FLODROUT.TXT FLODROUT DOCUMENTATION: Flood routing program written in house using "Hydrology Guide For Minnesota" and "SCS National Engineering Handbook", Section 4 - HYDROLOGY. NOTE: This program was originally written for the HP9830 which was very limited in memory. At the present time the flood routing program is being revised to take advantage of the P.C.'s increased memory capability. INFLOW HYDROGRAPH PROGRAM PURPOSE: To compute 1. Inflow hydrograph from a given rainfall distribution, drainage area, time of concentration, and curve number based on soil conservation methodology (see blue book "Hydrology Guide for Minnesota".) 2. Outflow hydrograph produced by routing runoff through storage (based on continuity equation.) ASSUMPTIONS: 1. Rainfall distribution can be type 1, type 2, or an input distribution. 2. Unit hydrograph is computed using constants from John P. Torgerson"s publication "Development of Synthesized Hydrographs of Runoff From Rainfall in Small Watersheds." 3. Method of computing inflow is from the same publication.` 4. To calculate storage and outflow exceeding the amounts given by the input data, the computer assumes a straight line with a slope established by the last two points. LIMITATIONS: 1. Rainfall distribution can be defined by a maximum of 14 points. 2. Storage and outflow curves can be defined by a maximum of 20 sets of points each. The first elevation given must be the point at which outflow or storage is zero. 3. The computer can calculate a maximum of 150 points for an inflow hydrograph and 240 points for an outflow hydrograph. 4. The ratio of rainfall duration divided by time to peak of the unit hydrograph must be less than 150. Therefore, the minimum allowable time of concentration is: Rainfall Duration Minimum Tc 24 hour 14.3 minutes 12 hour 7.2 minutes 6 hour 3.6 minutes 5. In cases where the computer calculates an outflow volume for a given time increment which is larger than the inflow volume combined with the storage volume, then instead of printing a negative volume for storage, it prints zero and an asterisk. At the end of the hydrograph, it prints a message that the outflow volume is incorrect. 6. The time increment used to compute the inflow hydrograph is based on the ratio of rainfall duration to the time to peak of the unit hydrograph. Since the time to peak for a unit hydrograph is directly related to the time of concentration, this calculating increment changes at the following points: Rainfall Duration Time of Concentration 24 hour 28.657 minutes 2.985 hours 8.955 hours 12 hour 14.328 minutes 1.493 hours 4.478 hours 6 hour 7.164 minutes 0.746 hours 2.239 hours Crossing one of these boundaries will cause a change in the peak of the inflow hydrograph. For an outflow hydrograph, it will affect the storage elevation by one or two tenths of a foot. INPUT: 1. To calculate hydrograph: A. Enter curve number, drainage area, and time of concentration. B. Choose whether or not you want unit hydrograph printed. C. If rainfall, storage and outflow are on diskette, type in data filename.. D. If they are not on diskette, follow these steps: a. Rainfall 1. can be type 1 or type 2 standard distribution. 2. can be user defined by a maximum of 14 points. b. If outflow hydrograph is desired: 1. enter storage curve values as: elevation, acre ft. (maximum 20 sets). 2. enter outflow curve values as: elevation, c.f.s. (maximum 20 sets). 3. first elevation of both curves must be the elevation at which storage or outflow value is zero. 2. To store hydrograph on diskette. A. Enter data filename. B. For an outflow hydrograph, the machine will try to continue calculations to the point where storage is zero. It has 240 memory locations for storing the hydrograph. If it uses up all 240 locations, it will stop, print the time, time increment, outflow (cfs), total outflow (acre ft.), and remaining storage (acre ft.). At this point, there are two options: 1. Store the hydrograph as is. The computer will also store the time at which it was terminated. Any future calculations done with this hydrograph (combine with another hydrograph, channel flow, flood routing) will be terminated at the same time. This method retains accuracy in the beginning portion of the hydrograph at the expense of the total volume at the end. 2. Double the time increment (reducing the increments already calculated from 240 to 120) and continue calculations from there. This method sacrifices accuracy because it uses a larger time increment. This loss of accuracy becomes very apparent when a hydrograph with a very short time increment is combined with one that has a very long time increment. It is therefore recommended that the smallest possible time increment be used for storing the outflow hydrograph. PURPOSE: To compute outflow hydrograph by routing a hydrograph previously stored on diskette through a storage area. ASSUMPTIONS: 1. If the hydrograph on diskette had been terminated early (before reaching its zero value), the program will stop flood routing at the same time duration. 2. Outflow hydrograph is limited to 240 points. 3. Storage and outflow curves can be defined by a maximum of 20 sets of points each. 4. In cases when the computer calculates an outflow volume for a given time increment which is larger than the inflow volume combined with the storage volume, then instead of printing a negative volume for storage, it prints zero and an asterisk. At the end of the hydrograph, it prints a message that the outflow volume is incorrect. INPUT: 1. To compute outflow hydrograph: a. Enter filename. b. Enter storage curve values as: elevation, acre ft. (maximum 20 sets). c. Enter outflow curve values as: elevation, c.f.s. (maximum 20 sets). d. If the hydrograph on diskette was terminated early (see 2b below), the computer will stop flood routing at the time the inflow hydrograph was terminated and print a message explaining what happened. 2. See input 2 write-up in "Inflow Hydrograph Program". PURPOSE: To add together two hydrographs. ASSUMPTIONS: 1. The combined hydrographs will be computed using an increment that goes through the peak of one of the input hydrographs. The user selects which peak it will go through. LIMITATIONS: 1. If one of the hydrographs on disk had been terminated early, the combined hydrograph will stop at the same time to avoid giving misleading results. A message will be printed explaining what happened. INPUT: 1. Enter data filename. 2. Computer will print time at which each hydrograph starts. Change the start time of either hydrograph if desired. 3. The computer will print the peak of each hydrograph. Select which peak you want calculations to pass through. PURPOSE: To compute the outflow produced by routing a hydrograph through a channel. ASSUMPTIONS: 1. Method used is from USDA Hymo Computer Program. 2. The velocity used for all calculations is this program is a weighted velocity defined as the summation of (qv) divided by the summation of q. LIMITATIONS: 1. The cross section can be defined by a maximum of 21 coordinates each for X,Y, and 'N'. 2. For a given discharge, the program needs to be able to find depth and velocity. To save time during calculations, a table of 20 stages is prepared in advance with the relationship of depth, discharge, and velocity. Once the table is prepared, the computer just interpolates values from the table. 3. If hydrograph on disk was terminated early, this hydrograph will be terminated at the same time. INPUT: 1. Enter data filename. 2. If cross section is on disk, enter data filename. Otherwise, enter number of points on cross section (maximum 21). For each point, enter the value for X, Y and 'N'. The 'N' value is for the region between the current point and the previous point. Therefore, the first 'N' can bo 0. 3. Enter reach length and slope. 4. Make corrections in cross section if needed. NOTE: If the hydrograph on disk was terminated early, this hydrograph will end at the same time and the computer will print a message explaining what happened. PURPOSE: 1. To print the hydrograph contained on a data disk. INPUT: 1. Enter data filename where hydrograph is stored. OUTPUT: 1. Computer will print hydrograph. If it was terminated early, computer will print time at which it was terminated. PURPOSE: To create your own hydrograph and store it on disk. LIMITATIONS: 1. Hydrograph can contain a maximum of 240 points. 2. Time increment must remain constant for entire hydrograph. INPUT: 1. Enter time in hours when inflow begins. 2. Enter time increment in hours. 3. When machine displays time, then enter appropriate discharge. 4. To stop, enter zero. 5. Enter data filename of the hydrograph you wish to store.