Generalized Watershed Loading Function Model Research Articles

Evaluating a parsimonious watershed model versus SWAT to estimate streamflow, soil loss and river contamination in two case studies in Tietê river basin, São Paulo, Brazil

Study regionThe Atibaia and Jacaré-Guaçu watersheds from the Tietê river basin, São Paulo, Brazil. Study focusThis study aims to compare estimates of flow, sediment yield and nutrients loads obtained from two distinct models with different structures and degree of complexity. The Generalized Watershed Loading Function (GWLF) and the Soil Water Assessment Tool (SWAT). We are particularly interested in understanding under which conditions the use of each model is to be recommended, namely when does the addition effort required to run the SWAT model leads to effective better results. As SWAT’s calibration procedure is cumbersome, the advantage of using a more detailed and distributed model fails to materialize when detailed data are not available or when monthly estimates are enough. GWLF model provides useful results with a reduced data gathering and calibration effort. New hydrological insights of the regionThe joint calibration of both models to two watersheds offered a robust set of parameter values for prevalent conditions of Tiête river basin given the existing data set, although not all modelled variables are reproduced accurately. The performance of both models is adequate when estimating streamflow at a monthly time, but decreases when estimating daily flow, sediment yield, and nutrients loads. The poor monitoring of sediments and nutrients concentration hinders the ability to fully calibrate the model’s water quality component.

The Improvement in GWLF Model Simulation Performance in Watershed Hydrology by Changing the Transport Framework

The correct and reasonable delineation of actual hydrologic processes is a footstone for the effective simulation of pollutants in watershed models. In this study, a simple but comprehensive semidistributed modeling approach based on the generalized watershed loading function (GWLF) was modified to enable the accurate simulation of hydrology in watersheds. The frame of the original GWLF model (ORM), with a lumped hydrological parameter, was modified by adding channel routing processes, which made it possible to introduce the concept of subbasins. Then, the revised GWLF model was applied to the Luanhe watershed (30,000 km2) on a monthly bias in comparison with the ORM and the previously revised version. The sensitivity analysis and generalized likelihood uncertainty estimation (GLUE) uncertainty analysis were individually conducted to evaluate these modifications. Eventually, we compared four extreme conditions for the daily streamflow simulations of the three model versions in the Tunxi watershed but without calibration. All of the results indicated that the stability and accuracy of the model and the validity of the parameters were all enhanced and improved by the new revised version of the model, which provided reliable simulation results and indicated that it is a prospective tool to support watershed management.

Comparison of SWAT and GWLF Model Simulation Performance in Humid South and Semi-Arid North of China

Watershed models have gradually been adapted to support both decision and policy making for global environmental pollution control. In this study, two watershed models with different complexity, the Soil and Water Assessment Tool (SWAT) and the Generalized Watershed Loading Function (GWLF), were applied in two catchments in data scarce China, namely the Tunxi and the Hanjiaying basins with contrasting climatic conditions (humid and semi-arid, respectively). The performances of both models were assessed via comparison between simulated and measured monthly streamflow, sediment yield, and total nitrogen. Time series plots as well as four statistical measures (the coefficient of determination (R2), the Nash–Sutcliffe efficiency (NSE), percent bias (PBIAS), and RMSE (root mean square error)—observations standard deviation ratio (RSR)) were used to estimate the performance of both models. The results show that both models were generally able to simulate monthly streamflow, sediment, and total nitrogen loadings during the simulation period. However, SWAT performed better for detailed representations, while GWLF could produce much better average values of the observed data. Thus, GWLF offers a user-friendly prospective alternative watershed model that requires little input data and that is applicable for areas where the input data required for SWAT are not always available. SWAT is more suitable for projects that require high accuracy and offers an advantage when measured data are scarce.

Modeling and Evaluating of Non‐Point Source Pollution in a Semi‐Arid Watershed: Implications for Watershed Management

Watershed models are cost‐effective and powerful tools for evaluating and controlling non‐point source (NPS) pollution. Generalized Watershed Loading Functions (GWLF) model, a relative parsimonious model, was applied to simulate watershed streamflow and nutrient loads in Liu River watershed, northern China. The model results were used to evaluate watershed NPS load, and the implications for NPS pollution mitigation measures were investigated. The temporal‐spatial distribution, the critical source areas (CSAs) at sub‐watershed level, and the best management practices (BMPs) efficiencies at CSAs were investigated by GWLF model. Due to the contrasting hydrological conditions, the NPS loads of wet year and flood season were much more than those of dry year and non‐flood season. Four sub‐watersheds were identified as CSAs, and the results showed that CSAs had high level of load intensities due to the high percentage of agricultural land and residential land. Through evaluating the efficiency and cost of seven BMPs, conservation tillage and vegetative buffers were selected as the measures to implement in the CSAs, and they can reduce 14.2% and 12.5% of total nitrogen and total phosphorus NPS loads in Liu river watershed. These findings can provide valuable information for implementing more effective and reasonable management measures to control NPS pollution in Liu River watershed and indicate the utility of GWLF with modest data requirements for such application.

Estimation of watershed hydrologic processes in arid conditions with a modified watershed model

Watershed models play an important role in modern water resource management, increasingly demanding a robust hydrologic data framework to estimate watershed hydrochemical processes. The Generalized Watershed Loading Function (GWLF), a typical watershed model with modest data requirements, has been applied to watershed-scale hydrochemical estimation worldwide. However, while it generally successfully estimates flows in humid regions, the model suffers from a weakness in hydrologic estimation during low-flow periods, which are projected to continue increasing with global climate change in many places. To address this issue, three algorithms describing functional responses of flows to saturated water storage, the segment function approach, linear function approach, and exponential function approach, have been proposed in this paper, integrated with a previous leakage mechanism for unsaturated water storage used in two earlier GWLF versions, and applied to a case study of Shuai Shui River watershed in China. Comparisons of this version, including new algorithms or algorithm linkages, with the earlier GWLF versions, show that all the new algorithms improve model accuracy in low-flow months; the linear function approach linking the leakage process has the best effect. This work refines the framework of GWLF model to address both humid and arid conditions that can be used as alternatives for future applications. These new functional dynamic responses should also have potential application in other similar watershed models.

Modification of generalized watershed loading functions (GWLF) for daily flow simulation

This study modified the generalized watershed loading functions (GWLF) model, and applied the modified model to simulate the water flow of the catchment area of the Lan-Yang River, by entering the current status of land use, hydrological data, and meteorological data into the model. This modified model took soil resistance into consideration when calculating evapotranspiration and added the parameters of moisture content in the unsaturated zone and hydraulic conductivity to calculate percolation. This model also considered the percolation that directly penetrated into the saturated zone. The modifications enabled the GWLF model to simulate the nature of daily stream flows. The results indicated that the modified GWLF model could improve the calculation of percolation and evapotranspiration in the unsaturated zone for the dry season. Because percolation enhanced groundwater flow, we adjusted the underestimations for low-rainfall periods to simulate the daily stream flow. The results showed that the modified GWLF model was appropriate for simulating not only monthly, but also daily stream flows.

Variations in source apportionments of nutrient load among seasons and hydrological years in a semi-arid watershed: GWLF model results

Quantifying source apportionments of nutrient load and their variations among seasons and hydrological years can provide useful information for watershed nutrient load reduction programs. There are large seasonal and inter-annual variations in nutrient loads and their sources in semi-arid watersheds that have a monsoon climate. The Generalized Watershed Loading Function model was used to simulate monthly nutrient loads from 2004 to 2011 in the Liu River watershed, Northern China. Model results were used to investigate nutrient load contributions from different sources, temporal variations of source apportionments and the differences in the behavior of total nitrogen (TN) and total phosphorus (TP). Examination of source apportionments for different seasons showed that point sources were the main source of TN and TP in the non-flood season, whereas contributions from diffuse sources, such as rural runoff, soil erosion, and urban areas, were much higher in the flood season. Furthermore, results for three typical hydrological years showed that the contribution ratios of nutrient loads from point sources increased as streamflow decreased, while contribution ratios from rural runoff and urban area increased as streamflow increased. Further, there were significant differences between TN and TP sources on different time scales. Our findings suggest that priority actions and management measures should be changed for different time periods and hydrological conditions, and that different strategies should be used to reduce loads of nitrogen and phosphorus effectively.

Comparison of approaches for snowpack estimation in New York City watersheds

AbstractSnow is a substantial component of historical annual precipitation in New York City (NYC) water supply watersheds in the Catskill Mountains, and the pattern of snow accumulation and snowmelt has important implications for the management of the reservoirs and watersheds that are part of the NYC water supply. NYC currently estimates reservoir basin‐scale snowpack throughout the snow season by extrapolation from biweekly snow survey data. These estimates are complemented by the NOAA Snow Data Assimilation System (SNODAS) product. Snowpack models are used in short‐term projections to support reservoir operations and long‐term simulations to evaluate the potential effects of climate change, land use change, and watershed management on the water supply. We tested three snowpack estimation approaches compared with snow survey data: the lumped‐parameter temperature index approach from the Generalized Watershed Loading Function (GWLF) watershed model, a spatially distributed temperature index (SDTI) model, and the spatially distributed NOAA SNODAS product. Of the spatially distributed approaches, SNODAS estimated the spatial variability of snow water equivalent (SWE) among snow survey sites within a basin better than the SDTI model. All three snowpack estimation approaches, including the lumped‐parameter GWLF model, performed well in estimating basin‐wide SWE for most of the basins studied. Copyright © 2013 John Wiley & Sons, Ltd.

Adaptation of Land-Use Demands to the Impact of Climate Change on the Hydrological Processes of an Urbanized Watershed

The adaptation of land-use patterns is an essential aspect of minimizing the inevitable impact of climate change at regional and local scales; for example, adapting watershed land-use patterns to mitigate the impact of climate change on a region’s hydrology. The objective of this study is to simulate and assess a region’s ability to adapt to hydrological changes by modifying land-use patterns in the Wu-Du watershed in northern Taiwan. A hydrological GWLF (Generalized Watershed Loading Functions) model is used to simulate three hydrological components, namely, runoff, groundwater and streamflow, based on various land-use scenarios under six global climate models. The land-use allocations are simulated by the CLUE-s model for the various development scenarios. The simulation results show that runoff and streamflow are strongly related to the precipitation levels predicted by different global climate models for the wet and dry seasons, but groundwater cycles are more related to land-use. The effects of climate change on groundwater and runoff can be mitigated by modifying current land-use patterns; and slowing the rate of urbanization would also reduce the impact of climate change on hydrological components. Thus, land-use adaptation on a local/regional scale provides an alternative way to reduce the impacts of global climate change on local hydrology.

Economic Analysis of Best Management Practices to Reduce Watershed Phosphorus Losses

In phosphorus-limited freshwater systems, small increases in phosphorus (P) concentrations can lead to eutrophication. To reduce P inputs to these systems, various environmental and agricultural agencies provide producers with incentives to implement best management practices (BMPs). In this study, we examine both the water quality and economic consequences of systematically protecting saturated, runoff-generating areas from active agriculture with selected BMPs. We also examine the joint water quality/economic impacts of these BMPs-specifically BMPs focusing on barnyards and buffer areas. Using the Variable Source Loading Function model (a modified Generalized Watershed Loading Function model) and net present value analysis (NPV), the results indicate that converting runoff-prone agricultural land to buffers and installing barnyard BMPs are both highly effective in decreasing dissolved P loss from a single-farm watershed, but are also costly for the producer. On average, including barnyard BMPs decreases the nutrient loading by about 5.5% compared with only implementing buffers. The annualized NPV for installing both buffers on only the wettest areas of the landscape and implementing barnyard BMPs becomes positive only if the BMPs lifetime exceeds 15 yr. The spatial location of the BMPs in relation to runoff producing areas, the time frame over which the BMPs are implemented, and the marginal costs of increasing buffer size were found to be the most critical considerations for water quality and profitability. The framework presented here incorporates estimations of nutrient loading reductions in the economic analysis, and is applicable to farms facing BMP adoption decisions.

A Hybrid Approach to Modeling Sediment for Total Maximum Daily Load Development

Total maximum daily loads (TMDLs) have been developed for sediment in more than 50 watersheds throughout Virginia. The majority of these sediment TMDLs have been developed using the Generalized Watershed Loading Function (GWLF) model and a reference watershed approach. In this approach, the TMDL is set based on area-adjusted, GWLF-modeled sediment loads in a similar unimpaired watershed. While this approach has been used extensively, it possesses significant shortcomings. The approach is extremely sensitive to reference watershed selection, and modeled sediment loads are rarely calibrated or referenced to any measured sediment load. To avoid these limitations and accentuate the strengths of the GWLF model, researchers in Virginia developed a hybrid modeling approach for sediment TMDLs that combines GWLF modeling with load duration modeling. This hybrid modeling approach utilizes the strengths of each modeling tool while avoiding some of the limitations. This approach has been used successfully for sediment TMDLs developed in the Rivanna River, South River, and Spout Run, Virginia.

Fluxes of water and nutrients from river runoff to the Mediterranean Sea using GIS and a watershed model

The Mediterranean Sea is an important regional European Union (EU) sea, often used to assess the global change of the environment because of its practically enclosed character. As most of the northern part is bordered by the EU, it is also of interest in the evaluation of the environmental and economic impact of the implementation of the EU Water Framework Directive and related legislation. Within this framework, nutrient loads from the adjacent land surfaces need to be assessed. For this purpose, the geographic information system (GIS)–interfaced hydrologic/water quality model ArcView Generalized Watershed Loading Function Model (AVGWLF) was applied to all coastal‐adjacent catchments of the Mediterranean Sea. Results of this exercise have shown that the modeled average streamflow and nutrient loads fall within the ranges reported in the literature. Therefore, successful application of this model is feasible. However, for improved representation of the actual Mediterranean Sea streamflow and nutrient status, more accurate input data are required, particularly for the Asian and North African regions.

AVGWLF‐Based Estimation of Nonpoint Source Nitrogen Loads Generated Within Long Island Sound Subwatersheds1

Abstract: The Generalized Watershed Loading Functions (GWLF) model and its ArcView interface (AVGWLF) were used to estimate and examine the components of the total nitrogen (TN) nonpoint source (NPS) load generated within New York and Connecticut (CT) watersheds surrounding Long Island Sound (LIS, the Sound). The majority of data used as model inputs were generally available from online sources, and the work involved an overall calibration to streamflow and TN data in accordance with generic guidelines recommended in the GWLF manual. The GWLF model performance for three calibration and two validation watersheds in CT was compared with results of a detailed model, Hydrological Simulation Program in Fortran, developed in a previous study. The results of the application illustrate the usefulness of the relatively simpler, less parameter‐intensive GWLF model in performing exploratory loading analysis in preparation for adaptive nutrient management in the LIS watersheds. The presented methodology is valuable for identification of priority watersheds for NPS pollution reduction and also for planning‐level evaluation of best management practices to achieve the desired reductions. It is estimated that ground‐water base flow may be the largest pathway for NPS TN to the Sound, contributing about 54% of the total NPS TN load, a finding with significant implications for LIS total maximum daily load reduction scenarios. In addition to ground water, septic systems are estimated to contribute about 17% of the total load, with the remaining TN load being mostly runoff from urban (17%), agricultural (5%), and low impact (e.g., forest) areas (6%).

Importance of diffuse pollution control in the Patzcuaro Lake Basin in Mexico

In the catchment area of the Lake Patzcuaro in Central Mexico (933 km2) the apportionments of erosion, sediment, nutrients and pathogen coming from thirteen micro basins were estimated with the purpose of identifying critical areas in which best management practices need to be implemented in order to reduce their contribution to the lake pollution and eutrophication. The ArcView Generalized Watershed Loading Functions model (AV-GWLF) was applied to estimate the loads and sources of nutrients. The main results show that the total annual contribution of nitrogen from point sources were 491 tons and from diffuse pollution 2,065 tons, whereas phosphorus loads where 116 and 236 tons, respectively during a thirty year simulation period. Micro basins with predominant agricultural and animal farm land use (56% of the total area) accounts for a high percentage of nitrogen load 33% and phosphorus 52%. On the other hand, Patzcuaro and Quiroga micro basins which comprise approximately 10% of the total catchment area and are the most populated and visited towns by tourist 686,000 people every year, both contributes with 10.1% of the total nitrogen load and 3.2% of phosphorus. In terms of point sources of nitrogen and phosphorus the last towns contribute with 23.5% and 26.6% respectively. Under this situation the adoption of best management practices are an imperative task since the sedimentation and pollution in the lake has increased dramatically in the last twenty years.

Modelling the impact of recent land‐cover changes on the stream flows in northeastern Puerto Rico

AbstractWe investigated the influence of recent and future land‐cover changes on stream flow of a watershed northeastern Puerto Rico using hydrological modeling and simulation analysis. Monthly and average annual stream flows were compared between an agricultural period (1973–1980) and an urbanized/reforested period (1988–1995) using the revised Generalized Watershed Loading Function model. Our validated results show that a smaller proportion of rainfall became stream flows in the urbanized/forested period compared with the agricultural period, apparently because of reforestation. Sensitivity analysis of the model showed that evapotranspiration, precipitation, and curve number were the most significant factors influencing stream flow. Simulations of projected land‐cover scenarios indicate that annual stream flows would increase by 9·6% in a total urbanization scenario, decrease by 3·6% in a total reforestation scenario, and decrease by 1·1% if both reforestation and urbanization continue at their current rates to 2020. An imposed hurricane event that was similar in scale to the largest recent event on the three land‐cover scenarios would increase the daily stream flow by 62·1%, 68·4% and 67·1% respectively. Owing to the environmental setting of eastern Puerto Rico, where sea breezes caused by temperature differences between land surface and the ocean dominate the local climate, we suggest that managing local land‐cover changes can have important consequences for water management. Copyright © 2007 John Wiley & Sons, Ltd.

MODELING THE HYDROCHEMISTRY OF THE CANNONSVILLE WATERSHED WITH GENERALIZED WATERSHED LOADING FUNCTIONS (GWLF)1

ABSTRACT: A previous modeling study used the Generalized Watershed Loading Functions (GWLF) model to simulate stream‐flow, and nutrient and sediment loads to Cannonsville Reservoir from the West Branch Delaware River (WBDR). We made several model revisions, calibrated key parameters, and tested the original GWLF model and a revised GWLF model using more recent data. Model revisions included: addition of unsaturated leakage between unsaturated and saturated subsurface reservoirs; revised timing of sediment export; inclusion of urban sediments and dissolved nutrients; tracking of particulate nutrients from point sources; and revised timing of septic system loads. The revision of sediment yield timing resulted in significant improvements in monthly sediment and particulate phosphorus predictions as compared to the original model. Addition of unsaturated leakage improved hydrologic predictions during low flow months. The other model changes improve realism without adding significant model complexity or data requirements. Goodness of fit of revised model predictions versus stream measurements, as measured by the Nash‐Sutcliff coefficient of model efficiency, exceeded 0.8 for streamflow‐0.7 for sediment yield and dissolved nitrogen (N) and 0.6 for particulate and dissolved phosphorus (P). The revised GWLF model, with limited calibration, provides reasonable estimates of monthly streamflow, and nutrient and sediment loads in the Cannonsville watershed.

Evaluation of non-point sources pollution impacts by integrated 3S information technologies and GWLF modelling

Assessing the potential of non-point source pollution to assist in the planning of Best Management Practice (BMP) is significant for improving pollution prevention and control in a river basin. In many cases, however, the grid-based modelling analysis is prohibitively laborious and hindered because of insufficient information. This paper presents a new and fast methodology for catchment land-use identification and waste load estimation by properly integrating the skills of remote sensing (RS), geographic information system (GIS), global positioning system (GPS), and the Generalized Watershed Loading Functions (GWLF) model. In this analysis, eight types of land-use patterns in the watershed area of the Kao-Ping River Basin were classified with the aid of SPOT satellite images, Erdas Imagine image processing system, and ArcView GIS system. Hydrologic and geographical features were obtained or derived by the Digital Elevation Model (DEM) and GIS technique simultaneously. The GWLF model was used to estimate the waste loads of non-point sources in terms of the total phosphorus (TP) and total nitrogen (TN). It shows that the variations of TN and TP loadings are closely related to the amount of rainfall over seasons. Final managerial policy can be made with respect to the identified three impact levels of nutrient loadings in the Kao-Ping River Basin, southern Taiwan, which could eventually perform as part of the Total Maximum Daily Load (TMDL) study in this region.

Modeling Water, Sediment and Organic Carbon Discharges in the Hudson-Mohawk Basin: Coupling to Terrestrial Sources

A previous modeling study (Howarth et al. 1991) showed the potential of a simple watershed hydrology model, the Generalized Watershed Loading Function model (GWLF, Haith and Shoemaker 1987) for estimating annual loads of sediment and organic carbon to the Hudson River from various land uses in the upper portion of the basin. We examined the quality and accuracy of model outputs after making two major modifications. First, we used a geographic information system (GIS) and several environmental databases to improve model estimates of several parameters. Second, we evaluated alternative methods for incorporating weather data.We examined seasonal variation of model output as well as annual averages. Annual fluxes increased over those of Howarth et al. (1991) by 10% for sediment and 20% for TOC for the Hudson-Mohawk basin, resulting in closer agreement with measurement-based estimates. The estimated fluxes exhibited a strong seasonal component, with greates sediment load occurring during a few sping events. Finally, model estimates of fluxes associated with forested and agricultural scenarios, characteristic of earlier periods of the region’s history, predicted a doubling of sediment and TOC loading in an agriculturally dominated Hudson basin but a reduction of sediment by 90% and of TOC by 60% in a completely forested basin.