Development and Use of a Hydrologic and Water-Quality Model of the Delaware Inland Bays Watershed
WRD
PROJECT #: MD149
PROJECT CHIEF: Gutierrez-Magness, Angelica
BEGIN DATE: 01-July-2000
END DATE: 31-December-2002
Customers currently supporting the project:
Delaware
Geological Survey
Delaware Department of Natural Resources and Environmental Control
U.S. Geological Survey
Problem
The Delaware Inland Bays have experienced significant environmental degradation due to human activities over the past several decades. Adverse impacts of human activities include degraded communities of benthic organisms, submerged vegetation, and fish. The impacts appear to be more severe in the northern Inland Bays.
Excessive nutrients and sediment are among the most severe environmental stressors in the Inland Bays. Trace amounts of pesticides and other toxic compounds have also been found. The sources of nutrients, sediment, and other contaminants include point-source discharges from industries and wastewater-treatment plants, runoff and infiltration to ground water from agriculture fields and poultry operations, septic-system effluent, and atmospheric deposition. In addition, the practice of agricultural ditching has further aggravated the environmental conditions in some areas of the Inland Bays watershed.
In order to determine how best to approach restoration of the Inland Bays, it is necessary to understand the relative distribution and contribution of each of the potential sources of nutrients, sediment, and other contaminants. It is also important to understand the hydrology of the Inland Bays watershed in order to effectively restore them. Understanding the complex interrelations and interactions between hydrology and the various water-quality inputs is a prerequisite to restoration.
Objectives
The proposed project will be a cooperative effort involving the Delaware Department of Natural Resources and Environmental Control (Department of Natural Resources and Environmental Control), the Delaware Geological Survey (DGS), and the U.S. Geological Survey (USGS). The objective of this project is to develop a hydrologic and water-quality model of the Delaware Inland Bays watershed that can be used as a water-resources planning and management tool. The water-quality constituents of concern will be suspended sediment and nutrients (nitrogen and phosphorus). A well-documented model, Hydrologic Simulation Program-Fortran (HSPF), will be used by USGS to meet the objective.
The USGS role in this project is to construct, calibrate, and demonstrate the use of the hydrologic and water-quality model. The following tasks are included in the USGS role: (1) Compilation of existing hydrologic, climatological, water-quality, and ancillary data into model data sets; (2) construction and calibration of a hydrologic model; (3) construction and calibration of a water-quality model for suspended sediment, nitrogen, and phosphorus; (4) use of the model to simulate selected scenarios of the allocation of point and nonpoint sources; and (5) presentation of the model results to Department of Natural Resources and Environmental Control and DGS in the form of electronic model files, a written USGS report, and training in use of the model.
Approach
The proposed project will be accomplished through use of the following five five methods:
- 1. Data compilation;
- 2. Hydrologic modeling;
- 3. Water-quality modeling;
- 4. Scenario generation; and
- 5. Delivery of results and final report.
Data Compilation
Numerous data will be needed to calibrate and verify the hydrologic and water-quality model. Many of the necessary data already already exist in computerized form in the data bases and files of the Department of Natural Resources and Environmental Control, DGS, and USGS offices. USGS will be responsible for gathering thsoe data and compiling them in model-ready format, as well as any necessary climatological data such as precipitation, air temperature, solar radiation, wind, and evaporation. USGS will also compile pertinent available streamflow and water-quality data from their files. As approriate, Department of Natural Resources and Environmental Control and DGS will supply USGS with electronic copies of their data holdings, including water-quality data from the six monitored stream stations. Department of Natural Resources and Environmental Control's contributions will include point-source data. All input data for the HSPF model will be converted to the appropriate format for the most efficient use in the model.
Hydrologic Modeling
This phase of the project will be aimed at calibrating the modeled hydrologic response of the Inland Bays watershed to measured streamflow at USGS stream-gaging stations. Calibration will be done for the six watersheds where data collection was conducted during 1999-2000. For the five stations that were newly established for this study, the entire new period of record will be used for calibration. For the station at the Millsboro Pond outlet, where a longer period of record is available, at least 1 year of the most recent data will be reserved for verification of the hydrologic model.
Water-Quality Modeling
Water-quality modeling will include simulation of concentrations and loads of suspended sediment, nitrogen, and phosphorus. Suspended sediment will be the first water-quality parameter modeled, because the sediment results will be needed for modeling of phosphorus. Suspended-sediment data that were collected at the six stations in 1999-2000 will be used to calibrate the HSPF model.
Nitrogen concentrations and loads will be modeled following calibration for suspended sediment. Department of Natural Resources and Environmental Control will supply or facilitate obtaining of data on fertilizer-application rates and timing, and other sources of nitrogen, such as point sources, septic systems, disposal of poultry wasters, and atmospheric deposition. Measured nitrogen concentrations at the six stream-gaging stations will be used to calibrate the HSPF model.
Phosphorus concentrations and loads will be modeled following calibration for suspended sediment and nitrogen. Phosphorus is transported mainly with sediment, so completion of the phosphorus component of the model cannot be accomplished prior to development of the sediment component. Department of Natural Resources and Environmental Control will supply or facilitate obtaining of data on fertilizer-application rates and timing of other sources of phosphorus, including point sources, septic systems, and disposal of poultry wates. Measured phosphorus concentrations at the six stream-gaging stations will be used to calibrate the HSPF model.
Because only about 1 year of water-quality data collection was conducted at the six stations for this study, verification of HSPF for water-quality simulations will not be possible if all data are used for model calibration. A potential approach for verifying the model for water quality is to reserve the data from one of the six monitored watersheds for verification. In that case, no calibration would be done for the watershed and model parameters would be based on the modeling of the other five watersheds.
Scenario Generation
Following model calibration and verification, a scenario generator, GENSCN, will be added to the HSPF model to meet the specific needs of Department of Natural Resources and Environmental Control and DGS and other agencies involved in the management of the Delaware Inland Bays watershed. Desired scenarios of various allocations of sediment and nutrient loads will be provided to USGS by Department of Natural Resources and Environmental Control and DGS by December 31, 2001, for simulation in the calibrated model. During the scenario-generation stage, the USGS will work closely with Department of Natural Resources and Environmental Control and DGS staff, as appropriate, to train them in the application of the model.
Delivery of Results and Final Report
USGS will submit semi-annual progress reports along with billings. The progress reports will describe accomplishments for the past six months and plans for the next six months. One year into the project, USGS will submit a report-planning package to Department of Natural Resources and Environmental Control and DGS for review and comment. The report-planning package will include a topical outline for the final report, as well as a Purpose and Scope section and lists of proposed illustrations and tables. During the Scenario Generation phase of the project, USGS will provide training to appropriate Department of Natural Resources and Environmental Control and DGS staff in the operation of the model.
USGS will document the application of the HSPF model to the Delaware Inland Bays watershed in a report in the USGS Water-Resources Investigations Report. The report will include all conventions used in the modeling, values for hydrologic and water-quality variables, and measures of calibration accuracy, as well as electronic compilations of all data used in the model and the model itself. The draft report will be submitted to Department of Natural Resources and Environmental Control and DGS for their technical comments by June 30, 2002, and the final printed report will be delivered by December 31, 2002, at which time the final billing for the project will be made.
