Comprehensive Site Development Plan ... - City of Kelowna

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Avocets at Glenmore Landfill 6 3.5 Conservation habitat at Glenmore Landfill If an engineered wetland at Glenmore Landfill is required to conserve the breeding population of avocets then several factors must be considered. Several design factors are critical to consider when designing a wetland suitable for breeding avocets. Size: After studying the movements and territoriality of nesting pairs at Alki Lake, Weir and Gyug (1999) suggest that each nesting pair requires 0.5 ha of foraging habitat. If we assume 12 breeding pairs (average number of breeding pairs in past 3 years) and 6 nonbreeding avocets (a total of 30 adult birds), then 6.6 ha would be required based on 0.5 ha/pair and chicks and 0.1 ha/nonbreeder (Robinson and Oring 1997, Robinson et al. 1997). Since avocets tend to use about 2/3 of suitable habitat available (Girard and Yesou 1991), 10 ha seems more appropriate. However, since other wetlands specifically engineered for nesting American Avocets have increased densities markedly (e.g., Tulare Lake Drainage District 1996), there is potential for providing habitat for more than 30 avocets in 10 ha. Surrounding Area: Land areas surrounding compensation habitat should be relatively flat and open with few trees so the area mimics prairie-like wetland habitat. In particular, all perch sites used by raptors (predators of avocets) should be cleared within 150 m from compensation habitat. To minimize human disturbance during nesting, the site needs to be designed so that there are no work operations carried out within 150 m of the site during the period when avocets are nesting (approximately May1 to August 15). Substrate: Clay or clay-silt should be used as substrate of compensation habitat as it is impermeable to water and thus stops underground water loss, forcing water losses through evaporation which aids in increasing salinity and alkalinity. Foraging Habitat: Shallow feeding areas of 1-17 cm depth are necessary in order for avocets to forage. Water depth in the majority of feeding areas could average 10 cm and be in the range of 5-13.5 cm deep. Small areas of deeper water (17-60 cm) should be scattered throughout the compensation habitat as some invertebrate species used as food may need deeper water at certain portions of their life cycles. Water Control: As water levels in compensation habitats fluctuate, it will be necessary to control water levels to keep nesting islands exposed in high water years and surrounded by water in dry years, to keep water depth in foraging areas at an optimal level, and to achieve a relatively constant water level through the incubation period. Outside the breeding season (May 1-August 15) these water levels can be manipulated for other landfill management purposes. Other considerations with water level control are 1) salinity and alkalinity, which may be reduced when water is flushed through the system instead of allowing solutes to build up through evaporative water loss, 2) impacts on invertebrate prey abundance, and 3) vegetation control. The site should be designed so water levels can easily be manipulated, particularly to raise water levels on some occasions to prevent buildup of permanent vegetation on low nesting islands and in shallow foraging habitat. Water quality: Water should be highly alkaline (>400mg/L), highly saline (>12,000uS), have high Total Dissolved Solids and low Dissolved Oxygen (Ambrozy 1999). Manning, Cooper and Associates
Avocets at Glenmore Landfill 7 Shoreline: Shoreline slopes should be 10:1 to 12:1 slope maximizing the shoreline area which can be used for foraging (Robinson et al. 1997). Nesting Islands: Compensation habitat should have numerous small islands or several large islands for nesting as outlined in Weir and Gyug (1999). Artificial nesting islands can be constructed in existing alkaline wetlands provided that foraging habitat exists already at those sites. In creating artificial nesting islands for American Avocets, a number of factors need to be considered (Robinson et al. 1997; Weir and Gyug 1999). These include: 1) distance and depths of water between island and shore, 2) size and distribution, 3) slope, 4) vegetative cover, 5) substrate, 6) height above water; and 7) durability. General recommendations for nesting islands (after Weir and Gyug 1999) include: • Minimum distance of 30 m to shore, and depth of water at least 1 m deep to protect against mammalian predators somewhere between shore and island. • Islands can be of almost any size, but if small islands are used they should be clustered. • Side slopes at 10:1 to 12:1 under water and above water (Figure 1). At Tulare Lake Drainage District in California, artificially created nesting islands with side slopes of 12:1 attracted large numbers of avocets but islands with side slopes of 3:1 were used to discourage avocet nesting (Tulare Lake Drainage District 1999). Burgess and Hirons (1992) constructed nesting islands for Pied Avocets (Recurvirostra avosetta) in Great Britain with side slopes of 10:1. • Vegetative coverage, if any, should be sparse and short on nesting islands. If vegetation is not to be controlled by water levels, then vegetation can be discouraged by placing several layers of weed resistant plastic over islands and then placing highly alkaline and saline clay on top of plastic. Salt can be spread over island surface to discourage plant growth. • Any natural material substrate is acceptable, but should be resistant to wave erosion. Islands with a base constructed of large rocks and clay topping is recommended. • Island height should be great enough to reduce chances of sudden flooding but should not usually exceed 30 cm because then the island would have to be very large to not exceed the recommended side slopes. Islands should also be low so that permanent vegetation does not establish, and thereby negate the value to avocets. On such low islands, both occasional flooding and a rooting zone that would extend into relatively toxic alkali waters are likely to keep most vegetation to a minimum. An alternative would be to construct islands with clay placed over a vegetation-impermeable plastic or other barrier. • Erosion caused by wave action can reduce island life. To prolong island life and avoid having to reconstruct them at regular intervals, artificial nesting islands constructed in Great Britain were designed to reduce erosion. Techniques included: 1) using a 10:1 slope at base; 2) covering island with plastic netting; 3) placing stakes on windward side of island; and 4) placing pebble like substrates along water margin of islands (Burgess and Hirons 1992). Nursery sites: Short vegetation in very shallow water 1-5 cm deep should be created near each nesting island for chicks to hide in. Such nursery sites should occur naturally if Alkali Saltgrass occurs. Saltgrass will not grow in deep water. Overall design: There are many possible wetland designs that incorporate all or most of the above recommendations. Obviously any design would need to incorporate existing site constraints and other factors, particularly the requirement to maintain high alkalinity. A “generic” example of a wetland design was developed by Weir and Gyug (1999), and is included here as a recommended concept (Figure 2). The design is for a 10 ha wetland (10 ha in size (250 m x 400 m). Five island ridges would run parallel to each other with shallow wide feeding lanes between each island. Island ridges would be 45 m apart from each other. The exact width of the Manning, Cooper and Associates
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Final Comprehensive Site Developmen
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Copyright 2008 by CH2M HILL. All ri
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Site Location Exhibit 2-1 Gener
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Refuse Clay Sand / Gravel Till Bedr
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Comprehensive Site Development Plan ... - City of Kelowna

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