Repeat the Spillway Crest Design Example $($see Lecture Slides

below$)$ for an elliptical approach crest, using a design

procedure that guarantees a minimum pressure head of $-15ft.$

Use a maximum discharge of $7,000cms$ instead of $5,666cms.$ Plot

the spillway shape. Use an arbitrary crest elevation of $100ft.$

Example: Spillway Crest Design

Problem Statement: For a maximum discharge of $200,000cfs$

$(5666\frac{m^3}{s})$ and a maximum total head on the spillway crest of $64$

$ft(19\mathrm{.}5m),$ determine the crest length with no piers, the minimum

pressure on the crest, and the discharge at the design head for the

standard WES ogee spillway. The height of the spillway crest, $P,$

is $60ft(18m).$ For this example, use the design procedure of

setting the ratio of the of the maximum head to design head to the

value of $1\mathrm{.}33.$

Solution:

Since $\frac{H_{\text{m}\text{a}\text{x}}}{H_d}=1\mathrm{.}33,$ then $H_d=\frac{64}{1\mathrm{.}33}=48ft(14\mathrm{.}6m).$

Also, calculate $\frac{P}{H_d}=\frac{60}{48}=1\mathrm{.}25.$

Then, from the figure $C_d$ for the WES standard spillway shape,

the value of $\frac{C}{C_0}=1\mathrm{.}02$ and $C=1\mathrm{.}024\mathrm{.}03=4\mathrm{.}11.$