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I I I I I I I I I I I I I I I II I. HYDROLOGY Runoff flows were detennined at various locations for return periods of 2-, 5-, '- '" OJ OJ ...., I "'0 "'0 :;c.... 0 ~ LL "'" '" '- OJ '" <>. OJ e: I 00 .~.... ...., .~ '0 e: 0 u '- OJ '" I- OJ ::s ...., I V> ::SU) Z LL 0 ...... - en l- e: - .~ >-0 ...., t!l Z '- 00 .~ '" --'u '" OJ 0 UJ >, "'l- I ClZ N >- UJ :I::E <>. zo ....--' M V>UJ <(> ::s~ UJ 00 UJ 0 . --' I 0 .~ ...., '" 00 > ::s <( =>UJ '-LL l- V>'" OJ :::> 0- LLI- E...... o=> - LL >- ...., 0::0 e: . <( z OJ'" :E<( UUJ :E '-~ :::>t!l OJ V> Z <>. - l- V> - X UJ OJ"'" 0-.... 0...... ~...., V> .... 10-, and 100-years so that a detennination could be made concerning the stonn frequency for which drainage facilities should be designed for both existing and future development conditions. The Colorado Urban Hydrograph Procedure (CUHP), was used to estimate these flows, from sub-basins delineated inside the Lafayette drainage basin. Drawing B shows the breakdown of the Lafayette basin into sub-basins for the hydrologic analysis, The basin was subdivided into smaller basins, whose hydrology is summarized in Table 3, The majority of the hydrologic work was compiled 1n the Phase A portion of this study. Rainfall The rainfall depths for design stonns of the 2-, 5-, 10-, and 100-year recurrence interval were obtained from the Stonn Drainage Design and Technical Criteria for the City of Lafayette and Surrounding Boulder County, and are summarized in Table 4. These design stonns were based on infonnation contained in the National Oceanic and Atmospheric Administration Atlas 2, Precipitation- Frequency Atlas of the Western United States, Volume 3, Colorado and on information resulting from the current Urban Drainage and Flood Control District research into temporal rainfall patterns. Soils and Infiltration s; ....,~ en'~ e:E OJ~ --' Soils within the Lafayette drainage basin are primarily of the Ascalon-Nunn- Manter Association, as defined by the Soil Conservation Service, These soils are characterized by deep soils of mixed alluvial and windblown materials, with nearly level to moderately steep slopes on terraces, valley sides and uplands. Most of the undeveloped areas of this soils group are cultivated or covered with .~ . <1>0 "'z '" I I I I "'.~ OJE '- <( e: native grasses. 12 000000000000000000000000000000 N~~~OON~~O~MM~~~OO~M~~~~OOMM~~OM N~MMNM~~MMN~MNM M~~MN~MMM~N~MN "~""""""""""""'" 000000000000000000000000000000 MOOON~ro~OOO~~M~M~~OMN~~~~~~OOO~OO~ M MNM~~~NM~MMNM M~~NM~MNMMN NM 000000000000000000000000000000 ~~~~OOM~~MqO~~m~~oomO~NM~~~OOOO~~M MM MMNMMM M M MMMMMMM M MM """"""""""""""" 000000000000000000000000000000 ~MM~~~~~~~~~~m~N~~M~~M~N~~OOMM~ M NM M MN N M M M 000000000000000000000000000000 ~~NN~~roOOMro~~~OM~~~~~~~~~~~~N~ ~~ NN~~ ~ ~ ~N~ N~~ ~ ~ """"""""""""""" 000000000000000000000000000000 NNOO~M~~N~MM~~~ONNM~~M~q~q~~NO~ ~~ ~ ~~ ~ ~ ~ 000000000000000000000000000000 MM~~N~MO~~MN~M~~M~O~~N~OON~MN~~ ~~ ~ ~ """"""""""""""" 000000000000000000000000000000 ~~M~~~~M~~~N~M~~~~~~~~~qN~M~~~ NOO~~~~~qN~M~~~~mOOqM~~O~MN~O~~ M~~MNMMM~~M~~MMN~MMM~~~~M~M~~~ """"""""""""""" ~~MOoo~~~oaMO~~O~~VaO~ONMNMO~~ ~ N~~~~~~~~~~MM~~MN~~N~MMMM~~~ O~NMN~~~~~~OM~~N~ro~~~ro~~OOON~M~ ~~N~N~~NO~~N~MM~OO~~M~~~M~~O~O 000000000000000000000000000000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OOOO~~~M~~~~~~m~MNro~roMO~~Mro~~M~~ oo~~~~o~~o~rn~o~o~ro~~~rn~~ro~N~~~m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......-t ~.......-( .......-( .... .... ........ .... .... M~oomornmrooo~~m~~~~O~~~~M~~~~~~OO ~O~N~......-tmNM~......-tO~......-t......-tO~N~~~m~......-t......-tNOO......-t......-t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . <(00 <~u<~~~uc~wu~~u~~uow<w<m~~OO......-tN ......-t......-t......-tNNMMMM~~~mmm~~~~~~~roro~~......-t......-t~......-t 13