Laserfiche WebLink
Diversion Records <br />Of the main data types required for surface water modeling, historical diversion records are the most <br />valuable and the most difficult to synthesize. Historical diversion records reflect an integration of all <br />the constraints and opportunities that were present at the time of the diversion, such as cropping <br />patterns, ditch capacities, irrigation methods, water rights priorities, administrative practices, <br />precipitation, temperature and available Streamflow. Though historical demands are relatively easy to <br />generate from climate parameters, translating that demand into an historical diversion requires <br />information about the constraints and opportunities that individual irrigators faced. The relationship <br />between historical diversions and streamflows is also unclear. Experience has shown us that diversions <br />can be larger or smaller than average in wet years, as they can be in dry years. A clear, predictive <br />relationship between streamflows and historical diversions does not exist. Unlike historical diversions, <br />streamflows and climate parameters may be more easily synthesized from other inputs or adjacent <br />stations. <br />For these reasons, the period of record for historical diversions will be the primary factor governing <br />study period selection. Given that diversion records are available digitally from 1950 to the present, the <br />study period is naturally bracketed by those dates. <br />We were originally concerned that diversion records in the 1950s might have been too sparse to be <br />useful. As a quick check to determine the degree to which diversion measurement intensity may have <br />changed since 1950, the number of structures (ditches, canals and reservoirs) associated with time- <br />series data was extracted from HydroBase. Figure 1 shows that the number of structures for which <br />records exist has been gradually increasing since 1950, particularly in Water District 20. However, the <br />number has not increased so dramatically that it casts doubt on the value of earlier records. <br />Division 3 Diversion Record Coverage <br />as <br />~ 350 <br />300 <br />N <br />y c 250 <br />3 ~ 200 <br />~ ~ 150 <br />,d <br />~ 100 <br />o y <br />L 50 <br />d <br />~ 0 <br />E <br />~ O N ~ c0 00 O N ~ c0 00 O N ~ c0 00 O N ~ c0 00 O N ~ c0 <br />z ~ ~ ~ ~ ~ (~ (~ (~ (~ (~ I~ ~ ~ ~ ~ 00 00 00 00 00 O O O O <br />O O O O O O O O O O O O O O O O O O O O O O O O <br />-~- WD 20 ~ WD 21 ~~ WD 22 t WD 24 ~~ WD 25 ~ WD 26 -i- WD 27 WD 35 <br />Figure 1. Number of structures with diversion data for water districts in Division 3 <br />Streamflow Data <br />The feasibility study identified dozens of Streamflow stations in the RGDSS study area, though only a <br />handful have periods of record that extend the entire length of the diversion period of record. Table 1 <br />C:Acdss\Task2-3.doc Identify Study Period April 16, 1999 Page 2 of 18 <br />