Prime Hook

Objectives

1. To support the U.S. Fish and Wildlife Service's Wildland Urban Interface (WUI) program at Prime Hook National Wildlife Refuge, Delaware, by applying remote sensing and Geographic Information System (GIS) techniques to delineate and monitor Phragmites response to control methods. The USGS is also aiding the USFWS's outreach effort on this project by creating custom maps and graphics for public information.

2. To design a hydrological study that will enhance understanding of seasonal water budgets for each refuge management unit. This scientific data will provide knowledge about hydrological processes critical to managing the Refuge's marsh complex which accounts for 75% of the Refuge's total acreage. This information will help predict and fine-tune the timing of surface-water manipulations in the marshes plus enhance water-level management planning and decision-making processes at the Refuge..

Statement of Problem

The Prime Hook Project has two tasks. The statement of problem for task 1 is:

The MD-DE-DC Water Science Center is currently assisting the US Fish and Wildlife Service (USFWS) at the 12,000 acre Prime Hook National Wildlife Refuge near Milton Delaware for the largest Wildland Urban Interface (WUI) project in the country by providing Geographic Information System (GIS) support.

The Refuge and its staff are particularly concerned with the invasive exotic species Phragmites australis (Cav.) Trin. ex Steudel (hereafter referred to as Phragmites). Phragmites is a large perennial rhizomatous grass or reed. A fundamental concern regarding Phragmites expansion on Prime Hook's coastal marsh areas is the grave fire hazard it presents with consequent threats and potential danger to local beach communities. Another concern is the reduction of biodiversity of many native plant species that are replaced by aggressive and competitively superior exotic genotypes that have also displaced former native Phragmites populations (Saltonstall 2002). Commensurate with a shift to an exotic Phragmites monoculture is a reduction in insect, avian, and other floral and faunal assemblages, which is also undesirable. The wildland/urban interface is defined as the line, areas or zone where structures and other human development meet or intermingle with undeveloped wildland or natural vegetative fuels. In light of the Los Alamos fires, and in reviewing current conditions on the refuge, it became evident that wildland/urban interface fire protection and prevention required immediate attention. Past marsh management practices along with deferred funding decisions have contributed to a build-up of highly flammable Phragmites fuels on refuge lands adjacent to private beach communities. The result is that fire hazards and higher associated risks, as well as an increasing beach population, have augmented the wildland/urban interface fire hazard potential, directly associated with refuge lands.

The statement of problem for task 2 is:

Biologist and Managers at Prime Hook National Wildlife Refuge, Delaware need basic hydrologic information that will enable them to enhance the management of the existing natural system. The hydrologic budget for the Refuge is poorly understood in regards to water-level management within the refuge. Critical information pertaining surface-water depths within the various management units and their relationships to established staff gage depth readings at all the water control structures is lacking. Data is required to better predict and fine-tune the timing of drawdowns in the marshes in order to create and/or maintain the best marsh conditions for specific wildlife needs.

Strategy and Approach

Efforts with the USFWS are been aimed at Phragmites stand delineation, herbicide application guidance, and vegetation response data collection. The project is currently using advanced GIS/remote sensing and conventional ground based techniques such as Infra Red Imagery, waveform resolving LiDAR, and Hyperspectral sensing for quantifying the effectiveness of aggressive herbicide, prescribed fire and mowing treatments in reducing and/or eliminating Phragmites within delineated well defined "problem areas." Perfecting vegetative interpretation techniques using GIS/remote sensing methods will be critical to monitor the success and/or failure of control treatments and regimes. John W. Jones of Eastern Region Geography (ERG) in Reston is generously performing Hyperspectral image processing.

A Hydrologic Budget/Water Balance approach would be used to monitor the hydrologic process at the refuge. The approach is based on the following equation:

P = Q + E + DSs + DSg where:
P = Precipitation
Q = Runoff/Runoff or Inflow/Outflow
E = Evapotranspiration
DSs = change in storage of the surface-water reservoir
DSg = change in storage of the ground-water reservoir

Precipitation (P) would be measured using rain gages co-located with a weather/evapotranspiration station. The existing Refuge weather station might be used for evapotranspiration measurements with the addition of a few instruments.

Surface water inflow/outflow (Q) measurements would be done with two different types of stations. The Inflow measurements sites would involve a surface-water gage station that would also use an Acoustic Doppler meter for measuring open channel discharge. These measurements would be used to determine the quantity of water entering the Refuge.

The traditional approach of developing a basic stage/discharge relation will not work at the selected sites due to the complexities of monitoring outflow at a control structure (fish ladder, flash boards, tide gages, etc.). We are recommending the use of a single index-velocity flow meter control structures. This instrument measures both stage and flow in two directions which would allow us to determine the influence of tides, fish ladders, changes in flash board heights, and other factors at each control structure. This new technology is designed to monitor shallow water depths and reverse velocities allowing us develop a discharge flow rating for the structure.

Change in storage of the surface-water reservoir will be measured using Pond Gage Sites. Pond gages measure actual surface water levels at various locations in the Refuge. This data, used in conjunction with the discharge data, will be used to develop relationships between staff gage levels at the Control Structures and water levels in the marshes. The data will also help monitor surface-water drawdown or impoundments. Staff plates will be installed at strategic locations and read frequently by Refuge staff to supplement continuous records.

Change in storage of the ground-water reservoir will be measured using monitoring wells which located next to the Pond Gages. Ground-water level measurements will be used to help determine ground-water inputs in the Refuge. Monitoring wells located upgradient of the Refuge would be used to determine ground-water flow paths and help study the influence of off-site water use (irrigation) on ground water in the Refuge.