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Home My WebLink AboutHydraulic Study s • �� ; � ' f w �- V Howard H. Chang Consultants R � � � � , `� � Hydraulic, Hydrologic and Sedimentation Engineering V P.O. Box 9492 Rancho Santa Fe, CA 92067 JUN 1 (619)756-9050, 594-6380, FAX: (619)756-9460 CITY OF YEMECULA ENGfNEERING DEPARTMENT June 15, 1998 Mr. Joseph Kicek, Director Department of Public Works City of Temecula 43200 Business Park Drive Temecula, CA 92590 Dear Mr. Kicek Subject: HYDRALTLIC STUDY FOR FEMA CONDITIONAL LETTER OF MAP REVISION (CLOMR) FOR MURRIETA CREEK IN THE CITY OF TEMECULA RIVERSIDE COUNTY, CALIFOIZNIA Pursuant to the request of Westside City II, I have prepared a hydraulic study to apply for a Conditional Letter of Map Revision (CLOMR) for Murrieta Creek in the City of Temecula, Riverside County, California. This application for CLOMR covers the channel reach of Murrieta Creek from Winchester Road to the city limit of Temecula at Cherry Street. Murrieta Creek along this reach has levees on both sides. The effective FIRM map (see attached) shows that the floodway extends outside the west levee of the channel. REASONS FOR THE CLOMR I have made the study to revise the effective Flood Insurance Rate Map (FIRM) for the Diaz Road and other development projects west of the stream channel. For these projects, the areas west of the levee will be raised to elevations above the base flood level. On the basis of federal and local regulation, the road and developments need to be located outside the floodway of Murrieta Creek. For this reason, it is necessary to delineate the new floodway for Murrieta Creek in order to implement these projects: It should be pointed out that the revision of the floodway requires no changes of the stream channel within the proposed floodway. The hydraulic study for the effective Flood Insurance Rate Map (FIRM), Community-Panel Number 060742 0005 B, for Murrieta Creek published by FEMA in June 1996 was made by Schaaf and Wheeler, a consulting firm in San Jose, California. According to this study, the computed water-surface profile may be contained in the leveed channel. However, the west levee was assumed to fail and thus the area west of the levee will be subject to flood inunda.tion. The ground level for the west area is only sightly below the computed base flood level. This area is under very shallow flooding (see attached figures) and it may thus be considered as an ineffective flow area for the stream channel under the base flood. 1 i i • . t • Failure of the west levee would occur if the levee is overtopped. This is because weir flow overtopping the levee has high velocities that would erode the earthen material. However, the levee will become a ordinary channel bank after the area on the west side is raised to be above the base flood level. Once the levee is eliminated, erosion failure due to overtopping will no longer be a possibility. The plans for Diaz Road and future development show that the ground level for these projects will be similar to the top of the levee, which is at least three feet above the base flood level. For these reasons, the west area will no longer be subject to flooding after the road and developments are completed. This application for CLOMR is to update the floodplain boundaries and to delineate the floodway for Murrieta Creek between Winchester Road a and Cherry Street for the development plans west of the leveed channel. The study channel reach starts from Section 80 at Winchester Road and ends at Section 160 at Cherry Street. HYDRAULIC ANALYSIS FOR THE CLOMR Hydraulic analysis for the CLOMR is based on the HEC-2 computer program developed by the U. S. Army Corps of Engineers. Locations of cross sections used in this study are listed in Table 1. Cross-sectional data for these sections are based on the Flood Insurance Study by Schaaf and Wheeler. Table 1. List of cross sections used in the study Section Location 60 80 Winchester Road 90 100 110 120 130 140 150 Cherry Street 160 Cherry Street 2 The study covers the following two models: (1) The existing model - This model was used by Schaaf and Wheeler for the FEMA study pertaining to the effective FIIZM map. (2) The proposed model - This model pertains to the same channel conditions as the existing model except the area west of the levee is raised to stay above the base flood level. The results for these case scenarios will be compazed. In order to satisfy the federal and local requirements, the increases in flood level due to floodway encroachment should be limited to one foot. In addition, the proposed floodway shall result in "no-rise" in the base flood level. The 100-yr flood discharges - The 100-yr flood is the base flood for this stream channel. The FEMA-adopted base flood discharges are as follows. Below the Santa Gertrudis Creek confluence (Section 80 and below): 28,500 cfs Above the Santa Gertrudis Creek confluence (Section 90 and above): 19,500 cfs Flood dischazges for the 10-, 25-, and 50-yr floods are not available for Murrieta Creek. Floodway Data Summary - The floodway data summary for the proposed model is given below. For the proposed model, the floodway is within the existing levees of the channel. FLOODWAY DATA, FLOODPLAIN, FOR THE PROPOSED MODEL ------- FLOODWAY ------- WATER SURFACE ELEVATION STATION WIDTH SECTION MEAN WITH WITHOUT DIFFERENCE AREA VELOCITY FLOODWAY FLOODWAY 60.000 289. 2639. 10.1 1019.5 1019.5 �.0 80.000 249. 2121. 12.5 1019.6 1019.6 .0 90.000 209. 2107. 8.2 1021.6 1020.9 .7 100.000 225. 1850. 9.4 1021.8 1021.0 .8 110.000 216. 1557. 11.2 1022.3 1021.8 .5 120.000 183. 1454. 12.0 1023.0 1022.8 .2 130.000 193. 1467. 11.8 1023.9 1023.8 .1 140.000 191. 1452. 12.0 1024.8 1024.7 .1 r 150.000 182. 1270. 13.7 1024.9 1024.8 .1 160.000 206. 1731. 10.0 1026.4 1026.4 .0 170.000 180. 1483. 11.7 1026.1 1026.1 .0 It can be seen from the floodway summary that the floodway as delineated will result in rises in flood level that are within the 1 foot limit. The floodway water-surface elevations for the two models are also summarized in Table 2 for comparison. It can be seen from the comparison that the proposed model will not result in rises of the floodway water surface. 3 Table 2. Computed water-surface elevations for the 100-yr floodway Computed water-surface elevation, feet Section number � Existing model Proposed model 60 1,019.6 1,019.5 80 1,020.9 1,019.6 90 1,021.6 1,021.6 100 1,022.1 1,021.8 110 1,023.0 1,022.3 120 1,023.8 1,023.0 130 1,024.8 1,023.9 140 1,025.1 1,024.8 150 1,025.4 1,0249 160 1,027.0 1,026.4 170 1,026.9 1,026.1 I will submit the CLOMR application package to you in a few days. After your approval, this package needs to be submitted to FEMA for their action. If you have any questions regarding this matter, please feel free to call me. , Sincerely yours, ; Howard H. Chang Ph.D., P.E. � t / / G �. 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I 010 ..................................:............................ � ' � ................................ ................................ ................................ . . . . . . ..... ...>...... � ..:... ... ioo� 4000 45a0 5000 5500 6000 8500 7000 7500 Station (looking downstxeam), ft �Iurrieta Creek � _ Cross—Sectional Profile at Sec. 80 Elev., ft 1035 iU30... ..............................:.....................................;.....................................<....................... . � � 1025 ............................. � ............._... ................:........ ... ... ..,.i.............. � : .......................... ...... ................. 102� ............._.,.................:.......................... ........ :......... ..... . .............. � ..................................�.. . ......... _ ................................ ........... ... .............�................. . .. � .. .. � 1015 ..................................:........................... .........:......... ..........................:.....................................;.....................................;.................................. _ ................................ 1010 ................... ..............:.............................. ..�...................................,. �. = � ......................... ................................ 1005 4000 4500 5000 5500 8000 �500 7000 7500 Station (looking do�anstream), ft � Murrieta Creek � Cross—Sectional Profile at Sec. 90 Elev., ft 1040 1035 ......................:..................... ...:...... .................:.......................... �................. . � � : .............. .................... .................... 103D......................:................. � : ; : : : ..................... .................... 1025 ...... ................:.............. .. ...:........ ... � ..................... ............ ........ ..................... ..................... .................... ....... . ........ . , . . . . . . . . . . . . ........., ...................... ..�.. . ..;... . . , . . ..,... ...... ....... .. _._�_ — ._;_ __._ � iQ20 ...................—�.......................:..----............ �.........................:.................. ...._................ ......... ....... .................... ..................... .................... . . • . . . ..... . . . . . . . ...... ...... 1015 ....................:........................:.........................�. : � ...... ..................... .................... ..._.............. ................. 1010 ..................... � ......................,.;.........................�. � : : ............... .................... .................... .................... 1005 48�0 v000 5200 5400 5600 5800 fi000 6200 64U0 6600 6800 Station {looking downstream), ft Murrieta Creek � Cross—Sectional Profile at Sec. 100 Elev., ft 1035 1030 ..................................:......................................:_...................................:..................... � ........................... ................................ ................................ 1025 ................................:....................... ........:.....................................:. � ................................ ................................. ................................ — — --- — — _. _. _: � _._. � �: � : 102U............ ....................:................. ...................:........... ....... � : : 1015 ................................:....................................:.....................................;.................................. :. ..............................�............ � .................... 1010 .................... ........:......................................s.....................................:........ _ : : : 10U5 4800 500Q 5200 5400 5fi00 5800 fi000 6200 Station {loaking doxnstream)� ft Murrieta Creek � Cross—Sectional Profile at Sec. 110 Elev., ft 1040 1035 ........................:...........................�. � ' � � ................ ....................... ...................... .... ............................. ........................,......................... ,. ° 103 0 ........................:...........................;...........................:. : : : : ............... ................... ........ 1025 .... ....... .......:........................... � .....,..... .............>...........................;...........................? .................. ..... ...................... ...... ............. ........ — --- � — � � 1020 ....................:........................._.............. � ...................;............ � : ' ............. .................. ........ ... ... . . . _ ............................................. � � ............... .... ..:.. .. 1015 ........................s.......................;............................;...........................:....... � .................... ....................... ....................... ...................... ........ . . ...................._.... ...;.. .;.. ' >.. 1010 4704 4900 5100 5300 5500 5700 5900 8100 6300 8500 Station (looking downstream), ft Murrieta Creek ' Cross—Seetional Frofile at Sec. 120 Elev., ft 1040 1035 ..........................:.............................:............................:.. ° ............... ....................... ........................ .................... 103t1 ......................... �................... . � : : ` ; ................ ........................ ....... ... . . . : ... ..... _ .......................................................... _............................,..... .......................,.......... . 1025 ............. ........... : ..... ........ .......... :............................;. .. � : : .................. .................. � ............... . � .. ......................._............................;..............,..............:......... ..;... ........�. ...... � — — -- — -- -- — -- — — i 020 ............... .... ....:........ .. .............. :............ � � ' .. .................._..... ................... � ................�.........................,.._............................;................ � ... ...... .,.. 1015 .................. ......:........ .................. :........ .. . ° � � ................. ...................... ........................ 1010 4800 50Q0 5240 5400 SgOQ 5800 6000 6200 B400 6600 Station {looking downstream}, ft Murrieta Creek • Cross—Seetxonal Profile at Sec. 130 Elev., ft 1040 1035 ..........................;............................:......................... � � ...................... ........................ ........................ .................. ....................... �030 .........................:.............................:............................:................ � ......;............................<.......................... ...................... ........................ 1 U25 .......... ..............s.............. .._........... . : : : : : .... � ........ ........................._............................:.............................. � ......,......... __.. -:_ _ , ;� _._. � _ _. -r. 1020 .......................:..........................:............................_............................_................... � � .......... � ............... ........:....... .....................:................. .................. .....,....... 10 i 5 ................... .....s....... .....................s............................ ;.............................<................. : : � ... ... ......... ....................... 1010 480Q 50410 5200 540� 5600 5800 6000 82t10 6400 8600 Station �la�ki�g downstream), ft Murrieta Creek ' Cross—Sectional Profile at See. 140 Elev., ft 1Q4fl 1035 .......................:..........................;.,.......................:..........................<. ,. � : ..................... ...................... ....... ...... 103U .....................:............. ..:.........................�.........................�.........................s.......,.............. ..................... ..................... .................... . ............ . . . . . . .. ..;... .. �... ..;.. ..:... .. .. ... 1025 ........ ...........:......................:.................... � : : � : ........ � .... � ............. . . • .......................:.........................- ...... ,......... .... ,......... .. ...._.. . .......................... ............................. ..... T . ___.. _.;. ____ _._. _.._ -:._ _ _; ._._ _..: _ � 1020 ......................:.........................:.:.......................:................... ' � � .... � ........ � ............. ......: .........................:................... .. ...:... .;.......... . . ... .......... ................ .. ........,.......... .. 1 � 15 ................ .....:..... ....................:.........................�.........................:;. � ........ ..................... .................... ...................... ..... ............ IOiO 4800 5000 5200 54U0 56Q0 580Q 8000 fi200 6400 6800 8800 Station (laoking doWnstream), ft Murrieta Creek ' Cross—Seetional Profile at Sec. 150 Elev., ft 1040 1035 ......................... :.............................:............. .......... .;. .. ..................... . .,...,...... .............. ................,....... ....................... ...................... ....................... 1030 ........................:...:............ .......:............................;............................;............................�. � .............. ....................... ............................:................................... ... � 102� .......... � ................s....... .__...._......... � ................. ........ .......,......... ....................... ................:...... . .._....... .....r........ . ;... ;... � 1020 ............... .........i....... ....................;............................;............................'. � ..........._............ ........................ ......................... ...................... . . ............................... . ;... ;.. ;.. 1015 .................. .� ..........................;............................�........... � : : ' : .--............. 1010 4800 5000 5200 5400 5600 5800 6000 62Q0 6400 6800 5tation {looking downstream), ft i Murrieta Creek , Cross—Sectional Profile at Sec. ig0 • Elev., ft 1040 1035 ...................:........................:.......................:.......... ' ............. .................. .. 1430 ....................<........................:.......................<........................:..................,....;............... ....... �.................... ........... ................... ................... ... � � 1U25 ................-......... .....; ............:............ .......:.. .. . ....... . .................. ................... .......:.......... ... , . .....'.. :... .. . ..;... �.. .; . 1020 ......... .......:........ ..............:.......................:........................:.................. ................. ................... .................. _ ................. ................... .. . ;... ..:.. ;... ..�.. ;.. ..:... 1015 ............. � ...............:.......................s........................;.......................:............ .. � ................... .................. ................... .. 1010 4800 5000 5200 5400 5600 580(1 8000 6200 6400 8600 680 Statian (looking downstream), ft i Murrieta Creek , _ Cross-5ectional Profile at Sec. 170 Elev., ft 1040 1035 .............................;.................................�..................... � ................. ....... .......:.................... ............................ ..... .............. � 1030 .............................�........_.......................;................................'................................�............. � � ..................... . .................. -�— — — 102� ................ ............= ......... ...... . . ..;.................................:. � ............... _ ......... ......... .......................... . ............. .............:....... .. ............;.. : : 1020 ............................'...............................;................................:. ' ................... ............................ ....................... .................................................................:......... � : 1015 ..................... :.... ....................,:.................................;..................... � ' ................. ....................... ........................... 1014 4800 5000 5200 5400 5600 5800 6000 8200 64U0 Station {looking downstream), ft