Water ResourcesQuality Modeling - UNESCO quality modeling using HSPF is generally not as easy as...

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Water Resources/Quality Modeling using Hydrological Simulation Program-Fortran (HSPF) and

Watershed Modeling System (WMS).

Ahmad M. Salah 1

[email protected]

E. James Nelson1 1. Environmental Modeling Research Laboratory (EMRL), 242 CB,Brigham Young

University, Provo, Utah, 84602, USA. Email: Salah: [email protected], Nelson: [email protected]

Abstract

Long term hydrological simulation is of major importance to water resources engineers and

decision makers. The existence of long term model input data does not always guarantee successful and reliable outcome. In this regard, there are some technical concerns facing water resources engineers in m odeling Nile basin watersheds. Some of t hese technical

problems are related to Hydrologic Simulation Program -Fortran (HSPF) and its interface in Watershed Modeling System (WMS). There are certain model-specific guidelines to pursue

in order to attain output that can be used reliably for sustainable development decisions. The main disadvantage of HSPF is that it requires a lot of input parameters. Yet, this disadvantage

might not be as severe if the listed guidelines are followed. This paper intends to illustrate various hurdles and difficulties that typically face water resources engineers in developing

long term hydrological models using HSPF and WMS. Solving these difficulties is considered the main objective of this paper. The HSPF graphical user interface (GUI) in

WMS is used to generate a User Control Input (UCI) file. The paper expands on this process by discussing various guidelines of running HSPF, viewing the generated hydrograph and

finally calibrating the results. As a result, an efficient watershed-independent modeling process is presented, including concern-specific strategies to facilitate and speed up short and long term model development. It is recommended that these certain procedures be conducted to develop HSPF models in WMS. It is also recommended that this process can be used and

extended to apply in short and long term simulations that incorporate water quality. Introduction

Water resources management is mainly aimed at mitigating or preventing the adverse effects of excessive runoff or water shortage. Hydrologic modeling has served as a valuable tool in water resources management for many years. Simulating the hydrologic and water quality

behavior of a watershed of interest is usually used to predict the impacts of proposed land use scenarios and to evaluate management strategies on both short and long term basis. On the

other hand, water resources/quality models have improved considerably over the last decade,

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which on one hand improves the reliability of model output and on the other hand, gives water resources/quality engineers better understanding of real world problems.

As an integral part of the FRIEND NILE project, HSPF is one of the models used by the Rainfall-Runoff component of the project as a hydrologic model than can be used to predict,

once calibrated, both water quantity and quality of Nile River basin sub-catchments effectively on short and long term.

HSPF is a semi-distributed, continuous simulation model that can perform a detailed

simulation of the hydrology (Figure 1) and water quality in a watershed. It is a versatile model that can simulate watersheds that vary greatly in size from parking lots to some major watersheds (Munson 1998). It was developed by HYDROCOMP, Inc. in the late 1960s under

contract for United States Environmental protection Agency (EPA).

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Figure 1: HSPF conceptual hydrologic model. (Source: Johnson et al, 2003)

WMS is GIS-based pre/post processing software that supports many hydrologic/hydraulic and water quality models widely used all over the world by water resources engineers. It provides a user friendly interface for developing necessary input files for these models as

well as provid es some graphics and animation capabilities, if applicable, to view the resultant output from these models (Nelson et. al. 2005).

Using WMS should make HSPF pre/post processing easier. The WMS tutorials (Nelson

2004) give users a clear step-by-step instruction on building User Control Input (UCI) file. However, since all catchments are different, there are some technical issues that might evolve

for some specific watersheds. These technical issues will be addressed in this paper in an effort to resolve some, if not all, of those concerns .

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The objectives of this research effort are to c omprehend uses of HSPF and WMS for water resources/quality modeling projects and to resolve most of the frequent model technical

difficulties in generating the UCI file. First, capabilities and limitations of both HSP F and WMS will be discussed.

Capabilities and Limitations

Models are abstractions of reality and they a ll have some capabilities and limitations.

HSPF Capabilities and Limitations

In HSPF, hydrology is generally easier to simulate; however, more advanced HSPF

applications (Figure 2) have modeled various water quality parameters, pesticides, best management practices (BMPs) and effect of climate and land use change (Munson 1998).

Hydrological modeling

The first step of an HSPF application is discretization of the watershed. The river is divided into a series of reaches, each of which is considered a perfectly mixed tank. Reach length is determined by flow constraints and transport considerations in the river. Each reach must be

large enough to avoid numeric instabilities, yet small enough to prevent excess numeric dispersion. Reach boundaries should also coincide with physical structures in the river, such

as dams, tributaries and lakes.

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Figure 2: Schematic Overview of HSPF. (source: Munson, 1998)

Figure 2 shows a schematic representation of the main processes/data required for the HSPF model. Because it is a continuous simulation model, HSPF is driven by meteorological data measured in or near the watershed. The hydrologic model distributes water throughout the watershed. Any water reaching the river, either via surface or subsurface flow, is routed

downstream using reach-specific stage-discharge relationship input by the user.

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Once an adequate stream flow calibration is achieved, HSPF can simulate water quality. HSPF includes routines to simulate water temperature, suspended solids, nutrients, pesticides,

biological oxygen demand, phytoplankton, pH and dissolved oxygen. In addition to these routines, HSPF allows the user to simulate any water quality constituent by specifying

sources, sinks, chemical properties and transport behavior (Munson 1998).

It must be noted that HSPF works poorly under dry weather conditions, which probably reflects the large contribution of non-storm related flows that are added to the system. It

might also have some difficulties estimating flow during small (<10 mm) storm events. The problem with small storms appears to be spatial heterogeneity in rainfall and the inability to resolve localized storm cells, especially in highly impervious watersheds. It also has limited

capabilities when applied to short (i.e. hourly) time scales. Temporal heterogeneity is probably more important than spatial heterogeneity for short time scale predictions

(Ackerman et. al. 2005). Water quality modeling

Water quality modeling using HSPF is generally not as easy as hydrologic modeling.

However, once a model is set for a specific watershed, and enough water quality data is available, it might be possible to take the model one further step to predict specific water

quality parameters in the watershed.

Calibrating a water quality model requires a great amount of data and preferably on an ongoing basis. Obtaining data of this size is not always an easy and affordable task. This

usually leads to ignoring water quality modeling or at most building a model that yet needs further development. Developing a reliable water quality model in HSPF might seem to be a

rigorous task, but the presence of sufficient data will make it a lot easier (Skahill 2004). WMS Capabilities and Limitations

WMS is a comprehensive graphical modeling environment for all phases of watershed

hydrology and hydraulics (Figure 3). WMS includes powerful tools to automate modeling processes such as automated basin delineation, geometric parameter calculations, GIS overlay computations (CN, rainfall depth, HSPF segments, roughness coefficients, etc.), cross-section

extraction from terrain data. WMS, version 7.1, supports hydrologic modeling with HEC-1 (HEC-HMS), TR-20, TR-55, Rational Method, NFF, MODRAT, and HSPF. Hydraulic

models supported include HEC-RAS, SMPDBK, and CE-QUAL-W2. Two-dimensional integrated hydrology (including channel hydraulics and groundwater interaction) can now be

modeled with GSSHA (EMS-I 2004). Figure 3 shows a conceptual representation of WMS. As we can see, the modeling process starts with pre-processing where WMS is generally used to generate specific models input files, utilizing available data sources. Those input files can then be used to run the model either embedded within WMS or in a stand-alone version. Later, WMS provides some tools for post-processing for some models that enables engineers to visualize outputs. Hydrologic models interface While tools such as WMS provide a mechanism to make portions of the hydrologic and hydraulic modeling process easier, there are no completely autonomous methods available to

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automate it. There are too many variations between data, problem details, and localized conditions to create a single algorithm that can adapt to all situations and fully automate this complicated process. A more reasonable approach is to provide a variety of semi-autonomous methods that can be applied for specific data and problem at hand. This is what typically happens in practice, where the engineer is able to select those modeling tools which provide the best approach to solving each specific problem. Furthermore, it is important for the engineer to use those models they are most familiar with and that have a good track record (i.e. agency acceptance) for solving specific hydrologic and hydraulic modeling problems. Automated tools should provide enough flexibility in data processing methods and model selection to give as much support to the modeling process as possible (Nelson et. al. 2005).

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Figure 3: Conceptual representation of Watershed Modeling System (WMS).

Water quality models interface

While the majority of the models in WMS are used for water quantity calculations, WMS also interfaces to the HSPF and CE-QUAL-W2 models. These models are well-suited to examine aspects of water quality. GIS layers of land use are used to calculate areas of land activity within each sub-watershed. Because multiple land-uses can be modeled, HSPF’s strength is in the estimation of non-point source contaminants in runoff to receiving water bodies (Nelson et. al. 2005). CE-QUAL-W2 is a laterally-averaged hydrodynamic and water quality model that has been applied to many reservoir systems. Newer versions are capable of modeling river systems (sloped bottom elevations) and link multiple water bodies (upstream lake, river, and downstream lake) so that water quality of coupled systems can be better evaluated. Within

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WMS, HSPF and CE-QUAL-W2 models are linked where the non-point source runoff computed by HSPF can be used to define input for the W2 model (Nelson et. al. 2005). Data Requirement

Figure 4 illustrates the workflow involved in every HSPF modeling process using WMS.

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Figure 4: Conceptual Representation of HSPF Interface in WMS.

Figure 4 depicts the major processes in using WMS and HSPF to model a watershed of interest. As seen, there are basically two main raw data needed to start a WMS project directed towards an HSPF modeling process; i.e. topological information and land use data. HSPF-specific data, as discussed later, is also needed to generate the UCI file. The later can be used to run the model in an iterative fashion till the output is reasonable consistent with observed data. Also noticed in Figure 4, there is another file referred to as WDM file. It will be discussed in details in the following sections. Watershed Data Management (WDM) A Watershed Data Management (WDM) file is a binary, direct-access file used to store data in a logical, well-defined structure. The WDM file provides the user with a common data base for many applications, thus eliminating the need to reformat data from one application to another. It may contain meteorological time-series data in a format used by HSPF (Hummel et al, 2001). The direct-access data library is designed to allow efficient storage and retrieval of data needed by hydrologic models, such as HSPF, that continuously simulate water quantity and quality (Flynn et. al. 2002). A WDM file must be already created for the development and running of the model. If this file is not readily available for use, it can be created using WDMUtil (Hummel et. al. 2001).

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The WDM file should contain all the attributes defining the data to be stored in each data set. It should also contain time series data for the corresponding data sets. Once the WDM file is in place and ready for manipulation, WMS can be used for the model pre-processing. Pre-Processing There are few major steps, discussed as follows, in using WMS to generate the User Control Input (UCI) file. Watershed Delineation Delineating a watershed is no longer a cumbersome process; WMS delineates a watershed in a very simple and straight forward manner. Depending on the size of the watershed and the resolution of the underlying topographical information, watershed delineation can take a very short time typically in the order of a minute or few minutes. WMS can delineate a watershed from a Triangulated Irregular Network (TIN) or a Digital Elevation Model (DEM), it can also do a map-based delineation (Nelson 2004). Incorporating Land Use Data As mentioned earlier, HSPF actually subdivides the watershed into discrete land segments and water reaches/reservoirs. These segments can be based on many hydro-topo-geo-structural features. One of the main feature based maps essential in segmenting the watershed is the land use map. Currently, there are three different ways to import land use data into WMS, either as a land use coverage, a land use grid, or a land use shape file. The importing of land use data into a WMS project can be summarized as follows.

• Land use coverage: In the map module, a new coverage of type “Land Use” needs to be created. Then, the land use shape file should be open while the land use coverage is the active coverage. An essential step that needs to be done at the time of importing the land use to the project is to map the land use code (LU Code) to the land use before finishing the import process.

• Land use grid: While the drainage coverage is the active coverage in the map module, the land use grid should be imported to the project.

• Land use shape file: The land use shape file should simply be added to the project in the GIS module.

Segmenting the Watershed At this stage, WMS is ready to start segmenting the watershed based on the imported land use. It only needs an attribute table (

Table 1) that is used to map the land use data to the attributes necessary for modeling.

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Table 1: Example of an LU Code Attribute Table.

LU Code Description Perviousness 11 "RESIDENTIAL" "impervious"

12 "COMMERCIAL AND SERVICES" "impervious"

21 "CROPLAND AND PASTURE" "pervious"

32 "SHRUB & BRUSH RANGELAND" "pervious"

42 "EVERGREEN FOREST LAND" "pervious" 83 "BARE GROUND" "pervious"

Table 1 shows an attribute table that is required by WMS to segment the watershed using the land use data. However, WMS requires a specific format (*.tbl) for that table (Nelson 2004). Defining Segment Activities The “Apply Parameters to Segments” feature in WMS enables users to enter some parameters for one segment and copy those entered parameters to other segments and hence reduce the amount of time for data entry. There are some recommended values for most of the parameters (Nelson 2004). Those values as we will see later on might change as we calibrate the model. The Current version of WMS (Nelson 2004) displays a context sensitive description of each parameter, when there is a mouse activity in the edit field of that parameter, in the status bar. This description has a range of plausible values that can be entered. Moreover, there are some tools, either database-related (USEPA 1999-b) or GIS-related (Al-Abed et. al. 2002), that can use land use and soil data to extract most of the required HSPF parameters. Currently, WMS does not support any of these tools. Fine tuning Once segment activities are defined, modelers are encouraged to start fine tuning their model. One of the most important steps is defining activities for the reach/reservoir portions of the watershed. Modelers can also aggregate and disaggregate segments as needed and define external sources and targets (Nelson 2004). External sources, targets and mass links are used to pass between pairs of operations in the same INGRP or between individual operations and external sources/targets (Bicknell et. al. 2001).

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Reaches Sub-Division One of the most important and time consuming processes in preparing a UCI file is to define an F-Table for each reach. An F-Table is used to specify, in discrete form, a functional relationship between two or more variables. For example, in the RCHRES module, it is assumed that there is a fixed relationship between depth, surface area, volume, and volume-dependent discharge component. An F-Table ( Table 2) is used to document this non-analytic function in numerical form (Bicknell et. al. 2001). Yet, before we go through how to define F-Tables, modelers must decide on how the watershed is going to be subdivided. Basically, there are two guidelines to decide how one should subdivide the streams in the watershed into reaches. Hypothetically, at this stage in modeling, users should plan a field trip to obtain cross sections based on the watershed subdivision. Subdivision guidelines are listed as follows: Sub-basin based: If the watershed has a natural subdivision, i.e. connecting streams, this internal outlet is recommended to separate the two different reaches. Distance based: It is advisable not to have very long reaches. But how long is very long? Unfortunately, there is no simple answer for this question. One can not say with confidence that the more reaches in the basin, the more accurate the results of the model. There is also a tradeoff between the accuracy needed and the limited resources and/or efforts. Modelers can more accurately model output at the expense of additional efforts and resources. One other factor to consider in deciding the reach length is the topography of the watershed being modeled. Watersheds that have a smoother topography, i.e. not varying so much, might produce reliable output with longer reach lengths than watersheds with roughly undulating land surface. Field accessibility to attain cross sectional data is also an important issue. Modelers may have a very long reach just for the simple reason that no one could access the river to obtain cross sectional data along this reach. It is also advisable to have smaller reach lengths downstream than in upstream. Typically, cross sections are planned to cut in the middle of the reach so that it can represent the whole reach with minimal error, yet this might not be achievable in some cases as of accessibility issues. Once the cross sections are collected, they can be easily used to generate an F-Table for each reach. Generating F-Tables Any spreadsheet package can be used to create a separate sheet ( Table 2) for every cross section, which may include plausible Manning’s roughness values, obtained in a format accepted by the “Cross Section Editor” in WMS (Nelson 2004).

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Table 2: Example of a Typical F-Table for a HYDR. Depth Area Volume Outflow 0.0 0.0 0.0 0.0 5.0 10.0 25.0 20.5 20.0 120.0 1000.0 995.0

Table 2 shows an example of a typical F-Table for HYDR section. Usually, every RCHRES will have its own F-Table , however, if RCHRESs are identical they can share the same F-Table. A “Cross Section” coverage in WMS should be created and made the active coverage. A feature arc approximately where one of the cross sections is taken should be created. The “Cross Section Editor” should be used to import the file generated by the spreadsheet package. The WMS channel calculator should be used to identify the cross section, unit, longitudinal slope and depth (i.e. the maximum water depth the cross section could convey). The channel calculator in WMS will compute the rating curves for flow, area of flow and top width based on the identified cross section. It should be noted that modelers should, before creating the rating curves, make sure to select the increment to correspond to the depth step appropriate for their model/cross section. For example, small cross sections should have small depth differences/large increments to depict changes. The generated graphs should then be exported to a spreadsheet package. And the reach length, represented by this cross section, should be obtained from WMS using the measure tool. The obtained reach length should be multiplied by the top width to attain the “area” field in Table 2, for every water depth required for the F-Table . Similarly, the area of flow should be multiplied by the length to obtain the “volume” field. Units should be consistent for the whole model; i.e. meter, hectare, million m3 and m3/sec for metric units and foot, acre, acre-feet and ft3/sec for British units for depth, area, volume and flow respectively. The previously mentioned process has to be repeated for every reach in the model. The created F-Tables should be inserted in the F-Tables block in the UCI file as appropriate (Bicknell et. al. 2001). At last, mass links should be created in WMS, and the UCI file should be saved and ready for running in HSPF. Running an HSPF Model As seen in Error! Reference source not found., there are two ways to run a UCI file. If WinHSPFLT is properly installed in the machine WMS runs on, the UCI file can be run from within WMS. Users might be prompted to locate WinHSPFLT executable file if it is not located where it should be. Alternatively, WinHSPF has to be installed as a stand-alone version, and it could be used to run the UCI file outside of WMS. Model Output Located in the same directory of the UCI/WDM files, the echo file (*.ech) should be examined and searched for warnings and errors. This simplifies the debugging process of a

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UCI file. The UCI file can be altered in a text editor, in WinHSPF or in WMS. However, if the later is chosen, the UCI file must be re-saved before changes take effect. A successful HSPF run usually means an error/warning free echo file. Once a successful run is obtained, WDMUtil can be used to view the results. The successful run should add at least one time series of the simulated flow. This time series is identifiable as the latest time series added to the time series frame, or by the start/end dates specified in the UCI file. It can also be identified by the word “simulated” or “computed” or whatever is specified for the run, as opposed to “observed”. When the overall simulated hydrograph shape is not satisfactory, either by knowing how it should look or by comparing it with an observed data, calibration process could start. Calibration HSPF parameters fall into two types: fixed parameters and process parameters. Fixed parameters represent measurable characteristics that remain constant, or at least assumed to be, throughout a simulation period. Examples of fixed parameters are the area of each segment and cross sections of water bodies entered into the F-Tables. Process parameters represent watershed properties that only become apparent during the movement of water across the watershed surface and through subsurface layers. Examples are amount of precipitation intercepted by vegetation, water ponded on the surface, and water stored in the soil (Al-Abed et. al. 2002). Previous research indicated that lower zone nominal storage (LZSN), lower zone storage (LZS), the air temperature below which evapotranspiration will arbitrarily be reduced below the value obtained from the input time series (PETMAX) and an index to the infiltration capacity of the soil (INFILT) are among the most important parameters that contribute the most to model sensitivity (Al-Abed et. al. 2002). It is hence advisable to pay close attention to those parameters while calibrating an HSPF model. There are actually a couple of packages to help with HSPF calibration and validation process. One of them is called HSPEXP (Lumb et. al. 1994), (USEPA 2000). HSPEXP is an expert system for the calibration of HSPF. It is developed by USGS to calibrate the hydrology section of an HSPF model (USEPA 1999-a). Another public domain package that can be used to assist with hydrologic calibration of HSPF is called PEST (Papadopulos 2004). PEST is a non-linear, model-independent, parameter estimation package. As opposed to HSPEXP, PEST can provide a unique “best” calibration. Obviously, both tools must have observed flow data and an already generated UCI file. Once a hydrologic model is setup and calibrated for a watershed, water quality can be modeled. However, the lack of continuous water quality data might be an obstacle to a successful and robust water quality calibration. Yet, the calibrated hydrologic model will generally serve as a base for any future water quality extension of the model as data permits. Conclusion and recommendations Understanding the watershed and the model in use is essential to produce reliable model outputs. Site specific parameter sensitivity analysis might be necessary for better and consistent model outputs.

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HSPF is a very efficient tool and can be straightforwardly used to model watersheds of interest. Once the hydrologic part of the model is set up and calibrated, it can be used for future predictions of discharges at the outlet of the watershed under investigation. WMS can simplify the application of hydrologic, hydraulic and water quality models by aiding in the pre/post processing phases of the modeling endeavor. Moreover, the use of automatic calibration tools would definitely enhance and speed up HSPF modeling, especially if compared to traditional calibration efforts. Water quality modeling can be easily done to form an integrated water resources model for the same watershed. This is usually done as a second step after the hydrologic model is set up and refined, provided that there is enough water quality data to calibrate and validate the model.

Acknowledgement The primary author is greatly indebted to Dr. E. James Nelson for the continuous support and educational guidance. The author also wishes to acknowledge the support he gets from the Environmental Modeling Research Laboratory (EMRL). UNESCO office in Cairo has also been instrumental in providing the right research environment for the FRIEND-NILE project. Bibliography Cited

Ackerman D., Schiff K.C., Weisberg S.B. (2005), “Evaluating HSPF in an Arid, Urbanized Watershed ”, Journal of the American Water Resources Association, April 2005, Vol. 41, No. 2, P 477-486. American Water Resources Association. Al-Abed N. A., Whiteley H.R. (2002), “Calibration of the Hydrological Simulation Program Fortran (HSPF) Model using Automatic Calibration and Geographical Information Systems”, Hydrological Processes, Vol. 16, P 3169-3188. John Wiley & Sons, ltd.. Bicknell B.R., Imhoff J.C., Kittle J.L., Jobes T.H., Donigian A.S. (2001), “Hydrological Simulation Program-Fortran (HSPF), version 12, User’s Manual”, AQUA TERRA Consultants, Mountain view, California, U.S.A. Environmental Modeling Systems, Inc. [EMS-I] (2004), “Watershed Modeling System, Version 7.1 ” URL: http://www.ems-i.com/WMS/WMS_Overview/wms_overview .html, last updated 2004. Flynn K.M., Hummel P.R., Lumb A.M. (2002), “A Computer Program for Interactive Hydrologic Data Management (ANNIE), version 4.1, User’s Manual”, U.S. Geological Survey, AQUA TERRA Consultants, Decatur, Georgia, U.S.A.. Hummel P., Kittle J., Gray M. (2001), “WDMUtil, version 2.0, User’s Manual”, AQUA TERRA Consultants, Decatur, Georgia, U.S.A., United States Environmental Protection Agency, 1200 Pennsylvania Ave, NW, Washington, DC, U.S.A. Johnson M.S., Coon W.F. Mehta V.K. Steenhuis T.S. Brooks E.S. Boll J. (2003), “Application of Two Hydrologic Models with Different Runoff Mechanisms to a Hillslope Dominated Watershed in Northeastern US: A comparison of HSPF and SMR”, Journal of Hydrology, Vol. 284, P.57-76, ELSEVIER. Lumb A.M., McCammon R.B., and Kittle J.L. Jr., 1994, “Users Manual for an expert system, (HSPEXP) for calibration of the Hydrologic Simulation Program – Fortran”, U.S. Geological Survey Water-Resources Investigation Report 94-4168, 102 p.

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Munson A. D. (1998), “HSPF modeling of the Charles River Watershed ”, M.Sc. thesis Department of Civil Engineering, Massachusetts Institute of Technology. Nelson E. J. (2004), “Watershed Modeling System, version 7.1, Tutorial”, Department of Civil and Environmental Engineering, Environmental Modeling Research Laboratory, Brigham Young University, Provo, Utah, U.S.A. Nelson E.J., Wallace R.M., Smemoe C., Salah A. (2005), “Automated Hydrologic and Hydraulic Modeling using Watershed Modeling System (WMS)”, International conference of UNESCO FLANDERS FIT FRIEND-NILE Project, Towards a better cooperation, 12-15 November 2005, Sharm El-Sheikh, Egypt, in press. Papadopulos S.S. & Associates, Inc. (2004), “PEST, Parameter Estimation” and “Calibrating a HSPF Model Using TSPROC and PEST”. Web site, URL: http://www.sspa.com/pest/pestsoft.html. Skahill B. (2004), “Use of the Hydrological Simulation Program-FORTRAN (HSPF) Model for Watershed Studies”, System-wide Modeling, Assessment ,and Restoration Technologies (SMART) technical note, ERDC/TN SMART-04-01, September 2004, U.S. Army Corps of Engineers, Vicksburg, Mississippi, U.S.A. U.S. Environmental Protection Agency (USEPA) (1999-a), “Technical Note 5: Using HSPEXP with BASINS/NPSM.”, Office of Water, EPA-823-R-99-010, URL: http://www.epa.gov/waterscience/basins/tecnote5.pdf. U.S. Environmental Protection Agency (USEPA). (1999-b) “HSPFParm: An interactive Database of HSPF Model Parameters, Version 1.0.”, Office of Water, EPA-823-R-99-004, URL: http://www.epa.gov/waterscience/ftp/basins/HSPFParm/hspfparm.pdf. U.S. Environmental Protection Agency (USEPA) (2000). “Technical Note 6: Estimating Hydrology and Hydraulic Parameters for HSPF.”, Office of Water, EPA-823-R-00-012, URL: http://www.epa.gov/waterscience/basins/tecnote6.pdf.

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