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â€¢ â€¢ â€¢ Rainfall Streamflow Evaluation ~ Urref" ~e\~u~ i A i Aehe!", ET is evapotranspiration J ~)(,f),\l~~ !1nww~~ GW is groun ~~=e:cl=~l=i=~~, e~priaH;iad j P ire han d i CJ[ This express ~ . _ te t e eace l'Jul!A'Jll.4!'"'.it"1~'1.L...,, 1 l:fbf.l'ilM':!ffl/t. The potenti ~ metric co/ n Survey over the past vlQ~...,. years ,.,,,,.t;,,.., /, low /, gradien~s and a decrease the Peace River draiRa~e basin +oea~ed upstream from..drawn that inflowoutflow gradients are aa~S~.i/ constan s of this section. a...,A4.d scussed in the concluding remarks can be considered approximately constant over a decade or more, therefore, expression (1) above can be reduced to P = SW + GW â€¢ A S ;lJ,..J) ( 2 ) o r The expression clearly demonstrates the functional relationship between IP and sw0 â€¢ â€¢ To determine what change~ if any, has. occurred in the relation_1 ! ... \ ' (Seaf?.:.el:I ~no{ /,&rr;;,!SrYI' 196~ ship between these variables, a series of doublemass curves ere prepared. Three precipitationstreamflow sets are shown: BartowBartow, WauchulaZolfo Springs, and ArcadiaArcadia . . Each relates cumulative values of rainfall to cum~lative e values of streamflow. This was done by tabulating th p annual rainfall for
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â€¢ â€¢ â€¢ ,o ~~1:.~ 47 ?,/. , ~.,~( I t:f '(/ f each se j a~~aring a second column of values by sequentially summing the values of annual rainfall totals. The same method was used to tabulate cumulative streamflow values. These two sets of data, rainfall and streamflow cumulations, were then plotted using the vertical axis as the rainfall reference and the horizontal axis as the streamflow reference. In theory the resulting plot~ be essentually a straight line if the ratio of ( proporti~~etween rainfall andf treamflow remains constant; a in the slope of (he data plot indicatesf hat a change has occurred in the ratio of proportionality .. Examination of these pl_ots resu J _ ___,_ identification of three major trends " the perieds 1934 th for ArcadiaArcadia nd WauchulaZolfo Springs ar showing approximately a 2 percent and a 22 percent period WRl==wi!l!tl@'8 a~~~rs,v &Rd 11pon fqr the 1949 th ~ 1958 and 1961 th 1'74?A 1<;..s?~ i Returning to expression (2) above;it is evident that a large change in the ratio /, p of proportionality between P and SW0 requires an equal and o ~site change in the ratios of proportionality for GWr and AS. The value, S, has been .~â€¢~,,,,,.,/ well documented by ~S. Geological Survey publications to be a small average . ,.... annual value; howeve~ it is a negative value during the last 19year period /\ _z_I
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â€¢ â€¢ â€¢ under consideration. The inescapable conclusion drawn from expression (2) is that the ratio of proport~onality for the GWr term must increase significantly in mag~itude, a condition which canonly result' from induced leakanc ~ ~ l;e .. groundwater withdrawals beneath the drainage basin. Additionally, in order ,.. to reestablish the inflowoutflow gradients, previously assusmed to be constant, an even greater increase in GWr would be required. In conclusion ~ streamflow reduction, increased groundwater recharge Jand_A, . ,,, ' ' ,4i. """"""we:,t,,,,,. ~reduced water in storage each correlate WMff. the timeframe 1961 thru 1979. A REFE t\l C(TEDI . / 9~tJ., ., ,'&,.,,'., ' a;~7+ 15~1' .~7 . 21â€¢
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â€¢ â€¢ â€¢ Rainfall Streamflow Evaluation The inputoutput relationships within the hydrologic system of a river basin may be described by the water balance. The expression P = ET + SW0 + GWr .AS { 1) is a w~ter balance equation in which Pis rainfall expressed in inches, ET is evapotranspiration expressed in inches, SW is surface water outflow GW is ground water recharge expre~sed in inches, expressed in inches,/and AS is the change in storage expressed in inches. This expression can be used to evaluate the Peace River streamflow by making the assumption that groundwater underflowing the basin is essentrally constant. The potentiometric countour mapping by the US Geological Survey over the past thirty years has documented an increase in the inflow gradients and a decrease in outflow from the ground water system beneath the Peace River drainage basin located upstream from the Aracdia discharge measurement station. At this point in the discussion the assumption is drawn that inflowoutflow gradients are essentually constant; the affects of departures from that assumption will be descussed in the concluding remarks of this section. The ET term can be considered approximately constant over a decade or more, therefore, expression (1) above can be reduced to p = SW + GWr .. a s 0 (2) The expression clearly demonstrates the functional relationship between P and SW0 â€¢ To determine what change if any has occurred in the relationship between these variables, a series of doublemass curves were prepared. Three precipitationstreamflow sets are shown: BartowBartow, WauchulaZolfo Springs, and ArcadiaArcadia . . Each relates cumulative values of rainfall to cumulative values of streamflow. This was done by tabulating tha annual rainfall for
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â€¢ â€¢ each set and preparing a second column of _ values by sequentially surrming the values rif annual rairifall totals. The same method was used to tabulate cumulative streamflow values. These two sets of data, rainfall and streamflow cumuJations, were then plotted using the vertical axis as the rainfall reference and the horizontal axis as the streamflow reference. In theory the resulting plot should be essentual.ly a straight line if the ratio of proportionality between rainfall and streamflow remains constant; a brake in the slope of the data plot indicatesthat a change has occurred io the ratio of proportionality. Examination of these plots resutled in the identification of three major trends irr the data or curves. These were the periods 1934 thru 1946, 1949 thru 1958 and 1961 thru 1979. The curves for ArcadiaArcadia and WauchulaZolfo Springs are nearly identical both showing approximately a 2 percent and a 22 percent reduction in streamflow per inch of rainfall for the 1949 thru 1958 and 1961 thru 1979 periods,respectively, when referenced to the 1934 thru 1946 period. For the BartowBartow stations the records do not include the early period, therefore ~he 1949 thru 1958 ~A, . ~,,,,,:._#lt:tCP/~/0,79~"'4.. period was used as the reference base. The indicated redu~ ion ,(ac 65 percent 0 a:~~ ul~~~~>w~~ . /.'t::. artd t:11:)eA el ose, examination u~e data suggest a 9eeeF16ar:: s ope 9f e,ert ~ere .,.,..,,,:Alfi ~q "lA~o/~A,, severe s treamfl ow reduction ~gl:1R in 197%) h8W&N' its s1.1rv9 t:las RQt beeR cl~l!l~ ,i:i!.._. / C,,'f'9 /'9S$~t!!J Returning to expression (2) above it is evident that a large change in the ratio of proportionality between P and SW0 requires an equal and oposite change in the ratio~ _ of proportionality for GWr and AS. The value, ~ S, has been well documented by US Geological Survey publications to be a small average â€¢ annual value, however it is a negative value during the last 19 year period
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â€¢ â€¢ â€¢ under consideration. The inescapable conclusion drawn from expression (2) is that the ratio of proportionality for the GWr term must increase significantly in magnitude, a cond1tion which can only result from induced leakance due to groundwater withdrawals beneath the drainage basin. Additionally, in order to reestablish the inflowoutflow gradients, previously assusmed to be constant, an eve~ greater increase in GWr would be required. In conclusion streamflow reduction, increased ground water recharge and reduced water in storage all each correlate with the timeframe 1961 thru 1979 â€¢ .
