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11/14/01 draft report, Schmidt and Box The model predicts that a proportion of the larval fish in each reach on each day is transported into backwaters. We assumed that larvae are transported across the shear zone that separates main flow and backwaters, and we assumed that the rate of transfer of larval fish into Ii<r backwaters is greater at high discharge than at low discharge, similar to dye studies (Graf 1995, (:/; f~"" Konieczki et al. 1997). We assumed that the rate at which larval fish enter and leave backwaters is \ \)~k. .)'I.~ ~nrela~ed to. the ~ensit~ ~f nurse~ fish ~hat are alr.ea~y in each backwater, and we assumed that as J r '\ 'fI) fish gaIn sWimmIng abilIty, some IntentIOnally sWim Into backwaters. J. &,' A v" We assumed that most larval fish remain in backwaters, but that some are swept back into ~("\ rT', the main flow. Thus, the model predicts that the population of larval fish in backwaters declines ,)- ~" .J ~ with time in relation to the computed "leakage" back into the main current. We assumed that the 'v~ "J )P rate of reentry to the main current is inversely proportional to the number of larval fish with ~ 1'\ fa- swimming ability and proportional to the rate of transfer of water between the main channel and \.} ..1 backwaters, which is directly proportional to discharge. ~. -<; A.!.,.J~. Fish that are nottransported into backwaters drift downstream to the next reach, where a _ \ ;\ (' ..:- proportion is transported into the backwaters there. Thus, during the period when larvae enter the l J 1\, t Green River, the population of fish in backwaters of each reach depends on the computed drift, ) ( \" 't\~. (,'J' f~ransport into backwaters, and leakage from upstream backwaters back into the main flow. Later in , . //J',the year, backwater populations exponentially decline in upstream reaches and support a low level ,)i ,x.,,\.1 of continuous drift. ~y:v odel components: hydrolol:Y (' <: We used mean daily discharge data, available for U.S. Geological Survey (USGS) gaging . . stations, in our model. We made assumptions about the length of the modeled reach to which specific gaging station data applied. Discharge of the Yampa River was either obtained for the gaging station at Deerlodge Park, CO (station number 09260050), or was estimated as the sum of measurements of the Yampa River made near Maybell, CO (station number 09251(00), and of the Little Snake River near Lily, CO (station number 09260(00). Discharge immediately downstream from the confluence of the Yampa and the Green River was determined from the sum of the Yampa Ri~er data and measurements of the Green River near Greendale, UT (station number 092345(0). Mean daily discharge measured at Jensen, UT (station number 09261000), was used as the discharge in the 142 kIn reach to Ouray, UT, where the Duchesne and White Rivers join the Green. Downstream from this point, the Green River discharge was determined as the sum of the Jensen data and data for the Duchesne River near Randlett, UT (station number 09302000) and the White River near Watson, UT (station number 09306500). In the model simulations, mean daily discharge was used to compute mean stream velocity, shoreline complexity, exchange rate of water across shear zones, and leakage rate of larval fish from backwaters into the main channel. 9 ....