Behavior Of Watersheds Research Articles

An Evaluation of the Contributions of Urbanization and Climatic Change to Runoff Characteristics in the Laurel Creek Watershed, Ontario

The hydrological consequences of urban growth and expansion of impervious surface area between 1950 and 2000 in the Laurel Creek Watershed, Waterloo, Ontario were investigated. Changes in the hydrological regime were assessed using annual summaries of census, climate (temperature and precipitation), land use and runoff data. Population growth has been linear (+1000% over fifty years) and urban (impervious) area expansion has been even greater over the same time period (about 1200%). The runoff ratio increased significantly over time, but other derived hydrological indices and climate variables did not. This research indicates that there are significant challenges in predicting the hydrological consequences of urban expansion in a changing climate using long-term data sets. Lack of evidence of hydrological impacts using analyses such as these may be a consequence of threshold-dominated watershed behaviour. Changes in land cover, precipitation timing and magnitude and water balance dynamics in the future may diverge from historical patterns, and should be considered by land use planners and others responsible for municipal water issues.

A distribution‐free test to detect gradual changes in watershed behavior

This paper presents a distribution‐free statistical test aimed at detecting gradual changes in the hydrological behavior of watersheds. The proposed test uses a rainfall‐runoff model to identify watershed behavior over successive time periods and a resampling approach to quantify the significance of trends. The method can be applied with any model deemed suitable for the studied watershed. To assess test efficiency, we used three different case studies: An afforested agricultural watershed, a burnt‐over forested watershed, and a watershed covered by old‐growth forest. All three watersheds had a long period of rainfall and runoff records (60, 35, and 40 years, respectively), on which stationarity could be tested. The test was shown to adequately detect gradual changes, and it can therefore be useful to identify hydrological trends, wherever rainfall and streamflow time series are available.

Low flow and high flow responses to converting natural grassland into bluegum ( Eucalyptus globulus) in Nilgiris watersheds of South India

A concern has been raised in many parts of the world over the effect of large scale planting of Eucalyptus on hydrological behaviour of small watersheds. Hydrological response of watersheds due to conversion of natural grasslands into bluegum ( Eucalyptus globulus) plantations on low flows and high flows has been presented in this paper. The concept of using low flow index (LFI) as a tool to study and quantify the effects of bluegum plantation on low flow regime has been demonstrated. Conversion of natural grasslands into bluegum plantations has resulted in decreased low flow volume as well as peak flow, which in turn increased the soil moisture losses. These effects were more pronounced during the second rotation (i.e. first coppiced growth) as compared to the first rotation. Significant reduction in low flow as a result of decline in base flow could be predicted with LFI decreasing by 2.0 and 3.75 times, in the first and second rotation, respectively. Moderation in peak discharge rates was also observed as a result of bluegum plantation. Probability plots of peak discharge tend to suggest that the effect of bluegum plantation on peak flows become insignificant for the floods with higher return periods. These results clearly suggest that caution need to be exercised while planning large scale conversion of natural grasslands into bluegum plantations in the catchments of hydro-electric reservoirs in the Nilgiris which adversely affects water availability especially during lean flow period.

Les eaux et les forêts. La forêt : un outil de gestion des eaux ?

Click to increase image sizeClick to decrease image sizeThe role of forest cover on the behavior of watersheds has long been a matter of debate, in France as well as in the rest of the world. This paper presents the main conclusions of a scientific synthesis, prepared on request of GIP ECOFOR. It lists and prioritizes the positive and negative side-effects of forest growth and forest management practices on the water cycle. It also reviews the possibilities for a better integration of forest management and water management guidelines, and makes practical recommendations for further actions on the legislative, technical and research sides.

An hybrid methodology for the modeling and the simulation of natural systems

In this paper, we first present concepts we developed in order to define an hybrid modeling and simulation methodology dedicated to the study of natural systems.These concepts are based on the object-oriented design, artificial neural networks and the geographic information systems. Then, we outline a general framework combining these three concepts.A first application allowing the forecasting of the hydrologic behavior of watersheds is described and some results are presented and commented.

An Hybrid Methodology for the Modeling and the Simulation of Natural Systems

In this paper, we first present concepts we developed in order to define an hybrid modeling and simulation methodology dedicated to the study of natural systems. These concepts are based on the object-oriented design, artificial neural networks and the geographic information systems. Then, we outline a general framework combining these three concepts. A first application allowing the forecasting of the hydrologic behavior of watersheds is described and some results are presented and commented.

Geomorphic impacts of timber harvesting

Timber harvesting influences (a) forest hydrology; (b) fluvial geomorphology; (c) terrain stability; and (d) integrated watershed behavior. Impacts on forest hydrology are well understood and include increased average runoff, total water yield, increased storm runoff and advances in timing of floods. Stream channels and valley floors are impacted differently by fine sediment, coarse sediment and large woody debris transport. Terrain stability is influenced through gully and mass movement processes that are accelerated by timber harvesting. Impacts on integrated watershed behavior are assessed through disturbed sediment budgets and lake sediments.

Assessment of the Geomorphic Impacts of Forestry in British Columbia

Abstract Timber harvesting in British Columbia influences (a) forest hydrology; (b) fluvial geomorphology; (c) terrain stability; and (d) integrated watershed behavior. Impacts on forest hydrology are well understood and include increased average runoff, total water yield, increased storm runoff and advances in timing of floods. Stream channels and valley floors are impacted differently by fine sediment, coarse sediment and large woody debris transport. Terrain stability is influenced through gully and mass movement processes that are accelerated by timber harvesting. Impacts on integrated watershed behavior are assessed through disturbed sediment budgets and lake sediments. The Forest Practices Code (1995) is a significant step towards sustainable management of the land in so far as it attempts to minimize these geomorphic impacts of forest in B. C.

Simulating runoff behavior in an urbanizing watershed

Land-use change in urbanizing watersheds has significant impacts on hydrolic processes and stream quality. Geographic information system (GIS) processing of spatial information is now commonly used to parameterize hydrologic models. We use and evaluate a system developed for the US Environmental Protection Agency (US EPA), coupling Hydrologic Simulation Program — Fortran (HSPF) with a commonly used GIS (ArcView®) to assess the effects of land-use change on watershed behavior. We extend this anlaysis to investigate relationships beetween runoff ratio and baseflow as a function of percent impervious cover and percent soil saturation for upper Gwynns Falls watershed, Baltimore, MD, USA. Hydrologic model output is used to define summary expressions to describe these relationships and condense complex system behavior. The summary expressions for the runoff ratio and baseflow relationships show that in upper Gwynns Falls from pre-urbanized times to 1990: (1) baseflow had declined by as much as 20%; and (2) only small changes in runoff ratio had occurred. The summary expression for the runoff ratio relationship indicates the existence of a threshold percent impervious cover (∼20%), above which the runoff ratio changes more dramatically. By 1990, the percent impervious cover for upper Gwynns Falls (∼18%) has not yet exceeded this threshold and may explain why only small changes in the runoff ratio had occurred.

Self-Heating of Combustible Vapour in Porous Material When the Fibres are Entirely Covered by Fluid

Abstract A mathematical model of the self-heating of (porous) lagging material soaked in combustible fluid is presented which considers the fibres to be completely covered by the fluid and with the ignition taking place due to oxidation of the vapour. Because the fibres are completely covered, the evaporation term in this model is not dependent on the amount of liquid present. This leads to a simpler equation set in the temperature and amount of vapour only (the liquid equation is decoupled). It is found that if the heat transfer between solid and gas is large (such that a lumped energy approach is valid) there can be situations where ignition takes place after an initial temperature decrease. The model ignores diffusive effects and considers both the heat transfer and mass transfer in a lumped approach extending the classical Semenov theory to include extra heat losses due to the evaporative term but with important watershed behaviour due to the fresh supply of reactant. The mass transfer equation descri...

Artificial Neural Network Modeling of the Rainfall‐Runoff Process

An artificial neural network (ANN) is a flexible mathematical structure which is capable of identifying complex nonlinear relationships between input and output data sets. ANN models have been found useful and efficient, particularly in problems for which the characteristics of the processes are difficult to describe using physical equations. This study presents a new procedure (entitled linear least squares simplex, or LLSSIM) for identifying the structure and parameters of three‐layer feed forward ANN models and demonstrates the potential of such models for simulating the nonlinear hydrologic behavior of watersheds. The nonlinear ANN model approach is shown to provide a better representation of the rainfall‐runoff relationship of the medium‐size Leaf River basin near Collins, Mississippi, than the linear ARMAX (autoregressive moving average with exogenous inputs) time series approach or the conceptual SAC‐SMA (Sacramento soil moisture accounting) model. Because the ANN approach presented here does not provide models that have physically realistic components and parameters, it is by no means a substitute for conceptual watershed modeling. However, the ANN approach does provide a viable and effective alternative to the ARMAX time series approach for developing input‐output simulation and forecasting models in situations that do not require modeling of the internal structure of the watershed.

Hydrologic behaviour of a mountainous watershed

A simplified watershed model has been developed to examine and analyze the high rainfall response of a small, steep, and forested watershed in coastal British Columbia. Hourly data for both rainfall and streamflow are used. Rainfall is measured at five points evenly distributed throughout the watershed. The model is found to perform well and indicates that the hydrologic response of the watershed is reasonably linear, except for intense summer rainstorms under dry soil conditions. The linearity and the rapidity of the watershed response is attributed to the response of the subsurface pipeflow. An analysis of a particular case of soil pipe development shows that the pipeflow system can respond linearly and rapidly to the rainfall input. Key words: watershed modelling, hydrologic response, soil piping.

Influence of silvicultural practices on the hydrology of pine flatwoods in Florida

Slash pine (Pinus elliottii Engelm.) flatwoods in diked watersheds were harvested and regenerated with high and low levels of disturbance. One watershed received machine harvesting, slash burning, windrowing, bedding, and machine planting, which are practices causing a high level of disturbance. A second watershed received manual harvesting, slash chopping, bedding, and machine planting, which are practices causing a low level of disturbance. Water regimes of the two watersheds were compared against that of the third, an undisturbed control. Water table levels were higher after harvest because of reduced evapotranspiration (Et) posttreatment. The differences in water table levels due to treatment were more pronounced at deeper soil depths, probably owing to a lower specific yield of the soil matrix with depth. Daily runoff during the first year increased somewhat in proportion to the area clear‐cut in each watershed. However, only the 15‐cm first‐year runoff increase from the high‐disturbance watershed was significant at 150% of predicted runoff. This increase dropped to 65% of predicted runoff 6 years later, suggesting a return to normal about 11 years after treatment. In contrast, an unexpectedly early decrease in runoff from the low‐disturbance watershed was apparent by the last year indicative of anomalous watershed behavior likely due to greater seepage through the perimeter dikes. A severe drought which occurred during the study caused a very slow recovery of the hydrologie regime; it took a full year of normal rainfall to restore runoff patterns. Moreover, the drought demonstrated the importance of pond storage in the attenuation of surface runoff. High‐disturbance site preparation resulted in many windrows oriented toward the drainages, less resistance to surface runoff, and some compaction of normally wet soils. The net effect was less infiltration and more storm flow. First‐year storm flow was increased on the high‐disturbance watershed, but flooding by large storms often overwhelmed this effect. Pine Et estimates were used in the annual water balances to calculate seepage. A seepage value of 3 cm/yr, or 2% of annual rainfall, showed good agreement with previously published information for pine flatwoods.

Alteration of Streamflow Characteristics Following Road Construction in North Central Idaho

Effects of logging access roads on seven streamflow variables were monitored on six forested headwater watersheds in north central Idaho. The streamflow variables were annual maximum streamflow, date of maximum streamflow, annual minimum streamflow, annual water yield, and streamflow equaled or exceeded 5% of the year, 25% of the year, and 75% of the year. The watersheds, ranging in area from 28.3 to 147.7 ha, had less than 5% of their area in roads. Two statistically significant (α = 0.05) changes occurred following road construction: an increase in the 25% exceedance flows in one watershed and a decrease in the 5% exceedance flows in another watershed. No significant changes were detected in other flow parameters on any of the watersheds. The results indicate that the hydrologic behavior of small forested watersheds may be altered when only a small area is disturbed by roads.

Mesoscale Meteorology/Hydrology Experiment?

Scientific progress in the field of surface water hydrology appears currently to be constrained by a lack of comprehensive field data involving the coordinated simultaneous observation of many meteorological and hydrologic variables at mesoscale. Mesoscale meteorological experiments are underactive discussion by (1) a U.S. interagency team and (2) the World Climate Research Program. The hydrologic research community should ensure that its interests are represented in the planning for these unique experiments.Historically, the field of surface water hydrology has grown out of an engineering need to provide adequate water supplies over the long‐term and to provide flood protection in the short term. Early work involved the collection and analysis of station records of precipitation and streamflow, and their use in developing lumped (i.e., one‐dimensional) models of the precipitation‐runoff behavior of watersheds.

Measurement and Mapping of Potential Evapotranspiration in a Small Mountainous Watershed

The potential evapotranspiration ETP can be estimated by using Brochet and Gerbier's formula (1972), which is derived from Penman's equation ETP ≡ mRg + n Ep (mm/day), where m and n are tabulated coefficients depending on season, latitude and shelter type, and where the variables are the global solar radiation Rg and the Piche evaporation under shelter Ep. In the small Ringelbach watershed (36 ha), in the Vosges Mountains (France), maps of daily ETP have been calculated with this formula, by mapping these two variables - maps of daily global radiation have been computed for sunny days from horizontally measured Rg, by taking into account slopes, aspects and orographic masks. - small and cheap Piche shelters, specially designed and calibrated, have been implanted over the whole watershed with Ep measured twice a day. The results obtained for Rg, Ep and thus ETP reveal important differences within the watershed. Their spatial patterns depend on weather type, topographic structure, and soil surface humidity. This mapping procedure, which gives a good estimation of ETP, enables us to better understand the hydrologic behaviour of any mountainous watershed.

A Unified Approach to Watershed Modelling

This paper summarizes the main points of a theoretical study of the general watershed behaviour, on the basis of the known deterministic physics-based approaches for overland flow, underground flow and unsaturated medium phýsics. A parameter z(θ) which describes the soil water movement in the unsaturated zone and accounts for evaporation is introduced. Thus, a differential equation which allows a state-space formulation of the processes in the watershed is obtained, and the solution of the state equation can be given the form of the Volterra Integral series. The obtained results are compared with those of previous studies.

A combined snowmelt and rainfall runoff model

An outline description is given of the University of British Columbia (U.B.C.) watershed and flow models, which are a set of computer programs for the calculation of hydrologic behaviour of watershed and river systems. The U.B.C. watershed model calculates snowmelt and rain runoff from meteorological data for mountainous watersheds. The model can be operated continuously for any number of years without reinitialization. The watershed model can be interfaced with the U.B.C. flow model which routes and combines the flows from a complex network of watersheds through downstream channels, lakes, or reservoirs.A revised temperature index for the calculation of snowmelt is presented and illustrated. In addition to using the mean daily air temperature, use is made of the diurnal temperature range to describe additional radiant energy input and the minimum temperature is used to approximate dewpoint and vapour exchange.The enhanced watershed response resulting from high intensity rainfall is examined and it is shown that this enhanced watershed response can be described by one additional parameter which modifies the normal watershed calibration. This additional parameter changes the normal infiltration behaviour of a particular watershed by a certain percentage, and, is found to be a stable parameter capable of describing a range of high intensity rain events.Application of the watershed and flow models for streamflow forecasting and planning studies are described. An outline is given of operational forecasting for the Fraser River system and of planning studies on the McGregor River. In the study of the McGregor River, streamflows were calculated for a 12 year period from meteorological data. Comparison with observed monthly flows showed a correlation coefficient of 0.96.The computer programs and documentation are available from the authors.

SEISMIC REFRACTION ANALYSIS OF WATERSHED MANTLE RELATED TO SOIL, GEOLOGY AND HYDROLOGY1

ABSTRACT: An extensive hammer seismic refraction survey was carried out in three contiguous watersheds (217, 89, and 190 acres) on a laccolith near Sturgis, South Dakota to test its utility in rugged mountain terrain. Isopachs (lines connecting points of equal mantle thickness), area‐elevation curves (hypsometry), and structure contours were used together with drill cores, petrography, hydrographs, and soil information to interpret the nature and role of porous mantle in the waterflow behavior of the watersheds. Refraction profiles produced only one geologically meaningful seismic contrast within the loccolith. Drill cores indicated a shallow stony profile on a sheeted horizon terminating on isotropic crystalline rock impervious except for tight joints. Means of refraction and core interpretations were not statistically different. Apparent seismic discontinuities deeper within the bedrock lacked geological identity. Storm hydrographs and water yields are better related to soil type differences and porous mantle distribution than to average porous mantle depth. On the other hand, slope of flow‐duration curves correlate with average porous mantle depth. Porous mantle isopachs also indicate that measured flow from each basin is total area flow. Thus, porous mantle isopachs and hypsometry, and soil type delineation are complimentary in our interpretation of watershed behavior.

Role of subsurface flow in generating surface runoff: 1. Base flow contributions to channel flow

The importance of the subsurface response of watersheds has been vastly underrated in most studies of watershed behavior, both in a quantitative sense and in a generic sense. The mechanism of base flow generation and the nature of watershed response in base flow dominant streams are examined with a deterministic mathematical model that couples three‐dimensional, transient, saturated‐unsaturated subsurface flow and one‐dimensional, gradually varied, unsteady channel flow. The channel flow model uses the single step Lax‐Wendroff explicit technique to solve numerically the full shallow water equations. The subsurface flow model uses the line successive overrelaxation technique to solve numerically the Jacob‐Richards diffusion equation. The results of the simulations on a hypothetical basin suggest a wide variability in watershed response under the influence of variations in rainfall properties, antecedent moisture conditions, and saturated and unsaturated subsurface hydrogeologic properties. This evidence for a wide range of watershed response functions leads to the development of a healthy skepticism toward black box rainfall‐runoff correlations, the concept of basin linearity, and the rationality of hydrograph separation.