**The title, authors, and abstract for this completion report are provided below.  For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**

Phase I Development of an Improved Sea Lamprey Barrier

K. A. Mazurek^1, A. Hallett², A. Aktar¹, J. Thomson¹, M. Amos¹ and C. Katapodis ³

 ¹ Department of Civil and Geological Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, Saskatchewan, Canada, S7N 5A9

 ² 41 Caddy Avenue, Sault Ste. Marie, Ontario, Canada

 ³ Freshwater Institute, Department of Fisheries and Oceans Canada, 501 University Crescent, Winnipeg, Manitoba, R3T 2N6

 

Abstract

Physical barriers to the upstream migration of sea lamprey (Petromyzon marinus) into the streams that flow into the Great Lakes are used as a part of an integrated pest management system to control lamprey populations in the lakes. Most often, these barriers are small weirs or low-head dams of that are typically less than 2 m in height. Although the barriers can be effective at blocking lamprey, by providing a sufficient drop between the barrier crest and water surface just downstream of the dam that is taken to be 30 cm, there are potential liability issues with the operation such structures. As with almost all current forms of weirs and low-head dams, the plunging flow over such a structure can create a large eddy in the flow downstream of the dam as part of what is termed a submerged hydraulic jump. The flow can look serene; however, it is deadly to those who may fall into it. The person becomes entrapped in the eddy formed by the flow and eventually drowns. Owners of these types of structures are starting to address the need to modify these flow conditions in order to improve public safety. This project represents the first phase of a research program to develop an improved design for sea lamprey barriers that would mitigate the hazardous conditions for drowning while maintaining the efficacy of the barriers to block the upstream migration of lamprey. The current work is further divided into two parts: (1) detailed study of the flow conditions at four existing fixedcrest, low-head barriers of varied design and effectiveness at blocking lamprey; and (2) assessment and recommendation of potential retrofit modifications to the barrier designs that mitigate the drowning hazard while still maintaining the required 30 cm drop between the weir crest and downstream water surface. The four barriers studied were the Duffins Creek, Wolf River, Salmon River, and Little Otter Creeks barriers in Ontario.

To perform the detailed study of the flow conditions at the four barriers, first a hydrological analysis was undertaken to assess the flow rates seen at the site. Flood frequency and flow-duration analyses were carried out and stagedischarge curves for the upstream and downstream water depths were developed. The data was used to develop scale models of the barriers, which were then tested in a laboratory flume. The models were of the most representative sections across the width of each barrier as the entire barrier could not be modeled because of the small scales required. The general flow behavior was assessed using flow visualization under varied flow and tailwater conditions. Then, detailed flow measurements were taken along the centerline of each modeled section for a set of site-specific flow conditions using a MicroAcoustic Doppler Velocimeter that covered the range of flow seen at the
site. From these measurements, the risk or percent time the flow would be considered hazardous with respect to drowning at each of the sites was calculated. It was seen the that submerged hydraulic jump is the most common form of flow at the Duffins Creek, Salmon River, and Wolf River Barriers; however, the Little Otter Creek barrier only operates in this flow condition under very high flows. The central portion of the Duffins Creek barrier that serves as a jump pool is shown to be hazardous 100 % of the time operated, while the main portion of the barrier is hazardous approximately 8 % of the time. The Wolf River barrier has a hazardous flow 45-57 % of the time. The most hazardous barrier was the Salmon River barrier, which operates with hazardous conditions 98% of the time. Conversely, the Little Otter barrier operates safely at least 99 % of the time.

Further, using the results of the hydrological analysis at the barrier sites, the probability of losing a 10, 15, 20, 30, or 35 cm drop between the barrier crest and the downstream water surface during the sea lamprey migration period was also assessed and compared with observations of barrier effectiveness provided in Lavis et al. (2003). Of note was the poor performance of the Wolf River barrier at maintaining any drop. For the period of record of the stream gauge near the site (1971-2005), the barrier did not provide a drop of at least 30 cm for 80 % of the time it operates during the lamprey run, a 20 cm drop is not provided 62 % of the time, and a 10 cm drop is not provided 43 % of the time. Thus, it appears that the Wolf River barrier may be undersized for its purpose as a barrier.

For development of the retrofit modifications to the barrier, a number of potential designs were tried using tests with the scale models in a laboratory flume. The goal was to prevent the formation of eddies that entrap bodies in the flow. It was found that they are two key elements to successful modification of the flow to prevent the hazardous flow conditions can that drown people. First, the water that overflows the barrier cannot be allowed to plunge towards the bed; it must be redirected to flow along the water surface, which could be done using rocks, steps, or an upturnedvane. Further, cross-flows must be created using angled baffles or other elements so that the uniformity of the flume across the channel is disrupted. Recommended geometries for modifications to the Salmon River and Duffins Creek barriers were developed. Ultimately, what option is considered best to modify a particular barrier appears to strongly depend on the local site conditions (in particular the stage-discharge curve for downstream side of the barrier), and availability and cost of materials at each site.