State of the Greater Fundy Ecosystem - Hydrology and movement

GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

Hydrology and Sediment Movement of the Point Wolfe River

Chris Coles1, Douglas Clay2, and David Hansen1
1Technical University of Nova Scotia, Halifax, N.S.
2Fundy National Park, P.O. Box 40, Alma, N.B. E0A 1B0

The Point Wolfe River discharges to the Bay of Fundy along the south shore of New Brunswick. The first 12 kilometers of the river are located inside Fundy National Park (Fundy NP). The next 11 kilometers of the river are outside the western boundary of the Park, in an area managed by the provincial government as crown license 7.

GOALS

The nature of sediment movement in a river can be a limiting factor for fish populations in that river. The object of this investigation is to describe the fluvial geomorphology of the Point Wolfe River by monitoring water and sediment movement in selected reaches for a period of two years. The data collected over this two year period will be used to calibrate a model designed to describe sediment movement throughout the river. This model will relate structure in representative reaches of the Point Wolfe River system to physical, climatic, and hydrologic factors. It shall assist in assessing how historic river use and present land use, is or has been, a factor in the morphology of the river and how it may affect the fish populations in the river.

The Point Wolfe River has been the focus of much interest in the past twenty years. Monitoring of discharge, water temperature, air temperature, precipitation and water quality has been undertaken by Parks Canada and Environment Canada. The data provided by past studies and long term monitoring associated with the river provide a base from which to develop and calibrate models relating precipitation events to river discharge and sediment movement. The findings of this research will provide support to studies currently in progress at Fundy NP relating to Atlantic Salmon habitat.

METHODS AND RESULTS

Ten reaches were identified as monitoring sites. The cross section of each of the selected sites were surveyed in August, 1996 and re-surveyed in July, 1997 to determine if any large- scale changes had occurred in the channel cross sectional geometry over the previous year. One reach where a change in the channel's cross sectional geometry was observed is located approximately 700 meters upstream of the covered bridge at the mouth of the river (Figure 1). This figure illustrates a net loss of material in the lowest portion of the channel from 1996 to 1997.

Figure 1.
Channel cross-section surveyed in 1996 (asterisk) and
resurveyed in 1997 (triangles). Site 104 is between the head of
tide and the gauging station run by Environment Canada.

At each sample site two to five scour chains were installed (site specific, depending on the variability within the cross section) during the summer of 1996. A scour chain is a device which measures the maximum depth of sediment movement. After significant flow events the scour chains are found, the depth of scour or deposition is measured and then reset.

One year of sediment movement monitoring has indicated that the maximum depths of sediment movement ranged from 0 to 0.235 m. The maximum depth of observed sediment movement (0.235 m) occurred in the reach shown in Figure 1. The majority of sediment movement observed occurred during the peak flows between the months of November and May, and is expected to have occurred during the spring thaw, usually late March and April.

A grid by number gradation analysis was conducted in October 1996 and July 1997 at all of the sample sites to provide surface gradation data. The size of the material in a mobile bed river is, in part, a function of the dominant discharge of the river. The dominant discharge of a river is the flow which shapes the river and tends to have a return period of between 1.5 and 2 years.

A commercial rainfall to runoff model will be used to relate precipitation events to discharge in the river. GIS data and standard topographic maps will be used to construct this model. Concurrent monitoring programs in Fundy NP have 32 years of rainfall and discharge data that will be used to calibrate and validate the rainfall to runoff model. Two pressure transducers have been installed in the river to provide enhanced river stage data to calculate discharge at points of significant inflow (Bennett Brook and East Branch River).

The next phase of this project will involve relating river discharge in the ten selected reaches, to sediment movement. A literature review has yielded several different methodologies for calculating sediment movement. These procedures, when applied to the same reach can yield results varying up to 100%. The sediment movement which is being monitored through the use of scour chain devices will aid in the selection of the most appropriate modeling methodology for the calculation of sediment movement on the Point Wolfe River.

Preliminary observations and a literature review have indicated that bed load movement occurs as discrete events resulting from high stream energy rather than as a constant gradual process. For this reason individual peak flows are significant. Annual variation in discharge is typically large. Figure 2 illustrates the discharge of the Point Wolfe River in 1973 overlaying a 30 year average (1966-1995) discharge in the Point Wolfe River. The 30 year average discharge indicates the cyclic (seasonal) pattern. The 1973 discharge data however is an example of how much variation in a discharge pattern may occur in any individual year. It is the short term spikes in discharge that are believed responsible for much of the bed movement. The significance of such activity for spawning redds of Atlantic Salmon depends on the timing and scale of such flows.

Figure 2.
Daily discharge of the Point Wolfe River for 1973, a year with many spikes
in the pattern of flow, overlaying the 30-year (1966-1995) mean flow (smoothed
by a running average of 7). Data are from the Environment Canada gauging station
above head of tide on the Point Wolfe River.

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