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HomeMy WebLinkAbout143-83 RESOLUTION• RESOLUTION NO. 143 - 83 A RESOLUTION;ADOPTING A MASTER SEWERAGE AND DRAINAGE PLAN FOR A PORTION OF THE CITY OF FAYETTEVILLE LOCATED ADJACENT TO ARKANSAS HIGHWAY 16 WEST. BE IT RESOLVED BY THE BOARD OF DIRECTORS OF THE CITY OF FAYETTEVILLE, ARKANSAS: That the Board of Directors hereby adopts the master sewerage and drainage plan attached hereto, marked Exhibit "A", and made a part hereof for a portion of the City of Fayetteville located adjacent to Arkansas Highway 16 West. PASSED AND APPROVED this 6th day of December, 1983. APPROVED: Mayor '°-a 1 1 1 1 1 1• EVALUATION OF STORMWATER DRAINAGE FACILITIES - t 14? :mio HIGHWAY 16 WEST FOR CITY:OF FAYETTEVILLE • • I • .. k ">`Li August, 1983 83-119 ‘-Prepared by • McClelland Consulting Engineers, Inc 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ■ EVALUATION OF STORMWATER DRAINAGE FACILITIES HIGHWAY .16 WEST FOR CITY OF FAYETTEVILLE August, 1983 83-119 Prepared by McClelland Consulting Engineers, Inc. TABLE OF CONTENTS SECTION PAGE NO. I Introduction 1 II Description of Project Area 2 III Description of Drainage Basin 3 IV Evaluation of Existing Streets and Roads 4 - 5 V Evaluation of Existing Drainage Facilities 6 - 8 VI Description of Known Flooding 9 - 11 VII Projected Stormwat'er Flows and Recommended 12 - 14 Culverts and Bridges VIII Discussion of Recommended Culverts and Bridges 15 - 17 IX Recommended Storm Sewers 18 - 19 X Discussion of Recommended Storm Sewers 20 - 21 XI Estimated Costs for Recommended Drainage Facilities 22 - 27 XII Channel Improvements 28 - 31 XIII Implementation of Recommended Drainage Facilities 32 - 33 XIV Municipal Participation in Drainage Facilities Costs 34 XV Conclusions 35 XVI Storm Drainage Design Criteria 36 - 37 SECTION XVII Appendices Figure Figure Figure Figure Figure Figure Figure No. No. No. No. No. No. No. 1 2 3 4A 46 5 6A Figure No. 6B Figure No. 7A Figure No. 7B TABLE OF CONTENTS Project Planning Area Map Flood Hazard Boundary Map SCS Hydrologic Soil Groups Existing Drainage Facilities, East Map Existing Drainage Facilities, West Map General Land Use Plan Recommended Culverts and Bridges, East Map Recommended Culverts and Bridges, West Map Recommended Storm Sewers, East Map Recommended Storm Sewers, West Map LIST OF TABLES TABLE PAGE NO. NO. 1 Characteristics of Existing Streets and Roads 5 2 Characteristics of Existing Drainage Facilities 8 3 Stormwater Flows and Recommended Drainage 14 Structure Sizes 4 Recommended Storm Sewer Facilities 19 5 Modification of Culvert Sizes If Storm Sewers are 21 Installed 6 Estimated Costs of Recommended Culverts and Bridges 23 - 24 7 Estimated Total Costs for Municipally Funded 25 Culverts and Bridges 8 Estimated Costs of Storm Sewers by Street Classification 26 9 Unit Costs Used for Drainage Pipe 27 INTRODUCTION I. INTRODUCTION In November, 1982, approximately 910 acres were annexed to the City of Fayetteville. This area is located along Highway 16 West (Wedington Drive) west of the Highway 71 bypass. At the time of the annexation, several subdivisions were in various planning phases under the Washington County subdivision regulations. Upon annexation to the City of Fayetteville, the Fayetteville Planning Commission has been approached by some of these potential developers concerning rezoning and/or development of portions of this annexed area. Other property owners have notified City officials of existing and potential stormwater drainage and sanitary sewerage problems. As a result of these somewhat opposing factions, and in an effort to determine a picture of the true consequences of development on these aspects of the annexed area, and contiguous areas influenced by, or exerting an influence on, the annexed area, the Fayetteville Planning Commission recommended to the Board of Directors that comprehensive engineering studies of drainage and sewerage needs be completed. McClelland Consulting Engineers, Inc. was employed by the City of Fayetteville on May 16, 1983, to complete these two studies. This document addresses the stormwater drainage needs for the project area, with a corresponding document addressing sewerage needs for the project area. Reviewers and users of these documents are cautioned to remember that these two subjects, only, are addressed. While the project area also needs street construction work, water distribution system improvements, fire hydrant installations, and related municipal facilities, these needs are not addressed in these documents. — 1 • 1 1 DESCRIPTION OF PROJECT AREA II. DESCRIPTION OF PROJECT AREA The project area about which this stormwater drainage study has been prepared consists of approximately 910 acres which were annexed to the City of Fayetteville in November, 1982. The area is located on each side of Wedington Drive (Highway 16 West), west of the Highway 71 bypass. Figure No. 1 illustrates the limits of the project area. Land use in this area is primarily agricultural with some low density residential areas located in the western half of the project area. Agricultural land uses in the area include small grain production, pasture, hay crops and poultry production. Areas that are cultivated, such as the small grain crops, tend to have higher stormwater runoff rates, as compared to non cultivated hay and pasture land uses. The eastern portion of the project area is relatively flat, with some rolling land existing in the western portion of the area. The overall drainage basin slope from the Owl Creek drainage divide southeast of the Ozarks Electric property to the Double Springs Road bridge is approximately 0.56 percent. Segments of Owl Creek near County Road 650 N are flatter than this average slope, tending to create wider flood plain areas. Relative to flood plains, the U.S. Department of Housing and Urban Development has published a Flood Hazard Boundary Map for Washington County. This map includes the project area and is reproduced on Figure No. 2. Approximately 55 acres of the project area are included in the Zone A flood hazard area designated on this map. The exact limits and/or location of the flood hazard boundary and flood water elevation cannot be determined from this map. It is expected that a detailed flood study, such as those completed on several streams within Fayetteville's previous corporate limits, has not been completed for Owl Creek. • DESCRIPTION OF DRAINAGE BASIN III. DESCRIPTION OF DRAINAGE BASIN In addition to most of the 910 acres within the project area, drainage structures in the area are influenced by stormwater runoff from adjacent portions of the drainage basin. The Double Springs Road bridge serves the largest drainage area of any of the structures evaluated. It receives runoff from approximately 1715 acres, the limits of which are illustrated on Figure No. 1. Land use in the balance of the drainage basin is basically agricultural, with less residential development as compared to the project area. A wooded hill exists in the southeast corner of the drainage basin. With the exception of this hill, the balance of the basin is flat to rolling in topography. Soil characteristics in a drainage basin greatly influence the amount and rate of stormwater runoff. The Soil Conservation Service includes in its county Soil Survey booklets information on the hydrologic soil classification for the various soil types in that county. These classifications range from Soil Group A with a low runoff potential to Soil Group D, with a high runoff potential. Figure No. 3 illustrates the drainage basin and the various soil group classifications. As indicated by this figure, much of the eastern portion of the drainage basin has soil types that have high or moderately -high runoff potentials. These are basically the same soil types that have severe limitations for septic tank leaching fields as discussed in the corresponding sewerage study. The reasons for these septic tank limitations and high runoff potentials include slow infiltration rates, high water tables, clay layers and/or rock layers. The Group D, high runoff potential soils, have a high clay content. Group C soils have slow infiltration rates due to moderately fine or fine textures. Group B soils cover the majority of the western portion of the drainage basin, with some Group C and D soils mixed in. Group B soils are moderately well drained to well drained soils, as a result of moderately fine to moderately coarse textures. Consequently, infiltration into these soils is higher than for Groups C and D soils and the resulting stormwater runoff is less. Only a very small area of Group A soils exist in the drainage basin, and this area is downstream from the drainage structures evaluated. EVALUATION OF EXISTING STREETS AND ROADS IV. EVALUATION OF EXISTING STREETS AND ROADS Although the scope of work under this project did not include any requirement for reviewing the current road situation in the project area, some awareness of the existing condition of these streets and roads is necessary, _in order to better understand the stormwater drainage needs. Table No. 1 summarizes the existing road conditions. County road numbers have been used where applicable. In some cases a direction designation has been added to the road numbers to delineate segments of the various roads. Figures 1, 4A and 4B illustrate the road locations, and projected right-of-ways are shown on Figures 6A and 6B. The projected right-of-ways are based on the street classifications discussed hereinafter. In some cases, these right-of-ways differ from those shown on City plat maps. With the exception of a few platted subdivisions, most of the streets are unplated and are expected not to be dedicated streets. As can be seen from the notes in Table No.1, and by careful review of the figures, most of the roads in the project area are narrow. Many have inadequate drainage ditches. Surfaces range from good asphalt to gravel to rocks to dirt. Many of the roads are dead ended. Part of these dead end roads serve several property owners, while othersserve rows of duplexes, which are apparently rental units. In almost every case, the roads and streets in the project area have one or more inadequate drainage structures. The remainder of this report addresses existing and needed drainage facilities. Recommended drainage facilities have been broken into two categories; culverts and bridges for the existing and proposed streets, and storm sewers with curb and gutter inlets for streets upgraded to City Street Standards. This second category of structures is proposed based upon the assumption that new streets illustrated on the Master Street Plan will be built in accordance with the street standards, and that existing streets will eventually be upgraded to the City Street Standards, thereby requiring installation of storm sewers. Some of the recommended storm sewers are for existing residential and private streets that may never be upgraded. Consequently, the interrelationship of street upgrading and drainage structure installations must be remembered. TABLE NO. 1 Y O Narrow for a major highway II c O V 0 L L c N c C a 0 O 0 L L U U 4-1 Y Y Y • a a -CI C C O O 0 O O 0 C C a U 3 3 A 0a 0a 4- L C L C L L a L a 0 = N N C N Ca Ca 3 0) co r0 0 o is i13 S- - q O a a '0 a 0• > > z 0 a Y 0 1.. a C Y •nN 0 • L 0 3 V V 0 a r0 L V a L N Y - 10 tF Y rt1Ip C L i > > 5- • 0 O r J N j L Y d.- 0 O a 0 q V O a CL C N L R T • N ry a N O 0 N L V L 4-I W (0' X 0 w Good condition, Good condition, narrow Good condition, narrow Some ditch work needed Fair surface Narrow, dead end 9 C A 0) x 0 0) Y r '0 J r 0. 4- 0 0 N Y • Y 0 O 0) L 0 4- L C C 0 C C C a a N Ln U Y 0 N r0 L S- o a 0) m 0 o O d Dead end, no ditches 0 v > > 4-1 N 0 !.0- rti 0 r0 r L L r0 rci CU r0 L I0 a CD 0 0) a Y L Y H N V J 0 W L h£ Y Y Y Y YC • Y C Y _ _ q • 0 CI 0 m m m 0 ▪ a m a a L L L L > • L > > > 0. c > >0 d d d VI r ill teLO LN • i L S. i Q Q • 6 Q 0 0 < 0 • 0 CD V CO 0 6 0 0 YL� O r0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O O Q' R ti V 10 tO V IO 10 0 CO 0 U) a Y tO 10 10 10 IO t0ID 10 OI t0 ID 0 1O CO 0 p N L C 1-' f7 V • .. • • N. • Y a-. N N N V N N N 'y VI J .y >1 "•••••- 4-.1 Y NL • C 3 Y Y OI 1 .-0 4- -r- SI - CC C 03 c O O O O O 0 0 0 0 O 0 O O 1 O 1 1 O CO OJ N CO LD tO 10 tD 1D ID ID ID IO LD 1 R Y C OJ V 0.1 C Residential Residential Residential Residential 0) 10 I Y > CU a C'.- a Y Y a L Y N ' T -0 0_ .O > > > N 0 L L a C S- 0- d O. C 0 0- C Y 0 a CD Y 5- CO Y C U L L 1.. L 111 ^ .- ft,.- r r •-- V- d fp q q ^ Y Y Y U S- d'� 0 V V U a -N L L L L L L i 0 a a N Y NC C a O a 0 a O a 1 1 1 I 1 1 I 1 I N ^ Y C Y 0 Y C Y 1-.- r - r - r 'p L L r L L .r i £ 0 dQ £Q £Q £Q 0 0 0 U L ▪ Z O Y • O CD a 0 C q CU L r0 Z 3 Y C Y Z L 01 N 0 ID C 0 LO ~ 0 0.03 3 3 C = L) S� K... Rupple Road S. in O C L c.N a— 3 3 Z N H N. O 0 n 0 O CO 01 10 n n 10 L] N 10 n CO n n 10 10 CO 0 ID 10 co fp 10 tD co co 10 LO t0 LO b V O V C C C C C C pv 0 V V U 0 V U 0 V V V 0 V V V U - 5 - • Clevenger Drive Michael Cole Drive Brook Drive EVALUATION OF EXISTING DRAINAGE FACILITIES V. EVALUATION OF EXISTING DRAINAGE FACILITIES Existing stormwater drainage facilities in the project area range from a reasonably sized bridge over Owl Creek on Double Springs Road to 15 inch culverts. Drainage structures included in this evaluation included all located structures under the previously listed public and private streets. Culverts under individual driveways were not included in this evaluation. Table No. 2 lists the characteristics and locations of these structures. Notes concerning the structure condition and any clogging are also listed. Each of the structures has been assigned a structure number. Figures 4A and 4B show the locations of these structures by number. Specific comments concerning some of these structures are as follows: Structure No. Comment 1 The Double Springs Road bridge appears structurally sound, however, a structural analysis of this or any other drainage structure has not been made. Wingwalls and guard rails are needed on the bridge. Some erosion of the road embankment is occurring due to the fact that there are no wingwalls. 2 & 3 These bridges are hydraulically and structurally inadequate. 4. This bridge is located immediately outside the project area, however, flows through the bridge will be influenced by the project area. The bridge appears relatively new and structurally sound. It is on the route of a proposed minor arterial street, as indicated by the Master Street Plan. 5 This culvert is fed by two driveway culverts to effect a "T" shaped structure. The driveway culverts include approximately 23 feet of 30 inch CMP and 27 feet of 18"X30" arch pipe. This installation has failed to pass stormwater flows, resulting in flood waters running across the street. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Structure No. 6 thru 11 Comment Many of the culverts under Highway 16 are combinations of concrete pipe, corrugated metal pipe and/or box culvert. Apparently as the highway was upgraded, culverts were extended by segments. 17, 22, 23, 26 These culverts are under roads that may be 27, 28, & 29 determined to be private drives. Structure 27 is a new low water bridge. 20 This structure consists of a concrete slab over a pile of rocks. Some flow passes through the rocks with the balance flowing over the slab in the nature of a low water bridge. TABLE NO. 2 CHARACTERISTICS OF EXISTING DRAINAGE FACILITIES Present Structure Street Name Existing Structure Open Length No. or No. Structure Size Condition % (ft.) 1 Double Springs Road 237 S.F. Bridge . Good 100 20 2 CR650N 54 S.F. Bridge Poor 100 14.5 3 CR650W 44 S.F. Bridge Poor 80 17.8 4 - CR648 - 112 S.F. Bridge Good 90 26 5 CR650S 7.8 S.F. RCB Good 100 28.6 6 Hwy 16 24" CMP Fair 80 37 7 Hwy 16 24" RCP & CMP Good 50 37 8 Hwy 16 24" CMP & RCB Good 80 ' 49 9 Hwy 16 36" RCP Good 100 39 10 Hwy 16 18" RCP & CMP Fair 50 28 11 Hwy 16 24" CMP & 2'X4' RCB Poor 100 37 12 Carriage Way 24" CMP Good 100 77 13 Carlsbad Trace 24" CMP Good 75 75 14 CR877 18" CMP Fair 5 34 15 CR878 36" CMP Good 50 40 16 Michael Cole Drive 18" RCP Good 100 29 17 Brook Drive 18" RCP Good 75 24 18 CR650W 14"X20" CMPA New 100 33 19 CR667 18" RCP Good 100 28 20 CR667 Conc. Slab - - No Opening 21 CR667 5'X3' RCB Good 100 12 22 Clevenger Road 24" RCP Good 75 26 23 Clevenger Road 15" RCP Good 100 20 24 Michael Cole Drive 24" RCP Good 100 66 '25 Michael Cole Drive 15" CMP Good 100 37 26 Michael Cole Drive 18" RCP Good 100 33 27 Michael Cole Drive 24" RCP and Low Good 95 15 Water Bridge 28 CR638 15" RCP Good 50 29 29 Michael Cole Drive 18" RCP Good 100 38 Abbreviations: RCP Reinforced Concrete Pipe CMP Corrugated Metal Pipe RCB Reinforced Concrete Box Culvert CMPA Corrugated Metal Arch Pipe S.F. Square foot opening size DESCRIPTION OF KNOWN -FLOODING VI. DESCRIPTION OF KNOWN FLOODING One of the principal contributing reasons for this study being authorized and completed is the fact that flooding has occurred in the project area, and the fact that if development is allowed to occur in the project area without adequate drainage provisions, increases in the frequency and severity of current flooding problems will occur. Drainage structures 2, 3 and 5 as previously described and as shown on Figure No. 4A and 4B are known to become submerged during major storms. Houses and structures where flooding is known to have occurred are as follows: Millard Goff Residence: This house is located on County Road 650 South, northwest of drainage structure no. 5. Flooding of the house garage occurred during last Summers storm, with the water level reaching within approximately 2 inches of the house floor level. Garage flooding has occurred on one other previous occasion. Flooding results when stormwater from drainage structure no. 6 (under Hwy 16 near Carriage Way) and from the drainage basin east of structure no. 5 exceeds the capacity of structure no. 5. Yard flooding on the east side of the road occurs, with water overtopping the road north of structure no. 5. This water spreads out in the yard around the Goff residence and subsequently enters the garage on the east end of the house. Elimination of this flooding could be achieved by upsizing structure no. 5, deeping the road drainage ditches and/or building up the road surface elevation. Reductions in the stormwater flows could also be achieved by installing a culvert at the intersection of Hwy 16 and Rupple Road, thereby diverting some of the flow south along the proposed extension to Rupple Road. Clevenger Duplexes: These duplexes are located alongside Owl Creek, east of County Road 650 North, and just upstream of drainage structure no. 2. Five of the duplexes closest to the bridge were flooded during last Summers storm. These buildings had 6 to 8 inches of water in them. Previous building flooding has not occurred in the 11 years that the buildings have been in existence, although the water level has gotten within 8 inches of the building floor levels several times. Part of the cause of this flooding may be attributed to backwater created by the bridge and it's embankment. However, the bridge and embankment are relatively small. It is expected that flooding would occur under major storm events if no bridge and embankment existed. It is believed that major channel improvements such as clearing and straightening, will be necessary to reduce most chances of flooding. Flooding possibilities could be reduced somewhat by constructing a low water bridge, flush with the natural drainage channels, or by constructing a very long bridge, that would have an opening large enough to prevent creation of backwater. Part of the problem in this area is the flat creek slope immediately downstream of this area (0.3%), which tends to slow the channel velocity and subsequently create higher upstream water levels, even without the backwater effects created by the bridge. Wayne Flora Residence: This house is located south of Michael Cole Drive, about halfway between Brook Drive and drainage structure no. 27. It is located beside and immediately downstream of a bend in Owl Creek. ,The house has been constructed approximately 5 years. Last summers storm resulted in approximately 3 inches of water in the house, submergence of the swimming pool southeast of the house and partial submergence of a barn and storage building. One previous storm resulted in water approximately 2 to 3 inches below the house floor level. Channel improvements would be necessary to reduce the chances of flooding at this house. It's location is sufficiently remote from existing drainage structures to rule out structures as the cause of this flooding. The flat creek slope, as listed above, wooded channel and bend in the channel all undoubtedly contribute to the severity of flooding at this site. The possibility of flooding in duplexes at the end of Brook Drive was suspected, however, conversations with the owner indicate that this has not occurred. The owner advised that the ground level had been built up somewhat and that an extra course of blocks had•been used in the footings of the south duplexes. The owner advised that the open flat field south of Brook Drive flooded, thereby shifting the flow away from the duplexes. An analysis of the three known flooding situations indicates some common characteristics; first of all the structures are relatively new, yet all three locations have either been flooded or threatened with flooding on occasions other than last Summers storm; second, major funding commitments are necessary in order to reduce the possibility of flooding of these three sites; third, with the exception of the possible flow diversions by the Highway Department at the Rupple Road/Hwy 16 intersection, no major changes have been made in the drainage basin since these buildings were completed. One might conclude that these buildings were constructed in flood prone areas, and that this mistake by the building owners does not justify any otherwise unwarranted expenses to the City of Fayetteville. An alternate way of viewing this situation is that a flooding problem is known to exist. Development in the project area that results in increased stormwater runoff will increase the frequency and/or severity of this problem. Consequently, developers would be liable for any incremental increase in damages. Under - 10 - this situation, what policy should the City of Fayetteville take concerning allowing development to occur? The remaining sections of this study estimate stormwater runoff rates under existing and developed conditions in the drainage basin, provide preliminary sizing of drainage structures to handle the projected flows and provide cost estimates for these facilities, all in an effort to better understand the existing and projected situations. Perhaps this information will better enable the City of Fayetteville to reach an informed answer to the question posed. above. PROJECTED STORMWATER FLOWS AND RECOMMENDED CULVERTS AND BRIDGES VII. PROJECTED STORMWATER FLOWS AND RECOMMENDED CULVERTS AND BRIDGES The Arkansas State Highway and Transportation Department has recently published an updated Drainage Manual. This manual establishes methods, criteria and guidelines for estimating stormwater flows, sizing culverts and bridges and designing storm sewers. This manual was used as the primary reference for determining the information and recommendations presented hereinafter. In some cases, some "short-cut" methods were utilized, since the purpose of this study is to obtain a preliminary structure size. If and when structures are to be constructed, detailed design analysis for each structure should be completed at that time, as localized conditions, changes in the drainage basin characteristics or projected land uses could all result in significant modifications to the structure sizes recommended hereinafter. Table No. 3 lists stormwater flows and recommended structure sizes for each of the existing drainage structures. In addition, drainage structures needed for new streets proposed on the Master Street Plan have been sized. Flows were calculated based on the Rational Method for small structures and based on the Soil Conservation Service method for large structures, in accordance with the Highway Department Drainage Manual. A modified formula was utilized to determine the time of concentration for the Rational Method calculations, as described in Section XVI. Existing and projected stormwater flows were based on current and projected land use characteristics. Projected land use characteristics were determined based on an amendment to Fayetteville's General Land Use Plan, as illustrated by Figure No. 5. The S.C.S. Hydrologic Soil Groups, as previously discussed and as illustrated by Figure No. 3, were also utilized in the S.C.S. calculation method for determining the stormwater runoff rates for the major structures. The estimated stormwater flows and recommended structure sizes have been calculated for various storm frequencies. Ten year and 25 year storm frequencies were used to calculate structure sizes for minor structures. Major structures were sized for.25 and 50 year storm frequencies. Culverts across Highway 16 were sized for 10, 25 and 50 year storm frequencies. Section XVI lists Highway Department criteria for recommended design storm frequencies. The City of Fayetteville generally requires the use of a 25 year frequency for minor structures and 50 year frequency for major structures. Based primarily on the Highway Department criteria, it is recommended that in general a 50 year design storm frequency be used .for major structures and for principal arterial streets (Hwy. 16), that a 25 year design storm frequency be used for minor arterial and collector streets, and that a 10 year design storm frequency be used for residential and private - 12 - streets. Structure sizes corresponding to these conditions have been marked on Table No. 3. Where the existing sizes appear adequate they have been "boxed" in. Of the 29 existing structures, 9 appear adequately sized, including the low water bridge (structure no. 27). The design storm frequencies recommended above should be reconsidered on a case by case basis when final design of these structures is completed. 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IO .N (.f •- ^.+(C S.'+ 1 Q 1p Qf1 .-I .r 'Ott) Y J C Cu'0.- .-. •_4_ Cs -4 .-'-4— P .+ .--I N10 N Y] 017N ^ a U O .-. .r .� V L O' N ^ • N N T N C C W d 1O.JIOPIONIO .-I InOON OIO OOOI IAN OOI0 N(7 p1 l.t .r Y LL IO I�GI bn< A A6 V N -N I�I.IPCO PbNI'11�f4PbVa O.ti I�I�NWNI�^.-I-I N .�...I� to O Gi O Cu-6)QN00 V L v .-. .+ I.1 .-ICI u]I-. n N in Cu_I Cu_I Y1 .-I .-I �y N O D C W 1 2- 00 .-N f70 V11O N,Q1010.-+N mO V1 .p V In 101U(O OI LZ -.-010 .-L. .r .�.�.�. .-I.-I .-IN CU Cu Cu NNNNNNNryN Qp]UOW LLOS W F 5- O - 14 - I I. 1 1 1 1 I I. I I ■ DISCUSSION OF RECOMMENDED CULVERTS AND BRIDGES VIII. DISCUSSION OF RECOMMENDED CULVERTS AND BRIDGES As can be seen from Table No. 3, the projected development in the project area results in significant increases in the future stormwater flow. This fact, combined with the fact that many of the existing drainage structures are currently undersized, results in the need for upsizing 20 of the 29 existing structures. Comments concerning specific structures are as follows: Structure No. Comment The existing DoubleSprings Road bridge is barely adequate for the estimated 50 year stormwater flow. It is estimated that this flow will reach the bridge steel and approach the bridge deck. Construction of angled inlet and outlet wingwalls will protect the bridges embankment and improve its hydraulic efficiency. 2 Extreme care will be required in designing a bridge for this site, in order to avoid creating backwaters that will flood the Clevenger Duplexes. This, coupled with the flat creek slope, is the reason that this bridge is sized larger than structure no. 1. 3 & 4 These two structures are hydraulically inadequate and structure 3 appears structurally inadequate, however, upgrading.. these structures could be given a relatively low priority from the standpoint that flood waters at these two structures will probably not cause major economic losses. 5 This structure has contributed to significant flooding problems due to its inadequate capacity. It should receive high priority for replacement. It could be downsized somewhat if proposed structure D is installed at Rupple Road. 6 thru 11 All of the structures under Highway 16 need to be enlarged in order to handle projected stormwater flows. Actual enlargement and selected sizes will be determined by the Highway Department. This Department should be advised of the City's development plans when any culvert upgrading planning is initiated. Structure no. 6 is sized based on the current flow patterns from Rupple Road to this - 15 - structure. If proposed structure D is installed across Highway 16 at Rupple Road, structure no. 6 and no. 5 could be downsized somewhat. 12, 14, 15, 19 These structures are considered undersized. They are 20, 21, and 24 located on public streets. 13, 16, 18 and These structures are considered adequately sized, and 25 from Table No. 2, all are considered to be in good condition. They •are located on public streets. 17, 22, 27 and These structures are located on what are assumed to 28 be private streets. They are in good condition and are considered to be adequately sized. 23, 26, and 29 These structures are located on what are assumed to be private streets. They are considered undersized. The street at structure no. 23 functions as a low water bridge, consequently additional culverts are not absolutely necessary for this application. A, B, C, G These structures will be required in order to and H accommodate construction of new streets proposed on the Master Street Plan. Locations of these new structures are listed in Table No. 3 and are shown on Figure No. 6A and 6B. D This new culvert would be constructed under Hwy. 16 at Rupple Road. It would reduce the flows to structure no. 6 and no. 5, and consequently, the flooding potential at structure no. 5 would be reduced. Table No. 3 indicates that this structure would receive approximately 32 cfs from a 7.8 acre drainage area. The Highway Department has also reviewed the needs for a structure at this location and arrived at a 27 acre drainage area and a projected flow of 80 cfs. Apparently, the Highway Department intended to regrade the Hwy 16 ditch west. of Rupple road, in order to direct flows from both Hwy 16 and Rupple Road through this structure. This increased flow through this structure would further relieve structure nos. 6 and 5, but would also increase the needs for drainage facilities along the proposed extension of Rupple Road, south of Highway 16 to Highway 62. For the purpose of this report, the lower flow rates listed in Table No. 3 have been used in determining the size of recommended storm sewers on Rupple Road South and on CR650S. In either - 16 - case, structure nos. 5 and 6 still need to be increased in size. E & F These two new structures would be installed to prevent stormwater from flowing over County roads 879 and 880 where they intersect Highway 16. There may be existing structures at one or both of these locations, however, they are not readily apparent and are not functional. - 17 - RECOMMENDED STORM SEWERS IX. RECOMMENDED STORM SEWERS Figure Nos. 7A and 7B depict recommended storm sewer facilities. They are further listed in Table No. 4. Design of these facilities was based on stormwater flow rates generated as previously described for projected land use conditions and on the Highway Department's Drainage Manual recommended design practices. Storm frequencies of 10 years were utilized for minor arterial streets, with the exception of the Rupple Road crossing of Highway 16, where the estimated 50 year stormwater flow of 32 cfs (as listed in Table No. 3) was utilized. Storm frequencies of 5 years were generally used for collector, residential and private streets. These storm frequencies result in structure sizes slightly smaller than if a 25 year storm frequency had been used, as listed in Fayetteville's Street Standards for drainage structures. However, considering the fact that the Highway Department recommends that a 2 year storm frequency be used for non-federal aid projects for storm sewers, it is believed that the recommended sizes are adequate for this application. Storm sewers were not,sized for Highway 16, s such would be determined by and completed by the previously noted under the section on culverts and sized for some private and residential streets that Fayetteville Street Standards, and consequently, structures installed. ince any installation of Highway Department. As bridges, structures were may never be upgraded tc may never have these As indicated in Table No. 4, the bulk of the recommended storm sewers are on existing and proposed minor arterial and collector streets. Existing and proposed county road 650 running east and west along the south project boundary has the greatest requirement for storm sewer facilities. - 18 - TABLE NO. 4 RECOMMENDED STORM SEWER FACILITIES Street Street Storm Sewer Lengths by Pipe Size Curb Classification Name 15" 18" 21" 24" 27" 30" 33" 36" 42" 48" 54" Inlets Minor Arterial Rupple Road 320 160 500 - •80 1090 80 - 1480 260 - 16 to Bridge A Minor Arterial Double Springs 210 350 600 600 - - - - - - - 6 Rd. North of Bridge 1 Minor Arterial Double Springs 500 - - - - - - - - - - 2 Rd. South of Bridge 1 Minor Arterial 648 North of 80 390 390 - - - - - - - - 2 Bridge C Subtotal Minor Arterial Collector Collector Collector Collector Collector Collector Subtotal Collector Residential Residential Residential Residential Residential Subtotal Residential Private Subtotal Private 1110 900 1490 600 80 1090 80 - 1480 260 650 East of - 880 - - - - 350 350 700 - - Bridge 8 650 East of 120 120 - 630 - - - - 50 -1640 Bridge 3 650 West of 60 120 550 - - 1100 - - - - - Bridge 3 650 North of - 60 360 - - - - - - - - Bridge 2 650 South of 1010 60 - - 720 - - - - - - Bridge 2 880 North of - - 60 200 - - - - - - - Hwy 16 1190 1240 970 830 720 1100 350 350 750 - 1640 650 North of - - - - - - 100- = 320 - Bridge 5 650 South of 50 600 - - - - - - - - Bridge 5 878 North of 50 200 - - - - - - - - - Hwy. 16 879 North of 510 - - - - - - - - - - Hwy. 16 667 East of Bridge.21 - 50 - 320 - - - - - - - 610 850 - 320 - - 100 - - 320 - Brook Drive 50 340 - - - - - - - - - 50 340 - - - - - - - - - 26 7 10 6 2 9 2 36 4 2 2 2 2 12 2 2 in DISCUSSION OF RECOMMENDED STORM SEWERS X. DISCUSSION OF RECOMMENDED STORM SEWERS In some cases, the storm sewers as shown on Figure No. 7A and 7B not only collect street drainage and drainage from the immediate vicinity of the street, but they also intercept major flows from natural drainage patterns. These flows require that the storm sewers be upsized considerably. In addition, special inlet structures will be required at these locations. The inlets shown on the figures represent the bare minimum. It is expected that final design of these facilities will indicate the need for more inlets and/or extended lengths of curb opening per inlet. As the area develops, additional inlets will also be needed at new street intersections. Certain areas where natural drainage basins are intersected by the storm sewers, therefore, requiring larger pipe sizes include: 1. Rupple Road South at the start of the 42 inch pipe. 2. County Road 650 South at the channel downstream from structure no. 6 under Hwy 16. 3. The intersection of CR650S and CR65OW, where the 42 inch pipe starts. 4. County Road 650N, south of the CR677 intersection, where the 27 inch pipe starts. The flat topography in the eastern end of the project area also contributes to the rather large size of some of the storm sewers, since pipes laid on a flat slope have less carrying capacity than those installed on steeper grades. The location of the storm sewers, as shown on the Figure Nos. 7A and 7B, was primarily determined based upon the discharge point being on the downstream side of bridges located at that point. The storm sewers could easily be shifted to the opposite side of the street, however in some cases, this would create the need for enlarging bridges or box culverts at the discharge point. Construction of this complete storm sewer system would allow structure no. -5,. on CR650S, to be considerably downsized. Other culverts would also be effected to some extent, as indicated in Table No. 5. The net result of installing the complete storm sewer system would be a slight reduction in the needed culvert improvements. This reduction has not been reflected in the cost estimates contained hereinafter, primarily because the sequence in which improvements are- completed probably will not allow this potential cost savings to occur. - -20- C) C C r a) ro a) N i Y i i N J J Y C Y a-` V •r U U C) J J J .0 S. C) S. S. 4 -IC Y Y 0 N i i i i i O a o 3 3 3 3 3 3 ai CL C OL n a) a) a) 0 a) v •r =4) J N (fl - U) N N N Cl 0 Y-0 Y Y E E E E E E 9- N C C C i i i i L L 0 C) OW a) a) O 0 0 0 0 0 +) 0)5- O) 0) Y Y Y Y Y 4' Y O C a) a C N N 4'Q) Y +' T >5 a T > >) i1 •C N a C .0 0 .0. .O .0 .O O a a OE U • U S. U a) a) a) a) a) Cl) r0 a) CO CC) C C) U U U U U U r N oY 0 or ro ro ro ro ro ro ro•r •r N •r r •r r r r r r r r N +' Y ro Y(0 d a a d N 01/) 04-' 04-' a) a) a a) Q1 (U )) U) 4 -IC J O J N J N i S. i i i i a) •r 0) LC) C t C - r a) t0 air a) •r Y Y Y +' Y +' C -a i ll' i i i -i i- i i a) •r a) U O) Cl a) a) a) a) a) a) U C) a) C C > > > > > > N O N 'r P.4 N 'r r r r r r r S. •r C •r a) •r Q1 J J J J J J DC) tint (n fl (n fl V V U U V U 01- -D a) r r ro a) W VN) 0= C H v E N E L LL O a a) a) n a a N a E N1- •1-0 (/1+• !n w a) "O M C a• E O E Z 0 U aJ CC LL ro a) F- N r C (fl LC) LL N rti LL V) m N Y U 5. - cc V "6 V U ro al a) a) v a) a) LL - Y Y Y Y Y +) a) a) a) a) a) a) v c'4 r r r r r r C 1 N a) a) a) a) 0) (0 N 0 C 0 0 C C .-i N C 0- 0 CL r aL aL CL U O V U U C N a' a1 ai cc cc a1 V V U O N. N. Cr) N = N N 1 d 1 - 1 1 N r--1 N N r-1 N N N N co O) V O] O) r-i — rr N N N O W ESTIMATED COSTS FOR RECOMMENDED DRAINAGE FACILITIES ii aM XI. ESTIMATED COSTS FOR RECOMMENDED DRAINAGE FACILITIES Table Nos. 6, 7, 8, and 9 contain cost estimate information concerning the various recommended stormwater drainage facilities. Specifically, Table No. 6 lists the estimated costs for the recommended improvements to the culverts and bridges, as previously listed in Table No. 3. Table No. 6 has been categorized by street classification, primarily because the City of Fayetteville may not become involved in funding facilities for Highway 16 and for private streets. Unit costs used to complete Table No. 6 are listed in Table No. 9. Table No. 7 totalizes those street classifications for which the City of Fayetteville may become involved in funding. It indicates that the recommended culverts and bridges needed for existing and proposed minor arterial and collector streets and for existing residential streets would cost approximately $470,000 to construct. It should be noted that while most of the costs are based on new structures sized to comply with standard street widths, the cost estimated for the Double Springs Road bridge (structure no. 1) is for recommended upgrading only (wingwalls, guardrails, miscellaneous renovation). Constructing a new bridge of sufficient width to meet the street standards could add approximately $90,000 to the project total listed in Table No. 7. Table No. 8 lists estimated costs for the recommended storm sewers, as itemized in Table. No. 4. Again these costs are categorized by street classification. Costs have not been estimated for Highway 16 and private streets, for reasons previously discussed. For all three street classifications a total cost of approximately $1,022,000 is estimated. Cost estimates listed in. these four tables are based upon the assumption that installation of these drainage facilities will occur concurrent with a major street construction or reconstruction project. Installation.of these structures on a piecemeal basis without any concurrent street work would result in costs significantly exceeding the estimated costs. This is because the costs of street repairs and the overhead costs associated with blocking a road are not reflected in the estimated prices. With the exception of relatively few structures that need immediate attention, it is expected that delaying installation of these structures until a major street project is completed will prove to be the most cost effective method of addressing this situation. Cost estimates are based on current estimating prices, with some allowance in the unit prices for the inlet structures for- oversized structures in some location. A contingency percentage is included to account for the miscellaneous small cost items that are not included in these preliminary cost estimates. - -22- TABLE NO. 6 ESTIMATED COSTS OF RECOMMENDED CULVERTS AND BRIDGES Structure Street Classification Street No. Structure Description PrincipalArterial Hwy 16 6 21 S.F. RCB, 60long Hwy 16 7 24" & 27" RCP, 60' long Hwy 16 8 19.5 S.F. RCB 75' long Hwy 16 9 33 S.F. RCB, 60' long Hwy 16 10 24" and 27" RCP, 60' long Hwy 16 11 2-30" RCP, 60' long Hwy 16 D 2-21" RCP, 60' long Subtotal Principal Arterial Minor Arterial Rupple Road South A 96 S.F. Bridge, 45' wide CR648S 4 195 S.F. Bridge, 45' wide PR648N C 60 S.F. RCB, 50' long PR648N H 2-30" RCP, 50' long Double Springs Road I Upgrade existing bridge Subtotal, Minor Arterial Collector CR650W 3 204 S.F. Bridge, 45' Wide CR650W 18 Existing 14"X28" CMPA, Extend 30" PR650E B 76 S.F. Bridge, 55' Wide PR650E G 18 S.F. RCP, 50' Long CR650N 2 264 S.F. Bridge, 45' Wide CR877 14 21" RCP, 50' Long CR880 E 24" RCP, 260' Long Subtotal, Collector Estimated Cost $ 13,200 5,700 15,000 16,800 5,700 6,480 4,680 $ 67,560 $ 31,500 60,000 22,500 5,400 7,000 $ 126,400 $ 63,000 1,200 30,000 9,250 85,000 1,950 11,700 $ 202,100 -2a- TABLE NO. 6 ESTIMATED COSTS OF RECOMMENDED CULVERTS AND BRIDGES (Continued) Structure Street Classification Street No. Structure Description Residential CR650S 5 51 S.F. RCB, 36' Long Carriage Way 12 2-30" RCP, 77' Long Carlsbad Trace 13 Existing Structure Adequate CR878 15 Existing 36" CMP and new 33" RCP, 75' long Michael Cole Dr. 16 Existing 18" RCP, Extend 10' • CR667 19 2-24" RCP, 36' long CR667 20 2-21" RCP, 36long CR667 21 30 S.F. RCB, 36' long Michael Cole Dr. 24 Existing 24" and new 30" RCP 66' Long Michael Cole Dr. 25 Existing 15", Adequate CR879N F 15" RCP, 36' Long Subtotal, Residential Private Brook Drive 17 Existing 18" RCP Adequate Clevenger Rd. 22 Existing 24" RCP Adequate Clevenger Rd. 23 Road acts as a low water bridge, no additional culverts recommended Michael Cole Dr. 26 Existing 18" and New 18" RCP, 33' long Michael Cole Dr. 27 Low Water Bridge Adequate Michael Cole Dr. 29 2-24" RCP, 38' long Subtotal Privat Estimated Cost $ 14,400 8,316 4,725 500 3,240 2,808 9,360 3,564 1,080 $ 47,993 1,122 3,420 $ 4,542 -24- TABLE NO. 7 ESTIMATED TOTAL COSTS FOR MUNICIPALLY FUNDED CULVERTS AND BRIDGES Street Classification Estimated Cost Minor Arterial $ 126,400 Collectors 202,100 Residential 47,993 Construction Subtotal $ 376,493 Engineering and Contingencies 94,123 Estimated Total $ 470,616 - 2 5 - O 0 0 O O O O O +� C 0 LCD V1 N LO tO N O O LU tO N O ^ n 1 ^ 1 1 ^ 1 I ^ 1 ^ ^ n n U ('J 0) 0) cY M W t0 .--1 CO — — N- W N O _ CT t 64 b9 r'I b4 C •r •r } Y C N Q) r 'O X •r W N Q) i O O O O O N C C LU1 N 1 I O 1 I ('4 I .--1 Q) LO LO CO M rl M J O I— Q U H W 0 0 0 O 0 0 0 0 0 0 0 O Ln LU Cl) O ('4 r1 O t0 O O O U) O O V CO I- N -0 1) OD Lt) CO 0) N- to I- LA N tO O Ch ('4 rl QQ) N ^ n n n n n n n n 1 n n n n n VI 0 M m N V' M 0 V N- V N- C O O �--I U 0 U ('4 N N N N M .ti r1 LO V r-1 L() 0_ '-I V r1 L[) F— 0 44 H} 44 W L i W C_ O i-) F- 1/) C Q) b r r m m rno • Co O In •r L Z O O O O Co O O O O O t0 m In Q) C O) �' n CO N O L!) N- I tO CO LU •r C rl N O) co n r -I C') M M N- tO W X Q) rl rl .-1 rl m in W Q F- E O V) N O O O O O O O O O O O O O O Cl) O O C O Ct N N O N W O I -- Q i-) N N. N- O (0 LD N m M M ^ -o O) Gt 0 Q) 0 n n n n n ^ n 1 n n n n n ^ C) O (ID0 0 N O co CO N M N. W O) O) N V U N N M rl m0) M a) ri M 00 N— !� t0 C O r N M O 0 it lrR y} 44 W i •r CL i C Q v - Y F-+ C i CL 1— o Q N N W O i Co rr r C L O O 0 O O O O O to t0 C In g rl O 0) O co CI) OO I m t0 1 N Q) •r C v O) l0 O Gt ('4 Ol. X Q) .-I rl rl .-a a W J •r 4-3 C 0 0 V C b -) O 0 In F C C A "- EL r r i Cl) (0 Q) 0 3 N _ _ _ _ _ _ _ _ _ - H tt 14 O M t0 N CO 0 C N N N ti H N N N M M M Gt d' LO d +.) •r •r i 0 CT C m N U Cl) W W - or - TABLE NO. 9 UNIT COSTS USED FOR DRAINAGE PIPE Culverts Storm Sewers Pipe Size Estimated Unit Cost Pipe Size Estimated Unit Cost 15" $30/ft. 15" $20/ft. 18" 34/ft. 18" 23/ft. 21" 39/ft. 21" 26/ft. 24" 45/ft. 24" 30/ft. 27" 50/ft. 27" 33/ft. 30" 54/ft. 30" 36/ft. 33" 63/ft. 33" 42/ft. 36" 75/ft. 36" 50/ft. 14"X20" 35/ft. 42" 59/ft. 18" S.F. 185/S.F. 48" 72/ft. 19.5 S.F. 200/Ft. 54" 90/ft. 21 S.F. 220/Ft. Curb Inlet 1,500/Ea 30 S.F. 260/ft. 33 S.F. 280/ft. 51 S.F. 400/ft. 60 S.F. 450/ft. 97 CHANNEL IMPROVEMENTS XII. CHANNEL IMPROVEMENTS It was noted in Section VI that channel improvements may be necessary to reduce the possibility of flooding in certain locations. Channel improvements are also needed in the vicinity of proposed drainage structures, in order to insure their effectiveness. Specifically, channel improvements are needed at drainage structures A, B, C, and 5 and at the entrance to the storm sewers leading to structure no. 5 as shown on Figure No. 7A. In general, the size of these channels should exceed the opening size of the receiving or discharging structure by at least 50%. The additional capacity is needed to allow for lower channel velocities and to provide for freeboard. The actual channel size, shape and construction material could vary significantly, depending upon the use of the adjoining property. A large trapezoidal shaped grassed waterway with flat sideslopes is most appropriate in agricultural areas, whereas a rectangular concrete channel maybe more appropriate in a commercial area. Due to this variability, no specific size and cost values are recommended for the needed channelization work. However, some general information for these channels is presented as follows: Channel Location Comments. Structures A & B •Channelization is needed at these two proposed bridges to provide proper stream alignment into and out of these structures. While rather economical earthen channels should suffice, caution must be used to insure that the storm sewer outlets do not create excessive erosion. Structure C Structure C is located on a proposed minor arterial street, where the street location runs parallel to a drainage ditch for approximately 250 feet. This creates a situation where a large box culvert (60 square feet opening) or an open channel is needed for this 250 feet length. In order to avoid excessive costs, an economical earthen channel is recommended. Riprap or concrete lining would be needed at the end of culvert C to prevent channel erosion. A trapezoidal channel with an eight foot wide bottom, 4 to 1 sideslopes, five foot depth and channel slope of 0.7% could be used at this -location. This channel would have a cross sectional area at the 4 foot depth level - 28 .- of,96 square feet, in comparison to a 60 square foot area recommended for structure C. Storm Sewer This channel would intercept the discharge from Near Structure structure no. 6 under Highway 16 and funnel it No. 5 to the storm sewer inlets north of structure no.. 5, as shown on Figure No. 7A. The estimated flow rate of 110 cfs (assuming culvert D or the Rupple Road storm sewer is installed) could be transported in a trapezoidal earthen channel with .a 4 foot bottom width, a 3 foot depth, 4:1 sideslopes and a channel slope of 1.3%. At a two foot water depth, this channel would have a cross sectional area of 24 square feet, as compared to approximately -12 square feet for the receiving storm sewers. Structure No. 5 Table No. 3 estimates a projected flow rate Discharge for this culvert of approximately 300 cfs, or approximately 268 cfs if structure D is installed. A 48 square foot structure is recommended for the 300 cfs. The receiving ditch channel has a cross sectional area of 12 to 16 square feet within its banks. This channel size should be upgraded to approximately 60 square feet of flow area. A trapezoidal channel with a 4 foot depth, 3 foot water depth, 8 foot bottom width, 4:1 sideslopes, and channel slope of approximately 0.8% could be used to meet these conditions. As previously discussed, alternate channel configurations could be used to minimize the top width of the channel. If, for general considerations, this channel was constructed from the structure 5 outlet to a point upstream of proposed structure C where the ground slope increases, approximately 1000 feet of channelization would be required. This could require approximately 3000 cubic yards of earthwork. At $5 per cubic yard, this work could cost in the range of $15,000. Structure No. 2 As noted in Section VI, flooding upstream Vicinity and downstream of this structure has occurred. Table No. 3 indicates that this bridge has an opening area of approximately 54 square feet and that an opening of approximately 264 square feet is recommended. The existing channel size - - 29 — within the creek banks is approximately 85 square feet. The total creek floodway cross section below the lowest building floor level is approximately 840 square feet. This should be sufficient to pass the projected flow of 1570 cfs without flooding the duplexes upstream from this bridge. Field surveys indicate that approximately 450 square feet of flow area is available between the top of the existing street surface and the lowest building floor level. This corresponds to a maximum water depth over the road surface of approximately 2.4 feet. Combined with the area under the existing bridge, approximately 500 square feet of flow area is available over and under the road surface, before the water level reaches the floor elevation. Calculations for weir flow in accordance with the Highway Department Drainage Manual indicate that. this available flow area should pass a flow approximately equal to the projected flow of 1570 cfs. Consequently, one would conclude that the flooding which occurred last Summer was either the result of the actual flow rate exceeding 1570 cfs or the result. of channel conditions and obstructions other than the existing bridge and road embankment. Downstream conditions that could contribute to backwater submerging the road and flooding the duplexes include the very flat slope of this section of Owl Creek (0.3%), the bends in the creek, the small channel size, and the trees and brush in and along the channel. If downstream control did contribute to the flooding, it would have been evident as a flat water surface profile across the bridge and street, during the maximum flood stage period. If, instead, there was a sharp drop in the water surface profile at the downstream side of the street, then the street embankment would have controlled the upstream water level and consequents, the extent of flooding. This was discussed with the Owner of the duplexes, however, the actual water surface profile across the street during the maximum flood period could not be verified. Since the actual flow rate which occurred last Summer is unknown, and the flow characteristics -30- across this street are also unknown, as discussed above, a determination cannot be made as to whether the flooding at the duplexes was. caused by backwater created by the bridge and street embankment, or backwater caused by downstream conditions. It is expected that if the bridge and street embankment caused the. flooding, the actual flow rate last Summer exceeded the projected 50 year design flow rate of 1570 cfs. An extensive hydraulic analysis of this channel segment might provide a determination of this matter, however, with the currently available information, the following conclusions can be drawn: A new bridge is"needed to replace structure no. 2. If downstream conditions control the water level during major storms, this new bridge would be of little value for flooding control during major storms unless channel improvements were completed. Channel improvements will be necessary in order to reduce the flooding potential at the Wayne Flora residence, downstream of structure no. 2 (See Section VI). These improvements could possibly relieve the flooding at the duplexes if this flooding is controlled by downstream conditions. In order to insure that the channel improvements were effective and that problems would not be created elsewhere, approximately 3600 linear feet of improvements would be needed. Based upon increasing the existing channel cross section by 300 square feet, 40,000 cubic yards of earthwork would be necessary, which would cost $160,000 at $4 per cubic yard. Less extensive channel improvements might be more justifiable economically. - 31 - IMPLEMENTATION OF RECOMMENDED DRAINAGE FACILITIES XIII. IMPLEMENTATION OF RECOMMENDED DRAINAGE FACILITIES As mentioned in Section XI, estimated costs for the recommended drainage facilities are based on these facilities being installed during a concurrent street construction or reconstruction program. In general, this policy is recommended for installation of these facilities. This is because of the following reasons: Total costs will be less. Although many existing structures are undersized for existing and projected flows, the economic consequence of most of these structures being flooded is minor. In most cases, storm water flows that exceed the capacity of existing culverts may cause some minor damage to gravel or paved streets, and short term inconvenience to the area residents. However, major damage, major economic losses, significant safety hazards, etc. will not result if the capacity of most of these structures is exceeded. In comparison, it is recommended that some structures receive immediate attention. These items are as follows: Priority 1 Replace structure no. 2 and no. 5, upgrade structure no. 1. For each of these three structures, a detailed evaluation of actual design needs and requirements should be made. A structural analysis should be completed for structure no. 1 to verify that appropriate upgrading steps are being taken. Careful consideration of the hydraulic conditions is needed for structure no. 2, to insure that the bridge does not contribute to, instead of eliminate, a flooding problem at the nearby duplexes. Storm sewers or improved road ditches may be needed in conjunction with structure no. 5, in order to insure that flows from structure no. 6 will reach structure no. 5, instead of continuing to overtop the street. Priority 2 Structure no. 3 should be replaced or upgraded, depending upon the results of a structural analysis. If the bridge is unsound, it could be replaced with a narrow structure that could eventually be upgraded to a width compatible with Fayetteville's Street Standards. Current utilization in this area hardly -32- justifies a 45 foot wide bridge. If the bridge appears reasonably structurally sound as is, or with minor improvements, consideration should be given to completing these minor improvements, adding guardrails and warning signs and otherwise leaving this bridge in service. While this bridge would be out of service during major floods, access to the area would be possible via the new bridge installed in place of structure no. 2. Since flooding of this bridge represents an inconvenience only, and would not contribute to property damage, top priority cannot be given to replacing this bridge. Priority 3 Channelization work in the vicinity of structure no. 2 and no. 5 is required for these structures to meet their potential for handling the projected stormwater flows. Specific channelization needs should be addressed when these two structures are designed. The magnitude of the channelization work, and its time of completion could depend to some extent on the cooperation of the affected property owners and on the City's policy concerning future development in the project area. While the projected flow rates are based on development in the watershed, it is entirely possible for these flows to be exceeded due to a major storm, under current watershed conditions. Consequently, a policy of no development will not necessarily prevent flooding. This was demonstrated last Summer. Priority 4 Installation of other drainage structures recommended herein would be completed as streets are renovated or constructed. -33- MUNICIPAL PARTICIPATION IN DRAINAGE FACILITIES COSTS XIV. MUNICIPAL PARTICIPATION IN DRAINAGE FACILITIES COSTS Municipal funding of the construction work needed immediately, relative to replacement or renovation of major bridges and culverts is recommended. Funding of channelization. work should be primarily municipally funded, without the condition that drainage easements are granted by the appropriate property owners. Funding of culverts that are installed or upgraded when the streets are upgraded or constructed should be provided by the organization constructing the streets. This could be the City of Fayetteville, a group of property owners or a developer. Funding of storm sewers should be handled likewise. However, if storm sewers are being constructed by a developer or a localized group of property owners, municipal funding for upsizing the storm sewers should be supplied. This will insure that undersized storm sewers are not installed in locations where future off -site drainage needs should be taken into consideration. Depending upon the rate of development in the project area, and the City's actual participation rate in funding the various drainage structures, the City's costs would range from approximately $133,000 for the Priority 1 structures, to in excess of $1.5 million. -34- CONCLUSIONS XV. CONCLUSIONS 1. Upon review of this report, one might conclude that construction of the recommended structures will prevent flooding in the project area under current and future development conditions. This is not true. The recommended structures are sized for specific storm return intervals. Storms exceeding the design rainfall intensity could occur at any time and could cause flooding at any time, regardless of the development level. The purpose of the structures is to provide greater capacity and thereby reduce the frequency of flooding. By reducing the flooding frequency the associated property damage costs are reduced. However, this report is not intended to convey the idea that the recommended structures will eliminate any future probability of property damage. 2. Review of Table No. 2 indicates that most of the existing drainage structures are in relatively good condition. Some maintenance work is needed for these structures that are clogged and/or in poor conditions. 3. Review of Table No. 3 indicates that significant flow rate increases can be expected as a result of development in the project area. Small areas planned for use as commercial or medium density residential land uses have the greatest percentage increase in future flow rates. 4. From Table No. 3, it is evident that while projected flow rates are higher than these estimated for current conditions, the drainage structures are undersized for current 25 year design flows, in most cases. In other words, most of the existing structures need to be upgraded new, regardless of the effect of future developments. Future development is reflected in the size needed for the upgraded structure. 5. Storm sewers in certain areas become quite large. In some cases, utilization of open ditches or relief ditches to Owl Creek may be warranted. This decision would rest primarily on the situation that existed at the time the facilities were being constructed. 6. Future annexation and development of property within the drainage basin, but outside the project area could significantly increase flows over those listed in Table No. 3. These flows are based on agricultural usage for this currently unincorporated area. Structures 1, 2, 3, 4 and A would be influenced by these higher flows. Some additional capacity should be built into these five structures for this reason. - 35 - STORM DRAINAGE DESIGN CRITERIA XVI. STORM DRAINAGE DESIGN CRITERIA As previously noted, the Arkansas State Highway and Transportation Department's Drainage Manual (July 6, 1982) was utilized as the primary reference for this report. This Manual includes complete guidance on all drainage matters related to street construction. In some cases, the Manual's design procedures are quite extensive, as needed to insure proper design. However, for the purpose of this report, the entire design process was not utilized in all cases. This was considered acceptable, since the purpose of this report was to provide a preliminary sizing instead of a detailed design for each drainage structure. Final structure design should consider all design aspects, as listed in the Drainage Manual. Included in the Design Manual are recommended storm frequencies for various structure and street classifications. These are reproduced below: STORM DESIGN FREQUENCIES FOR CULVERTS Interstate Projects: 50 Year Primary Projects: 50 Year Secondary Projects: 25 Year Non -Federal Aid Projects: 10 Year* * Drainage area less than two square miles; ADT less than 750. If either is exceeded, use 25 -year flood frequency. STORM DESIGN FREQUENCIES FOR STORM SEWER CROSS DRAINS Interstate Projects: 50 Year Primary Projects: 50 Year Federal Aid Urban Projects: 25 Year Secondary Projects: 25 Year Non -Federal Aid Projects 10 Year* * Drainage area less than two square miles; ADT less than 750. If either is exceeded, use 25 year flood frequency. STORM DESIGN FREQUENCIES FOR STORM SEWERS Interstate and/or Interstate Type Projects: 50 Year Other Federal Aid Projects: - 10 Year Non -Federal Aid Projects: 2 Year -36- The Drainage Manual further points out that these storm frequencies should not be utilized blindly. Consideration should be given to the economic consequencies of flooding and the capacity of adjoining drainage facilities. It is believed that these design frequencies more reasonably address the needs for culverts and storm sewers on collector, residential and private streets, as compared to the 25 year frequency indicated in the Fayetteville Street Standards. In general, design criteria that would result in the most conservatively sized structure was utilized in obtaining the preliminary sizes listed in Table No. 3. Improving the hydraulic efficiency of these structures by improving inlet conditions, lowering the flow line to allow a greater headwater depth or inlet and outlet channel improvements could result in variations in the final design size. One specific deviation from the Drainage Manual's recommendations. concerning the Rational Method for calculating peak runoff from small areas was utilized. This deviation was the method in which the "time of concentration" was calculated. The Drainage Manuals process for determining the time of concentration is somewhat cumbersome. A more direct formula, as listed in "Soil and Water Conservation Engineering", published in 1966 was used as listed below: Tc = 0.0078L0,77 S-0.385 where Tc = time of concentration in minutes L = maximum length of flow in feet S = the watershed gradient in feet per foot For very small areas a 5 minute time of concentration for impervious areas and a 10 minute time of concentration for pervious areas was utilized. A third reference utilized in this report was Pipe Association Design Manual (1974), which was sizing the smaller culverts and storm sewers. the Arkansas Concrete utilized primarily for - 37 - APPENDICES 2 A 01 __ ° rDROJECT LIMIlI"S Zo A O 11 i o N ® McCLELLANO CONSULTING ENGINEERS, INC. little rock feyettevllle FIGURE NO. 2 FLOOD HAZARD BOUNDARY MAP HIGHWAY 16 WEST DRAINAGE STUDY CITY OF FAYETTEVILLE 83-119 ' Y • _ 1111.1 • • 1 w �.' „ t • ,iJ , Y ,-- • - 111 i 1 1" '-� /. • rihl lJ 1 - • } I{ r • .� m ,III '. 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Z ."i.. d C� ' 4 I i l h IIII III Q - C0 U w N r��1'y �. t,f 11111111 �1 a' I, hil K• •`":-- 111' 7, Ski ly a w n. 11 .� 11O ¢ N i Cy: CTe 111111 .., 1 �, 1`�'PI 1 ��% byi x= x xa9 xa U ' 1 I ' � 11'1-'}' a w x z w .' ,�I�I 1I U N O ' II'c'1411 o .7 } .- ��� t. �'�, vi 111 • ,U' III ��Fr_ c. u• 1 ,I'�I '� - ® ® 111111 'I:IZ_�� - 111 - m 1 1111111 • �4rr'li' 1 7 I III •r � \�• ' ^ / — 111 <_ii; y �� /•- _ _ -_ ( ' .; . --.!<v,r%. FIGURE NO. 3 SCS HYDROLOGIC SOIL GROUPS ® McCLELLAND CONSULTING ENGINEERS, INC. HIGHWAY 16 WEST ' DRAINAGE STUDY little rock fayettevllle CITY OF FAYETTEVLLE August, 1983 83-119 GENERAL PLAN .ALTERNATE 1 Low Density Residential 1 • n .... a '1, may: ,,• . Office Medium Density Residential 'd z Commercial it' Agricultural ``''``' 12 I Y •' INb ' j i•• b •� .• l' �.Iln . 1 � . i...--I. ...�.. •a..".' .,.,. •..,. ,• • it • • 1 ••.: • I • •y..N 1 ••j ••• •• L I I •♦• ••• •TTY • • .;• ♦ _••• • ••• • ✓•.' — 1.:. __ I bI 11 1 r + I{ J a I /., ( T .I Y J7 • I n a _ A J , aTTT'\\. I y _ I•• -- k'A CONSULTING ENGINEERS, INC. little rock fayettevllle FIGURE NO. 5 GENERAL LAND USE PLAN HIGHWAY 16. WEST DRAINAGE STUDY CITY OF FAYETTEVILLE August, 1983 - 83-119