OCE 311 Coastal Ocean Laboratory, Student Designed Experiment

Instructor: Malcolm Spaulding

April 12, 2004

 

 

Background

 

The US Fish and Wildlife Service (FWS) propose remediation of a former landfill, primarily located in the Sachuest Point National Wildlife Refuge, Middletown, RI.  The marsh system consists of two major, interconnected basins. The northern basin is connected to the Sakonnet River by a natural tidal inlet through the beach and culvert under Third Beach Road. The southern basin is connected to the northern basin via three culverts installed under Connector Road that separates the two basins.The northern and southern basins have been referred to in prior studies (Roman et al ,2002) as the unrestricted and restricted portions of the marsh, respectively. The landfill consists of two separate dumpsites; high and low fill areas located in southern(restricted) section of the marsh (Figure 1).  The proposed remediation calls for the material from the low fill area to be placed on the high fill area. The project is expected to result in a net gain of 3.4 acres (1.37 hectares) of wetland habit.  FWS is proposing to restore at least a portion of this area to salt water marsh.

 

The RI Coastal Resources Management Council (CRMC) has tentatively found the project to be in compliance with the Coastal Zone Management Act for the State of RI, but has requested that FWS provide clarification of the impact of the remediation on the hydrodynamics of the marsh system. Specifically CRMC wants to know how the remediation will affect the flow of water from the Sakonnet River to the marsh and the water fluxes and levels within the marsh system.

 

To address this question Spaulding and Grilli (2003) have applied an inlet basin model to predict the impact of the restoration of the restricted marsh on the water elevations in the two marshes and the flows between the ocean and the unrestricted marsh and between the unrestricted and restricted marshes. In order to apply the model they needed to have a detailed characterization of the storage capacity of the unrestricted and restricted marshes; specifically data on the surface area versus water level of each marsh.  This data (Table 1) was provided R. Schauffler, Fish and Wildlife Service, based on an analysis of the existing topographic data, using tools in the ArcInf geographic information system(GIS).

 

Fish and Wildlife Service (FWS) personnel and Spaulding and Grilli( 2003) have expressed concern that the underlying data base supporting Schauffler’s estimates is not very accurate, particularly in the critical elevation range of –0.3 to 1.0 m. Spaulding and Grilli ( 2003) have also noted that model predictions are very sensitive to the basin storage capacity. Uncertainties in estimates of the storage capacity of the marsh will adversely affect the accuracy of model predictions of the impact of marsh construction on circulation in the marsh system.

 

 

Table 1             Surface area of the Sachuest restricted and unrestricted marshes versus elevation. Elevation values are given relative to National Geodetic Vertical Datum (NGVD).

 

Sachuest Basins

 

Schauffler

Elevation

Area - Unrestricted

Area - Restricted

m/NGVD

m2

m2

-0.3

0.001

0

0

1120.6

0.001

0.3

4581.5

1796.6

0.6

11519

3593.2

0.9

24124

22022

1.2

47203

48133

1.5

71806

62542

1.8

81824

71518

2.1

83323

82831

2.4

83879

97089

2.7

84221

1.07E+05

3

84394

1.13E+05

 

 

 

 

 

In prior work on the marsh system, Roman et al (2002) have noted that the low water level in the marsh is substantially higher than in the adjacent Sakonnet River. In fact the water level in the marsh appears to remain at about 20 cm (NGVD), independent of the tidal forcing in the Sakonnet River.  This value has been confirmed by Spaulding and Grilli’s (2003) modeling studies.  FWS scientists would like to know why the low water level in the marsh does not go below 20 cm and what they might do if they wished the marsh to drain further at low tide.

 

Study Objectives

 

The objectives of the student-designed project are to:

 

  1. Determine the storage capacity versus water level in the restricted and unrestricted marsh.
  2. Determine why the water level in the marsh remains at about 20 cm (NGVD) independent of the tidal range in the Sakonnet River.

 

Figure 1            Sachuest Marsh study area showing the locations of the unrestricted and restricted marsh areas and the high and low fill areas in the restricted marsh. Source: US Fish and Wildlife Service.

 

 

Guidelines and considerations:

 

  1. Each section of the class needs to develop and perform their own experiments to address the study objectives.
  2. The class has been granted access to the Sachuest Wildlife Refuge by the Fish and Wildlife Service. Our point of contact is Sharon Ware (Sharon_ware@fws.gov). She has been informed that a student-designed experiment will be performed some time during the month of April 2004. You need to inform her at least three days in advance of the date on which you will be performing your experiments.
  3. You must not walk in either of the marshes, as it adversely impacts the marsh grasses and wildlife living there.
  4. You need to be aware that there is, at times, significant traffic on the roads in the wildlife refuge and must be careful to avoid accidents.
  5. The waters in the marsh, and adjacent coastal areas, are often closed to fishing, shell fishing, and water contact sports by the RI Department of Environmental Management due to fecal coliform contamination. Exercise caution.

 

Schedule:

 

The schedule for this module is as given below:

 

April 12, 2004, 1-3 PM, Sheets 117

Background and project objectives (M. Spaulding)

 

April 14, 2004, 12:30 – 3:00 PM (Section 1), 3:15 –5:45 PM (Section 2), Sheets 117

Proposed experimental approach plan, tasks, schedule (Students)

 

April 14-30, 2004

Perform experiment (on your own schedule)

 

May 4, 2004, 5 PM

Final report due, must be submitted in electronic form (CD or via email attachment). This is a team report experiment with not more than 3 to 4 members per team.

 

References:

 

Roman, C., K. Raposa, S. Adamowicz, M. J. James-Pirri, and J. G. Catena, 2002. Quantifying vegetation and nekton response to tidal restoration of a New England salt marsh, Restoration Ecology Vol 10, No. 3, pp 450-460, September 2002.

 

Spaulding, M. L. and A. Grilli, 2003. Impact of land fill remediation/restoration on the hydrodynamics of the Sachuest marsh system, Middletown, RI, prepared for US Fish and Wildlife Service, Charlestown, RI. (posted on OCE 311 web site)

 

Other information:

 

 

Chapter 6 of the CEM presents a detailed summary of inlet hydrodynamics and is useful background reading.

 

 

This NOAA National Ocean Service web site contains preliminary observations of the water levels at sites throughout the US.  Newport is site number 8452660. There is no data for the Sakonnet River. Spaulding and Grilli(2003) provide a procedure to estimate Sakonnet River water levels given observations at Newport, RI.