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J-7 � pf C� ranged from 0.3 to 3.7 feet, with a mean of 1.4 feet. These means were not significantly different (Ziewitz et al. 1992). In summary, comparisons of sandbar area, channel width, mean elevation, and maximum elevation of nest sites versus systematic sample sites in the Platte River suggest that least terns use wide channels with a large area of dry, sparsely vegetated sand. By these two measures alone, habitat availability was considerably greater on the lower Platte River than on the central Platte River. Although nest sites also had higher mean and maximum elevation than systematic sample sites, these differences were not statistically significant in either river reach. On the central Platte River, the mean elevation of nests was less than the mean site elevation at half of the nest sites (FWS 1997). These differences between nest and systematic sample sites and between the lower and central Platte River suggest that habitat availability is limited in the river channel along the central Platte River. Along the central Platte River, a greater number of least terns and piping plovers nest on sand and gravel spoil piles than on the river (Table 1 -2). Many researchers believe high usage rates of the sand pit habitat by least terns is an indication that adjacent riverine habitat is limited, Low flows followed by sudden peaks in early and late July resulted in the inundation of eight of the thirteen nests surveyed at central Platte River sites in 1988. The median elevation of these nests equates to a stage of about 2,895 cfs at the Grand Island gage. Flows higher than 2,895 cfs during June 16 to August 31, the latter half of the nesting season, occurred in 18 of the 30 years from 1959 to 1988, suggesting that nest inundation is likely to be a common occurrence given present habitat conditions (FWS, unpublished data). Nesting Habitat at Sand and Gravel Mining Operations '" 6"7 Sidle and Kirsch (1993) analyzed the use of sand pits by least terns and piping plovers along the entire Platte River. There are about 255 sand and gravel mining sites along the Platte, Loup, and North Loup rivers; the majority occurring along the central Platte River. Most (99 percent) were within 1 mile of the rivers, and 178 provided no suitable nesting substrate. Few sand and gravel mining operations occurred along the Loup and North Loup rivers. The number of mining sites with suitable nesting habitat was similar along the central and lower Platte River, but most unsuitable sites occurred along the central Platte River. Size and shape of suitable sand and gravel pit habitat varied. Some had roughly linear lakes with chains of sand and gravel piles jutting from the bank. Others contained circular lakes with sand and gravel on one or more banks with an occasional peninsula of sand and gravel extending into the lake. Three sand pits contained an island of sand and gravel in lakes. Sites along the Platte River ranged in size from 1.5 to 197 acres in size and averaged 59 acres (n = 57). The sand and gravel component ranged from 0.5 to 92 acres and averaged 18.3 acres, and the surface area of water ranged from 1 to 150 acres and averaged 27.4 acres (FWS 5