Site Preparation

In May 1992, SJAEI volunteers began preparing the site for the upcoming field investigation. While the work provided the opportunity to refresh diving skills and police the site, the primary objective was to develop and fabricate a stable structure around the bow.

SJAEI's dive platform consisted of a 28 ft. pontoon boat lashed to a 28 ft. barge. In order to anchor the dive platform over the site, three large concrete mooring anchors were placed around the bow of the Maple Leaf. The stable platform supported a surface supplied air system utilizing two band masks with hard wire communication.

Adjusting the existing baseline was the first task completed to prepare the site for upcoming field work. The base line installed by SJAEI in 1991 had to be raised above the river bottom and leveled. Originally, each end of the cable was secured to a steel clamp placed on the stem post at the bow and the rudder post at the stern. The cable attachments were not level relative to each other and the cable stretched over and around several obstacles distorting its alignment. The clamps were removed to raise the cable attachment points above the obstacles. A long pipe was welded to each clamp with an adjustable eye bolt to facilitate leveling. The clamps were then reinstalled, the cable attached to the eye bolts situated above the obstacles and leveled.

Next, to accomplish detailed site documentation, a "friendly" working environment had to be created. Past experience demonstrated that an exposed hole in the river bottom quickly filled with aquatic grasses and trash moving in the current. In addition, there is no visibility on the river bottom due to suspended silt. To isolate the work area from these limiting factors, a solid barrier had to be erected on the river bottom. The structure had to be strong enough to withstand the current and divert the flow around the site. It also had to allow the relatively clear river water to reach the main deck level to provide visibility necessary to take accurate measurements.

The first experimental barrier was a non-rigid structure consisting of a long narrow tarp attached to wooden poles at 7.5 ft. intervals. Divers attempted to erect two preassembled 15 ft. sections on the site but the river current caused the tarp to billow. This condition made it impossible to deploy the sections and suggested a rigid structure built in small sections might work better.

The second experiment utilized rigid panels to build a small enclosure. Each panel measured 6 ft. long and 4 ft. high with a frame constructed of 1 in. square steel stock welded at the corners. Fence wire was welded to the frame to provide backing for geotextile silt barrier fabric used to cover the entire panel. The geotextile fabric acted as a barrier to block the current. The small panels were easily taken down to the site by divers, despite the current, and mounted on pre-placed poles with plastic tie wraps. A 12 ft. square area around the stem post was enclosed and left unattended for two weeks. In that time, the structure suffered no damage from the current and no grass or debris accumulated inside.

This experimental barrier proved so successful, that the next step was to mass produce panels using readily available materials. A local farm supply store stocked heavy gauge wire panels ideal for making the frame. These "cow" panels, measuring 16 ft. long by 52 in. high, were cut into 8 ft. sections and covered with geotextile silt barrier fabric. Once in the water, two divers easily positioned the panels and fastened them to pre-placed poles with plastic tie wraps. Strong currents influenced the decision to build modular barriers with a diamond shape to deflect the flow.

By the end of June, the first 24 ft. square barrier was in place around the bow, ready for site documentation to begin. As the summer progressed, two adjoining 24 ft. square barriers were added. The barriers were designated SB-1, SB-2, and SB-3 (Figure 6). It soon became apparent that shape had relatively little effect on the stability of the barrier. As long as the support poles were firmly anchored, the current had minimal impact. Future work will benefit from this knowledge, speeding construction and greatly enlarging the area enclosed.