Test Procedure

Please follow the procedure below in completing the test. You will be graded on your written and graphical explanations of steps you took, justification of assumptions and approximations made, and final determination of change in runoff. Please include this information in a loosely structured ``paper'' (i.e. grammar is relatively unimportant, but I must be able to understand your logic and results), which can be printed or delivered via e-mail or removable computer media by the due date.

1. Assemble needed information, including this document, class handouts, etc.
2. Download the ZIPfile containing WMS input files, if desired, from which Figs. 1-2 were prepared. Because of an apparent bug in WMS 8.0 the following files must be loaded separately
   1. background image files (for now just 67723232.tif, the DOQQ downloaded from Seamless)
   2. the land-use code table midtermLand.tbl (load from Hydrologic Modeling/Calculators/GIS Attributes dialog for
3. Delineate subbasins associated with the two culvert locations ``A-B'' using WMS or Fig. 1. Be sure current coordinate units are meters in the Topaz dialog!
4. Determine topographic basin characteristics (primarily slope ``S'', area ``A'', and basin length $L$). Remember that English units are required for the Rational Formula (ft and acres)
5. Estimate a time of concentration $t_c$ for the two subbasins using the Upland Method. Justify your assumption of landuse type. You can use other methods, but please justify your choices. See WMS 8.0 Tutorial Volume 2, Chp. 3 for additional guidance.
6. Determine rainfall intensity $i$ for a design storm in Collin County with a return period of 10 years, with the time of concentration determined in the previous step (use TxDOT spreadsheet referenced in the Rainfall lecture notes
7. Determine peak discharge expected from pre-construction conditions (i.e. those shown by Figs. 1-2).
   1. determine runoff coefficient $C$ for each landuse type, assuming the STATSGO hydrologic soil group for the UTD campus (Group D) is correct.
   2. Feel free to discuss whether you think that assumption is justified
   3. Note $C$ ranges from 0-1, and therefore is different than SCS Runoff Curve Number $CN$. Use the tables in Fig. 3 to find $C$ for each land-use/slope/recurrence-interval combination in this problem
   4. if using WMS, assign this C value to each land-use polygon, i.e.:
      1. copy the Land Use coverage, rename the copy ``Runoff Coefficient''
      2. hand-edit each polygon, e.g. by double-clicking on it, and enter your best guess for C
      3. use the ``Calculators/GIS Calculator'' choice under the Hydraulic Modeling module to compute a composite C for each basin, as we did in the tutorials

   5. use the Rational Method (2), or WMS to estimate peak discharge for outlets A-B

   Figure 3: Tabulated values of Rational method runoff coefficient $C$, after McCuen (2004). Select a value of $C$ given range of storm recurrence interval, hydrologic soil group, average basin slope, and land-use type.

   

   Figure 4: Typical composite Rational method runoff coefficients, after McCuen (2004).

   

8. Adjust land use designations (or really runoff coefficient $C$) to reflect present-day land use on campus in either of two ways:
   1. download the most recent (1995) free USGS airphoto of campus from National Atlas
   2. subdivide existing land-use polygons to reflect presence of large areas of pavement/roof/sidewalk (e.g. eastern parking lots, Waterview apartments, student center, gym, engineering buildings)
   3. adjust $C$ to reflect addition of impermeable areas over the last decade. Explain your reasoning.

9. Estimate change in peak discharge for the design storm resulting from UTD construction (repeat procedures outlined in step 7)

10. Prepare a short paper or outline detailing your procedure in solving this problem, justifying assumptions or estimates made, and illustrating your results and any intermediate steps (e.g. subdividing initial land-use polygons)

Good luck. If the assignment is taking an inordinate amount of time, contact me. I'm hoping that some of you choose the non-computer approach, but those comfortable with WMS should find it a big time-saver. I am available to clarify the questions and procedures, but I'll try to avoid showing you how to carry out the steps themselves.