COASTAL PROCESSES AT ISLAND VIEW BEACH REGIONAL PARK Updated: April 9, 2015

The Dune/Beach/Spit Complex

The Dune/Beach/Spit Complex

Coastal Processes

In this section several concepts will be covered:

• Island View Beach Regional Park is part of a beach/dune/spit complex.

• There is a complex interplay between freshwater and saltwater.

• Human activities have influenced foreshore and backshore areas.

• The park is at or very near to current sea level.

Regional Sand Ecosystems

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Regional Sand Ecosystems

Coastal sand ecosystems are relatively rare on the rocky shores of southern Vancouver Island and the Gulf Islands. These ecosystems are important for both ecological and cultural values.

Island View Beach is one of the most significant examples remaining on southeast Vancouver Island.

Island View Beach is part of a large sand ecosystem complex including: (1) Cordova Shore, (2) James Island, and (3) Sidney Island.

The common orientation on all three sites reflects the local bedrock geology orientation from southeast to northwest.

The overlying deposits left by the glaciers have been reformed and distributed in a common orientation due to prevailing currents and winds.

Page, N. 2010. Cordova Shore Conservation Strategy. Unpublished report prepared for CRD Regional Parks, Tsawout First Nation, and Canadian Wildlife Service. 66 pp + appendices.

Longshore Current

http://revisionworld.com/gcse-revision/geography/coastal-landscapes/coastal-processes/longshore-drift

Longshore Current

The strongest winds in the region are from the south-southeast in the winter months, while the most frequent winds year-round are from the south-southwest.

This wind energy combines with tidal currents to drive waves onto shore creating a longshore current.

Mobile sediments are transported along the shore in a northerly direction.

http://revisionworld.com/gcse-revision/geography/coastal-landscapes/coastal-processes/longshore-drift

Prevailing Wind + Current

Adapted from Page et al. 2010

Coastal Process

Parks Canada

Parks Canada

Cowichan Head

Cordova Spit

Transport

Deposition

Erosion

Coastal Process

The longshore current transports sediments from a source of active erosion to an area of deposition.

At the park, ocean currents move sediment derived from Cowichan Head, northwest along the beach to Cordova Spit. As the current moves past the spit it curves around the tip, loses velocity and deposits sediment primarily on the northwest shore.

These natural processes may be accelerating as sea levels rise and storm frequency and intensity increase. Implications for society and our infrastructure are considerable.

There are bluffs that are active today (shown in red) and there are stable bluffs that are now forested (shown in orange). These bluffs would have been active at higher sea levels in the past.

These shifts in active shoreline illustrate its dynamic nature and ability to adapt and adjust to changing conditions through time.

Page, N. 2010. Cordova Shore Conservation Strategy. Unpublished report prepared for CRD Regional Parks, Tsawout First Nation, and Canadian Wildlife Service. 66 pp + appendices.

Hydrology

Island View Beach Regional Park exhibits a high water table on a low lying area that is affected by both salt and fresh water.

Tide levels on daily, monthly and annual cycles along with storm surges affect the amount of salt water from the ocean moving through groundwater and overland flow (tidal and storm surge).

Seasonal changes in precipitation affect the amount of freshwater on the land, as it moves through ground water or flows overland.

Fine Clay/Silt layer (each about 1m thick)

Soil Permeability

Bobrowsky and Clague 1991.

Soil Permeability

The surficial materials at Island View Beach Regional Park influence groundwater flow. Coarse sand and gravel are quite permeable and are often rapidly drained.

Within the Island View Beach soil profile, there are two layers of fine silt and clay at 3 ½ m and about 9 m depth that are each nearly a metre thick.

NEOTECTONIC INVESTIGATIONS ON VANCOUVER ISLAND (9:!B, F). 1991. P.T. Bobrowsky, B.C. Geological Survey Branch; J.J. Clague, Geological Survey of Canada

Bobrowsky and Clague 1991.

Soil Permeability

Water Flow

Soil Permeability

These more impermeable layers can slow down the movement of water causing horizontal flow driven by water pressure from precipitation or tidal flow.

Both freshwater and saltwater move back and forth below the ground and can rise to the surface in low lying areas.

This horizontal flow of water can be seen on erosion scarps at Cowichan Head (see photo), where water can be seen seeping out.

Environmental Technology Program Camosun College

Ground Water

Ground Water

The Camosun College Environmental Technology Program has assessed groundwater at Island View Beach with a study conducted in 2013 and 2014.

The study looked at seasonal changes in salinity in a series of groundwater wells installed at over 30 locations.

On these maps, the orange and red zones are considered salt1 water, the yellow and light green would be considered brackish1 (between salt and fresh) and the darker green would be considered fresh1 to mildly brackish.

The data show that in late summer and early spring the area is dominated by salt and brackish water. During the peak of the rainy season in December, the influence of freshwater is slightly more, particularly in the southern portion of the study area, but water is predominantly brackish.

1The US Office of Naval Research defines brackish and fresh water criteria. Freshwater salinity is usually less than 0.5 ppt. Water in between 0.5 and 17 ppt is called brackish. Water above this value is considered salt water. Average ocean salinity is 35 ppt. and ranges about 32 and 37 ppt. Office of Naval Research http://www.onr.navy.mil/focus/ocean/water/salinity1.htm

Dr. David Blundon. 2014. Unpublished data. Camosun College Environmental Technology Program. Victoria.

Environmental Technology Program Camosun College

Ground Water

Ground Water

The 2013-14 study also measured groundwater depth.

On these maps, dark blue indicates the water is less than 10 cm from the ground surface or above the surface. In winter and late spring, almost the entire area is saturated or has standing water.

In late summer, during the driest time of year, the water table is lower but the water remains within 50 to 70 cm of the surface in most of the landscape. It is much higher in the area to the northwest of the park on Tsawout Nation land.

Prior to the ditching program in the 1930s, local farmers estimated that at least 30% of the low lying lands here were under water 6 months of the year. Today, a considerable amount of the winter landscape still remains underwater or a few centimetres above the water table.

Dr. David Blundon. 2014. Unpublished data. Camosun College Environmental Technology Program. Victoria.

Randhawa, G. J. Gendall, J. Webb. 2012. Historical and Successional Baseline Study of Island View Beach: A summary of the historical land-use and aerial photograph analysis since the 1930s. Unpublished manuscript for Camosun College Environmental Technology Program. 39 pp.

Saanich Archives (dated 1937) Saanich Archives (dated 1937)

Island View Beach – 1936

Island View Beach – 1936 ditch excavation.

Island View Beach – 1936 Sea wall construction.

Island View Beach – 1936

In the past 85 years, the biggest change to the landscape has been the efforts to remove water from the site for increasing agricultural value and reducing mosquito habitat.

These archival photos illustrate the effort invested in ditching the area for drainage and constructing a large berm along the shoreline to hold back the tide.

Based on local historical information, this work was conducted in 19361 although the photos are dated 1937 in the archival records. It is not clear if this work spanned two years, although the project was large, and quite a construction accomplishment at that time.

1 Friends of Island View Beach (Accessed Nov. 2014): http://www.friendsofislandviewbeach.com/

Randhawa, G. J. Gendall, J. Webb. 2012. Historical and Successional Baseline Study of Island View Beach: A summary of the historical land-use and aerial photograph analysis since the 1930s. Unpublished manuscript for Camosun College Environmental Technology Program. 39 pp.

Ditch Length 7 km

Ditch Width (avg) 3.34 m

Water surface area Low water

(1.5 m width) 1.1 ha

Water surface area High water

(3.0 m width) 2.1 ha

Drainage Ditches

Drainage Ditches

There are two ditch systems separated at the northern park boundary. Approximately 7 km of drainage ditches have been constructed and maintained throughout the area. About 40% (3 km) of these ditches are in the park. Due to the low relief and a lack of gradient, the ditches are imperfectly drained and have limited flow.

The CRD Parks Committee has given direction to maintain the ditches in the park and so, there is a need to better understand their function and influence on the ecology. In an assessment of mosquito habitat D.G. Regan and Associates found that although ditch maintenance reduced saltmarsh habitat, they surmised that the ditches may have actually created new habitat as they retained stagnant water promoting mosquito development during late July and August.

The definition of drainage ditches at Island View Beach Regional Park is unclear. The measurements presented here were determined using information from a physical survey of the ditch system conducted in 2011 and from a detailed elevation model derived from remote sensing.

Fediuk, Curtis. 2012. 2012 Mosquito Control Summary Report. D.G. Regan and Associates. Submitted to CRD Regional Parks. October 31, 2012.

Drainage Ditches Elevations

Ditch “A”

Drainage Ditches Elevations

The ditches are not consistently engineered so ditch width was calculated by selecting 10 random ditch segments across the entire system and averaging the values.

For example:

Ditch A is a secondary ditch at the northwest boundary of the park. It was surveyed as approximately 1.4 m wide and 20 cm deep. The elevation profile indicates a 2.5 m width and 40 cm depth.

Ditch Profile

Drainage Ditches Elevations

Ditch “B”

Drainage Ditches Elevations

Ditch B is the main Lamont Road collector ditch near the tidal valve and behind the artificial berm. The surveyed width is approximately 4.6 m wide and 1.2 m deep. On the elevation model, the ditch is 8 m wide and 2m deep.

A 1.5 m and 3m wetted width is shown in blue shading within the ditch profile.

These ditches have been assessed annually and maintained as required since 2011 under a collaborative program with the District of Central Saanich.

Light Detection And Ranging (LiDAR)

• Collected in 2013 forIsland View Beach

• Detailed elevationmap

Sea Level Elevation

Sea Level Elevation

LiDAR, or Light Detection And Ranging, is a remote sensing technology that captures very detailed surface elevation data from an airplane. LiDAR data was collected in 2013 for Island View Beach at a low tide of 0.2m above mean sea level (amsl).

There are over a half million elevation points captured within Island View Beach (~50 ha) that are used to create the elevation model.

Sea Level Elevation

Sea Level Elevation

We can drape an air photo over the terrain to add colour and texture.

The data was collected at a 0.2m low tide.

Elevations are shown without overlying vegetation (bare earth elevation).

Sea Level Elevation

Sea Level Elevation

Using elevation data, we can illustrate that the ditch elevations are almost entirely below a 2.0m elevation. This illustration does not reflect true water flow since we don’t account for the role of the artificial berm, tidal gate and the groundwater movement.

Given the low elevation of the ditches and very limited elevation change across this landscape, it is easy to understand the challenge of effectively draining these lands.

Coastal Processes Summary

Island View Beach Regional Park is part of a regional beach/dune/spit ecosystem from Cowichan Head to Cordova Spit. These ecosystems have high conservation value.

The bluffs of Cowichan Head provide shore material to the park through erosion and deposition of material on the beach, driven by wind, tide and wave energy.

Dynamic coastal processes occurring on the landscape enable adaptation to changing environmental conditions.

The park is at or near current sea level and there is a complex interplay between freshwater and saltwater.