Hailstone Reservoir 



Climatic setting. The net annual precipitation balance for 

 Hailstone Reservoir (from the MAPS database) is -28 inches, placing 

 it among the most strongly evaporative of the sample sites. 

 Average monthly precipitation for the Rapelje climatic station 

 shows a strong May-June peak. The 3-year running average of total 

 annual precipitation shows apparent periodicity, with 6 to 9 years 

 between peaks. Between the early 1970s and 1992, the 3-year 

 average remained mainly above the average for the period of record. 

 Data for 1993 and 1994 were not recovered for this station. 



Geologic setting. Hailstone Reservoir occupies a structurally 

 controlled basin underlain by medium-to-fine-grained sandstone of 

 an unidentified formation (Lennep Sandstone?) bearing intervals of 

 oyster shell conglomerate with a sandy matrix. Surficial sediments 

 within the lake basin include fine-grained, mucky silt, extensive 

 areas of precipitated salts on low-gradient shorelines, and well- 

 sorted, ripple-marked sand in higher-energy littoral areas. 



Hydrologic type. Hailstone Reservoir is a managed impoundment 

 which probably had a history as a natural wetland prior to the 

 construction of the dam which now controls outflow. Although the 

 reservoir has a spillway and has discharged water in the past, at 

 the time of sampling in April 1993 and during follow-up 

 investigations in October 1994, lake stage was more than 5 feet 

 below the spillway crest. U.S. Fish and Wildlife Service personnel 

 responsible for Hailstone Reservoir report that no spill has 

 occurred since the early 1980s. For classification purposes. 

 Hailstone Reservoir is considered to be effectively lacking surface 

 discharge. 



Basin characteristics. Hailstone reservoir has an intermediate 

 ratio of catchment to wetland area when compared to hydrologically 

 similar sample sites. Attempted sounding of the reservoir was 

 terminated by the near-arrest of the surveyor; a single depth 

 measurement of 6.5 feet is thought to be close to the maximum for 

 the reservoir. Low topographic gradients around most of the 

 reservoir imply highly transient shoreline positions as lake stage 

 changes. The sampling site WET24 is along one of the steeper, 

 comparatively less transient reaches of shoreline. 



Active ground-water seepage through the dam supports a small flow 

 in Cedar Creek immediately below the dam face, and provides for 

 some export of solutes under the observed low-water conditions. 



Water chemistry. When sampled in April of 1993, Hailstone 

 Reservoir water was a "eusaline" sodium sulfate brine with low 

 carbonate and bicarbonate concentrations. Mineral equilibria 

 indicate substantial supersaturation with carbonate species and 

 slight supersaturation with gypsum. [Possible errors in calcium, 

 magnesium and alkalinity analyses render these saturation indices 

 uncertain. ] 



