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HomeMy WebLinkAboutSan Sevaine Basin #3 Watershed HYDROLOGIC MODELING OF SAN SEVAINE BASIN No.3 WATERSHED AND HYDRAULIC, DESIGN OF RICH BASIN & HAWKER CRAWFORD CHANNEL . / // 0, / / /rr, /p / / , SO 70 ,y 40 49" 4 MODEL FLOW CHART to 60 70 A m 20 m 60 m CC 70•B \\ RICH BASIN n O © O T HAWKER © ©� f , C� ANNEL O `" ''� \z §.\ C © o O � Z�.. i \ BO CD le 60 90 Q • SAN SEVAINE BASIN No. 3 AL O Q m, Ata jot, O 4 PREPARED FOR J.P.KAPP & ASSOCIATES Ri VERTECH INC TABLE OF CONTENTS 1. INTRODUCTION 1 1.1 BACHGROUND 1 1.2 SITE DESCRIPTION 1 1.3 PURPOSE AND SCOPE 4 1.4 CONCEPT 5 1.4.1 DESCRIPTION OF ULTIMATE CONDITION 5 1.4.2 DESCRIPTION OF EXISTING CONDITION 5 1.4.3 DESCRIPTION OF INTERIM CONDITION 7 1.5 CRITERIA 7 1.6 ORGANIZATION OF THIS REPORT 8 2. METHODOLOGY 9 2.1 DESCRIPTIONS OF CONDITIONS 9 2.2 DESCRIPTIONS OF PROGRAMS USED 10 2.2.1 AES -RATSB 10 2.2.2 AES -FLOOD 10 2.2.3 HEC-C 10 2.2.4 LOSS RATE CAICULATOR 10 2.3 DESCRIPTION OF HYDROLOGIC PARAMETERS 11 2.3.1 RAINFALL 11 2.3.2 MAXIMUM LOSS RATE AND LOW LOSS FRACTION 11 2.3.3 LAG 11 2.3.4 WATERSHED AREA 11 2.3.5 BASEFLOW 11 2.3.6 S CURVE VALUES 11 2.3.7 PRECIPITATION-DEPTH AREA- FACICPS 11 3. HYEMIOGIC MOMS 11 3.1 MJDEI, NO. 1 11 3.2 MODEL, NO. 1.1 . 13 3.3 M3DEL NO. 2 13 3.4 FEDEL NO. 2.1 13 3.5 1 DEL.S NO. 3 AND 3.1 13 3.6 MCCELS NO. 4, 4.1 AND 4.2 14 4. INTRAULIC DESIGN OF EPOIMERAWOOSURDI (ILL AND RICH BASIN 14 4.1 DESIGN OF BSATN AND CHANNEL FOR ULTIMATE CONDITION . . . 14 4.2 DESIGN OF BASIN FOR INTERIM CONDITION 16 1 1 LIST OF FIGURES 1.2a REGIONAL AND PROJECT' IDCATION NAP 2 1.2b VICINITY NAP 3 1.4.1 CONCEPT OF REGIONAL SIDRA WATER MANAGEMENT AS A RESULT OF HUNrERS RIDGE DEVELDIMENr 6 3 SUMMARY OF HYDROIDGIC rim RESULTS 12 ii s 1 LIST OF EXHIBITS EXHIBIT A . . HYDROLOGY CCM:PON/EMS — ECESTING CCNDITICM EXHIBIT B . . HYDROLOGIC COMPONENTS — ULTIMATE CONDITION EHIIBIT C . . HYDZOIOGY OATS — INTERIM CONDITION EXHIBIT D . . WERSHED BOUNDARIES & 2 —YEAR ISCHYF AIS E)HIIBIT E . . WATERSHED BOUNDARIES & 10 —YEAR ISOHYETLS EXHIBIT F . . WATERSHED BOUNDARIES & 100 —YEAR ISCHIETAIS Fx 1IBIT G . . EX STING LAND USE & HYDZOIOGIC SOIL COVER EXHIBIT H . . ULTIMATE ATE LAND USE EXHIBIT I . . INTERIM LAND USE & HYDROLOGIC SOIL COVER r EXHIBIT J . . TOPOGRAPHIC DATA FOR RATIONAL ME IHOD CCM UPATION EXHIBIT K . . INTERIM AND ULTIMATE GRADING PLANS FOR RICH BASIN— HYDRAULIC DFSIG (ULTIMATE) HAWKER—C RAWFC1RD CHANNEL iii 1 LIST CF APPENDICES SUPPORTING CALCULATIONS AND INPUT/OUTPUT DATA FOR THE NOM 78 S APPENDIX A . . DEVELOPMENT OF RAINFALL DATA Al A42 APPENDIX B . . DEVELDPNTNr OF LAG PARAMETERS B1 -B207 APPENDIX C . . DEVELOPMENT OF LOSS RATE PARAMETERS. Cl-C72 APPENDIX D . . DEVEIDANENr OF DATA FOR BASIN ROUTING —D16 APPENDIX E . . INPUr DATA FAR HYTI OGRAPHS E1 INPUT DATA FOR HYDROGRAPHSS (ECU TING CONDITION) E2 E10 (INTERIM CONDITION) E11 -E19 (UIJrI SITE CONDITIONS) E20 -E30 (OTHER) E31 -E37 APPENDIX F . . MODEL OUTPUT DATA F1 F183 SAN SEVAINE BASIN NO. 3 Norm (EXISTING C VDITICT) Fl -F49 (ULTDIN E CCmITION) F50 -F107 (INTERIM CONDITION) F108 -F158 RICH BASIN MODEL, CULT CONDITION) F159 -F163 (INTERIM CONDITIC I) F164 -F171 (EXISTING CONDITION) F171.1- F171.6 SAN SEVAINE BASIN NO. 3 MODEL - SINGLE AREA ANALYSIS (ULTIMATE O(t DITICT) F172 -F175 (EXISTING CONDITICiT) F176 -F179 (INTER M CONDITION) F180 -G183 APPENDIX G . . I WF R- CRAWFta D CHANNEL HYDRAULICS G1-G20 • iv I � 1. IlJTCTICN 1.1 BACKGROUND First City Properties, Inc. is planing to develop approximately 568 acres of land known as Hunter's Ridge. The proposed development is located within the City of Fontana in the County of San Bernardino. Consequently, the planning must be consistent with the policies, criteria and requirements of both the County of San Bernardino and the City of Fontana. J.P. Kapp & Associates has been retained by the developer, First City i Properties, Inc., to provide consulting engineering services and to prepare plans and specifications for the construction of the proposed development. Rivertech Inc., which specializes in hydraulics, hydrology and sediment transportation, is providing services to J.P. Kapp & Associates in developing cost - effective solutions for regional drainage facilities. Ills document contains descriptions of regional facilities to manage the increased stontmwater as a result of the planned Hunter's Ridge development. The improved regional drainage facilities are recommended to achieve the following objectives: • Provide solutions that have low construction and maintenance costs. • Be consistent with the criteria and requirements of the County of San Bernardino and the City of Fontana. • Conform to the development plans being prepared by J.P. Kapp & Associates. 1.2 SITE DESCRIPTION ' is of the San Bernardino National The site is located at the foothills Forest. Figure 1.2a shows the relative location of the project site to major cities in the area. As can be depicted in Figure 1.2b, Hawker - i 1 NO D IS Z f en m O di rtn �, m 0 44 m allig Z Si y a II rn el lb n fl Z� o . 0 0 a m Z 1 la — > -- G) — I � /© I c in r 0 d+ z m D ";.: iiii O a -I • O < m m Z m on / > 3 de r •cs go v .. "1:1 m �.rl +r P c 0 SIERRA AV . m NO C) -I . 0) ... 01 +r 0 > m C) .. > °° m • - I m XI O Z • 1. • v z e 0 e a 'I I) _ / ... al 33 2 N. m O O. O MO 2 as di Aat ao NORTH 0 4 00 0 2000 '""" ULTIMATE SAN SEVAINE BASIN #3 WATERSHED MIN ern SA BERNARDINO NATIONAL FOREST • - ' • PLANNED NO HUNTER'S RIDGE /• Rives BASIN • DEVELOPMENT /. • • Cc . . . . / HAWKER CC CRAWFORD CHANNEL SUMMIT AVE. *1 -• SAN SEVAINE ) #2 +� BASINS �4 w 40011110110, ar HIGHLAND AVE. s .r • / RIVERTECH / FIGURE INC VICINITY MAP 1.2 • r // � 3 err Crawford Channel flows through the planned Hunter's Ridge development. This channel is a major regional drainage facility and is planned to be improved for ultimate conditions. Hawker- Crawford Channel conveys stornwater from Rich Basin to San Sevaine Basin No. 3. The system of the San Sevaine retarding facilities consists of five existing basins constructed in series. A consortium of developers who each own a portion of the watersheds draining into the system of San Sevaine Basins plan to improve and enlarge San Sevaine Basins No. 4 and No. 5. The Envirormiental Public Works Agency of the (aunty of San Bernardino (EPWA) is coordinating these improvements. Rich Basin is a flow-through retarding basin upstream of Hawker- Crawford Channel. It provides insignificant flood attenuation in its existing condition. Rivertech has reefed improvements to this basin to provide regional flood control benefits for interim and ultimate conditions. The drainage area of the watershed contributing to San Sevaine Basin No. 3 in its present condition is measured at 7,260 acres. Based on the City of Fontana's Master Drainage Plan, the drainage structures tinder Freeway 15 north of Sunnit Avenue are planned to be enlarged. This would permit additional areas to discharge from west to east across the freeway. Consequently, under the ultimate condition, the drainage area to San Sevaine Basin No. 3 will be increased by 19 percent to 8,640 acres. The planned Hunter's Ridge development occupies about 6.6 percent of the ultimate watershed draining into San Sevaine Basin No. 3. 1.3 PURPOSE AND SCOPE The purpose of this study is to identify and recommend cost- effective improvements to the regional facilities in order to offset the increased runoff resulting from the planned Hunter's Ridge development. The system of San Sevaine Basins described in section 1.2, together with Hawker- Crawford Channel and Rich Basin form the backbone of the regional drainage facilities at the project site. Hydrologic modeling and 4 hydraulic analysis have been performed to identify cost- effective improvements to Rich Basin and Hawker - Crawford Channel to net the project objectives. San Sevaine Basin No. 3 establishes the downstream limit of this study. The results of this study provide vital informatioaz to those involved in watershed modeling downstream of San Sevaine Basin No. 3. Converse any improvements downstream of San Sevaine Basin No. 3 has no impact on the results of this study. The scope of this study also included the hydraulic design of Rich Basin and Hawker - Crawford Channel. The reach of Hawker- Crawford Channel, which was hydraulically designed extended from Rich Basin to downstream of SulTanit Avenue. 1.4 CONCEPT 1.4.1 DESCRIPTION OF UIMIMAiE CONDITION Figure 1.4.1 graphically describes the regional drainage concept at the planned Hunter's Ridge develolxnent. In the ultimate condition, it is assumed that the entire watershed drainim to San Sevaine Basin No. 3 is fully developed according to the General Land Use Plans prepared by the City of Fontana and the County of San . In addition, a preliminary ultimate grading plan for Rich Basin was prepared by Rivertech to maximize the excavation within the County of San Bernardino's right-of-way. The basin outlet channel and Hawker- Crawford Channel were hydraulically designed to convey ultimate discharges safely following the criteria required by the EPWA. 1.4.2 DESCRIPTION OF EXISTING CONDITION DITION In the existing condition the watershed draining to San Sevaine Basin No. 3 is essentially undeveloped. Rich Basin has insignificant retarding capabilities and Hawker - Crawford Channel is unimproved. 5 9 co co co o N 2 .� m C r m m< z Y a x �, E m - ,z -+in '` �' m O.m z M ...1 X a K�o i0 OW Z m� m CD z v v D –1 —1m z I,. Z 0 m 6 < n 0 x v co my C7 � m O �'V •� w 1 li. r ` z 0 0 c x /�� . --� z _ D • co 3 z nm \ \. E O 0 v mx • > z x D co ca II D D xoxv Nv* *c co z p c m m D a r 2 to ^ Qom c� < 1 -+ -� m 0 Q D �< i m � 0 d �D " 1l C c c C D . ry °m � - o x m C _ z m m r r' --� D m ° m i ° ° • —I ° _ v w I .q z Cn O ° !� D r y ®' • • �� m x xa • co v Z 3 m Z� x �� o = 0 ?� 2 mm f — �z cu • o* z 0 rri D 0 u z 0 D .-1 m -+ to m m r m� xi 0 0 > - D N� _� 0 m m I o vy m m m ° z Z K - K z m m cn —I m -+ m Z Q P z m Z r � ,� m n 0 , D D (� (n z 0 r* x ` x c +i m .. Z z r 03 O � . .� „ x .► an ° 4 c --I m Nr rw rywrr v .. •.. 1.4.3 DESCRIPTION OF INTE t M CMIDITION i In the interim condition it is assumed that the entire watershed draining to San Sevaine Basin No. 3 remains as in the existing condition ay with the exception of the following: • Hunter's Ridge development is completely in place. • Ultimate Hawker - Crawford Channel is constructed. • Rich Basin is excavated sufficiently to offset the increase in .• discharge at San Sevaine Basin No. 3 as a result of the Hunter's r Ridge development. MR As can be seen in Figure 1.4.1, there are a number of major streams that drain into San Sevaine Basin No. 3. The interim concept is based on the assumption that flows in all other streams draining to San Sevaine Basin Id No. 3 remain the same as in the existing condition except that from Hunter's Ridge and in Hawker- Crawford Channel. By increasing the retarding capability of Rich Basin, the discharge in Hawker - Crawford channel is reduced sufficiently to offset the increased flaw from the Hunter's Ridge to San Sevaine Basin No. 3. 1.5 CRITERIA r The results of the study included in this report are based on the following criteria and guidelines: -- • San Bernardino County Hydrology Manual prepared in August, •t 1986. • Los Angeles County Flood Control District, Hydraulic Design di Manual prepared in March, 1982. (Also adopted by MA) • Detention Basin Design Criteria for San Bernardino County prepared by EPWA of San Bernardino County. 7 IS 1 1.6 ORGANIZATION OF THIS REPORT This report summarizes the results of the hydraulic analysis and hydrologic modeling corresponding to a 24 hour storm having a return period of 100 years. Details of the analysis are included in the Appendices which are submitted separately. The contents of the Appendices are as follows: ■r Appendix A: Includes the rainfall data for each watershed. ,R Appendix B: The results of Rational Method of Computing times of concentration for each watershed under existing and .,.. ultimate conditions. Appendix C: Development of Loss Rate Parameters. In 1988 Rivertech developed an interactive catputer mod named "Loss Rate Calculator Version 2.1 ". This model was used to ei calculate Loss rate F and law loss fraction Y. Appendix C includes these parameters for each watershed es under existing and ultimate conditions. - Appendix D: Development of data for basin routing. Elevation- ' storage and elevation - discharge relationships have been ,.� developed for San Sevaine Basins No. 1, 2, and 3 as well r as Rich Basin. Appendix E: Input data hydzoggaphs. Data described in Appendices A, B, C and D have been summarized and tabulated for use se in the AES -FLOOD program. Appendix F: Hydrologic models using the AES -FLOOD program are s` included In Appendix F. Appendix G: Hydraulic analysis and design of Hawker- Crawford Channel e and Rich Basin are included in Appendix G. The remaining chapters of this report include: Chapter 2: METHODOLOGY - In this chapter existing, interim and ultimate conditions are further discussed. The hydrologic parameters and the computer programs used in the study are described. 8 r • Chapter 3: HYDROLOGIC MODELS - Results of the models for different land use conditions and at different locations are described. Chapter 4: HYDRAULIC DESIGN OF RICH BASIN AND HAWKER C AWFORD CrtNNEL - Hawker awford Channel and the cutlet of Rich Basin are hydraulically analyzed. Results of the analysis are discussed. 2. NErRODDICGY 2.1 DESCRIPI'ICUS OF CONDITIONS so The hydrologic components and their corresponding model darts for the existing, ng, ultimate, and interim conditions are shown in Exhibits A, B, and C respectively. The drainage network shown in Exhibit A has been tra verified with that adapted by Hall & Foreman. The two networks are essentially the same. of ... In Exhibit A, because of the limited culvert capacity under the freeway, so only a portion of the flow is allowed to reach node 80 from node 70. In Exhibit B, drainage is diverted from watershed 70A to the channel upstream of Rich Basin. Also, drainage from watershed 70B is diverted across the freeway to Hawker- Crawford Camel. These diversions are in accordance with the City of Fontana's Master Drainage Plan. It is assumed that adequate culverts will be designed and constructed to permit watersheds 70A and 70B to drain to the west. Because of the significant change in watershed size between existing and ultimate conditions, a comparison of discharge at San Sevaine Basin No. 3 for the two conditions will provide little information. However, the ccparison between existing and interim conditions would be very meaningful. The reason being is Rich Basin will be excavated sufficiently to offset the increased discharge from Hunter's Ridge development. After measuring the areas, calculating the hydrograph parameters and 9 using the AES -FLOOD program, watershed models were developed in accordance with the model charts shown in Dchibits A, B and C. 2.2 DESCRIPTIONS OF PROGRAMS USED sr In developing watershed models and analyzing channel hydraulics, four ie different programs were used. These programs are described in the following paragraphs. so 2.2.1 AES -RATSB is This is the Rational Method ployicuu developed by Advanced Engineering Software for San Bernardino County. In calibrating the FLOOD program, 10 AES has used the Rational Method to compute the lag. Accordingly, Rivertech has used this program to compute the lag which is a required input parameter for the FLOOD program. al 2.2.2 AES -FLOOD is This program is also developed by AES for San Bernardino County. Option 1, which generates hydrographs for a watershed is based on the unit hydr'ograph procedure. 2.2.3 HEC -2 se -- This is a water surface profile program developed by the U.S. Army Corps of Engineers. It was used to develop rating curves for San Sevaine Basins No. 1, 2 and 3. The program was also used to develop water r surface profiles for Hawker - Crawford Channel and Rich Basin di 2.2.4 IDES RATE CALCULATOR This program was developed by Rivertech early in 1988. It was used to calculate loss rate F and low loss fraction Y. r ei is 10 2.3 OPTION OF HYI>R'OIOGIC PARAMETERS +r The parameters required by the FLOOD program are as follows: as 2.3.1 RAINFALL - Using Exhibits D, E and F and data described in Appendix A, rainfall values were calculated for each watershed. 2.3.2 OAK LOSS RATE AND LW LOSS FRACTION - computed by using to "Loss Rate Calculator". Information shown on Exhibits G, H, I .m were used as raw input data for the "Loss Rate Calculator". e� 2.3.3 LAG - lag is muted as 0.8 x the time of concentration. Exhibit J shows the data used in the AES- RATSBC program. 2.3.4 WATERSHED AREA - measured on the U.S.G.S. quadrangle maps. so 2.3.5 BASEFLOW - assumed zero in all watersheds. 2.3.6 S CURVE VALUES - were estimated based on land use condition and W topography of the watershed. 2.3.7 PRECIPITATION- DEFIi- ARFA- FACIOI the FLOOD program was used with "dtmany" areas to calculate the precipitation-depth-area- factors at the concentration points under consideration. In addition to the above parameters used in generating hydrographs, other parameters such as channel dimensions and elevation- storage relationships for the basins were used to route the flood hydrographs. These parameters are shc»m in Appendix D. ey 3 HYIIDLOGIC MJOELS es Four master hydrologic models were developed. These varied according to it their location of point of concentration, condition of land use and type of routing as represented graphically in Figure 3. +r 3.1 MODEL NO. 1 0. so Model No. 1 established the constraints for Model No. 3. Several "" interim grading plans and outlet channels at Rich Basin were tried until mei 11 ai A W cc 0 M Al n tL .• •• O �v /]J gs Ogg uIrJ (i; m i •• J 1 MA 1 OH 2 0 0 W E 0 Z o J w ‹ cilH qPg co S lii igA 'd O 2 L ? w n 1 o g 8 ►► 11 x' 8 02° m .. 0 w 2 J 0 Q c, 0 tl > , p w 0 >-. Z u) 2 a LL 110g g 0 l' 00 V I O Q N 00 NF1 0e N >.. co .. .. r ri ko M rd • w ►► a •• CC W o i iillil alai re c 0 w c U O m J 0 1 '- V 2 ul c >' a) L 1 2 ,� ©© . • H O ligi ww 0 1-4 •• •• r 00 HH 1. Mdi Ilidi r=i z k 12 the outflow of Model 3 was less than the outflow of Model 1. di 3.2 MODEL NO. 1.1 4111 Model No. 1.1 was developed by modifying Model No. 1. This modification me was made by deleting the processes downstream of Rich Basin. In addition, the precipitation - area - depth - factors corresponding to the watershed area at Rich Basin were used to compute the peak inflorw and �• outflow rates for existing conditions at Rich Basin. di 3.3 MODEL NO. 2 di Model No. 2 corresponds to the ultimate conditions in the watersheds 4111 el upstream of San Sevaine Basin No. 3. The purpose of this model is to compute the ultimate discharge at San Sevaine Basin No. 3. r 3.4 MODEL NO. 2.1 it Model No. 2 was modified to produce Model No. 2.1 which computes the 4141 ultimate design discharge for Hawker - Crawford Channel. This Iss modification was made by deleting processes downstream of Rich Basin in Model No. 2. In addition, the precipitation- area - depth- factors corresponding to the drainage area at Rich Basin were used in the is watersheds of Model No. 2.1. 4141 3.5 MODELS NO. 3 AND 3.1 4141 41 Model No. 3 was developed to find the sizes of Rich Basin and the outlet notch at Hawker - Crawford Channel for interim condition. These sizes , were computed such that at San Sevaine Basin No. 3, flow during interim condition is less than existing condition. Model No. 3.1 was developed 4111 to calculate the discharge during interim condition at Rich Basin outlet. This provided the discharge to develop a water surface profile ""' for interim condition along Hawker - Crawford Channel. di d 13 Mg eft AB 3.6 14ODELS NO. 4, 4.1 AND 4.2 or Models No. 4, 4.1 and 4.2 were developed to verify the results of Models 1, 2, and 3. Models 4, 4.1 and 4.2 correspond to single area hydrographs without channel or detention basin routings. In comparing the results of ultimate with existing and interim - conditions, one should note that the drainage areas for ultimate mmr condition at San Sevaine Basin No. 3 and Rich Basin are significantly larger than those for existing and interim conditions. These increases in drainage areas are as a result of the City of Fontana's Master Drainage Plan. ImOm err 4. HYIRADLIC DESIGN OF CHANNEL AND RICH BASIN AIM r 4.1 DESIGN OF BASIN AND CHANNEL FOR ULTIMATE CONDTTION AIM Sr The first step in the design of Rich Basin and Hawker- Crawford Channel was to develop a feasible ultimate grading plan for Rich Basin. Exhibit K shows Rivertech's rec mimended grading plan for ultimate Rich MINN Basin, to be constructed at a future date when the upstream watershed is rr developed. The following lists the constraints for the recommended ultimate grading plan: • Except at the outlet of the basin, maintain the existing levee oft heights. r • A nththium of 50 feet setback from the right-of-way line for the ,.. County of San Bernardino. r • Provisions for construction of concrete channels at locations where the water course enters the ultimate detention basin. Although no concrete channels are shown in the grading plan, the concept assumes that concrete chutes (steep channels) will be constructed in the future to permit safe entry of flood waters from adjoining water courses into the detention basin. r 14 r osi di lau • Provisions for Rich Basin to have uses other than flood control '• such as park, lake, or groundwater recharge areas. wr Once the proposed ultimate grading plan was complete, different outlet channels were tested in Model No. 2 described in the previous section. Results of the model analysis indicated that a cost- effective solution would be a 14 -foot wide rectangular channel. The following reasons were the basis for selecting this dimension for the ultimate channel. or • A channel narrower than 14 feet will create a 1000 -year water mi surface elevation in Rich Basin that would exceed the existing levee crest elevations. r • It is the most efficient cross - section as the normal depth of flow is approximately half the width. mm • Engineers at J.P Kapp & Associates and at the Cauhty of San Bernardino recommend 14 -foot wide box culverts across Hawker Crawford Channel at Summit Avenue and Interior Collector am Street. A 14 -foot wide channel would require no transitions upstream and downstream of these culverts. •r The ultimate condition elevation- storage relationship shown in Exhibit rrr K, and the outflow rating curve for the 14 -foot wide channel were used as input parameters for the Model Vo. 2. Model results showed that the mil maximum 100 -year basin elevation reaches 1601.6 feet. At this elevation, the storage capacity of the ultimate Rich Basin would be 242 acre At the entrance to Hawker - Crawford Channel the elevation of the top of am the channel is selected at 1601.6 feet. Results of the HEC -2 analysis revealed that at this location the ultimate 100 -year and 1000 -year water surface elevations would be 1595.34 feet and 1598.02 feet respectively. Therefore, at the entrance to the rectangular channel. the 100 -year and me 1000 -year freeboards would be 6.26 feet and 3.58 feet respectively. 00 The basin is provided with a free flowing outlet channel without a standard type of spillway structure. Therefore, Rivertech believes that mg 15 ei this arrangement of storage does not fall tinder the jurisdiction of the Division of Safety of Dams, State of California. +r The horizontal alignment of the ultimate Hawker - Crawford channel is shown in Eibit K. As can be seen on the alignment plan, the channel di is provided with a curve having a radius of 800 feet. In accordance with the criteria of the Los Angeles County Flood COntrol District (which is also adopted by the EPWA of San Bernardino County) the freeboard in and in the vicinity of the curve is increased by an additional 2 feet. The freeboard in the straight portions of the channel is selected as 2 feet above the ultimate 100 -year water surface profile. These freeboards are consistent with the channels whose design +■I velocity is less than 35 feet per second. W There are two additional curves along the Hawker-Crawford Channel between Summit Avenue and the 800 -foot curve. Each of these two curves have radii of 3600 feet and lengths of 99.31 feet and 101.25 feet respectively. Because of the extremely large radii and short lengths the effects of these curves on channel hydraulics is assumed to be 10 negligible. +i The values of the channel hydraulic parameters are presented in tabular form in Exhibit K. Height of the wall shown in this table is the sum of depth and the required freeboard. In the vicinity of the channel entrance, the height of the wall is selected as the 1000 -year depth or di 100 -year depth plus freeboard, whichever is greater. The profile of Rich Basin along its thalweg is also shown in Ekhibit di K. As can be seen in this profile the basin will remain dry during normal periods since the lowest elevation in the basin is its spillway 40 elevation of 1583.34 feet. As shown in FXdhibit K, this arrangement also permits the construction of a recharge lake. 41 4.2 DESIGN OF BASIN FOR INTERIM OONDIT' a Er Rivertech's concept for the design of Hawker - Crawford Channel and Rich 16 di di 41' Basin is based on the recommendation that the ultimate channel be AN constructed concurrently with the development of Hunter's Ridge. In addition, it is recoai rnded that only a portion of the ultimate basin be constructed initially to provide the required flood control benefit. •• Ihe grading plan recQlii ernded by Rivertech for the interim condition is shown in Exhibit K. The following two constraints established the ws basis of the interim grading plan. di • Provide sufficient storage such that at San Sevaine Basin No. 3 4111 flow during interim condition is less than the flow during •� existing condition. • Storage is less than 50 acre feet. w di As described previously, Rivertech believes that neither the interim basin nor the ultimate basin would fall under the jurisdiction of the Division of Safety of Dams. Nevertheless, the storage capacity of the di interim basin is selected to be less than 50 acre feet to avoid any "" unnecessary pmt processing activities. d i The above constraints required that a 10 -foot wide notch be constructed err at the entrance to the ultimate Hawker-Crawford Channel. When the ultimate Rich Basin is constructed this notch would be removed. r w r mn di di •i di 44 di M► di 17 mi