CONTENTS Abstract ..................................................................................................................................................................................1 Introduction ............................................................................................................................................................................2 Purpose and scope .........................................................................................................................................................4 Previous investigations ..................................................................................................................................................4 Acknowledgments .........................................................................................................................................................5 Description of the study area .........................................................................................................................................5 Climate..................................................................................................................................................................5 Hydrology, soils, and topography .........................................................................................................................5 Water use...............................................................................................................................................................6 Model development................................................................................................................................................................6 Overview of the hydrological simulation program - FORTRAN (HSPF).....................................................................6 Model assumptions........................................................................................................................................................8 Watershed segmentation ................................................................................................................................................8 Land use.........................................................................................................................................................................8 Development of nutrient application rates...................................................................................................................11 Animal counts, animal units, and the manure land-use category........................................................................11 Organic fertilizer calculations.............................................................................................................................13 Nutrient requirements and goal yields ................................................................................................................13 Total nutrient applications...................................................................................................................................13 Method of fertilizer application ..........................................................................................................................18 Schedule of organic fertilizer application ...........................................................................................................18 Schedule of mineral fertilizer application...........................................................................................................18 Planting and harvesting dates..............................................................................................................................20 Atmospheric deposition...............................................................................................................................................20 On-site wastewater disposal system information ........................................................................................................20 Point sources................................................................................................................................................................20 Meteorological data .....................................................................................................................................................21 Development of water-quality data base for model calibration...................................................................................22 Model calibration approach..................................................................................................................................................22 Calibration of hydrology .............................................................................................................................................23 Parameter estimation...........................................................................................................................................23 Objective function for parameter estimation ......................................................................................................23 Calibration of total suspended solids and nutrients.....................................................................................................24 Analysis of model calibration and results ............................................................................................................................24 Calibration of hydrology .............................................................................................................................................26 Annual and monthly water balance.....................................................................................................................26 Mean daily streamflow time series .....................................................................................................................28 Calibration of total suspended solids...........................................................................................................................31 Annual edge-of-stream yields .............................................................................................................................31 Hourly concentration time series ........................................................................................................................31 Calibration of nutrients................................................................................................................................................31 Annual edge-of-stream yields .............................................................................................................................34 Hourly concentration time series ........................................................................................................................36 Summary and conclusions....................................................................................................................................................40 References cited ...................................................................................................................................................................40 iii Figures 1a. Hydrogeomorphic regions of the Delmarva Peninsula and location of the Delaware Inland Bays watershed ...........................................................................................................................................................2 1b. Detailed view of the Delaware Inland Bays watershed, Sussex County, Delaware................................................3 2. Soils map for the Inland Bays watershed showing percent organic matter, soil permeability, and a hydrologic characteristics grouping code (STATSGO group number)...............................................................7 3. Hydrological Simulation Program–FORTRAN (HSPF) Inland Bays watershed model segmentation, locations of U.S. Geological Survey stream-gaging stations, hourly and daily precipitation stations, and the major nutrient point source near Georgetown, Delaware...........................9 4. Generalized land-use map of the Delaware Inland Bays watershed .....................................................................12 5. Crop hectare allocations for the model..................................................................................................................13 6. Grouping of model segments with identical parameter values, indicating the calibration model segment source for those values ........................................................................................................................25 7. Monthly simulated and observed streamflow for the six calibrated basins during 1999......................................27 8. Simulated and observed daily flows, with daily precipitation intensity, for the six calibrated basins during 1999.............................................................................................................................................29 9. Simulated daily edge-of-stream streamflow components and total streamflow simulated at the end of the reach for the five single-segment calibrated basins during 1999 ...............................................30 10. Simulated total suspended solids yield during water year 1999 by model segment ............................................32 11. Simulated hourly total