WORLD METEOROLOGICAL ORGANIZATION 
HOMS COMPONENT 

Explanation of the criteria for classification and numbering of components  K35.2.03 (DEC 99) 

Explanation of the dates on the component's description  
LAG AND K ROUTING (NWSRFSLAG/K) 

1. Purpose and objectives Lag and K routing is a storage routing technique. 2. Description Examination of historical flood hydrographs of varying magnitude
provides a basis for establishing lag and K relationships for a reach. Constant lag implies that all possible flows are always to be lagged with the same fixed lagged time. A table of points defining a lag versus inflow
relationship is needed for use of variable lag. Linear interpolation is used to determine lag for flows which fall between points. Highly variable lag versus inflow relationships may show two or more discharges occurring
at the same time on the lagged inflow hydrograph. This "multiple intercept problem" occurs as a result of the hydrological technique, but it does not exist in nature. The problem is handled by adding the area under the lagged inflow curve at each time interval to maintain the correct volume. K can be thought of as the ratio of storage to discharge. It has the dimensions of time, and can be constant or variable. For variable K, a K versus outflow table is constructed. Linear interpolation is used to determine values of K between points. Since K is related to storage and discharge, it can be used to solve the storage routing (continuity) equation. A curve is developed of outflow versus twice the storage per time interval plus outflow values; values for outflow are found by linear interpolation from this curve. 3. Input Line input of inflow time series data; parameters defining the lag and K relationships; and initial inflow, outflow and storage values. 4. Output Printed output. Instantaneous outflow time series are generated. 5. Operational requirements and restrictions a. One person with knowledge and experience in hydrological processes, b. With the qualifications described above, 12 days of training is c. Program is written for use on the HP Unix computer, but could be d. Max. array sizes are variably dimensioned and are specified by the 6. Form of presentation Compressed file on the Internet; written documentation is furnished. 7. Operational experience This technique has been used extensively by the National Weather Service with good results; implementation is difficult but not complex. 8. Originator and technical support Originator: George Smith, Hydrologic Research Laboratory, NOAANWS. 9. Availability From the HOMS National Reference Centre for USA. 10. Conditions on use


Reclassified from J72.2.01 MAR 1987
(First entered:03 FEB 81 
Last updated: 06 DEC 99) 