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<br /> 2. <br />0 20 <br />Q <br />K <br />Vl <br />"- <br />U IS <br />.S <br />" <br />~ 10 <br />0 <br />.t:. <br />" <br />.. <br />0 <br />"" . <br />0 <br />" <br />Q. <br /> 0 <br /> <br />20 <br /> <br />40 <br /> <br />8 <br /> <br />. <br /> <br />Urbanization Factor <br />C , , --.... <br />00% <br />~l <br /> <br />Figure 3.12. Peak discharge rate for Mill Creek as a <br />jUnction of return frequency at differ- <br />ent levels of urbanization. <br /> <br />UrbanIzation Foetor 10 <br />c,':::-----.. <br />eo% <br />60% <br />50% . <br />45% <br /> <br />6 <br /> <br />1 <br /> <br />Mill Creek 01 Subwotershed 7 <br />(see Figure 2.2) <br /> <br /> <br />10 W ~ 40 ~ ro 70 00 00 <br /> <br />Return Frequency in Percent <br /> <br />4 <br /> <br />~ W ~ ~ ~ w ro BO ~ 00 <br /> <br />40 <br /> <br />35 <br /> <br />~ <br />K 30 <br />Vl <br />"- <br />U <br />.S 25 <br /> <br />Big Cotlonwood Creek at Subwotlllrshed 5 <br />(see Figure 2.2) <br /> <br />.. <br />'" <br />l; <br />"fi 20 <br />.. <br />o <br /> <br /> <br />"" <br />g 15 <br />Q. <br /> <br />'0 <br /> <br />. <br /> <br />o <br /> <br />6 <br /> <br />80 <br /> <br />20 30 40 <br /> <br />Return Frequency in Percent <br /> <br />100 <br /> <br />10 W ~ ~ ~ 00 ro 00 ~ 100 <br /> <br />25 <br /> <br />35 <br /> <br />100 <br /> <br />20 30 <br />15 ~ <br /> 25 <br /> K <br /> Vl <br /> "- <br /> U <br />"' 2 <br /> .5 <br /> .. <br /> '" <br />5 l; 15 <br />.t:. <br /> " <br /> .. <br /> 0 <br /> "" <br />0 0 10 <br /> If <br /> 5 <br /> <br />30 <br /> <br />2S <br /> <br />- 20 <br /> <br />litlle Cottonwood Creek at Subwat'fsned 5 <br />(see Figure 2.2) <br /> <br /> <br />" <br /> <br />10 <br /> <br />Urbanization Factor <br />CI'~ <br />80% <br />60% <br />~%~ <br /> <br />5 <br /> <br />20% <br />i5% <br />'0% <br /> <br />a <br /> <br />10 W ~ ~ ~ 00 ~ 00 00 100 <br /> <br />4. <br /> <br />Return Frequency in Percent <br /> <br />Figure 3.14. Peak discharge rate for Little Cotton- <br />wood Creek as a jUnction ofretum fre- <br />quency at different levels ofurbaniza- <br />tion. <br /> <br />40 <br /> <br />35 <br /> <br />Table 3.3. Precipitation and associated computed <br />runoff rates corresponding to rainfall <br />events or specific frequencies within the <br />urban portion of the study area. <br /> <br />30 <br /> <br />25 <br /> <br />____~....:.-_~~cipitation in incher <br />Duration of Precipitation Event <br /> <br />20 <br /> <br />Precipitation <br />Return Period 30 min. 1 hr. 2 hr. 3 hr. 6 hr. <br />2 years .41 .52 .62 .72 .96 <br />5 years .60 .70 .76 .88 1.23 <br />10 years .75 .72 ,90 .97 1.40 <br />25 years ,85 1.00 1.10 1.17 1.67 <br />50 years 1.00 1.15 1.24 1.26 1.88 <br />100 years 1.15 1.30 1.40 1.44 2.08 <br /> <br />i5 <br /> <br />20% <br />i5% <br />'00 <br /> <br />B. Discharj.!;e in cubic feet PeI second (cfs) <br /> <br />Stream and Station Number (see Fig).lres 1.1 and 2.7) <br />Uttle Big <br />Cotton- Cotton- Jordan <br />Runoff Jordan wood wood Mill River <br />Return River Creek Creek Creek 1705 + <br />Period 1673 1677 1685 1700 1710 <br />2 years 900 100 200 50 900 <br />5 yeaIS 1300 400 600 100 1300 <br />10 yeaIS 1700 700 900 200 1700 <br />25 years 2100 1000 1200 300 2500 <br />50 years 2400 1200 1400 500 2800 <br />100 years 2700 2500 3000 1400 3400 <br />aFrom records published by the U. S. Department of Com- <br />merce, National Oceanic and Atmospheric Administration. <br /> <br />Figure 3.13. <br /> <br />Peak discharge rate for Big Cottonwood <br />Creek as a jUnction of return frequency <br />at different levels of urbanization. <br /> <br />40 <br />