Scientific Investigations Report 2006–5036
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5036
Measured inflows to and outflows from the refuges were used to make a separate estimate of refuge water use for comparison with those based on evapotranspiration estimates. Project inflows include all water originating from the Project that is drained or pumped into both the Tule Lake and Lower Klamath refuges.
Mean annual Project inflows to and outflows from the Lower Klamath refuge for 2003–2005 are based on measured flow data collected at D Pumping Plant, Ady Canal at State Line Road, and the Klamath Straits Drain at State Line Road. For water years 2003–2005, the combined mean annual inflow into the refuge through D Pumping Plant and from the Ady Canal was approximately 89,000 acre-ft, and mean annual outflow through the Klamath Straits Drain was approximately 15,300 acre-ft (table 6). The resulting net inflow was approximately 73,700 acre-ft. This amount is comparable to the estimated needed water delivery of approximately 77,600 acre-ft for the non-Area K refuge units located south of State Line Road that are irrigated by Project water.
Mean annual net inflow to the Lower Klamath refuge was approximately 49,800 acre-ft for 1962–2005 in contrast to about 73,700 acre-ft for 2003–2005 (table 7). Although mean April–September net inflows for 1962–2005 and 2003–2005 have remained fairly constant, mean October–March net inflow has increased considerably for 2003–2005. Increased flow deliveries during the autumn and winter since the mid-1980s reflect a significant change in refuge management, as more units have been managed as seasonal wetlands than in the 1960s and 1970s (fig. 3). In water years 1963, 1973, and 1984, there was no net inflow during the winter months of October–March, because more water was draining out of the refuge than was being pumped in. In the summer of water year 1965, there also was no net inflow of water to the refuge. Because of severe flooding in the previous October, the refuge already had saturated conditions and less water delivery was required.
Changes in the management of both refuges also can be observed in figure 4, which are graphs of monthly flows from 1961 through 2005 for Ady Canal, Klamath Straits Drain, and D Pumping Plant. Figure 4A shows an increase in flow deliveries to the Lower Klamath refuge during the fall and winter since the late 1980s. During this period, flows also decreased in the Klamath Straits Drain (fig. 4B). Both these trends are a reflection of the increase in the number of units that were flooded in the autumn and winter and managed as seasonal wetlands. Beginning in the early 1990s, more water was held in Sumps 1A and 1B to maintain a minimum elevation under ESA guidelines for sucker habitat protection. This change in management is seen in figure 4C. Significantly less water was pumped out of the sumps in the 1990s than during October–December in the three earlier decades. It also is possible to discern historical wet and dry periods from figures 4A-4C. During wet years, such as 1965, 1984, and the late 1990s, there is some correspondence between the D Pumping Plant and Klamath Straits Drain flows. More water is pumped through the D Pumping Plant to drain the Tule Lake sumps, and much of that water then passes through the Lower Klamath refuge. In dry years, such as 1981 and the early 1990s, more water deliveries were made through the Ady Canal (fig. 4A).
Most of the Project water is delivered to the Tule Lake refuge via the N Canal, Lost River, and numerous pumped inflows. Although there are no permanent flow gages on these canals or on the Lost River at locations near the refuge boundaries, some estimates of flow into the refuge by way of these waterways can be derived from a USFWS surface-water budget analysis of the refuge sumps. Mean annual inflows from the N Canal, Lost River, and miscellaneous pumped inflows were estimated to be approximately 46,100, 24,600, and 81,300 acre-ft, respectively (table 6). The USFWS analysis of Sump 1A and 1B had a deficit between surface-water inflow and outflow of approximately 30,300 acre-ft/yr. This amount includes surface-water-flow measurement error as well as probable unmeasured ground-water flow. Because there is an eastward ground-water head gradient along the western margin of the refuge, it is likely that there is some seepage entering Sump 1A and 1B from the Lower Klamath refuge and BOR Project lands to the west. The same USFWS analysis also showed a surplus between surface-water inflow and outflow from Sump 3 of approximately 11,300 acre-ft/yr. Ground-water flow from the southern part of the Tule Lake subbasin is consistent with hydraulic head data as well as historical accounts. The surface-water balance for the entire refuge had a deficit of approximately 19,000 acre-ft/yr. This amount includes both surface-water-flow measurement error and probable unmeasured ground-water flow. As stated earlier, the proportion attributed to surface-water measurement error versus the proportion attributed to ground-water flow is unknown. Most surface-water outflow from the refuge is through the D Pumping Plant and the N Canal. Estimated annual flow through the D Pumping Plant and the N Canal was approximately 59,600 and 35,300 acre-ft, respectively. Subtracting the sum of estimated surface-water outflows from the sum of estimated surface-water inflows and net ground-water inflow results in an annual net surface-water inflow to the refuge of approximately 76,100 acre-ft. This volume is consistent with the estimated needed water delivery total of 82,800 acre-ft shown in table 5 on the basis of open-water evaporation and evapotranspiration estimates. However, both methods of estimating water use, using evaporation and evapotranspiration estimates or inflows and outflows, have a wide range of uncertainty. Evaporation and evapotranspiration rates represent only average conditions, whereas much of the Tule Lake refuge inflow and outflow data were based on miscellaneous (rather than continuously monitored) flow measurements.
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