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<br />[ftl/s. cubic fOQt per secQnd; (ft3/s)lmi, cubic fQQt per secQnd per mile] <br /> <br />Table 4. Water balance for selected reaches of the South Platte River on selected dates <br /> <br />Surface water <br /> <br />Ground water <br /> <br />Total Incramenta' <br />apeelllc &pee"'c <br />discharge discharge <br />(It"/s) [(<<"/s)/ml] <br />08/28/92 389 380 9,0 2.5 0 <br />09/23/92 240 318 78 17 24 <br />11/02/92 207 259 52 15 20 <br />12/02/92 143 154 II 3.1 7.0 <br />01/19/93 340 245 -95 -27 0 <br />05/19/93 798 710 -88 -25 0 <br />07/27/93 355 405 50 14 12 <br />09/28/92 127 165 38 4.5 27 <br />10/30/92 157 181 24 2.8 13 <br />12/01/92 212 273 61 7.3 22 <br />01/15/93 192 226 34 4.0 15 <br />05/17/93 366 414 48 5.7 13 <br />07/28/93 315 379 64 7.6 19 <br />08127/92 480 605 125 16 21 <br />09/24/92 228 265 37 4.6 16 <br />10/29/92 243 285 42 5.2 15 <br />1l/30/92 354 399 45 5,6 II <br />01/14/93 237 257 20 2.5 8.0 <br />OS/25/93 361 372 II 1.4 3.0 <br />07/29/93 364 382 18 2.2 6.0 <br />BReach I extended 3.54 miles from the SQuth Platte River at 64th Avenue to the South Platte River at 88th Avenue~ except fQr the 09/23/92 <br />measurement, which extended 4.6 miles foom the SQuth Platte River at 64th Avenue to the South Platte River at McKay Road. <br />bReach 2 extended 8.4 miles from the South Platte River at I 04th A venue to the South Platte River upstream from the Brighton Ditch headgate. <br />CReach 3 extended 8.01 miles frQm the SQuth Platle River at 160th Avenue tQ the South Platle River at Highway 52. <br /> <br />Raach <br /> <br />Date <br /> <br />Tota' <br />Inflow <br />(!t"/s) <br /> <br />'I <br /> <br />"2 <br /> <br />'3 <br /> <br />Small-Area Flow System <br /> <br />The quantity of ground-water discharge from <br />the small-area flow system to the South Platte River <br />was estimated from direct measurements of instanta- <br />neous ground-water discharge made at the 30 cross- <br />section sites. Instantaneous ground-water discharge <br />from the small-area flow system ranged from - 1,360 to <br />1,000 (tt3/s)/mi, with a median value of -5.8 (tt3/s)/mi <br />at the 30 cross-section sites (fig. 4 and table 9). The <br />maximum ground-water discharge rates measured <br />for the small-area flow system are 50 to 60 times <br />higher than previously estimated ground-water <br />discharge rates for this reach of the South Platte River <br />(Gaggiani and others, 1987) and are higher by a similar <br />magnitude than maximum incremental ground-water <br />discharge rates measured by mass balance in this study <br />(table 4). Furthennore, measurements ofthe large-area <br /> <br />Totsl <br />outflow <br />(It"/a) <br /> <br />Percent 01 <br />surface-water <br />outflow <br /> <br />flow system indicated that ground water continuously <br />discharged to reaches 2 and 3 (table 4 and fig. 3), <br />whereas measurements of the small-area flow system <br />indicated that surface water recharged the aquifer <br />as frequently as ground water discharged to the river <br />(fig. 4). The reversals in flow direction and the high <br />rates of instantaneous ground-water discharge from <br />the small-area flow system are plausible if they reflect <br />transient conditions in a small volume of the flow <br />system, Measurements of river stage and discharge <br />from the MWRD plant indicate that changes in river <br />stage were related to hourly changes ilJ eflluent- <br />discharge rates from the MWRD plant (fig. 2). These <br />frequent changes in river stage, although typically less <br />than about 0.25 ft, may have provided a stress on <br />the small-area flow system large enough to cause the <br />transient discharge conditions that were measured at <br />the sediment/water interface. <br /> <br />12 Quantity and Quality of Ground.Water Discharge to the South Platte Rlvar, Denver to Fort Lupton, Coloredo, <br />August 1992 Through July 1993 <br />