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PROCEEDINGS OF THE DESERT FISHES COUNCIL Methods and Materials Reclamation planners initially negotiated with the District to ensure project compatibility with District irrigation needs and water rights. A field review, consisting of Recovery Team and District personnel, visited the Phantom Lake Springs property on August 31, 1991, discussed project scope, and conducted preliminary engineering surveys. Subsequently, the Recovery Team developed guidelines for design of the facility. These included creating a protected refugium channel with mesohabitat heterogeneity, facility operation capability over a variety of spring discharges, ability to manipulate water elevations in the refugium over a range of flows, and establishment of a cross-sectional channel profile that maximized shallow water habitat at all flows while still providing faster velocity habitats. Reclamation staff provided engineering design and specifications for the project. A contractor was selected to conduct the construction of the refugium. National Environmental Policy Act and Endangered Species Act compliance were performed by Reclamation. Funding was secured through Public Law 102-27, Emergency Drought Assistance Act. Results and Discussion In spring, 1992, a fence was constructed around the entire Reclamation property to preclude livestock and human use and protect the endangered fish refugium. Texas Parks and Wildlife Department (TPWD) personnel will regularly monitor the integrity of this feature. Construction for the refugium channel commenced in February, 1993. A 110 in channel was excavated parallel to the existing canal and lined with a low density polyethylene liner to minimize water loss (Figure 1). Native materials from the channel excavation were used to create habitat features. Construction of the refugium occurred without disturbance of the existing canal and its resident aquatic population until water was initially diverted into the refugium. Two large (10 m long x 8 in wide) and two smaller pools (10 in long x 5 in wide) were formed, with intervening run habitat. Terraces were constructed at 150 mm vertical intervals on all cross sections, yielding extensive shallow habitats at all water elevations. Engineering estimates indicate that, for flows up to 0.3 m'/s (11 cfs), evaporative losses are less in the refugium than the irrigation canal. Pro,jec t Plan View r 1gare 1. Phantom Lake Springs Endangered Fish Refugium Plan. 1993 - VOLUME XXV Water was initially diverted from the existing canal into the refugium via a stoplog weir on June 7, 1993. Total refugium flow capacity is approximately 0.4 m3/s (13 efs). Spring discharge above that capacity will spill into the existing canal and the cienega. The refugium outlet structure is comprised of an adjustable aluminum "Cipoletti" weir. This weir allows manipulation of water velocity and elevation within the refugium. The weir was also constricted at an elevation higher than the downstream canal, creating a waterfall to restrict upstream fish movements. A stoplog weir was also placed in the lower irrigation canal to allow dewatering of the canal between the refugium channel's inlet and outlet structures. Reclamation biologists observed the initial refug,*ium filling activities, and, once water elevation had stabilized, began transferring aquatic vegetation and associated invertebrates into the refuinum channel. Reclamation personnel manipulated the elevation of the facility to determine, at the existing spring discharge of approximately 0.1 m3/s (4 cfs), a suitable velocity to protect the unstable substrate. It was immediately discovered that excessive velocities could be produced within the refugium that cause significant head-cutting of substrate in the lower refugium and threatened to impact the refugium's integrity. A locking mechanism was therefore placed on the weir to restrict manipulation of elevation. Biologists have subsequently maintained the weir at a higher setting to provide maximum wetted habitat areas and reduced channel velocities. The waterfall, while apparently creating a barrier to centrarchid and ictahu-id migration into the refugium, was unsuccessful in restricting movements of Mexican tetra Astyanax mexiconus into the refugium. Astvanav mexicanus were attracted to the increased downstream velocities created by the waterfall, and were observed readily leaping waterfall elevations of up to approximately 500 mm. A floating, self cleaning fish barrier, constructed of cross-laid PVC pipe, was subsequently installed below the waterfall and apparently has successfully restricted movements of A. mexicanus. On September 20 and 21, 1993, members of the Recovery Team seined the lower canal areas and collected Cyprinodon elegans and Gambusia nobilis for transfer into the refugium. A total of approximately 135 G. nobilis and 2 C. elegans were collected.. Biologists carefully introduced these fish into refugium pool habitat, while lightly disturbing the substrate in an effort to increase water turbidity and thereby reduce possible A. mexicanus harassment and/or predation. After release, G. nobilis were seen utilizing the abundant aquatic vegetation that had colonized after the early summer vegetation introduction. Overhanging riparian grasses have also colonized the refugium's bank and appear to increase habitat diversity and 23