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HSPF Modifications for South Florida Hydrology |
Client: South Florida Water Management District, West Palm Beach, FL
Since 1995, AQUA TERRA Consultants has been providing watershed model development and application assistance to the South Florida Water Management District. The scope of work for this ongoing project includes development, testing and documentation of new hydrologic capabilities for HSPF; linkage to a fully dynamic routing model (FEQ); and implementation/calibration of the enhanced/linked modeling system on the St. Lucie Estuary Watershed (SLEW). HSPF has been modified to enable representation of the region-specific hydrologic features prevalent in South Florida. The goal of the model modifications was to develop a viable simulation package that represents the South Florida hydrologic conditions and can be used to evaluate the impacts of management options that must be applied to maintain discharge to the St. Lucie estuary within an acceptable range. The modifications provide the capability to handle control structures (i.e., pumping, gates, weirs, culverts, etc.) that are dominant features in the SLEW, and better represent such phenomena as wetlands hydrology, high water table, irrigation practices, and detention/retention ponds. AQUA TERRA's work for the District has resulted in the following tasks:
Task 1: Development of a Linkage Between HSPF and FEQ to Provide a Fully Dynamic Routing Capability
Under Task 1, new capabilities to represent culverts with risers and weirs with bleed-down mechanisms were added to FEQ. FEQ is a software package for fully dynamic hydraulic routing; it is the product of 20 years of development and testing, and is a state-of-the-art, non-proprietary tool endorsed and used by the Water Resources Division of the USGS, and numerous other clients. Dr. Delbert Franz, the developer of FEQ, designed, implemented, tested, and documented the new features. He also presented a five-day training workshop to District personnel, and assisted in designing and documenting a prototype linkage between HSPF and FEQ, using the District's DSS time series data system. This linkage was refined during the implementation of the modeling system on the SLEW.
Tasks 2 and 3 were accomplished together, and were a cooperative effort between AQUA TERRA personnel and Hydrocomp, Inc. Dr. Norman Crawford, the original author and a recognized expert on the existing hydrologic process algorithms in HSPF, designed changes to the algorithms to accommodate high water table conditions and create a wetlands simulation module. The modifications were based on a detailed review of the available literature on South Florida wetlands conditions and a site visit/investigation of the SLEW wetlands by Dr Crawford and other Team Members. Dr. Crawford and the Hydrocomp staff implemented a prototype of the new PERLND hydrologic module, and tested the module using South Florida data. Following review of the associated System Design Document by the District, AQUA TERRA personnel implemented the algorithms (as revised during the review) in HSPF and performed beta testing and sensitivity analyses under conditions representative of the SLEW.
Task 4, application of the linked modeling system on the SLEW, was primarily a cooperative effort between AQUA TERRA and Dr. Franz, and involved the following subtasks
AQUA TERRA had responsibility for simulation plan and database development, and HSPF model development and calibration, while Dr. Franz took the lead in developing and calibrating the major canal models using FEQ. As defined in the completed simulation plan, FEQ was applied to the three major canal subbasins in the SLEW, i.e., C-44, C-23, and C-24. FEQ was also used to represent the aggregate of the secondary and tertiary canals in these subbasins, in the form of 'level-pool reservoirs'. HSPF was calibrated to obtain an overall water balance, and then provided the nonpoint source flows to the FEQ-based canal system. Iterative adjustments to the two models were made to achieve consistency in the predicted water levels. HSPF was also calibrated on the other subbasins where FEQ was not applied, and provided flows directly to the estuary, or utilized HSPF's stream hydraulics routines (RCHRES) for routing.
Database development involved rainfall and evaporation time series data, and detailed canal design and control structure (pumps, weirs, culverts, etc.) specifications and locations. Observed data for the calibration included primarily canal flow and stage information and groundwater levels at various locations in the basin. A key issue that was resolved involved the source and timing and model implementation of irrigation on the citrus and irrigated pasture in the basin. In this task, implementation by AQUA TERRA and subcontractors was carried through the calibration phase, with District personnel taking responsibility for subsequent verification and simulation of alternative scenarios.
In Task 5, a completed modeling system, including source code, executables, test inputs, and SLEW model inputs, all designed for a Sun Sparc 10 Workstation, will be delivered to the District. The associated documentation package (in WordPerfect format) will contain the following components: 1) HSPF User's Manual with documentation of new/modified modules, including HSPF-FEQ linkage, and discussion of the water quality implications of the new components; 2) detailed FEQ users documentation; and 3) the SLEW model calibration report from Task 4.
In May, 1996 AQUA TERRA provided a modeling workshop (Task 6) for SFWMD that included customized materials related to model modifications for South Florida hydrologic conditions. The 3-day presentation also provided an update on the St. Lucie Watershed HSPF application. In 1997, AQUA TERRA developed enhanced irrigation algorithms and input/output formats for HSPF, and validated the new algorithms using scenarios and data provided by the District.