals of abandoned mines is a serious environmental problem in wet, mountainous regions where steep hydraulic gradients ensure that fresh recharge waters are continuously flushed through the workings. Hydrogeological characterization of these sites is hampered by their geological complexity and their frequent inaccessibility. This paper presents a material balance model for the groundwater capture zone associated with influx to a mountainside adit. The model can be used to estimate bulk hydraulic properties of the rock surrounding an adit from hydrograph data commonly recorded at its portal. This application is illustrated using data from the Myra Falls mining camp, Vancouver Island, British Columbia. By simultaneously fitting base flow recession slopes for hydrographs of discharge, water table elevation and head in an underground borehole, the model yields plausible and well‐constrained estimates of hydraulic conductivity, porosity, skin factor, and hydraulic gradient.

SCARP RETREAT, SLOPE STABILITY, AND THE EVOLUTION OF PIEDMONT ASSEMBLAGES

ABSTRACT The behaviour of escarpments in various structural and topographic settings determines style and rate of landscape development and of the piedmont landform assemblage. Where there is little or no overland flow and no basal sapping or erosion, slope recession is slow. The upper slope becomes rounded. The bluff is worn backwards and upwards by basal sapping and is eventually eliminated. The faceted slope is converted to a graded sigmoidal form. Detritus accumulates at the base of the slope. Convex upward bedrock slopes evolve. Where the slope is worn back as a result either of basal erosion or overland flow or strong sapping of the bluff, the cliff recedes and its height and inclination are maintained. Reduction of catchment causes retardation of retreat, and scarp-foot weathering assumes greater importance. A characteristic assemblage of forms is developed by the subsequent etching of the scarp-foot zone. Capped piedmont residuals fronting scarps are related to mass movements on the hillslopes above. Dip slopes are fronted by similar assemblages but are locationally stable. Slope behaviour in space and time is relevant both to the question of models of landscape evolution and to the problems posed by very old palaeosurfaces.

Generality of drought flow characteristics within the Arkansas River Basin

Drought flow measurements from 11 river basins, contained within and surrounding the Cooperative Atmosphere‐Surface Exchange Study (CASES) in the Walnut River watershed in Kansas, were subjected to a recession slope analysis. This analysis was based on the Dupuit‐Boussinesq groundwater formulation and made use of the Historical Streamflow Daily Values published by the U.S. Geological Survey. The long‐ and short‐term response features of the riparian aquifers were found to be practically identical to those observed in an earlier study in the Washita River basin in Oklahoma. As both study areas lie within the Osage section of the Central Lowland physiographic province, these findings support the applicability of regionalization and scaling of low‐streamflow‐related basin characteristics within the same geomorphic domain.

Basin‐scale geohydrologic drought flow features of riparian aquifers in the Southern Great Plains

Low‐streamflow hydrographs from 22 subbasins in the U.S. Department of Agriculture‐Agricultural Research Service (USDA‐ARS) Washita River Experimental Watershed complex in central Oklahoma were subjected to recession slope analysis; this method, after that of Brutsaert and Nieber [1977], was derived from a Dupuit‐Boussinesq formulation for the groundwater outflows from the adjoining phreatic aquifers. The longtime aquifer response characteristics were generally found to be close to linear, and the short‐time response characteristics were consistent with Boltzmann similarity. Representative values of the resulting basin‐scale effective groundwater parameters were (35 days)−1 for the low‐flow extinction coefficient (i.e., a storage half‐life of 25 days); 0.021 m2 s−1 for the hydraulic diffusivity, Dh; 0.0035 m2s−½ for the hydraulic desorptivity, Deh; 8 × 10−4 ms−1 for the hydraulic conductivity k; and 0.018 for the drainable porosity (or specific yield), ƒ. The variabilities of Dh, Deh, and k from basin to basin could be better represented by the log‐normal than by the normal distribution; ƒ could be described nearly equally well by both. The storage half‐life is moderately and positively correlated with basin size; in the case of k the correlation is negative but weaker. Any scale dependence of Dh, Deh, and ƒ appears to be negligible.

Characterization of pharmacodynamic recession slopes for direct and indirect response models.

Direct pharmacologic effects are known to recede over time with largely linear slopes (Levy's k.m product, J. Pharm. Sci. 53:342, 1964) and indirect responses have similar behavior. Pharmacodynamic slope properties were examined mathematically for the Hill function with monoexponential drug disposition and simulations were carried out for other pharmacokinetic functions. Both types of pharmacodynamic profiles exhibit a single terminal inflection point (fp) when drug concentrations exceed the EC50 (that concentration causing one-half maximum effect, Emax). For direct effects it was found that Cfp (the drug concentration at fp) = EC50, the determinants of inflection time were identified, and Slopefp = -lambda z gamma Emax/4 where lambda z is the terminal disposition slope and gamma is the Hill coefficient. These characteristics were explored for the four basic indirect response models which also exhibit recession profiles with slight sigmoidity and a single terminal inflection point at higher doses. The drug concentration at inflection Cfp is < or = IC50 or SC50 (drug concentrations causing half-maximal inhibition or stimulation), while the inflection response (Rfp) attains constant values at larger doses. Indirect Response Models I, III, and IV have nearly linear return slopes for a wide range of doses which are governed by the disposition slope lambda z of the drug, loss constant kout of the response, maximum inhibition (Imax) or stimulation (Smax) factors, and a unique fractional constant (0 < G < or = 1). Model II exhibits more complex behavior with recession slopes which are less likely to be parallel for various doses. Most indirect responses are expected to show nearly linear recession slopes which are parallel for moderate to large doses and mainly governed by an identical combination of pharmacokinetic (lambda z), system (kout), and dynamic capacity factors (Imax or Smax).

The egion fault, earthquake-related and long-term deformation, Gulf of Corinth, Greece

On 15 July 1995, the Egion earthquake (Ms = 6.2) occurred in the vicinity of Egion, west-central Greece. Macroseismic observations along the 12 km long E-W trending Egion fault represent short-term or earthquake-related deformation characterized by fairly straight E-W trending surface ruptures with small displacements that mimic the Egion fault geologic offsets and segmentation. Hanging wall converging slip vectors along the Egion fault are clearly related to fault motions at depth. Furthermore, peak accelerations of the built-up area of Egion amount to 0.54 g, that is double the estimated peak acceleration of the Egion coastal area, showing thus close relation between fault trace and attenuation of the ground motion. The Egion fault, with a total geological throw of 200 m and dips to the north at about 55 °, accommodating active tectonic deformation of the Egion area. Its morphotectonic expression reflects long-term deformation in competition with the 1995 earthquake related deformation. The Egion fault is controlling the geomorphic evolution of the Egion area as follows: 1) The fault is defining the evolution of fan-deltas (offshore) and the Meganitas river alluvial plain (onshore). 2) The hanging-wall's greatest subsidence is observed, at the Egion bay, at the central portion of the fault. The Egion bay is located at the central part of the fault showing a strong relationship between the long term slip-rate ratio and the recent coastal morphology. The subsidence gradient or the tectonic activity along the fault is defined by the valley-floor width to valley height index (V f ) of small rivers draining the fault scarp. The Meganitas river course is tilted, when crosses the Egion fault trace, towards the area with the highest subsidence along the fault. 3) Stream incision is more important than slope recession at areas close to the fault trace. All these observations suggest that the Egion fault, which probably hosted the last earthquake, are geomorphically controlling the evolution of a 15 km-long by 5 km-wide zone, fairly similar in dimensions to the surface length of the fault.

Estimating Ground‐Water Recharge from Streamflow Hydrographs for a Small Mountain Watershed in a Temperate Humid Climate, New Hampshire, USA

AbstractHydrographs of stream discharge were analyzed to determine ground‐water recharge for two small basins draining into Mirror Lake, New Hampshire. Two methods of hydrograph analysis developed for determining ground‐water recharge were evaluated, the instantaneous recharge method and the constant recharge method. For the instantaneous recharge method, recharge is assumed to be instantaneous and uniform over the basin. For the constant recharge method, recharge is assumed to be constant and uniform over the basin for a period of weeks to months. Both methods require that a ground‐water recession slope be determined. The recession slope is used directly in the calculation for the instantaneous recharge method, and it is used as a base of reference for fitting a type curve in the constant recharge method. Results of the study indicated that the estimates of ground‐water recharge for both methods agree to within about 10 percent. Two approaches to the instantaneous recharge method, manual and automated, were also evaluated, and the results were statistically similar.The baseflow component of streamflow commonly is assumed to be equivalent to ground‐water recharge; therefore, two methods developed for determining the baseflow component of streamflow, graphical partitioning and digital filtering, were evaluated also. Baseflow values determined by graphical partitioning of hydrographs were about 25 percent less than the ground‐water recharge values. Baseflow values determined by two different approaches to the mathematical digital filtering method were generally less than baseflow determined by graphical partitioning. However, one of the approaches to digital filtering agreed reasonably well with graphical partitioning if an appropriate filter constant was used. The other approach to digital filtering resulted in baseflow values that were much less than the other baseflow values and was therefore deemed inappropriate for use on these small mountain watersheds.