Loading...
HomeMy WebLinkAboutDrainage Reports - 01/20/1992THIS FINAL DRAINAGE STUDY AND REPORT FOR CLARENDON HILLS SIXTH FILING (FILING 6) WAS PREPARED BY LAND DEVELOPMENT SERVICES USING THE CITY OF FORT COLLINS STORM DRAINAGE DESIGN CRITERIA, dated May, 1984. The results of this drainage study are reported in the enclosed text and supporting documents, and are shown in further detail on the Utility Plans submitted concurrently with this report. This report is a revision of the original report dated December 2, 1991. Signed this $th—Qar-a£ January, 1992. Dennis L. Donovan, P.E. = " Land Development Services 92 309 W. Harmony Road — Unit A =�D: Fort Collins, Colorado 80526 ( 303 ) 225-9244 1 ••• .....�� s `•` AK ro � / I;v e Ve1,,-)e1hzv CLARENDON HILLS SIXTH FILING PRELIMINARY AND FINAL STORM DRAINAGE REPORT I. GENERAL INFORMATION Clarendon Hills Sixth Filing (Filing 6) is a proposed single family subdivision in the City of Fort Collins, Colorado. The sixth filing — as well as the remainder of the Clarendon Hills Subdivision — is located in the West 1/2 of Section 2, T6N, R69W, Sixth Principal Meridian, Larimer County, Colorado. Generally, Clarendon Hills is located in Southwest Fort Collins on the east side of South Shields Street from about one —quarter mile to one mile south of Harmony Road. ,Originally, the subdivision area was 160 acres. During the Master Plan stage, the storm drainage for the 160 acres was reported by Stewart and Associates. Their investiga— tion determined that there are three (3) major storm drainage basins (A, B, & C) within the 160 acres of land. See ExhiUt 8 for a copy of the master drainage report. In 1989-90, 12 acres of property adjacent to the Clarendon Hills Subdivision was annexed into the subdivision, thereby increasing the subdivision size to about 172 acres. The 12 acre "Orchard at Clarendon Hills" was the fourth area developed in the subdivision, but it was platted and the storm drainage report was made under the Orchard name — rather than the fourth filing. Filing 6 is part of the original Clarendon Hills Subdivision of 160 acres of land, which has been through not only the Master Plan phase but also the final subdivision processing phase for five previous filings (1st through 5th) in the City of Fort Collins. The fourth filing was developed in the summer of 1991. The fifth filing has not yet been developed, -but is scheduled for development in 1992. The sixth filing is also scheduled for development in 1992. The sixth filing will contain a total of 24 single family lots. The sixth filing is located in Drainage Basin B, as designated in the master drainage study. Drainage Basin B (total area of 82.3 acres) contributes storm drainage to the "Fossil Creek Drainage Basin", as designated in the City of Fort Collins. The sixth filing is located on the Clarendon Hills subdivision adjacent to contains only about 7 acres. The sixth planned as a church site. The revised fourth filing treated the church site a off —site drainage sub basin. west side of the Shields Street. It filing was previously study and report for the s an existing, undeveloped 12#C CLARENDON HILLS SIXTH_ FILING PRELIMINARY AND FINAL STORM DRAINAGE REPORT However, during 1991 the church site, which is now being platted as the sixth filing, was traded to the developer for vacant land in the northwest corner of Clarendon Hills. That property was originally planned for office and multi —family housing uses. The sixth filing, the 6.2 acres of land in the northerly portion of the fourth filing (Lots-1 through 18), and the back lot areas of Lots 19 through 23 in the fourth filing south of the sixth filing all contribute storm runoff to the southwest corner of the street intersection of Hinsdale Drive and Clarendon Hills Drive. As was identified in the master plan and fourth filing drainage reports, there are extensive detention facilities downstream of Hinsdale Drive and Clarendon Hills Drive. To handle runoff and detention storage requirements resulting from development of the Orchard project, the spillway at the east end of Drainage Basin B in Clarendon Hills (at Pond A) is to be raised by 0.5 feet. The raising of the spillway is scheduled to occur early this year, and will have to be certified by a registered engineer when complete. This improvement, however, does not allow the sixth filing to be developed without providing additional detention facilities. Accordingly, the detention facility design at the southwest corner of Hinsdale and Clarendon Hills Drive is ncluded in this report. There is one active irrigation ditch that affects the sixth filing. This irrigation ditch exists from 15 to 20 feet north of the south end of the sixth filing. The ditch provides irrigation water to the Applewood Subdivision and property owners east of the Orchard at Clarendon Hills. The open ditch irrigation system was replaced in the second filing of Clarendon Hills and the Orchard at Clarendon Hills by a series of 18 and 15 inch PVC culverts, diversion structures and associated improvements. The improvements se.em to be working adequately in the field. The ditch will be replaced in the sixth filing with a pipe culvert extending from Shields Street to Clarendon Hills Drive. The pipe has tentatively been identified by the Applewood Irrigation Associations' representative as a heavy guage 14 inch plastic pipe. The pipe will be owned and maintained by the AIA. The new streets in the sixth filing are to be constructed at or below existing grade. According to the soils investigation and report, existing bedrock will be more than 30 inches below the new street subgrade elevation. Therefore, street subdrains will not be required for Filing 6. F,4 r,F, Z The Clarendon Hills Homeowners Association will own maintain the greenbelts and storm drainage improvements located in City of Fort Collins rights of way. The same required for the sixth filing, and a note to that effect the Final Subdivision Plat. CLARENDON HILLS SIXTH FILING PRELIMINARY AND FINAL STORM DRAINAGE REPORT The construction of improvements on this site will not change basic drainage patterns or characteristics, and property damage is unlikely if runoff, or discharge flows greater than during the 100 year frequency storm should occur. Other than the irrigation ditch, there are no surface drainage facilities that enter the sixth filing. and e— s not �o wil be is on The storm drainage improvements identified in this report will complete the necessary requirements for the single family portion of the Clarendon Hills Subdivision. When the new church site is developed at some later date, the firm preparing the storm drainage report for the church site will need to identify the proposed storm drainage system for that property. II. DESCRIPTION OF THE PROPOSED STORM DRAINAGE SYSTEM The fourth filing storm drainage report, which was prepared by this office, identified the southwest corner of the Hinsdale at Clarendon Hills Drive intersection as the key point of design for this portion of Clarendon Hills. The original church site, which is now the sixth filing, is required to provide the storm drainage detention improvements that will ensure compliance with the original recommendations. This report will provide the detention facility design that is consistent with the goal of minimizing the storm drainage impact from the development of the fourth.filing and the sixth filing development. The just completed fourth filing development (northerly portion) consists of six storm drainage sub basins Ws 1 through 6). The sixth filing, after development, will have eight sub basins Ws 6-1 through 6-8). Sub basins 6-7 and 6-8 consist of the westerly one—half right of way for Clarendon Hills Drive. The on —site area of the sixth filing (sub —basins 6-1 through 6-6). as well as the backyard areas of Lots 19 through 23 (sub —basin A) in -the fourth filing will flow northeasterly to the Hinsdale/Clarendon Hills Drive intersection. The design of the two (2) cul—de—sac streets in the sixth filing provides for sump inlets that drain into a storm sewer at about Station 1+00 in Alexa Court, and at grade, or continuous grade, inlets above the same storm sewer as it passes under Ashford Court. FAG e3 I CLARENDON HILLS SIXTH FILING PRELIMINARY AND FINAL STORM DRAINAGE REPORT The southwest corner of the intersection of Alexa Court and Clarendon Hills Drive has been designed to allow storm runoff from sub basin 6-7 to flow westerly into the sump in the south side of Alexa Court, at which point it enters the storm sewer system. The storm sewer system for the sixth filing releases into a Proposed detention system in Tract A (Sixth Filing) and Tract C (Fourth Filing). Information on the detention system at this location follows in this report. As previously reported, the northerly 18 lots in the fourth filing has six storm drainage sub —basins. Due to o �i mo of that report, it is not included as an exhibit to thi.s__r_eport. e i in report, as wel'1 as the storm dr nia age report for all other filings previous drainage department of the s on file in the storm As generally defined for the northerly portion of the fourth [and ling, sub —basins 1, 2, and 4 flow into and southerly along arendon Hills Drive to a storm sewer system inlet just west of e northwest corner of the intersection of Clarendon Hills Drive Hinsdale Drive. Sub —basins 3 and 5 will contribute storm runoff to Hinsdale Drive west of Clarendon Hills Drive and flow easterly to the same storm sewer system. Sub —basin 6 of the fourth filing, along with sub basins 6-1 through 6-7 of the sixth filing will contribute storm runoff to the southwest corner of the Clarendon Hills Drive and Hinsdale Drive intersection. Storm runoff from all of the sub —basins identified above pass through the storm drainage facilities on the west side of Clarendon Hills Drive at Hinsdale Drive. The Minor (2 Year) and Major (100 Year) storm runoff both pass from west to east through the intersection of Hinsdale Drive with Clarendon Hills Drive. All flows occur within the general flow constraints established by the City of Fort Collins in the referenced "Storm Orainage� ✓� Design Criteria" manual. The two year storm drainage discharge is totally contained within the storm sewer pipe system, and the one —hundred year storm discharge both crosses under Clarendon Hills Drive in the existing 18 inch culvert and weir flows over the crown in Clarendon Hills Drive easterly into a series of additional existing detention facilities. All of the sub —basin flows are consistent with those ✓ anticipated in the Master Drainage plan. The sub —basins are shown and the flow directions and amounts identified on the Overall Grading and Drainage Plan (Sheet 6 of 8 ) in the Utility Plans. A print of that plan is included as Exhihii E to this report. 1246 5- 4L i CLARENDON HILLS SIXTH FILING PRELIMINARY AND FINAL STORM DRAINAGE REPORT On the following page, Table 1 is provided to show the hydrologic characteristics and estimated storm drainage runoff amounts for the 2 and 100 year storm events occurring within the eight fully developed sub —basins in the sixth filing. The same information appears on the Overall Grading and Drainage Plan, although the length, slope and detail on time of concentration calculations are not included on the chart in the grading plan. The plan and profile information for the storm sewer system is also provided in Sheet 6 of 8 of the Utility Plans (Exhibit B). Th for sewer is relatively large in diameter (24 and 18 inches) because of a re ativellat grade along the culvert, the tailwater conditions during a 100 year storm for r_u,noLf stored in the d_e_t_ention facj ity at the downstream end, and the fact —hat the entire s{orm sewer system as een esis_ned frr a -iajor Storm. The detention facility was designed for a 100 year storm runoff from all of the areas contributing to the release point of Clarendon Hills Drive at Hinsdale Drive. Sub —basins 1 through 6 of the 4th filing and Sub basins 6-1 thru 6-6 of the 6th filing all contribute to the point of release. Tables 2 through 5 are provided following Table 1 to show the design and performance of the detention facility. Table 2 is a rating curve for the capacity (storage volume) of the facility as graded according to the Grading and Drainage Plan at Exhibit B. Table 3 provides an Outlet Rating Summary for the 18 inch RCP culvert under Clarendon Hills Drive and for weir flow over the crown in the low point of Clarendon Hills Drive — as well as for the combined flows from the two methods of release from the detention system. Item 4. of Table 3 shows the Stage — Discharge Curve of the combined release flows for flood routing calculations. Table 4 provides the Unit Hydrographs for the 100 year storm runoff that will flow into the detention facility from the 4th filing, the 6th filing, and a composite flow from both sources. The Unit Hydrographs are designed according to the City of Denver Urban Drainage Flood Control District criteria. This method yields a conservative evaluation of storm water inflow to the facilities. Table 5 is the flood touting information that shows the balance of inflow, outflow and storage of runoff volumes occurring during both the 100 year storm in the detention pond from the combined 4th and 6th filing flows as the flood passes from west to east through the Hinsdale Drive and Clarendon Hills Drive intersection. PA G r'� 6 IWTERMILL LAND SURVEYING, INC. 1301 North Cleveland Avenue LOVELAND, COLORADO 80537 (303) 669-0516 Z JOB CLA-R9tJj2,QA1 dILL.5 Cr"- El't I SHEET NO. 1 OF CALCULATED BY- 2 LD DATE I 2q —11— CHECKED BY DATE i� , , � '-r'A 1-.7 , I r- I rT�rrl!9)L T7-u- r 0!g LAIN lw� R -c- J5 1:1 Ar- IN7ERMILL LAND SURVEYING, INC. 1301 North Cleveland Avenue LOVELAND, COLORADO 80537 I7A�\ LGn Ae 1 L v00=M1nft.tumor.0 mm.rodaevMMUmaI-MM ro JOB CLARr-wPom H ILLS 6 "FiINe SHEET NO. AT; CALCULATED BY y LP DATE 1 — 7-5 ' INfERMILL LAND SURVEYING, 1301 North Cleveland Avenue LOVELAND, COLORADO 80537 (303) 669-0516 CL 9M DO Al 't 1 LLS C TµF1L)A1. INC.JOB CSHEET NO. 3 OF 3 CALCULATED BY 1/ L D G DATE ' = 7 1 CHECKED By DATE No Text JOXLAR AMON DILLS INfERMILL LAND SURVEYING, INC.. SHEET NO. I OF 1301 North Cleveland Avenue CALCULATED BY 0 LQ DATE LOVELAND, COLORADO 80537 (303) 669-0516 CHECKED BY DATE A- R L r-- 7) SCALE .......... 151 A 0 Joe cLARE11DAM t't/LLS INTERMILL LAND SURVEYING, INC. SHEET NO. OF 1301 North Cleveland Avenue l7 /_ D .... i — -7 Z h vroax,T ���. mm� rs mm. m as wvE rou r+�,amasemo FMMW2W�nccwm.m mm. roOft MMTMi11H 14MM o INTERMILL LAND SURVEYING, INC. 1301 North Cleveland Avenue LOVELAND, COLORADO 80537 Pane% cce n¢Ic R1000CTMICAWI�Gro l4SOlM.To Oro*RMTOLLFEEl.M225 E0 TDB GLAReNDON 1 1LL5 6 " Icil- A& SHEET OF CALCULATED BY 12 LD DATE I —7—1 `-, ------- --- JOB CI-ARC-NOOM NIL-1-5 rH F) L I 'INiERMILL LAND SURVEYING, INC. SHEET NO. 3 OF 3 1301 North Cleveland Avenue CALCULATED BY 12L-D -DATE LOVELAND, COLORADO 80537 PROD= 2SIQMMU?ae_Gmm. Man 41M. TQOm. MWETOLL FM MM�M JOB C1-4 k r=A1 Da hl l7 /LL.S to TN /LILAC 114TERMILL LAND SURVEYING, INC. SHEET NO. �I7 of V CALCULATED 1301 North Cleveland Avenue CAATED By 1L D DATE % — 2—F Z LOVELAND, COLORADO 80537 (303) 669-0516 CHECKED BY DATE PMWMM`= Rf1a rnOt01.ToOft MWTOLLFRM14M.M= AV CLARENDON HILLS SIXTH FILING PRELIMINARY AND FINAL STORM DRAINAGE REPORT The 100 year storm event does create weir flow over Clarendon Hills Drive. The storm water elevation peaks at approximately 5066.76 during the 100 year storm. This elevation is less than one (1) foot deep in the cvrb and gut eT-r� at­_fhe 10 foot inlet on the west side of Clarendon Hills Dr_i_ve,_a.rLd_it_is Sess than one foot deep in t.h.e_c.ur_b_an.d_gutter of Hinsdale Drive at the inlets on the we5.t_sA_d.a—nf fha i_n_f_arcerfinn. Also, the depth of flow o Hips Drive will be only about Both of t-he C y criteria of 1 flowline of the gutter and 0.5 street are not exceeded. ne of Clar v.1..J Teed ourlfty lne Ilalur Sturm. inch maximum depth above the feet deep at the center of the The detention facility does improve the system drainage and will also allow for a aesthetically pleasing pond and landscaped area for the subdivision. �77 The Hydraulic Calculations for the storm sewer are provided at Tables 6 through 10. III. STREET FLOW CONDITIONS AND INLET DESIGN The streets in the 6th filing are classified as local streets. The grade of the streets are basically at 2 to 3 Percent. However, as Alexa Court drainage flows approach the inlets to access the storm sewer, the street longitudinal grades are at a minimum of 0.4 percent. According to Figure 4=1 of the Design Criteria, a 0.4 Percent street grade, a street cross slope of 2 percent anima Manning's Cgopfficient of Roughness of 0.016 (Z/n = 3,1251)'allows abouV8 cfs — after the 50 percent reduction factor from Figure 4-2 ✓✓ to flow within the allowable depth and spread encroachments for a 2 year storm (i.e. contained between the back of curb and crown of the street). The largest gutter flow in the s. h filing occurs in Alexa Court from sub —basin 6-6, at 1.9 cf during a two year storm. In fact, the maximum 100 year gutter flow at the same location (7.1f cfs) is within the Minor Storm street flow criteria. Obviously, other than during ponding in the detention facility and resulting) overtopping of Clarendon Hills Drive during the 100 year storm are minimal. For inlet design considerations, the largest combined flow (from sub —basins 6-6 and 7) at any individual inlet during the 2 year storm is 2.2 cf . The inlet requirements for Catch Basin #4 to be constructed at this location on the south side of Alexa Court were determined as follows: Q2 = 2.2 cfs * 80 Reduction Factor for a 4 foot City Standard Inlet * Yo = 6 inches PA-G r-, 6 -T� 13L� 6 N z "ru0 US I� 0 1 u r p U N oz O e ( � A110013A - r) W Q ' 1 131. 00 W U Z p > > ~ ~ •N � Z } H V U Nlllo"ANOo W7 Q laJ Y ~ ryy1 � � OJ p W Q N to > W > i o u u Q e J Ra U Z W R In J Lt1 J Q X 3 / W `+3 = J W o Q u t + _ F Z If. 0 J it CKmo �1 11 11 W F + vy - Z O V) Z Z a 3 pz F %L O O a V Q Q o° W~_ O > > o W {� oc o o Y N V) W W W a Z o _ ~ s JW Ill uQi49 Z Z In V a Q IS = SV Z _ 3 3 0 W a s W O Z v = F H _ h V LI)H W Z p a =5 N 2 Z U q S U O w to = o U W Q p u WQ T If 11 'lV = ValO a'ca } o ao �� Wa W, W aU = — >a = oc = a �y i ¢ Q t i t� W i G ? U) rlu1ll tarn MAY 1984 Figure 6-1 DESIGN COMPUTATION FORM FOR CULVERTS 6-2 DESIGN CRITERIA t Iv ~ Z J ; U N In (� H W I AA13013A N 1 A31A00 Z 1 N H F U V N1110YAN07 m V1 H Y CJ O W Q La ta rn > ¢ _ G G « « ! f Q w J W Q U Z 0: W R In ; N = w a x cn W (b N W Q 3 Z J, = J W O 1- ©3 O U J O !V tt� J W ¢ Z u a a c v9 O Z Z O O 0-1 ; Uo 1- - Q a W W 0: O = O O J J in 0 (� _ U1 o Z W W CY O In N ,1 W �� hH i; N = H _ Z � 33 W 81-sla N Z 0 - = U J J Q¢ J H N= U Ht` U= Z O O Da Z (� U)y — N } Z Z� y N O m IV) W O U F- of-O r o U W cc W cr, '7 O O if is« 'ON � O w O ,I O N O c a O �� 1- ► >,- d �l } W CC " in Q x >� O y H UW = (A - From BPR Figure 6-1 DESIGN COMPUTATION FORM FOR CULVERTS MAY 1084 6-2 DESIGN CRITERIA -TA-BLE 8 .. y 0, _ N) I + lV w U N# c ; � M- JI0 11, Q N N ,� N 0 J '2 AA10017A eQ W I \ A71100 I W I N p V M Z O Q V N111011114 3 W WI— Y F O O l W N W W > > S C O N N Q wJ Q \\J\ W W = U o Z H I Ul J Q X S Qh W w i J = J O t W Q + f. S a. I 2 ; " J cr1 + al - J I I o ¢ Z 11 11 W Q 1- Z 0i vy Z 2 3 c z _O t` O O �� a ►- v ° = as _ U) W G cc0 W J J n 0 • Y •/ Z W W N O in _ J 0 GC Q _y N Z Z a s W 8 S J 3 3 �W W O N vcc = a _ ;�o H O c� �- ►- u = p III p _ N u c N N Z U1 -Z aZ II Z Y N LU V OC u U c� ? W i 0 -' W h- O a u N W a:W o J O O_ U 11 N Z a m `� o a v �% '' p. W a w ' cc a = J w < t- a u no a U W : \U 6- .4 N I iwn urn Figure 6-1 DESIGN COMPUTATION FORM FOR CULVERTS MAY 1984 6-2 DESIGN CRITERIA t M1 -TAaL-E 9 �! N H 2 ill i w # W ►- JIO � � J o QH I W I N A11]01]A 1711(10 W V --� W W Q O O N1110Y1N0] M F 3 W Q Y.J J U) N W W > G G % n u w J Q W W S U u 2 ix 0: O N H N 3 J o Q X M W l9 w J = J W O c F4 = c lYl 3 M1M1 Z 10 _ J U (X J w 11 11 W H H z + �y N Z O Z Z ; U O O a 1. v \g QQ °_�_ > > o It W ¢ O W W J J ho O O Q V) Z W W N O O n Q � J ►- _`I` W U_ W W y 41 N V ca + Q Q W Z V - _ O W 33►-N O z = Q Q sa z o Q W o c —� ~~ H o Z W y Z 11 O o Q N W W z� Y T U' W W s O N V W F— W( O p O c� cc O u N N Z s Q J O a _ W 0. >a z Q JU N z w UW O N � N • •r �• M 91 Figure 6-1 DESIGN COMPUTATION FORM FOR CULVERTS 1 MAY 1984 6-2 DESIGN CRITERIA T�►s�E 10 J' h fl V) �O N ►�- �I�ILa, = 3 a VI * 4- IY7 F ih o q w 0 .2 + U S ` /L H o n`Ic S I�A410017A �� A71A00 q q p r� all Z - Z V J La N1110Y1NO3 M (1 Y Q O O WQ N H > > = M � 0 q Ir Q w J W U Z � I W ¢ cc \\ I ) J I Q X M Wa „�.'n"1111 ii _� it J W o r Q ra- � q I I U J MTICS 1t W 1- +IN m kn _ Z Is it O Z Z a 3 o u e9 _ O O �1 0 ►- o _ _ Z F W W p p • tJ J Z W W O h r — cr m } O x O 2 = 4 fQ - H fA N U Z Q W v O Z = 33 as it N O V Q Q u i Z o MMN W ~~ N u A Q Z W II Z G to N w U W V W O C W G U Q p N0 cr w 13 O - u u M itlV O O C H 0 F. O r \ m C 0 0 �� a;: �- a = W S v >� W LO a no di la u w z c w N rrvin OrR Figure 6-1 DESIGN COMPUTATION FORM FOR CULVERTS MAY IOU 6-2 DESIGN CRITERIA CLARENDON HILLS SIXTH FILING PRELIMINARY AND FINAL STORM DRAINAGE REPORT * h = 8 inche / * Yo/h = 0.7575 L/ * Q/L (from Figure 5-2) = 1.2 cfs per linear foot in theoretical capacity * Q/L Design = 1.2 x 80% = 0.96 cfs per linear foot Therefore, the Length of Inlet required wring a two year storm = 2.2 cfs / 0.96 cfs/ft = 2.3 feet. G100 = 8.2 cfs * 80 % Reduction Factor for a 4 foot City Standard Inlet * Yo = 11.5 inches * h = 8 inches * Yo/h = 1.44 * Q/L (from Figure 5-2) = 2.6 cfs per linear foot in theoretical capacity * Q/L Design = 2.6 x 80% = 2.08 cfs per foot Therefore, the Length of Inlet required dur' g a one hundred storm = 8.2 cfs / 2.08 cfs/ft = 3.94 feet. A four foot inlet is adequate. USE ONE FOUR FOOT LONG STANDARD CITY CURB OPENING FOR CATCH BASIN # 4 Since the flows entering Inlet #3 are less than for Inlet #4, a four foot standard inlet should again be used. For the grated area inlet, the area of opening is about 1.25 square feet. From Figure 5-3, that area creates a ponding depth of less than 0.3 feet for flow (Q100 year = '7-4 cfs) per square foot of open area at 80 percent efficient. For Inlet #1sr1 and 2, the design discharge is-t h same from _ the contributing basins�(Ii.e. 6-2 and 6-3) at 1.2 cfs for the-- minor storm and 4.3 cfs for the major storm. Using Figure 5-5. and S = 2.0%, Sx = 2.0%, n = 0.016, T,= 7' For 2 YR flow and T = 10.5' for 100 year flow, we find that for a four foot long inlet the flows inte�reepted by the continuous grade inle�t�are 0.5 cfs✓ Y (Qi/Q = 0.48during the 2 year storm and 1.0 cfs'"(Qi/Q = 0.29)✓ during the 100 year storm runoff. P I eases �p r d ✓; d e �rd� � IV. GRADING AND)EROSION CONTROL<< s 5 e,_t� Notes are included on the grading and drainage sheets in the Utility Plans regarding erosion control. Seeding of disturbed (graded) areas should be provided after the earthmoving is completed. A mixture of annual rye and perennial grass seeds, with appropriate fertilizer, should be provided after grading in the areas outside of street rights —of —way and utility easements. During earthmoving, dust control should be accomplished by _ watering. E 1 h.; s i svi '1- '✓�r �J $'��Y'` , Vse ��_ ��v5�6� ! �T �� � [ >C / V ic�NiTy MAP ,cfe CN� -7 A r.�x h i � 11 +- A DRAINAGE REPORT CLARENDON HILLS FORT COLLINS, COLORADO James H. Stewart and Associates, Inc. Fxh� il �-i} Clarendon Hills is a proposed single family residential subdivision situate in the West 1/2 of Section 2, Township 6 North, Range 69 West of the Sixth P.M.. It contains 161 acres and borders South Shields Street from the South line of the Larimer County Vo-Tech. School South to Fossil Creek Drive. The overall density of the sub- division is 2.1 units per acre. The entire subdivision is located in the Fossil Creek Drainage Basin which has a Master Drainageway Planning Study by Simons, Li & Associates dated August 1982. The subdivision is broken down into three subbasins. Drainage Basin "A" contains 10.1 acres and is situate in the Northwest cor- ner of Clarendon Hills and drains Northeasterly to an existing drainageway in the Larimer County Vo-Tech School property. That drainageway flows Easterly along Harmony Road to Mail Creek at the Burlington Northern Railroad. It continues Easterly as Mail Creek to its confluence with Fossil Creek West of Lemay Avenue. All of Drainage Basin "A" is located in future filings and will have onsite detention designed at the time the final plat is made. The amount of detention required is 94,176 cubic feet and the allowable outlet rate is 2.57 cubic feet per second. The three drainage basins are depicted on the enclosed drainage plans. The drainage plans show existing contours, two year developed runoff quantities, direction of flows and discharge points. Drainage Basin "B" contains 82.3 acres and is generally the South 1/2 of the Northwest 1/4 of said Section 2. It drains Easterly in an existing thalweg thru Brookwood Subdivision, across the Bur- lington Northern Railroad, thru Cameron Park and enters Fossil Creek on the West side of South College Avenue. Drainage Basin "B" will have 10.58 acre feet of 'detention in a series of five ponds located in Tracts "B", "D" and "E" of Clarendon Hills, First Filing. The ponds were designed using a mass diagram that required 10.46 acre feet of detention to detain the 100 year developed storm and release at a two year historic rate which is 14.3 cubic feet per second. Two of the ponds and perhaps a third one will be overexcavated to provide a permanent pool of water. The deten- tion capacity will beabove the permanent pool There will be a provision for irrigation water to supplement the permanent pool and thereby alleviate any stagnation. Some ground water surfaces in this thalweg presently and feeds several existing ponds down- stream. Drainage Basin "C" contains 68.6 acres and is located in 1/2 of the Southwest 1/4 of said Section 2. Fossil Creek Easterly along the Southerly portion of Clarendon Hills. Tributary of Fossil Creek enters Fossil Creek in this are cause of the close proximity to the Fossil Creek and Burn tary it was determined that no onsite detention would be James H. Stewart and Associates, Inc. the West traverses The Burns a. Be- s Tribu- required. The Fossil Creek Drainage Basin Master Drainageway Planning Study also states that no detention is required. A drainage easement that encompasses the 100 year flood plain limits with future basin conditions was dedicated on the plat to prohibit any improvements being built in the flood plain. The rear lot lines of the lots backing onto the creeks follow the centerline of the creeks. The maximum depth, in this reach, from the stream bed to the 100 year flood elevation is 9.6 feet at the confluence of Fossil Creek and Burns Tributary. The average depth is approx- imately 4 feet. The runoff quantities were calculated using the Rational Method. The storm drain inlets were sized to take the two year storm. The runoff is to be carried in the streets based on the criteria of the two year storm not topping the top of curb. Inlets and storm drains will be provided where the runoff cannot be carried in the street. The drainage calculations and mass diagram are enclosed and two year developed runoff quantities are shown on the drainage plan.. l J�l.t1l.dvry C-1 • ��-iL Richard A. Rutherford, .E. & L.S. James H. Stewart and Associates, Inc. Ex hlbt+ f� DRAINAGE SUMMARY TABLE Drainage Basin "A" Onsite Area: 10.1 acres Offsite Area: 0 acres C (hist.): 0.2 Hist. Time of Concentration: 37 min. Q (2 year hist.): 2.6 c.f.s. Q (100 year hilt.): 10.5 c.f.s. C (dev.): 0.5 Dev. Tc: 21 min. Q (2 year dev.): 9.1 c.f.s. Q (10 year dev.): 16.1 Q (100 year dev.): 31.9 c.f.s. Detention Required: 2.16 acre feet Drainage Basin "B" Onsite Area: 82.3 acres Offsite Area: 0 C (hist.): 0.2 Time of Concentration: 65 min. Q (2 year hist.): 14.3 c.f.s. Q (100 year hilt.): 49.8 c.f.s. C (dev.): 0.5 Dev. Tc: 45 min. Q (2 year dev.): 45.3 c.f.s. Q (10 year dev.): 82.3 Q (100 year dev.): 195.5 c.f.s. Detention Provided: 10.46 acre feet James H. Stewart and Associates, Inc. X� i b,`A Drainage Basin "C" Onsite Area: 68.6 acres Offsite Area: None sheet flowing, discharge via Fossil Creek and Burns Tributary C (hist.): 0.2 Hist. Time of Concentration: 30 min. Q (2 year hist.): 20.3 c.f.s. Q (100 year hilt.): 71.7 c.f.s. C (dev.): 0.45 Dev. Tc: 22 min. Q (2 year dev.): 53.7 c.f.s. Q (10 year dev.): 95.1 c.f.s. Q (100 year dev.): 189.1 c.f:s. Detention Required: None James H. Stewart and Associates, Inc. EX%i%r'- A r - -_--- COMPUTATIONS James H. Stewart & Associates, Inc. I 214 N. Howes St. Ft. Collins, CO 80521 (303) 482-9331 By: R. A• Q. Date Client: ___ A4 i TcNecc. Lo: Sheet No. of Chkd By: Date Project: C L A F.y now Pa-,_ Job No. . Subject Mass —1)7A/S„2A4 — 13As/A/ #A" (AA At E 7-x o x Z— — _l. 2. II : Lo -- -- I `31 I 4-•1 _-- — __ 3GL_ _ _ G I I 13_2. ,4 -- - - - - - - ' I I lO�f, 97o f — — - — - — — - - — — -- — I_... so, IDA i I C I i f Tp I- , LO I I. -- — - i ' f ��� COMPUTATIONS James H. Stewart & Associates, Inc. 214 N. Howes St. Ft Collins, CO 80521 (303) 482-9331 By. R. A.R. Date &////g/g Client: A%4 PTcaal_tl -Sheet No. of Chkd By: Date Project: C I- A R_ ea nemi khLl r Job No. Subject AA A g s J-) i s_/-g A A A A /Al #A* NJ mom N N NO Omp e�lL� No Em .� NO No Text 1. No Text ':fir. t . a..', \'� � �.. '. '• 'L .t ' •:/� __ te YJ(� 0 16 g RCt L7rei•. ? " 3 8» ^« Y ono » o'o - ^» R _CY r s��'•j aai iieaa: 7Z.r�:_ �... »»A t s Its It .: 2. Note • 1f•V //waJ ' i • is l• i �- I d ;_I_ •29 q f �' .;..':�..•• �_ •1 ` I it - / ? v - - c•.•_ F„ ; d tip'd ice-- I •/• "L.��•. ..y :. ' � • � � V �_ _ � g »-. 6- _ �� —ter S'i •. .1; .OV1 ��i�`. .. / `�``C�`• I,•,i�a``� � II'l •�,� IIJ v-'• ygQY =5 iCe' -..1-»_�• .r. ;•-•_-...��''• '�� 11. i �IL .,� E -•�. Yee Zsn Y�`'L . ,•' ry . �o . I ' 1 / /'•' 1i .:� i M/7L^//ELL ! CO _.i�\;; � _. �,'•� • .. �: I', ' I � 1� , , . ,I/ '� � � •- • � .1 i O.C.O/it/.06! PION • - o i.�'.'• -.�-- . ` L' V x ie" G•rciiie Be. Cva,.ear._ � ` •• • •. i � . .. _ re Kiivaa-ao-C.N.0 Af r,"& ' -L ..Do sw.e.nr Sfqcffr - .IV CYru..c 'FI,,V6 PS Oi I •i PA•f CGf A I. C.Y `v�cf .11 f _ »�,��� 3.7 r••.-r .••. ter,+�»L- .i�r•�+... �. r.. ........... ....-..��. _.�..+r �•...».. •L , � r