woo. oqo" FEASIBILITY STUDY for IMPROVEMENTS t0 ADDICKS and BARKER RESERVOIRS PREPARED FOR: HARRIS COUNTY FLOOD CONTROL DISTRICT MARCH, 2000 Codie/Z), Jam. mm- 040 a If I CI JOB NO. 19-96083-04 I FEASIBILITY STUDY for IMPROVEMENTS t0 ADDICKS and BARKER RESERVOIRS I PREPARED FOR: HARRIS COUNTY FLOOD CONTROL DISTRICT PREPARED BY: COSTELLO, INC. 9990 RICHMOND AVENUE SUITE 450, NORTH BUILDING HOUSTON. TEXAS 77042 . a . - 68937 a fggf?rgz??a I0 9, MARCH, 2000 TABLE OF CONTENTS INTRODUCTION PURPOSE AND SCOPE AUTHORIZATION PROBLEM STATEMENT ELEVATION DATUM REFERENCE DOCUMENTS II. DESIGN CONSIDERATIONS A. GENERAL INFORMATION 1. Project History 2. Current Reservoir Status a. Ratcheting Effect b. Erosion Damages RESERVOIR HYDROLOGY AND OPERATIONS 1. Updated Development Conditions 2. Future Development Conditions 3. Operations Policy DESIGN ALTERNATIVES No Action Fringe Area Buyouts Excavation within Reservoirs Interconnection of Reservoirs Katv Freeway Corridor Outfall to White Oak Bavou avast-new Brazos River Outfall a. Peek Road Alignment b. Harlem Road Alignment COST SUMMARIES FRINGE AREA BUYOUTS EXCAVATION WITHIN RESERVOIRS A. B. 23 18 18 I TABLE OF CONTENTS (Continued) . PAGE C. INTERCONNECTION OF RESERVOIRS 19 D. KATY FREEWAY OUTFALL TO WHITE OAK BAYOU 19 E. BRAZOS RIVER OUTFALLS 20 IV. CONCLUSIONS AND RECOWENDATIONS A. CONCLUSIONS 21 I B. RECOMMENDATIONS 23 V. EXHIBITS LOCATION MAP FRINGE AREA MAP ADDICKS RESERVOIR TOP OF CURB ELEVATIONS BARKER RESERVOIR TOP OF CURB ELEVATIONS ALTERNATIVE OUTFALL LOCATIONS LH. 10 CORRIDOR UTILITY PROFILE ALTERNATE CONDUIT TERMINUS ALIGNMENTS VI. APPENDICES A. Stage-Frequency Study for Addioics and Barker Reservoirs, Phase 1, Data Coiiectioa and Review, by Dr. Ralph A. Wurbs, December 1997. September 1998. C. E??ects of Urban Deveiopmertt on In?ows and Reservoir stages in the Ba?aio Bayou Watershed, by Dr. Ralph A. Wurbs, June 1999. D. Summary Report, Operation ofAddicks and Barker Reservoirs, by Dr. Ralph A. Wurbs, . January 2000. ii I B. Stage~Freqaeacy Anaiyses for Addicks and Barker Reservoirs, by Dr. Ralph A. Wurbs, Caste/?3, jut; MARCH. 2000 I. INTRODUCTION A. PURPOSE AND SCOPE The purpose of this feasibility study is to present the results of investigations performed which address several concerns relating to the operations of the Addicks and Barker Reservoirs in western Harris County. These investigations include evaluating potential ?ood mitigation projects such as increasing discharges from the reservoirs, modifying the Operations of the reservoirs and structural improvements to the reservoirs to increase the level of ?ood protection the facilities provide to the watersheds they serve. The service areas of the Addicks and Barker Reservoirs are depicted on Exhibit 1. B. AUTHORIZATION This study was authorized by the Harris County Commissioner?s Court through the Agreement for Engineering Services to develop a master ?ood control plan for the Buffalo, Addicks and Barker Watershed Systems, dated August 27, 1996. This contract authorized Costello, Inc. to perform engineering services to support the Harris County Flood Control District in evaluating and documenting potential design alternatives for modifying the operations or the structural con?guration of the reservoirs to improve the ?ood protection potential of the facilities. C. PROBLEM STATEMENT The potential for ?ooding upstream of the dams and within the "fringe" areas has been a growing concern due to the continuing development within these areas. During the Winter of 199] and Spring of 1992 the reservoirs reached the highest recorded ?ood elevations. Disruptions to the transportation systems within the reservoirs occurred and lasted for several weeks, with the reservoirs taking several months to drain to non?threatening levels. These occurrences have prompted the concerns of the residents, business owners and government representatives to be expressed regarding the level of protection that the reservoirs provide to the property upstream of the dams. Feasibility Study for Improvements to Addieks and Barker Reservoirs Page 1 Caste/g, jnc. MARCH, zoos In order to address the concerns of the residents and business owners within the effected areas, a better understanding of the operations, reservoir performance and the potential ?ooding hazards is needed. The current operational policies of the reservoirs and. the continuing development of the areas upstream and of the reservoirs must be reviewed and updated in order to provide accurate predictions of potential ?ood hazards within the fringe areas and the areas of the reservoirs. The mechanisms by which the reservoirs approach ?ood stages, performance, also require a more careful evaluation. The Texas Department of Transportation recently purchased the railway right-of?way adjacent to I.H.-10 east of the reservoirs. This purchase presented the with a possible opportunity for adding an outlet structure to the reservoirs and prompted the analysis of various methods of changing the operational or performance characteristics of the Addicks and Barker Reservoirs. Presented with the concerns of the residents and business owners within and around the reservoir fringe areas and the potential access to a new outfall corridor, the undertook a two phased approach to the analyses of the Addiclrs and Barker Reservoirs. The ?rst phase of the analysis, performed by Dr. Ralph A. Wurbs, addressed the hydrology and Operational procedures and their effects on the reservoir storage characteristics. The results of that analysis are presented in the Appendices and are discussed later in this text. The second phase, performed concurrently with the ?rst, assumed that an increased potential for flood damages in the reservoir fringe areas would be signi?cant enough to warrant a major improvement project to the reservoirs, dams, outlet capacities or Operations procedures. This phase of the analysis is presented below. Upon completion of Dr. Wurbs' analyses these assumptions were re-evaluated and addressed in subsequent paragraphs. Feasibility Study for Improvements to Addicts and Barker Raservairs Page 2 Casing-r, Jinn. MCI-1.2000 D. ELEVATION DATW All elevations used in this report are referenced to the 1929 National Geodetic Survey, 1973 Adjustment. 1 1. Regulation Manual for Addicks and Barker Reservoirs, Bu??aio Bayou Watershed, U.S. Army Engineer District, Galveston, April 1962. 2. Hydroiogy, Addicks and Barker Reservoirs, Bujfaio Bayou and Tributaries, Texas, US. Army Engineer District, Gaiveston, August 1977. 3. Hydraulic Studies, Buffalo Bayou and Tributaries, Harris County, Texas, prepared I E. REFERENCE DOCUMENTS by Bernard Johnson Incorporated for US. Army Corps of Engineers, Galveston . District, Contract December 1978. 4. Reconnaissance Report, Section 216 Study, Addicks and Barker Reservoirs, Houston, Texas, US. Army Engineer District, Galveston, October 1995. 5. Addicks Reservoir Watershed Management Study, Phase I Report, prepared for Harris County Flood Control District by Bernard Johnson Incorporated in 6. Addicks Reservoir Watershed Management Study, Phase Report, prepared for Harris County Flood Control District by Bernard Johnson Incorporated in association with Brown St. Gay Engineers, Inc., March 1995. 7. Katy Freeway Corridor Flood Contra! Study, Harris County Flood Control District . Planning Department, May 1996. Study for Improvements to Addicks and Barker Reservoirs Page 3 I association with Brown Gay Engineers, Inc., March 1991. Caste/g), ?ns. MARCH. zoos II. DESIGN CONSIDERATIONS GENERAL INFORMATION 1. Proiect History The construction of the Addicks and Barker Reservoirs in the 1940's, by the U.S. Army Corps of Engineer?s (CUE), was a result of the authorization by the US. Congress of the COE to Sponsor local ?ood control projects through the River and Harbors Act of 1938. The Buffalo Bayou Project, of which the reservoirs were an integral part, was in response to major ?oods in the Houston area in 1929 and 1935. The original Buffalo Bayou Project, designed for the ?ood protection of downtown Houston and the Houston Ship Channel, included the construction of three detention reservoirs: Addicks, Barker, and White Oak; along with a system of canals to convey releases from the Addicks and Barker Reservoirs to Galveston Bay, and from the White Oak Reservoir north of Houston to the San Jacinto River. In addition, a levee was to be constructed along the Buffalo Bayou and Cypress Creek watershed divide so as to prevent over?ows from Cypress Creek from entering Addicks Reservoir. The dams along the periphery of each reservoir were to each have four uncontrolled outlet conduits and one controlled outlet conduit. The Corps of Engineers purchased the property within the reservoir area with elevations up to three feet above the predicted pool elevation which would be caused by a storm similar to the 1935 flood event. This left privately owned properties with the potential for floodng up to the maximum pool elevations of 1140 feet for Addicks and 107.0 feet for Barker. These areas are referred to as the "fringe" areas. The rapid development in the Houston area at the time the project was being constructed delayed and eventually eliminated the ability to construct the relief canals. In their place, gated structures on the Addicks and Barker reservoirs were constructed to limit ?ows into Buffalo Bayou. The levee separating the White Oak and Addicks watersheds was also abandoned due to increasing development in the watersheds. Additional storage capacity Feasibility Study fer Improvements to Addicts and Barker Reservoirs Page 4 Caste/?1, jaw. MARCH, anon was included in the Addicks Reservoir through the purchase of property up to 3.6 feet above the elevation of the previously purchased property to accommodate the over?ows from White Oak Bayou. The COE abandoned the White Oak Bayou reservoir concept in the early 1950's. At that time the C013 rc-evaluated the entire project concept and formulated an alternate plan for regional ?ood control which included recti?cation of White Oak, Brays and Buffalo Bayous. In 1960, the COE completed a report addressing the feasibility of gating all of the outlet conduits on the two reservoirs. That report concluded that the reservoirs could contain the standard project ?ood with only minor ?anking of the dams and minimal associated damages. The channel recti?cation projects on White Oak Bayou and Brays Bayou were undertaken and completed in accordance with the alternate regional plan. Local opposition to the recti?cation of Buffalo Bayou along with encroaching deveIOpment along the Buffalo Bayou channel caused that project to be canceled. By the mid-1960's the COE installed gates on all of the remaining outlet structures, thus establishing manual control of the discharges from the reservoirs. Throughout the time of the changing structural facilities and operational changes on the reservoirs, the non-damaging ?ow rate along Buffalo Bayou of the dams has been re-evaluated. The original discharge rate into Buffalo Bayou was planned to be 16,000 cfs. This rate has been reduced to its present rate of 2,000 cfs, due to the amount of development which would potentially be damaged by higher flows. In accordance with current COE operation procedures on the dams, this rate cannot be exceeded unless potential darn breaching or over?ow of the dams is imminent. 2. Current Reservoir Status The C013 purchased a large portion of the land upstream of the reservoirs with elevations below the maximum pool elevations established for each reservoir (1 14.0? for Addicks and 107.0? for Barker). However, not all of the land below the maximum pool elevation was purchased. These areas, referred to as the "fringe" areas are subject to potentially severe Feasibility Study for Improvements to Addicks and Barker Reservoirs Page 5 amid}, .9116. MARCH, soon ?ooding as the reservoirs reach maximum pool elevations. In recent years, a signi?cant amount of development has occurred around the reservoirs and also within the fringe areas. Exhibit 2 depicts the developed areas in the vicinity of the reservoirs. These areas are generally privately owned tracts or structures which have been allowed to develop in the ?ood plain of the maximum probable ?ood of the reservoirs. Much of this property is heavily developed, and the undeveloped areas are expected to deveIOp in the foreseeable future. Approximately 5,000 structures presently exist in the 4,000 acres of Addicks Reservoir fringe, and approxirnately 1,000 structures exist within the 4,600 acres of Barker Reservoir fringe. A large majority of these structures are residential structures; single-family subdivisions or multi-family developments. The remainder of the structures consist of commercial and business structures along with numerous governmental SIIUCCUIES . The developed areas within the fringes are typically developed through the use of ?ood plain fill or lot ?ll in order to raise the slab elevations above the published IOU?year ?ood elevations shown on the Flood Insurance Rate Maps (FIRMS). A brief investigation of the elevations of the developments within the fringes was performed using recorded subdivision plat information from various sources including County records, ?les and local engineer's ?les. Elevation contours within the fringes of the reservoirs were also compiled from topographic maps of the area including U. S.G.S. Quadrangle maps and Corps of Engineers l-foot topographic maps, where available. The results indicate that the lowest top of curb elevations found within the Addicks Reservoir fringe are 106.7, 107.8 and 107.9, as shown on Exhibit 3. The natural ground elevations within the fringe area of Addicks Reservoir range from 107 to 112. The lowest top of curbs found within the Barker Reservoir fringe are 93.5, 99.1 and 99.2, as shown on Exhibit 4. The natural ground elevations within the fringe area of Barker Reservoir range from 97 to above 101 with several developments constructed on minimum ?ll elevations as high as 105. The current operational procedures used by the Corps of Engineers for determining when to allow discharges from the reservoirs into Buffalo Bayou include two major components: 1) The discharge rate at the Piney Point Stream Gage on Buffalo Bayou, and 2) the Feasibility Study for improvements to Addicks and Barker Reservoirs Page 6 Carma), jets. MARCH. zoos predicted occurrence of rainfall within the Buffalo Bayou and the upper reservoir drainage areas. These procedures lead to two of the major concerns regarding ?ooding both upstream and of the dams. Two of the major consequences the 2000 discharge litnitation has on the reservoirs are the length of time required to drain the facilities after rainfall events and the environmental and erosion damage to Buffalo Bayou caused by prolonged releases of this discharge rate along the bayou below the dams. a. Ratcheting Effect The flow rate in Buffalo Bayou at the Piney Point gage is maintained at a maximum rate of 2000 when reservoir discharges are the only source of water in the bayou. This rate of ?ow has been determined to be the highest non- damaging ?ow for existing structures and improvements for properties of the dams. When the National Weather Service predicts rainfall in the general Buffalo Bayou watershed area, the gates are closed to allow any runoff ?ows for the tributary areas along the reaches of the bayou to drain into the bayou. Under these operating procedures, any ?ooding along Buffalo Bayou, of the dams, can be attributed to the rainfall over the local watershed and not from runoff from upstream of the dams or releases from the reservoir. The time required to drain the reservoirs with this relatively small discharge rate, in relation to the volume of runoff into the reservoirs, has given rise to a phenomenon referred to as the ratcheting effect. As the region experiences a wet season over a period of several months, the reservoirs slowly increase in stage even though no single large rainfall event may occur. As the pended water surfaces in the reservoirs increase to levels which approach key roadways or structures, moderate rainfalls may occur which would then cause ?ooding within the fringe areas. For the purposes of these initial investigations, it was assumed that the ?ooding potential of the existing structures and infrastructure in the fringes would cause signi?cant economic and traf?c mobility problems. Feasibility Study for Improvements to Addicfct and Barker Reservoirs Page 7 ante/g2, Jim. MARCH, 2000 b. Erosion Damages The environmental and erosion damages along the lower reaches of Buffalo Bayou caused by prolonged releases of 2000 from the reservoirs have proven to be signi?cant in the past several years. As development has encroached along the banks of the bayou, erosion control measures have been attempted for maintaining the existing channel banks and bottoms. Prolonged ?ows tend to saturate soils and increase the potential for erosion which then washes away vegetation. The total effect is a degradation of the ecosystems within the channel banks and potential damage to adjacent structures and improvements. Several possible solutions to solve or reduce the ratcheting effects within the reservoirs were investigated at the same time as the evaluation of the reservoir hydrology and operations was being performed. These alternative solutions to changing or increasing outflows from the reservoirs are presented below. Erosion control or prevention issues along Buffalo Bayou of the dams was not included in the scope of this study. B. RESERVOIR HYDROLOGY AND OPERATIONS The COE has performed a number of studies relating to the changes in the discharge rate from the two reservoirs. These studies did not address the potential iinpact the reduced discharges might have on the storage levels within the reservoirs. These studies also did not address any potential impact future development within the areas tributary to the reservoirs might have. The engaged Dr. Ralph A. Wurbs to perform investigations into the potential impacts the current and future development conditions would have on the storage levels within the reservoirs. The results of these studies are presented in the various reports provided in the Appendices. Along with updating the hydrologic modeling, Dr. Wurbs also performed analyses to simulate the operational procedures currently in use by the COE. A summary report of the results of those various studies was prepared by Dr. Wurbs to demonstrate the itnpacts of various operational Feasibility Study for Improvements to Addicks and Barker Reservoirs Page 3 ?ne. MARCH, zoos scenarios on the ?ood elevations within the reservoirs. This summary report is presented in Appendix D. The paragraphs below brie?y outline the analyses performed by Dr. Wurbs and the results of those studies. 1. Updated Development Qonditions The amount of development within a watershed typically has a great impact on the peak runoff and volume of runoff into a drainage system. In the case of detention reservoirs, such as the Addicks and Barker Reservoirs, the volume of runoff is a more critical factor to storage levels than is peak runoff rates. Peak runoff rates are more critical to the design and operation of the various channels which convey ?ows from the tributary areas into the reservoirs. A study, see Appendix C, was performed to determine how the changes in development conditions has effected the in?ow volumes and storage levels in the reservoirs over the past 50+ years. That Study used the Runoff Curve Number (CN) method for determining runoff for differing levels of development. Curve numbers for the drainage areas upstream of Addicks Reservoir, Barker Reservoir and Buffalo Bayou above the Piney Point Gage, based on development levels from approximately 1970 to present, were determined using historical ?ow and storage level records for each of the reservoirs. These curve numbers were then used to determine runoff for use in various scenarios where changes in the discharge characteristics of the reservoirs were simulated. The study concluded that due to the variability of the rainfall patterns and the likelihood of high antecedent soil moisture contents during wet periods, that no pattern of curve number changes could be determined from the available data. 2. Future Development Conditions Base on the curve numbers established for the updated conditions described above, a fully developed condition curve number was chosen for the three subareas studied. Runoff volumes into the reservoirs were computed and various discharge conditions were simulated. The results of that analysis indicated that even as the runoff curve numbers were increased for additional development, the effect on storage levels in the reservoirs was relatively small. This can be attributed to the fact that as a watershed becomes saturated over a period of time the undeveloped land (bare earth, grass cover, tree cover, Feasibility Study for Improvement: to Addicks and Barker Reservoirs Page 9 Gdfeigy, Jane. MARCH, 2000 etc), will exhibit runoff characteristics very similar to developed impervious cover types (pavement, roofs, etc). Since the conservative assumption of a saturated watershed at the beginning of a simulation is typically used, the effects of urbanization on the storage levels in the reservoirs is not the major factor leading to high stages during wet seasons. 3. Operations Policy The study investigating the effects of urbanization on the reservoirs concluded that the overriding factor effecting the storage levels, and therefore the ?ooding potential within the fringe areas, was the discharge characteristics of the outlet structures. This factor is the direct result of the operation policies currently in use by the COE for both Addicks and Barker Reservoirs. A surmnary of the investigations performed on the various aspects of reservoir operations was prepared and is presented in Appendix D. As indicated in Table 3 of Appendix D, the best estimate of the IOU-year recurrence interval water surface elevations within the reservoirs are 102.6 and 97.7 for Addicks and Barker, respectively. The elevations are based on the current operation policy for the reservoir outlet structures. The elevations of the government owned land (GOL) are 106. 1 and 97.3, respectively, for each reservoir. Comparison of these elevations to the natural ground and minimum top of curb elevations, presented previously, would indicate that the Addicks Reservoir provides a level of protection in excess of a IOU-year recurrence interval, and the Barker Reservoir provides a level of protection less than a 100- year recurrence interval. The summary document further recommends that the operation policies for the reservoirs be reviewed by the COB and possibly be updated to utilize modern technologies of rainfall predictions, real-time stream?ow measurements, updating damaging ?ow rates and elevations, and possible interconnection of the two reservoirs . Feasibility Study for Improvements to Addicks and Barker Reservoirs Page 10 Coats/?, ?rst; MARCH. 2000 C. DESIGN ALTERNATIVES As stated above, the investigations into potential improvements to the outfall and storage characteristics of the reservoirs were performed concurrently with the investigations into the current operations and performance analyses performed by Dr. Wurbs. This feasibility study assumed that de?ciencies in the levels of protection which the reservoirs provide the fringe areas would be signi?cant enough to warrant a major improvement project to the reservoirs, dams, outlet capacities or operations procedures. In order to determine the most feasible alternative for irnproving the level of protection provided by the reservoirs, several alternatives were evaluated. The costs associated with each alternative are shown along with a brief discussion of the advantages and disadvantages of each for comparison purposes. 1- mam This alternative would leave the reservoir discharges at a maximum rate of 2,000 with all gates being closed whenever impending rainfall in the watershed is predicted or expected. This is the current COE operation procedure. This alternative would not change the flooding potential within the reservoirs or fringe areas as presented in Appendix D. As shown on Exhibit 4, approximately 450 acres of prOperty lies within the IOU-year ?ood elevation within Barker Reservoir. Based on currently available information these properties are undeveloped. Current Harris County ?ood plain management policies would require that these properties be removed from the reservoir ?ood plain prior to approval of development plans. The is currently developing a watershed management plan for the Addicks Reservoir Watershed and has plans for developing a watershed management plan for the Barker Reservoir. There are no direct costs associated with this alternative, however the flood damage costs would remain as potential costs for each ?ood occurrence. Feasih?ity Study for Improvements to Addicts and Barker Reservoirs Page 11 6051533522, jars. MARCH, 2000 2. Fringe Area Buyouts This alternative addresses the impact of a generalized buyout of properties within the fringe areas of the reservoirs. The buyout would include all property shown to be within the fringe areas, both developed and undeveloped. Proposed bene?cial uses for this property are not within the scope of this study. The bene?t of the buyout alternative is the elimination of the majority of the potentially ?ood prone structures, thereby reducing long term damage costs. Approximately 7800 acres were identi?ed as potential buyout properties as shown on Exhibits 3 and 4. These properties include approximately 550 residential properties over $200,000 each; 2,500 properties under $200,000 each; 50 commercial properties; and various other properties including a US. Postal Service facility. The projected cost of this alternative, based on 1998 actual sale prices adjusted to 1999 prices, of properties within the fringe areas is approximately $588,250,000. The above unit prices for this real estate was based on actual sale prices obtained from real estate sales records obtained from Ref Max Realtors. An adjustment to approximate 1999 prices was made by adding 10% to the unit prices based on Harris County Appraisal District average property valuation increases for 1999. 3. Excavation within Reservoirs Excavation within each of the reservoirs would add to the total storage capacity of the reservoirs, thereby increasing the level of flood protection provided. This alternative could be staged over a number of years to slowly add volume as development increased. The dif?culties in implementing this alternative include disposal of the large amounts of material excavated, the environmental impacts to the existing vegetation and wildlife within the basins and the design of a system by which the excavated areas could be kept dry. The existing outfall structures present a ?xed flowline elevation, below which any excavation would have to be pumped dry to be maintained as available storage. The bene?ts of adding storage capacity to the reservoirs would be the reduction of the [00-year ponding elevations and a delay in the impacts of the ratcheting effect on the existing fringe areas. Additional analysis of a speci?c reduction in ponding elevation Study for Improvements to Addicks and Barker Reservoirs Page 12 Codief?, jaw. MARCH, 2000 would be required to determine actual bene?ts and costs. In lieu of these actual target . reductions and costs, an approximate improvement was assumed and the costs determined. The existing reservoirs have capacities of 113,263 (Addicks) and 83,410 (Barker) acre~ feet. Preliminary estimates of excavation costs are approximately $8,500,000 per 1000 acre feet of storage volume. An increase of only 5 98 capacity within each basin would add approximately 9,800 acre-feet of storage at a cost of $83,300,000. The cost of pump stations within each reservoir, sized to discharge 2,000 (897,720 would be approximately $40,000,000 for a total cost of $123,300,000. This alternative presents an undetermined bene?t for comparison with other alternatives since no speci?c improvement goal can be determined from the reservoir hydrology and operations analyses discussed later in this text. 4. l_nterconi1ection of Reservoirs This alternative would allow for the interconnection of the two reservoirs via a gravity structure would be an inverted siphon type design in order to provide a conduit to allow the two reservoirs to equalize under most ponding conditions. This structure would be gated on each end in order to maintain operational control of the discharges from one basin to the other. A pump station would be required to convey water from Barker to Addicks due to the elevation difference between the reservoirs under conditions when Barker nears its Spillway elevation. A triple 12'x 12? box culvert conduit would allow the equivalent of a 44-inch rainfall (4,300 acre-feet of runoff) over the Addicks watershed to be conveyed to Barker in approximately 24 hours. An equivalent pump station would be approximately 1,000,000 g.p.m. The cost of this alternative would be approximately $12,000,000 for the gravity structure and $20,000,000 for the pump station for a total of $32,000,000. I . structure to allow ?ows to be conveyed from Addicks to Barker Reservoir. The gravity Feasibility Study for improvements to Addicks and Barker Reservoirs Page 13 Casing), jam. MARCH, 2000 The main bene?t this alternative provides is the ability to operate the two reservoirs cooperatively by utilizing storage in one reservoir as the other approaches critical levels due to ratcheting effects. 5. Katy Freeway Corridor Outfall to White Oak Bayou This alternative would allow increased discharges from the reservoirs to be conveyed eastward along the Freeway corridor to White Oak Bayou. This design would require a large conduit be constructed within right-of-way owned by the Texas Department of Transportation in particular, the recently obtained railway corridor parallel to the freeway, see Exhibit 5. This conduit would be operated to control flows from the reservoir which would not adversely impact the existing ?ood levels on White Oak Bayou. Several major channels are crossed by this alignment, including Langham Creek, Turkey Creek, Rummel Creek, Briar Branch, Spring Branch Creek, and HCFC Units W137-00-00 and For this study it is assumed that these channels, when under flood conditions, could be partially diverted into the proposed conduit when the reservoirs are discharging less than the capacity of the conduit. This would allow some relief of existing ?ooding problems within those watersheds, however the determination of the amount of relief which could be provided is not within the scope of this study. The proposed conduit will require construction methods which utilize specialized tunneling techniques. Standard tunneling methods practiced in the Houston area generally incorporate round conduits with diameters of up to 11 feet. The allowable head room for the proposed conduit is only 10 feet, based on the existing ?owlines of White Oak Bayou and the reservoirs and the existing ?owline of Spring Branch and Langham Creeks, see Exhibit 6. In order to obtain adequate flow rates in the conduit, several barrels would be required. Tunneling contractors contacted regarding this project indicated that parallel tunnels would be extremely dif?cult and expensive to construct, if possible at all. A rectangular or other elongated cross sectional shaped tunnel should be evaluated further, prior to design of the conduit. Standard open cut construction techniques would require an extremely wide work area due to the depths required (20 to 50 feet) and would disrupt traf?c at every major road crossing along the alignment. Construction traffic added to the Feasibility Study for Improvements to Addicks and Barker Reservoirs Page 14 Colloid, jnc. men. 2000 already congested major intersections should be considered when evaluating this alternative. The alignment of the proposed conduit, as shown on Exhibit 5, is adjacent to l.H.-10 from the reservoirs, eastward to the I.H.-610 interchange. From that point, continuing to the east, the railway right-of?way diverges from the freeway corridor and is located in an industrial area up to White Oak Bayou. Discussions with and the Missouri Kansas and Texas Railroad Company (MKT) indicate that this portion of the railway right? of?way may have limited use for drainage purposes and may also present dif?culties in obtaining permits for construction underneath existing active rail lines. Two other alignments for this portion of the proposed conduit were investigated. One followed a northerly course between Hurst Street and the railway, however this alignment would require acquisition of numerous industrial tracts. The other alignment investigated followed I.H.-10 eastward to White Oak Bayou. This alignment is signi?cantly longer than the other two and has indicated that approval for following that alignment would be dif?cult to obtain since that section of freeway is currently under construction and any disruptions to traf?c would not be acceptable. Exhibit 7 depicts the congestion and numerous potential con?icts along these alignments. The proposed conduit would be approximately 80,000 feet in length and would require a minimum of 4 - 120?inch diameter barrels to convey approximately 2,000 at a velocity of 6.4 (4 IDS-inch diameter barrels at 7.9 fps). Estimated construction costs for this alternative are $481,230,000, which includes access and muck shafts. This alternative offers the bene?t of an additional outlet for the reservoirs which would reduce the ratcheting effect within the reservoirs during extended wet periods. This additional outlet would direct discharges into the White Oak Bayou channel, thus bypassing Buffalo Bayou through the western portion of Houston. It is anticipated that the discharges from the reservoirs would be able to be maintained for long periods of time, except when large storms over the White Oak Bayou watershed occur and flows in that channel increase above a critical level. Feasioitity Study for Improvements to Addicts and Barker Reservoirs Page 15 Codie/g), jive. MARCH, zone 6. Brazos River Outfall Another potential alternative for increasing out?ows from the reservoirs is the construction of additional conveyance facilities from the reservoirs to the Brazos River. Preliminary evaluation of several alignments were made including one which followed the MKT right- of-way westward to the river. This alternative was abandoned due to the distance involved and the fact that two cities, Katy and Brookshire are adjacent to this alignment. Two other alignments to the south of the Barker Reservoir were brie?y investigated and are shown on Exhibit 5. Each of these alignments would require some internal modifications within Barker Reservoir in order to convey runoff to the invert of a proposed outlet structure. These alignments would only provide outfall for Barker Reservoir unless a connector structure between the basins was constructed. This alternative offers the bene?t of an additional outlet for the reservoirs which would reduce the ratcheting effect within the reservoirs during extended wet periods. This additional outlet would direct discharges into the Brazos River, thus bypassing lower Buffalo Bayou through the western portion of Houston. It is anticipated that the discharges from the reservoirs would be able to be maintained for long periods of time, except when large storms over the watershed along the diversion occur and ?ows in that channel increase above a critical level. Since these alignments are located primarily in Fort Bend County and involve diversion of runoff into a different watershed, obtaining the necessary permits and easements may be dif?cult. The potential permitting, environmental, political and public relations issues which may arise from these alternatives are not within the scope of this study. a. Peek Road Alignment This alignment provides the shortest length of underground conduit along with major channel improvements to Jones Creek in Fort Bend County. Preliminary investigations indicate that this route potentially has the fewest con?icts due to the limited development along the corridor at the present time. The natural ground Feasibility Study for improvements to Addicks and Barker Reservoirs Page to Codiet?, ?ne. MARCH. 2000 elevations along this route are very ?at as shown on the U.S.G.S. Quadrangle maps of the area, therefore adequate slope of the conduit may be dif?cult to maintain. Construction costs are estimated to be $44,000,000. b. Harlem Road Alignment This alignment would follow the existing Harlem Road right-of?way from Barker Reservoir southward to U.S. Highway then to the river. This alignment traverses the Texas Department of Criminal Justice property. This alignment also crosses Oyster Creek, which could be an expensive structure. The Oyster Creek watershed of this location is highly developed, and diversion of signi?cant runoff ?ows into the creek would not be advisable. Construction costs are estimated to be $92,000,000. Feasibility Study for Improvements to Addicks and Barker Reservoirs Page Costa/?2, jive. MARCH. 2000 COST SUNIMARIES A. FRINGE AREA BUYOUTS Buyouts within the fringe areas between the limits of the Government Owned Land and the maximum pool elevation within the reservoirs was based on a per unit basis. The average list price for properties were obtained through a commercial real estate sales representative and are based on end of year prices for 1998, adjusted for 1999 prices as described above. Tvne of Development Units Quantity Price Total Residential Units 35 200,000 8.: above EA 550 315,000 173,250,000 Residential Units below 200,000 EA 2,500 120,000 300,000,000 Commercial EA 50 1 ,300,000 65 ,000,000 Other (includes AC 200 300,000 60,000,000 warehouses, Government and vacant land) Grand Total 598,250,000 B. EXCAVATION WITHIN RESERVOIRS Excavation within the reservoirs was evaluated based on an assumed percentage increase in reservoir volume. A pump station within each reservoir would be required in order to empty the reservoir at the maximum rate of 2000 cfs. Description Units 1 Quantity Price Total Excavation 1000 Disposal Ac-Ft 9.8 8,500,000 33,300,000 Pump Station @l,000,000 Ea 2 20,000,000 40 000 000 Grand Total 123,300,000 Feasibility Study for Improvements to Addicks and Barker Reservoirs Page 18 Coate?a, jag. MARCH. C. INTERCONNECTION OF RESERVOIRS The interconnection of the two reservoirs would require a large gravity structure to convey,r ?ows from Addicks Reservoir to Barker Reservoir, and pump station to convey flows from Barker to Addicks . Description Units Quantity Price Total Gravity Structure 3-12'x lZ'Boxes w! Gates LF 3,000 4,000 12,000,000 Pump Station @1,000,000 Ea 1 20,000,000 20 000 000 Grand Total 32,000,000 D. KATY FREEWAY OUTFALL T0 WHITE OAK BAYOU This alternative includes the tunneling of an outfall along the I.H .-10 corridor from the reservoirs east to White Oak Bayou. Conduit size is based on available hydraulic slope of 0.05 Description Quantity: Access Shafts Ea 4 20,000 80,000 Muck Shafts Ea 120 10,000 1,200,000 4-10' Dia Tunnel LF 30,000 6,000 480 000 000 Grand Total 481,280,000 . Feasibility Study for Improvements to Addicks and Barker Reservoirs Page 19 603.32%, j?c. E. BRAZOS RIVER OUTFALLS MARCH. 2000 This alternative investigated two alternative routes from Barker Reservoir south to the Brazos River. The ?rst, along Peek Road and then along Jones Creek, includes underground conduit and open channel. The second, along Harlem Road, includes only underground conduits. _p_Dmri tinn Unis DLHtitx ital.._ Peek Road Alignment 3-12?x 11? Boxes LF 16,000 2,000 32,000,000 Channel Excavation CY 800,000 10 8,000,000 R.0.W. (Assume 160' width) LF 200 20,000 4 000 000 Grand Total 44,000,000 Harlem Road Alignment 3-12'x 11' Boxes LF 45,000 2,000 90,000,000 ROW. (Assume 60' width) LF 100 20,000 2 000 000 Grand Total 92,000,000 Feasibifiry Smdy for Improvements to Addicks and Barker Reservoirs Page 20 Caste?i, Jim. MARCH. zucu IV. CONCLUSIONS AND RECOWENDATIONS A. CONCLUSIONS The results of the Feasibility Study for Improvements to the Addicks and Barker Reservoirs are presented below. . The current operational procedures of the Addicks and Barker Reservoirs are signi?cantly different than the original design concept for these ?ood control facilities. The current operations create conditions within the basins which contribute to the "ratcheting" effect of the reservoir ponding levels during wet periods. I Modi?cations to the operational procedures or the reservoir facilities could provide ?ood protection bene?ts to the fringe areas. Several ways of improving the level of protection afforded by the reservoirs were investigated. Structural improvements to the basins, such as excavation of additional storage volume or interconnection of the basins, would provide some measure of additional protection to the fringe areas. Such improvements would not improve the conditions caused by the long term discharges required to empty the reservoirs after signi?cant runoff events have raised ponding levels. - Improvements to the discharge capabilities of the reservoirs would lessen the ratcheting effect and allow the basins to operate in a marmer more in accordance with the original design concept of the facilities. Additional outlet structures would provide discharge capabilities without impacting ?ooding conditions along Buffalo Bayou. - The Katy Freeway corridor provides one alignment for an additional outlet structure. This alternative would allow ?ows to be diverted from the two reservoirs eastward to White Oak Bayou. Potentially, this design could incorporate drainage improvements to several tributaries which now cross the freeway corridor. Feasibility Study for improvements to Addicks and Barker Reservoirs Page 21 Georgia, ?ne. MARCH. Two possible alignments from Barker Reservoir southward to the Brazos River were investigated. These alignments would traverse through Fort Bend County, one along the Peek Road corridor and then along Jones Creek, and a second along the Harlem Road corridor directly to the river. These alternatives would require the approval of the Fort Bend County Conunissioner?s Court and possibly other entities. The costs for implementing the various alternatives investigated for improvements to the reservoirs or the operating procedures of the reservoirs are tabulated below: Fringe Area Buyouts 588,250,000 Excavation within Reservoirs 123,300,000 Interconnection of Reservoirs 32,000,000 Katy Freeway Outfall 481,280,000 Brazos River Outfalls Peek Road Alignment 44,000,000 Harlem Road Alignment 92,000,000 The stage-frequency, urbanization and operations analyses performed by Dr. Wurbs, on behalf of the concluded that the operations policies currently in use by the COE for the Addicks and Barker Reservoirs have the greatest effect on storage levels within the reservoirs. Top of curb and natural ground elevation within the fringe areas were identified, as shown on Exhibits 3 and 4. The minimum top of curb elevations are above the IOU-year ?ood levels within the respective reservoirs. Approximately 450 acres of fringe area lie within the Barker Reservoir [00-year ?ood plain. Based on the stage?frequency and operations studies performed by Dr. Wurbs, structural improvements to the reservoirs or the outlet structures are not warranted. Construction of additional outlets, either the I.H.-10 corridor or Brazos River diversion alternatives are not warranted at this time. Feasibility Study for Improvements to Addicks and Barker Reservoirs Page 22 605252555), ?ne. MARCH, 2000 B. RECOMNIENDATIONS Based upon the above conclusions and the associated cost estimates, the following recommendations regarding improvements to the Addicks and Barker Reservoir operations are presented. 0 Based on the conclusions of the Summary Report, Operation of the Addicks and Barker Reservoirs, it is recommended the petition the COE to undertake a stud);r to evaluate possible changes to the operation policies and methods of determining release rates and outlet gate operations on both dams. II Should additional outfall capacity from the reservoirs be determined to be necessary in the future, the diversion of stored waters from the Barker Reservoir to the Brazos River should be investigated further. The Peek Road alternative identi?ed above is signi?cantly less expensive than all other alternatives involving additional out?ow capacity. Feasibility Study for Improvements to Addicts and Barker Reservoirs Page 23 V. EXHIBITS 1' - 5 HILES 5 ADDICES RESERVOIR SERVICE AREA BARKER RESERVOIR SERVICE AREA GRAND s.n.as LEGEND CosteII09 ENGINEERING MID SURVEYING DIN ED LLHD RESERVOIRS LREL FEASIBILITY STUDY RESERVOIR SERVICE LOCATION MAP JOB NO. BITE: HIRCH 2000 EXHIBIT "041 SPENCER MASON RD. Can I: BEAR CREEK ADDICKS RESERVOIR BARKER RESERVOIR IESTHEIIE LLIEF - cLuDl?E CosteMog Inca ENGINEERING AND SURVEYING ADDICKS - BARKER RESERVOIRS FEASIBILITY STUDY FRINGE AREA MAP FILE DATE =02!23!99 :1?:50 103 HO. 196053-01 DATE: HAY acne EXHIBIT HQ: 2 In 21 SEALS: - 2000? TOLLWAY FRY HUUSTUN Fax-'- 4- CLAV RD. CLAY 5AM ADD I CKS LEGEND: RESERVOIR -1DE 10? 109 ELDRIUGE RU. 111 112 113 114 115 LOWEST KNOWN TOP OF CURB ELEVATION FRINGE AREA Costello Inc. nonn- - mm? "mum! mu PKWY 99 U.SCALE 1" - 2000? BARKER RESERVOIR 5' MASON ~39 . - Ewart LEGEND: LOWEST KNOWN TOP OF CURB FRINGE AREA LIMITS Cailnno lac. Fu? 4? ?I?ll "Elm - nun Illm?ll rul?l?h? mm BARKER RESERVOIR TOP or CURB II DESIGN ALTDESIGN ALThm:- Mg i, a. war; 2 I .Ll? 1 -?m-nmwm Cutollo Inc. Wm In Mr (:outnua, Inc. t. . hull Initial! nun: I.H. ID CORRIDOR UTILITY LH-BIO - [500' .- Cancun, Inc. built-I. l- IDIICII - In?ll ALTERNATE COHDUIT 1r: nmus ALIGNHENTS