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in this publication compute 100-year peak discharge rates and are based upon data from floodplain studies previously designated by the ewes. Regression equations have been developed for nine major river basins within the :;tate and a number of subbasins. The appropriate equation from these guidelines for flooding sources studied in La Plata County is as follows: Q= 589.2(A)0.512 A= Drainage area in square miles (kA<760 sq m) Q= 100-year peak discharge in cfs A 100-ye,lf discharge rate for the Florida River dOV/llHream of Lemon Reservoir was computed by three C.ifferent methodologies. Details of these three approaches are provided below along with a recommendation of which to utilize. I. ~Jage Analysis. A flow frequency analysis of USGS (J age No. 09363000 (Florida Ri ver Near Durango) has been carried out. This gage has 46 ye ars of record between 1901 and 1960 which is a period before the completion of Lemon Dalll in 1963. The gage location is apprQ).imately 5.5 miles below Lemon dam dowl~stream of Red Creek and has a drainage area of 97.4 sq mi. Flood frequency analysis of the gage record was carried out using the HEC-l'FA (U.S. Army Corps of Engineers, Hydrologic Engineering Center, May 1992) software package which utilizes the procedures of United States Water Resources Council Bulletin #17B (1981). The computed 100-year dischalW~ rate at the gage using this approach is 3,130 cfs. 2. Regional Regression Equation Ana~.!i. Applicatiol of the previously pre:sented CWCB region al regression equations to the 97.4 sq rni drahage area to the USGS gage location yields a discharge rate of approximately 6,140 cfs. Tb is value is substantially higher than the IOO-year discharge rate determined by gage analysis. A serious shortcoming of the regional regres~;ion approach is that it does not account for an)' attenuation of peak flows by Lemon Reservoir. Though it has no dedicated flood stora,ge IJool, the reservoir could provide some flood control benefit depending on storage levels at the time of the event. Because of this possibility, the regional regression approach likely ov'~restimates peak flows below the dam and is not recommended. 3. Dam Outlet Capacity + Regional Regressio!l.r:9..m1i~l1LAT]!llysis. The approach adopted by the US ACE in its analysis of the Los Pinos River below ValIecito Reservoir was to assume a discha~ge rate from the dam equivalent to its outlet works capacity (3,100 cfs) and add to this peak flow rates d(:termined by hydrologic modeling (HEC-l) of the portion of the watershed located below the dam. A similar approach could be adopted for the Florida River below Lemon Dam. The outlet works capacity for L.(,mo:l Dam is 900 cfs. CWCB regional regres,:ion equations could then be applied to drainage areas located below the dam and computed peak flows added to the assumed dam discbarge. For the location of the USGS Florida River Near Durango gage, this drainage area is 28,4, sq mi and would generate a peak discharge of 3,270 cfs. Including dam releases of 900 c:fs, the 100-year peak discharge rate computed by this methodology for the USGS gage locntion would be 4,170 cfs. ;)