Estimate the $100-$year return period peak streamflow discharge for a $332\mathrm{.}8$ acre basin using the

design storm approach. The $100-$year design is provided below. The $\backslash$phi $-$index for the basin is $1\mathrm{.}2$

inches$/$hour and the average baseflow at the site is $10$ cfs$.$

a$)$ Based on your knowledge of the properties of unit hydrographs, the volume of direct runoff $($V d$)$

of a unit hydrograph for this basin should be $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$ acre$-$feet. $($Hint: Do not use any

information below to answer this question.$)$

b$)$ Compute the rainfall excess $($P e$)$ for each $30-$minute time step for the $100-$year design storm.

CLEARLY MARK YOUR FINAL ANSWER in the space below.

Incremental Rainfall for $100-$year Design Storm

Time, t Precipitation, P

$($min$)($inches$)$

$0$

$0\mathrm{.}6$

$30$

$2\mathrm{.}7$

$60$

$1\mathrm{.}6$

$90$

c$)$ In the material gathered for this project, you see that two unit hydrographs that have already been

developed for this basin. To predict the direct runoff hydrograph for the $100-$year design storm, the

$\_\_\_\_\_\_\_-$minute unit hydrograph must be used.

$30-$minute Unit Hydrograph $60-$minute Unit Hydrograph

Time $30-$min UH Time $60-$min UH

$($min$)($cfs$)($min$)($cfs$)$

$0000$

$151283096$

$3025660264$

$4538490240$

$6028812072$

$751921500$

$9096$

$1050$

$10$

d$)$ For the unit hydrograph you selected in part c$),$ calculate its volume of direct runoff $($Vd$)$ from the

unit hydrograph values and check that it is $($or is not$)$ correct $($i$.$e$.,$ the same as computed in part a$).$

e$)$ Predict the direct runoff hydrograph for the $100-$year design storm using unit hydrograph methods.

Enter the unit hydrograph you selected in part c$)$ in the space provided $($assume it is correct,

regardless of the outcome for part d$).$ Show your calculations and CLEARLY MARK YOUR FINAL

ANSWER in the space below. Enter the time for each time step of the total direct runoff

hydrograph $($more than enough entries have been provided below for this event$).$

Direct Runoff Hydrograph Prediction

Time UH

$($min$)($cfs$)$

$0\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_$

$\_\_\_\_\_\_\_$

f$)$ The estimated $100-$year peak streamflow discharge is $\_\_\_\_\_\_\_\_\_\_\_\_\_$ cfs