| 5.1 | BASEFLOWHEC1 | BaseFlow using HEC-1 Method | ||||||
| Purpose: | ||||||||
| Compute baseflow using recession formula from HEC-1 | ||||||||
| Calling Sequence: | ||||||||
| Call BASEFLOWHEC1(TIMEINTERVAL, RECESSIONRATIO, INITIALBASEFLOW, FINALBASEFLOW, RATIORECESSIONFLOWTOPEAK, PEAKFLOW, RECESSIONTHRESHOLD, NUMBERFLOWS, DIRECTRUNOFF(1), BASEFLOW(1), TOTALFLOW(1)) | ||||||||
| Declarations: | ||||||||
| INTEGER | TIMEINTERVAL | |||||||
| DOUBLE PRECISION | RECESSIONRATIO | |||||||
| DOUBLE PRECISION | INITIALBASEFLOW, FINALBASEFLOW | |||||||
| DOUBLE PRECISION | RATIORECESSIONFLOWTOPEAK, PEAKFLOW | |||||||
| DOUBLE PRECISION | RECESSIONTHRESHOLD | |||||||
| INTEGER | NUMBERFLOWS | |||||||
| DOUBLE PRECISION | DIRECTRUNOFF(NUMBERFLOWS), BASEFLOW(NUMBERFLOWS) | |||||||
| DOUBLE PRECISION | TOTALFLOW(NUMBERFLOWS) | |||||||
| Augument Description: | ||||||||
| TIMEINTERVAL | (Input) | Time interval, minutes. | ||||||
| RECESSIONRATIO | (Input) | Ratio of a flow on the recession curve to flow one day later. | ||||||
| INITIALBASEFLOW | (Input) | State of baseflow, volume per second, corresponding to first element of DIRECTRUNOFF array | ||||||
| FINALBASEFLOW | (Output) | State of baseflow, volume per second, corresponding to last element of DIRECTRUNOFF array | ||||||
| RATIORECESSIONFLOWTOPEAK | (Input) | If this value is greater than zero, the combined peak flow(direct runoff plus base flow) is multiplied by this ratio to obtain the flow where the falling limb of the hydrograph and the recession curve intersect. This flow is used instead of RECESSIONTHRESHOLD. | ||||||
| PEAKFLOW | (Input) | Initial value for peak flow to be used with RATIORECESSIONFLOWTOPEAK, volume/second. | ||||||
| PEAKFLOW | (Output) | peakflow for the current hydrograph, volume per second. If direct runoff is zero, peak flow is reset to baseflow. PEAKFLOW is not used if RATIORECESSIONFLOWTOPEAK is less than or equal to zero. | ||||||
| RECESSIONTHRESHOLD\ | (Input) | Flow where the recession curve begins, volume per second. This is flow where the falling limbof the hydrograph and the recession curve intersect. | ||||||
| NUMBERFLOWS | (Output) | Number of hydrograph ordinates. | ||||||
| DIRECTRUONFF | (Output) | Direct runoff ordinates, volume per second. | ||||||
| BASEFLOW | (Output) | Difference between total flow and direct runoff ordinates, volume per socond. | ||||||
| TOTALFLOW | (Output) | Total flow, baseflow plus direct runoff, volume per second. | ||||||
| REMARKS | ||||||||
| In HEC-1's view, baseflow has two components, a baseflow and recessionflow. | ||||||||
| Baseflow recedes from an initial value using the formula | ||||||||
| Qb=Q0Kt | ||||||||
| Qb is base flow; | ||||||||
| Q0 is initial base flow; | ||||||||
| K is a recession constant; | ||||||||
| ti is time | ||||||||
| Baseflow is added to derect runoff. When the total flow is less than recession flow, Qt, the total flow is replaced by Qt, and baseflow becomes the difference between the recession flow and derect runoff. | ||||||||
| Qt=QrK(t-tr) | ||||||||
| Qr is flow where base flow recessionstarts; | ||||||||
| tr is time when recessionstarts. | ||||||||
| At the time when the falling limb of the total flow hydrograph intersects the recession flow, recession flow starts receding according to the above formula. | ||||||||
| When direct runoff reaches zero, the baseflow curve is reset from baseflow based on Q0 to baseflow based on Qr | ||||||||