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<br />44
<br />
<br />M. J, COHEN ET AL.
<br />
<br />Source
<br />
<br />Table 2. RelUl11 flows to the Colorado Rive,' lIIainSlem below Morelos Dam.,
<br />1992-1998. Mean anllual discharge (10" 111")
<br />
<br />Non-flood years Flood years
<br />
<br />KM 27 wasteway
<br />San Luis Rio Colorado effluent nr. Km 27
<br />KM 38 wasteway
<br />Colector del Sur drain
<br />Principal del Sur drain
<br />Total return flows to the river (Q,r)
<br />
<br />22
<br />12
<br />1.3
<br />11
<br />24
<br />70
<br />
<br />220
<br />12
<br />6,5
<br />12
<br />29
<br />280
<br />
<br />Table 3. \ValeI' balllllce /01' lhe Colorad!) River mainSlem belo~l' Morclos Dam,
<br />1992-1998. Mean annual discharge (106 nr')
<br />
<br />Inflows and outflows
<br />
<br />Non-flood years
<br />
<br />Flood years
<br />
<br />Wasteways al.Limitl'ophe*
<br />Discharge at upstream boundary (Q",)
<br />Return flows to the river (Q,r)
<br />Precipitation (P)
<br />Tributary inflow (T,)
<br />Evaporation from open water surfaces (E)
<br />Evapotranspiration (ET)
<br />Change in aquifer storage (LlS.)
<br />Discharge to Laguna Salada sub-basin (Q,~)
<br />Discharge at the downstream boundary (QdJ
<br />Residual
<br />
<br />3,0
<br />28.3
<br />70
<br />0.2
<br />0,6
<br />4
<br />9
<br />5
<br />o
<br />26
<br />56
<br />
<br />3'1
<br />2620
<br />280
<br />0'2
<br />0'5
<br />270
<br />9
<br />460
<br />200
<br />2200
<br />- 240
<br />
<br />.. Ifl<lSI€U'<IJ'S <I' Limill'Of>he aggregates the records of the three wasteways that discharge into the Iimitrnphc:
<br />these flows are included as parI of the 'Tolal al SIB',
<br />
<br />below the SIB, and consumption of surface water by other vegetation, or errors in the
<br />calculated Qds' Most notable is the difference, of two orders of magnitude, in
<br />discharge at the upstre~lm houndary, Evaporation from open water surfaces and change
<br />in storage hoth rdicl:t the cft~cts of inundation of the floodplain, which greatly
<br />increased the potential 1111' inliltration and evaporation, Change in storage here repres-
<br />ents only gains. and does not retlect losses due to phreatophytes, sub-surface flows, or
<br />other fal:tors. Evapotranspiration only reflects that of emergent wetland vegetation;
<br />mean annual ET 11)1' the mainstem was estimated at 210 x ]Obm-'.
<br />Table 4 shows the values for the variables in the water balance equation for the
<br />Cienega de Smml Clara for the years ]992-1998, The estimated losses to MODE
<br />discharge due to evaporatilm and seepage between t11e SIB and the Cienega
<br />(0'39 x 10 mt'year" I) represent less than 0,4% of total discharge and were not included
<br />in the water balance. In 1993, discharge t11rough t11e MODE was disrupted by the Gila
<br />River flood event. Total recorded discharge at the SIB in the bypass extension that year
<br />was 75,8 x lOb In'', In ] 993, Wellton-Mohawk ceased discharging to the MODE on 2]
<br />February (contributing 2S% of total annual discharge). From 21 February through 30
<br />May the MODE contained Gila floodwaters (S8eX, of total discharge); discharge from 31
<br />May to 4 November were from Yuma Valley ground-water wells (17%), and for
<br />t11e remainder of the year the discharge consisted of San Luis, Arizona effluent
<br />
<br />~.
<br />
<br />WATER BAlANCE FOR THE COLORADO RIVER DELTA
<br />
<br />,I'.
<br />
<br />Table 4. WaleI' balance/Ol'llte Ciellega de Sallla Clara, 1992-/998
<br />
<br />Inflows and outflows
<br />
<br />]0"11)'
<br />
<br />Discharge at upstream boundary (Q"s)
<br />Return flow (Qrl)
<br />Precipitation (P)
<br />Tributary inflow ('1',)
<br />Evaporation from open water surfaces (E)
<br />Evapotranspiration (ET)
<br />Change in aquifer storage (LlS.,)
<br />Discharge at the downstream boundary (Qd')
<br />
<br />128
<br />16
<br />2
<br />o
<br />84
<br />60
<br />2
<br />o
<br />
<br />w
<br />
<br />c-,,~.
<br />c::;:;
<br />~"l'
<br />t"",1
<br />
<br />Table S. WaleI' bakmcc/or El India W'elkmds., 1992-1998
<br />Inflows and outflows
<br />
<br />lOb m3
<br />
<br />Discharge at upstream boundary (Q"s)
<br />Return flow (Qrr)
<br />Precipitation (P)
<br />Tributary inflow ('1',.)
<br />Evaporation from open wllter surfaces (E)
<br />Evapotranspiration (ET)
<br />Change in aquifer storage (LlS.)
<br />Discharge at the downstream boundary (Qd')
<br />
<br />18
<br />o
<br />0,2
<br />o
<br />]
<br />4
<br />3
<br />]0
<br />
<br />(. <] 'X.) (I~~C, 1993). The interruption in flows through the MODE decreased the
<br />size of the C1enega and led to the mortality of 60-70% of the marsh foliage (Zengel et al
<br />1995). "
<br />
<br />Arte'sian spr,in~s at the soutll-eastern edge of t11e delta sustain pocket wetlands, many
<br />of extremely hmlted area yet supporting greater plant diversity (Ezcurra et ai., 1988)
<br />than the w~tlands sustained by agricultural drainage (Luecke el aI" 1999). Glenn et al.
<br />(] 996) estimate that these artesian springs discharge approximately] 07 m' year - I.
<br />Table 5 ~hows the mean annual values for t11e variables in the water balance equation
<br />ro~ El Indlo ,,:etlands for the years ] 992-1998. The Plan de Ayala drain, serving
<br />Irngated areas 111 the San Luis valley, discharges to a point behind the levee on the left
<br />bank of the Colora~o River. CNA records for this drain served as discharge at the
<br />upstream boundary for tl1e system. The results of the mass balance equation for EI Indio
<br />reflect t11e limited data available and uncertainty regarding the fate of water entering t11C
<br />system. Qd' was derived from the mass balance.
<br />
<br />Discussion
<br />
<br />Discharge t11rough the delta, and particularly through the mainstem Colorado River-Rill
<br />Hardy C()n1plex, demonstrated marked variability between flood and non-flood years,
<br />Flood years also showed greater discharge tl) tile mainstem from wasteways 11I1d
<br />agricultural drains relative to non-flood years, consistent with increased deliv~ries lIr
<br />Colorado River water to Mexico in these years, As a result of increased surface arell dlll'
<br />
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