Attachment_2_-_Anchor_Conditions.pdf

National Park Service

Summary of GRTE’s Concessionaire-managed Dock & Anchor Conditions Excerpts from End of Fieldwork Memo

NPS Submerged Resources Center 8-1-2018 tcarson Text Box Relevent Excerpt from:

Overview

The following summarizes the work conducted at Grand Teton National Park (GRTE) from August 5-15, 2018, by the National Park Service Submerged Resources Center (SRC). This project’s primary goal was to document submerged cultural resources in the park and to evaluate areas around existing docks for current conditions and possible development.

Specifically, the SRC objectives were to document a small shipwreck at Signal Mountain and identify the mooring systems for NPS-owned docks, managed through a concessions contract, using side scan sonar, photographs, and hand documentation.

The dock and mooring assessments identified location, condition, and degradation of the intact anchoring systems. Basic data were collected on the anchor systems’ depth, orientation, and distances. The assessment included grading of integrity of the attachment hardware, i.e., chains, wire rope, shackles, swivels, and u-bolts. The anchoring material was also evaluated for deterioration levels via an examination of concrete, barrel, and metal deadweight anchors.

Finally, the assessment identified the substrate for suitability as the proper anchor system for the substrate is critical to anchor holding power and stability.

Signal Mountain Boat Ramp

Signal Mountain Boat Ramp Dock is a floating structure with one shore side connection and water side held by an anchoring system. The anchors are connected to the north and south corners of the northwest facing dock (Figure 24). The south corner of the dock is connected to a wire rope, which runs at 350⁰. The wire rope connects directly to a swivel and is 85% intact. A wire rope is then connected to the other end of the swivel. This wire rope is wrapped around the cement anchor and through a u-bolt. The cement anchor, measuring 2 feet x 2 feet x 3 feet, is 90% intact (Figure 25-26). The edges of the anchor is suspended about 1.75 inches above the cobble substrate at 38 feet.

The north dock corner connects to a wire rope which runs 319⁰. The wire rope connects directly to a swivel and is 80% intact. A wire rope is connected to the other end of the swivel, then wraps around the cement anchor and through a u-bolt. The cement anchor measures 2 feet x 2 feet x 3 feet and is 95% intact (Figures 27-28). The edges of the anchor are suspended about two inches above the cobble substrate at 45 feet. An unattached concrete barrel was observed during the investigation of the block attached to the southern dock post. An image was taken for documentation purposes, but no other details were recorded.

Recommended actions: None

Conclusions and Recommendations

The following are brief mooring system recommendations for the future:

When using deadweight cement anchors, it is recommended to use these anchors in a mud or mud/silt environment. This substrate will create suction and a secure hold for the anchor. A cobblestone substrate, as seen at a number of sites, acts as a shifting base and the anchor will move on top of the rocks instead of settling. In addition to suitable substrates, dead weight cement anchors work best when placed with a chain leader to increase holding power. Large Danforth anchors work especially well in cobble stone substrates. All anchors in environmentally exposed conditions (i.e., high winds and/or ice shifts) should be inspected annually. Additionally, all connection hardware should be replaced when it reaches 60% intact or 40% degradation.

In terms of cultural clearance for future dock or anchor work, the sonar did not uncover any cultural resources. For purposes of Section 106 compliance, cultural clearance is recommended with the standard stipulation that should archaeological remains be uncovered during the implementation of any part of a project, the appropriate federal agencies be contacted immediately.

Figure 24. The hand-drawn map of the mooring system at Signal Mountain boat ramp.

Figures 25-26. Side scan images of the blocks attached to the southern (left) and northern (right) docks posts at Signal Mountain boat ramp.

Figure 27. Image of the south block at Signal Mountain boat ramp resting on cobbles.

Figure 28. Image of the north block at Signal Mountain boat ramp resting on cobbles.