FLOOD05393

• County: Statewide
• Basin: Statewide
• Title: Flood-Hydrograph Analyses and Computations
• Date: 8/31/1959
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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EM 1110-2-1405
31 Aug 59

APPENDIX I

LIST OF SYMBOLS

d=depth of flow, in fed;
e=vapor-prrssure, in millibars;
y=acceleralion due to gravity (32.2 feet per second pcr second);
qp=pesk rate of diseh8l'gc of unit hydrograph for unit rainfall duration, i" in c;f.~ pPJ" squar(' mih.;
qil'R=peak rate of discharge of unIt h~rdrograph for unit rainfall duration, tHI in c,f,s. Pf'J' sqURrl' mill';
tp=lag time- from mid-point of unit rainfall duration, in to ppak of unit h:nlrograph, in hours;

t,~unit rainfall duration, equal to ;.~, in hours;

t,R=)ag time from mid-point of unit rainfall duratibn, iSI to p<,ak of unit hydrogrnph, in hours;
t~=unit rainfall duration othpr than standard unit, iT, adopted in sp<"cific stucl~~, in hours;
A=drainage areR. in squart" miles;
AJII=area within Thi(>SSpn polygon and basin, in square milps;
C,,=co<.'fficient d{lp<"nding upon units and drainagp basin charactpristics;
r,=coefficient dppending upon units and drainagC' basin charaetpristics;
J:n,=infiltration index, in inches per hour;

}~=conver5ion factor=J~fJB XAp;
".

L=river mileage from the given station to the upstrpam limits of tll(' drain8gt. arpa;
Lm=river mileage from th(" station to center of gravity of the draillagp art'a;
P=precipitation, in inches;
P..=avera.ge depth of rainfall within ,Thi,'ssen polygon, in ind..s;
p.'fJ=totaI rainfall at observation station in Thi('SS('n polygon, in incll('s;
Q.=pcak rate of discharge of unit hydrograph, in cubic feet p,'r S('cond;
Re = rainfall excess;
W-50=width of the unit hydrograph, measurcd at discharge ordinatl' equal to 50 I",rc,'nt of tI.. pl'ak
ordinate, in hours or minutes;
W-75=width of the unit hydrograph measured at discharge ordinatc l'qual to 75 pl'Cl,,'nt of tI.. pl'ak
ordinate, in hours or minutes"

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