Simulation of the rainfall runoff process from a watershed by using a microcomputer

With the recent advent of the microcomputer, a powerful new tool is available for use by engineers and hydrologists. Some relevant characteristics of the microcomputers are the language used for programming (BASIC), its simplicity of operation, low cost, small size and easy transport to the office, laboratory or field for both data acquisition and model simulation;To accomplish the objectives of this research, the entire organization of the hydrologic part of the Kentucky Watershed Model (KWM) was restructured to fit the operational characteristics of an Apple II-Plus microcomputer with 48 K bytes of memory capacity. The resulting computer model (Apple-KWM) consists of a single program and 7 text files containing input/output data. The program permits the user to run it on a daily or yearly basis;The effectiveness of the model was tested using 1976, 1977, 1979 and 1980 water year data from Four Mile Creek Watershed, near Traer, Iowa. The results were compared with those obtained by using the original program written in FORTRAN. From the results of this study, it appears that the efficiency and precision of a hydrologic simulation process when using a microcomputer are as good as those from using large computer systems. The current Applesoft version of the KWM gives essentially the same simulation results as the original FORTRAN version when applied to Four Mile Creek Watershed. Small differences were observed which can be attributed to round-off error of the microcomputer;The Apple-KWM program requires about 16 K bytes of memory. On a yearly basis computation, 1.2 K bytes are needed for variables, 8.7 K for arrays and only 3 bytes for strings. About 10 K are still available for further modifications and/or additions. By using the compiler program TASC (Microsoft Inc.) computation time was reduced to 40 minutes as compared to its Applesoft counterpart which takes 5.5 hours for a full year computation;The daily basis option of the program permits the user to calculate the streamflows from a watershed on a day-by-day basis. This alternative gives the designer up-to-date information of the runoff process which can be used advantageously in forecasting flood discharges