U.S. Geological Survey (USGS)                         stlk1 and stwt1

NOTE: Any use of trade, product or firm names is for descriptive purposes
      only and does not imply endorsement by the U.S. Government.

NAMES
     stlk1 and stwt1 - Computer programs for analysis of hydraulic 
                       interaction of stream-aquifer systems


ABSTRACT
     Computer programs STLK1 and STWT1 calculate changes in groundwater
     levels at an observation well or piezometer, seepage rates between
     a stream and connected aquifer, and bank storage that occur in 
     response to time-varying stream-stage or recharge stresses that are
     specified by the user. The programs are based on analytical solutions
     to the groundwater-flow equation for several cases of hydraulic
     interaction between a stream and a confined, leaky, or water-table
     aquifer. The aquifers can be semi-infinite in width or of finite 
     width, and a semipervious streambank may be present between the 
     simulated stream and aquifer. STLK1 was developed for application to
     confined and leaky aquifers, and STWT1 was developed for application
     to water-table aquifers. The programs can be applied to the analysis
     of a passing flood wave, determination of groundwater-discharge rates
     in response to recharge, and determination of aquifer hydraulic
     properties.  


METHOD
     STLK1 and STWT1 are based on Laplace-transform analytical solutions
     to the groundwater-flow equation that are numerically inverted by use
     of the Stehfest (1970) algorithm to obtain real-time step-response 
     functions. These functions are then used in a convolution (or
     superposition) integral to calculate aquifer heads, streambank
     seepage rates, and bank storage in response to time-varying
     stream-stage fluctuations and basinwide recharge or evapotrans-
     piration. 
 

HISTORY

     STLK1 and STWT1 versions 1.0 09/01/1998 - Initial versions. (Initial
        release on USGS webpages, 12/04/2009)


DATA REQUIREMENTS
     Each program requires preparation of a data-input file that contains
     information on the types and hydraulic parameters of the aquifer,
     aquitard (if present), and semipervious-streambank material (if
     present) being simulated; initial conditions in the aquifer; stress
     inputs to the aquifer; and solution parameters.     


OUTPUT OPTIONS
     Primary output of the programs are calculated heads, seepage rates,
     and bank-storage volumes. Result and plot files are generated by
     each program. The result file contains detailed information on the 
     model simulation, whereas the plot file contains an abbreviated listing 
     of model results that can be used for graphing.


SYSTEM REQUIREMENTS
     STLK1 and STWT1 are written in Fortran 77. Input and result file names 
     are queried by the programs and read from the screen. The programs also 
     can be run in batch mode by redirecting program execution from the screen 
     to a batch file that contains the names of the input and output files.


DOCUMENTATION

Barlow, P.M., and Moench, A.F., 1998, Analytical solutions and computer 
programs for hydraulic interaction of stream-aquifer systems: U.S. Geological
Survey Open-File Report 98-415A, 85 p.

Examples of the use of the programs are provided in:
DeSimone, L.A., and Barlow, P.M., 1999, Use of computer programs STLK1 and 
STWT1 for analysis of stream-aquifer hydraulic interaction: U.S. Geological
Survey Water-Resources Investigations Report 98-4212, 61 p.


REFERENCE

Stehfest, Harald, 1970, Numerical inversion of Laplace transforms: 
Communications of the Association for Computing Machinery (ACM), v. 13, no. 1,
p. 47-49.


CONTACT
    Paul Barlow
    U.S. Geological Survey
    10 Bearfoot Road
    Northborough, MA  01532
    pbarlow@usgs.gov