1954 Report to Congress on San Lorenzo Creek (concluded)



FLOOD PROBLEMS AND SOLUTIONS CONSIDERED

48. Flood problems.-- The flood problems on San Lorenzo Creek fall into two categories: namely, inundation and bank erosion. From B Street to Hesperian Boulevard, high velocities of flood flows combined with tortuous channel conditions cause severe erosion damage at bends and at points of softer bank material. Man-made obstructions in the stream cause turbulence and direct the flows against the opposite banks, resulting in additional damages. Downstream from Hesperian Boulevard, the alinement is more favorable but the capacity is inadequate for all but low flows. In this section, erosion has often caused breaches in the banks and levees, resulting in extensive inundation. Throughout the basin, erosion has uprooted trees growing in the channels and along the banks, which causes or augments debris jams and impedes flood flows. Inundation is confined primarily to the area on the alluvial cone downstream from Bridge Street. It occurs as a result of overflow from floods exceeding the channel capacity or from the breaching of levees or banks.

49. Problems on tributary streams.-- Other than on the two small streams draining Castro Valley, there are no known existing or potential erosion or inundation problems on tributaries of San Lorenzo Creek, as those tributaries flow in steep, sparsely populated valleys. In Castro Valley, however, urban development is progressing rapidly and encroachment upon the stream channels has occurred in several instances. Apparently little or no provision has been made for dramage in this newly developed area and, as a result, local flooding has occurred. As urbanization continues, the situation will be further aggravated. However, the local people now have under consideration a plan for providing adequate storm drainage which, if adopted, will alleviate this problem. One deterring factor in performing this work is the adverse influence exerted by residents in the flood plain who oppose any improvement that might add to the flow in San Lorenzo Creek and thus aggravate the flood and erosion problem in the downstream areas.

50. Water-supply problems.-- In previous years, much of the water supply for this area was obtained from wells. Water for domestic consumption was obtained almost entirely from deep wells, while shallow wells provided water for irrigation. San Lorenzo Creek and adjacent streams flowing over the San Lorenzo cone provided the principal source of replenishment for the shallow wells; however, it has generally been established that the deep wells were replenished from Niles cone and the Alameda Creek Area south of San Lorenzo Creek. Since the East Bay Municipal Utility District has extended its water lines to the area surrounding Hayward, and since the Hayward system has been connected to San Francisco's Hetch Hetchy supply, the present need for deep wells has been practically eliminated. From surveys recently made by the San Francisco District, it appears that only a small amount of surface flow infiltrates from San Lorenzo Creek into the shallow aquifer below Foothill. Boulevard. Plans of channel improvements considered in the investigations for this report, however, included provisions which would permit infiltration substantially as under existing conditions.

51. Power development and water conservation.-- In view of the limited intermittent runoff from this small watershed and the lack of favorable storage sites, it is apparent that neither hydroelectric power nor water conservation by surface storage would be economically feasible.

52. Solutions considered.-- Topographic and economic conditions precluded any possibility of effecting control of large discharges by diversions or bypass channels. Permanent evacuation of the area subject to inundation is impractical because of the cost involved and the fact that areas suitable for residential and industrial development in the East Bay are at a premium. Damages to some movable commodities might be averted by temporary evacuation, but the greater part of the damages sustained by inundation, and all damages by erosion, are to permanent improvements, lands, and crops. In view of the foregoing, it was concluded that the flood problem could be resolved only by reservoirs, channel works, or a combination of both.

53. Reservoirs.-- The multiple-purpose and flood-control measures were investigated in connection with five possible reservoir sites as follows: (1) on Crow Creek immediately above its confluence with Cull Creek; (2) on Cull Creek approximately 0.23 mile above its confluence with Crow Creek; (3) on Palomares Creek at mile 2.45; (4) on Palomares Creek at mile 0.36, hereinafter referred to as the Palomares site; and (5) on San Lorenzo Creek immediately below its confluence with Palomares Creek, hereinafter referred to as the B Street site. After a preliminary examination, the Cull Creek, Crow Creek, and upper Palomares sites were eliminated from further consideration for reasons of excessive costs of storage and very limited effects on peak flows. Summaries of the studies of the remaining two reservoirs are presented in subsequent paragraphs.

54. Possible B Street Reservoir. -- The investigation of the B Street site for flood control and multiple-purpose development included detailed topographic surveys, geologic reconnaissance, aud hydrographic illvestigations. This reservoir, which offered the greatest flood-control and water-conservation possibilities, would reduce the peak flows at Bridge Street by about 75 percent. However, because of the excessive erosion in the lower channel and its obstructed bay outlet, some channel work would be required in addition to the dam. The cost of a flood-control project at this site, including necessary downstream chaunel work, was found to be substantially in excess of $8 million, which would give rise to aunual charges far in excess of the prospective benefits. Providing additional storage capacity for water conservation would increase the project cost by approximately 75 percent. Preliminary estimates indicate that the economic aspect of such a project would be less favorable than for the single-purpose flood-control reservoir.

55. Possible Palomares Reservoir. -- The iuvestigation of the Palomares site also included the necessary hydrographic studies, geologic recounaissauce, and topographic surveys. This reservoir would provide a relatively low degree of flood protection, reducing the peak flow at Bridge Street by only about 37 percent. Added reservoir storage at other sites or channel works would be required, and the total cost of all of these features would far exceed the benefits that might accrue.

56. Channel improvements. -- Several methods of flood and erosion control by channel improvements were considered, of which the most effective are (1) channel clearing in the upper reaches aud levee construction in the lower reaches; (2) various channel alinements aud drop structures in the upper reaches and channel and levee sections in the lower reaches; (3) various channel alinements with revetments at critical points in the upper reaches and levees and channel sections in the downstream areas; and (4) revetment protection in the upper reaches aud lined channels iu the lower reaches with possible provision for percolation outlets. The latter plan was found to give the greatest degree of protection and was most favorable economically.


FLOOD-CONTROL PLAN

57. General plan of improvement. -- The plan of improvement of San Lorenzo Creek for flood control consists of an improved channel below B Street with levees below a point about 1,600 feet downstream from Lorenzo Avenue. From B Street to Foothill Boulevard, the channel improvement would consist of the removal of trees, brush, and gravel from the channel and the revetting of the channel banks in those reaches where bank erosion is a problem. At the downstream ends of the revetted sections, the channel bottom would be protected where necessary to prevent degradation by construction of a derrick-stone sill. From Foothill Boulevard to a point about 1,600 feet downstream from Lorenzo Avenue, the channel would be enlarged to a uniform trapezoidal cross section and lined with reinforced concrete. This type of channel section was found to be the most feasible in the investigations made for this report. The final selection of a section, however, would be determined in the planning stage of the project. Below the lower end of the paved section, the improvement would consist of channel enlargement and levees, stabilized with riprap lining.

58. Design flood.-- The proposed improved channel and levees would carry the standard project flood of 9,700 cubic feet per second in San Lorenzo Creek at Bridge Street.

59. Design of proposed improvements.-- The plan of the proposed improvements and pertinent details of their design are shown in enclosure 2. The excessive cost of major realinement of a channel through a deeply developed area made it necessary to limit realinement of the channel to those reaches where the problem of bank erosion is particularly critical due to the short-radius curves of the existing channel. The concrete-lined channel is required because of the high-velocity flows to be produced in that reach by the design flood. It would have a bottom width of 20 feet and side slopes of 1 vertical to 1 1/4 horizontal. Riprap would afford ample protection in the indicated portion of the channel where lower velocities would be experienced. In the upper portion of the riprapped reach, the channel would have a bottom width of 45 feet and side slopes of 1 vertical to 2 1/2 horizontal. The lower portion of the channel would have a bottom width of 38 feet and side slopes of 1 vertical to 3 1/4 horizontal. The flatter slopes are required in this latter section because of the relatively poor foundation conditions. The bottom width was designed to give the same normal depth for the design flow as in the upper portion of the riprapped section. The levees would have a crown width of 12 feet and landside slopes of 1 vertical to 2 1/2 horizontal. The channel has been designed to carry the design flood with a freeboard of 1 foot in the paved portion and 3 feet in the riprapped portion.

60. The concrete channel lining would be underlaid by a gravel blanket having a minimum thickness of 6 inches. Continuous 4-inch tile drains would be placed in this gravel behind the concrete slope lining and at the toe of the slopes. Outlet through the paving would be provided at 100-foot intervals. In addition, in the reach from about Lorenzo Avenue to Hazel Street, open holes in the concrete would be provided on 10-foot centers to permit the percolation of a portion of the flood runoff into the underlying aquifers.

61. Alteration of bridges and utilities.-- Under the proposed plans of improvement, public vehicular bridges at Lorenzo Avenue, Hesperian Boulevard, and East 14th Street, and the railroad bridge near the mouth of the creek would be modified. One privately owned vehicular bridge (a timber structure located below Lorenzo Avenue) would be removed and abandoned. The vehicular bridges at Lorenzo Avenue and Hesperian Boulevard are obsolete aud are to be replaced or altered in the near future. Local interests have consulted with the Corps of Engineers to coordinate their plans for the structures with the improvements proposed in this report. The bridge at East 14th Street would be replaced as a part of the proposed plan of improvement in order to provide the required cross-sectional waterway area at the bridge and to improve the channel alinement in the reach. The railroad bridge would be raised about 3 feet, the piers streamlined, and the bridge approaches raised as required to provide an acceptable grade. The crossing provided by the privately owned timber bridge would be abandoned. All existing 12-inch water pipeline crossing San Lorenzo Creek near Lorenzo Avenue would be lowered about 5 feet to put it below the proposed improved channel bottom.

62. Construction period.-- It is anticipated that the proposed improvements would be constructed within a total time of about 2 years. This would permit the accomplishment of most of the work during those months (May through October) when stream flow is so small that it could be pumped or channeled by the construction without undue difficulty. As a measure for preventing possible failure due to poor foundation conditions near the lower end of the project, it has been considered that the levees in this reach would be constructed in two stages. In the first stage the levees would be constructed 3 feet below their designed height, equivalent to the water-surface elevation of the design flow without freeboard. The foundation would then be allowed to consolidate a sufficient length of time to increase its strength, after which the levee would be raised to its full height. It is expected that a period of about 2 years may be required before the second-stage construction could be initiated.

63. Construction materials.-- It is anticipated that a considerable part of the material planned to be excavated in connection with enlarging the creek channel would be suitable for the proposed levee construction. Unsuitable and excess material would be wasted in any of the nearby low-lying areas that would be benefited by the fill. Gravel for the filter blanket to be placed under the concrete channel lining could be obtained from any of several commercial plants in the vicinity. Riprap material would have to be obtained from sources outside the drainage basin, but there are several possible sources from which it could be obtained at reasonable cost.


ESTIMATES OF FIRST COST

64. Cost estimates.-- The first cost of the proposed plan of improvement, based on prevailing prices in the San Francisco Bay area as of December 1952, is estimated at $4,275,000. Details of the estimated first cost are given in appendix IV [not printed], while the basis for cost allocation between Federal and non-Federal is described in paragraph 80. Principal features of the cost estimate areas follows:

                                                                     Percent
                                                         Amount      of total

Federal:
Lined channel and levees ----------------------------   $3,391,000   --------
Reconstructing railroad bridge ----------------------      215,000   --------
Clearing, revetments, and sills ---------------------      134,000   --------

Gross Federal 1st cost ------------------------------    3,740,000   --------
Less non-Federal cash contribution ------------------       96,000   --------
Net Federal 1st cost --------------------------------    3,644,000      85.2

Non-Federal:
Lands, easements, and rights-of-way -----------------      264,000   --------
Replacement of bridges ------------------------------      269,000   --------
Replacement of utilities ----------------------------        2,000   --------

Net non-Federal 1st cost ----------------------------      535,000   --------
Cash contribution -----------------------------------       96,000   --------

Total non-Federal 1st cost --------------------------      631,000      14.8
Total project 1st cost ------------------------------    4,275,000     100.0


ESTIMATES OF ANNUAL CHARGES

65. Economic cost of the improvement.-- The economic cost of the proposed improvement, which is assumed to have an economic life of 50 years, consists of the interest on the first cost, amortization of the first cost in 50 years, and mamtenance and operation of the improvement durmg that perIod. There would also be the cost for replacement of those features having an estimated economic life of less than 50 years. After its completion, maintenance of the improvement wIll be a non-Federal responsibility. Interest charges are computed at the rate of 2 1/2 percent per annum for both Federal and non-Federal investments. The Board of Supervisors of Alameda County Flood Control and Water Conservation District, the agency which has given assurances that it will provIde the required local cooperation discussed in subsequent paragraphs, has indicated that it expects to issue bonds at a rate of interest not to exceed 2 1/2 percent. In addition, it is quite likely that the State of CalIfornia, under its existing water resources development policy, will bear practically all of the non-Federal first costs for lands, easements, rights-of-way, and bridge replacement or reconstruction. In view of these facts, the use of 2 1/2 percent for non-Federal costs is fully justified.

66. Federal annual charges.-- It is estimated that the benefits from the proposed channel improvements would accrue coincident with the progress of the work. In computing the Federal annual charges, no item for interest during construction has been included, and the federal investment would be the same as the net Federal first cost. The annual charge for interest and amortization of the first cost over a 50-year period is $128,000. In addition, there would be an annual cost of $500 for periodic inspections of the completed works after the project is transferred to local interests. The total estimated Federal annual charge would be $129,000.

67. Non-Federal annual charges.-- Non-Federal annual charges consist of interest and amortization of the non-Federal investment and charges for maintenance, operation, and replacements. These charges are estimated as follows:

Interest and amortization ------------------------------------ $22,200
Maintenance and operation ------------------------------------  12,500
Replacements -------------------------------------------------   2,000

Total non-Federal annual charges ------------------------       36,700


68. Total annual charges.-- Federal and non-Federal annual charges, as presented above, total $165,700.


ESTIMATES OF BENEFITS

69. Types of benefits.-- The improvements proposed in this report would provide full protection against damage from floods of magnitudes up to, and including, the standard project flood. The benefit creditable to the proposed improvements is the difference between the average annual damages under existing physical conditions and under proposed project conditions. This reduction in damages is the pnmary purpose of the proposed improvements. Additional benefits would result from the higher utilization of lands now subject to frequent flooding, and from the replacement of existing obsolete bridges.

70. Benefit from elimination of flood damages.-- From surveys of damages from experienced floods and from estimates of damages expected to be incurred from future floods if the improvements are not constructed, it has been estimated that the annual direct and indirect damages from inundation and erosion in the San Lorenzo Creek flood plain during the estimated 50-year life of a possible project will, if no protection works are constructed, average $180,500. The improvements which would afford complete protection against floods of magnitudes up to, and including, that of the standard project flood, would eliminate all of this damage. The benefit for elimination of flood damages is therefore estimated at $180,500. It is considered proper to adjust this benefit in recognition of the beneficial effect of the numerous existing works constructed by local interests. By estimating the benefit from these works to be equal to the cost of their maintenance and giving consideratIon to their remaining useful life, it was estimated that without additional construction or maintenance, those works would effect benefits equivalent to $1,300 per year over the life of the proposed improvements. The net benefit from reduction of flood damages is therefore estimated at $179,200.

71. Benefit from higher land utilization.-- The rapid real estate development of portions of the San Lorenzo Creek flood plain in recent years has been noted earlier in this report. Extensive areas of land formerly used for agriculture are now occupied by residential and business properties. This development would extend to an additional area of about 139 acres but for the fact that local authorities have withheld permits until such time as an acceptable degree of flood protection shall have been provided. It is probable that the land would be used for residential building sites. The benefit from the higher land usage has been estimated in appendix III [not printed] to be equal to $1,6000 per acre or $222,000 for the 139 acres. Using a 5-percent return on the increase in land value results in an evaluated average annual benefit due to higher land utilization of $11,000.

72. Replacement of existing bridges.-- Of the bridges which would be replaced oymodified if the improvements proposed in this report are constructed, the vehicular bridges at Lorenzo Avenue and Hesperian Boulevard are obsolete and will require replacement at an early date whether or not the improvements proposed herein are constructed. This report contemplates the replacement of these bridges with new structures providing ample waterway capacity for flood flows. The estimate of benefit for prevention of flood damages therefore includes the benefit creditable to the additional cost of the bridges to provide that capacity compared to the cost of smaller bridges which otherwise might have been considered adequate for traffic needs. The full cost of the new bridges has been included in the estimate of the cost of the proposed project. In order that the flood control project be not penalized by this cost it is considered proper to include a benefit for the replacement of the obsolete bridges in recognition of the improvement in the flow of traffic. This benefit has been estimated on the basis of the cost of the proposed new bridges at Lorenzo Avenue and Hesperian Boulevard, estimated at $106,000 less the estimated present value of $10,000, or $96,000. Based upon an interest rate of 2.5 percent and an estimated useful life of 50 years, the initial cost of $96,000 would give rise to annual charges, for interest and amortization, of approximately $3,000. An annual benefit of $3,000 is therefore credited to the proposed project for the prospective improvement in traffic conditions to result from the replacement of the existing bridges over San Lorenzo Creek at Lorenzo Avenue and Hesperian Boulevard.

73. Summary of evaluated benefits. -- The prospective average annual benefits creditable to the improvement of San Lorenzo Creek, as proposed in this report, total $193,200. The benefits are summarized as follows:

                                                     Percent
Type of benefit:                           Amount    of total

Prevention of flood damaages -----------  $179,200      93
Higher land utilization ----------------    11,000       6
Replacement of obsolete bridge ---------     3,000       1

Total ----------------------------------   193,000     100


74. Intangible benefits.-- Construction of the proposed improvement would give complete protection against inundation and bank erosion from floods of magnitudes up to that of the standard project flood, and would remove the fear that owners of property in the flood plain have of loss or damage to their lands and improvements, including their residences and household furnishings. Also, too community would be protected against the undesirable after effects of a flood, such as interruption of normal activity, the possibility of epidemics, and a general lowering of morale. Potential housing areas, now undeveloped because of recurring floods, would be made available to alleviate the shortage of convenient areas for medium-priced homes in the environs of Oakland.

75. There are several areas in the drainage basin and also adjacent to San Lorenzo Creek which are rapidly being developed into highly urbanized communities. One of the problems adversely affecting the development is that of providing adequate local drainage systems. Diversion of the drainage into San Lorenzo Creek affords an economic and ready means of disposal of the drainage. Residents in the flood plain of San Lorenzo Creek have strongly opposed such measures. They fear that with the present channel already inadequate to carry all but minor flows, particularly in the lower reaches of San Lorenzo Creek, the local drainage works would result in increasing the flood peaks and add to the existing flood problem. If the proposed channel improvements for San Lorenzo Creek are constructed, the opposition to construction of the necessary drainage systems and diversions would be eliminated.


COMPARISON OF BENEFITS AND COSTS

76. Ratio of evaluated average annual benefits to annual charges.-- The average annual benefits expected to accrue from the construction of the improvements proposed are estimated at $193,200, and the Federal and non-Federal annual charges are estimated to total $165,700. The ratio of benefits to cost is, therefore, 1.17 to 1.0.


PROPOSED LOCAL COOPERATION

77. Requirements of local cooperation.-- In accordance with existing flood-control acts under which local channel-improvement and levee projects are authorized, the construction of the improvements proposed in this report would not be undertaken until a responsible local agency had given assurances satisfactory to the Secretary of the Army that it will (a) provide without cost to the United States all lands, easements, and rIghts-of-way necessary for the construction of the project; (b) ho]d and save the United States free from damages arising from the constructIon of the proposed works; and (c) maintain and operate all the works after completion in accordance with the regulations prescribed by the Secretary of the Army. The Alameda County Flood Control and Water Conservation District is properly constituted to assume such responsibilities. Federal policy under existing law requires that, with the exceptIon of railroad bridges, the cost of replacement or modification of bridges and utilities required in connection with flood-control projects shall be borne by local interests as a part of their obligation to provide the lands, easements, and rights-of-way. In addition to the above minimum requirements it is considered proper in view of the local nature of some of the benefits expected to result from the project to require local interests to contribute a substantial amount in cash toward the cost of the improvements, or in lieu thereof perform part of the construction equivalent to the amount of the cash contribution.

78. Willingness and ability of local interests to meet requirements of local cooperation.-- The improvements proposed in this report have been discussed with local interests, who have evinced their interest in a comprehensive flood- and erosion-control program by forming the Alameda County Flood Control and Water Conservation District. This district has recently formed a flood-control zone for the area affected by San Lorenzo Creek. Local interests were afforded an opportunity to review the proposed plan of improvement and were advised of the requirements of local cooperation. In a resolution adopted January 15, 1953, and as amended at a later date, the Board of SuperVisors of Alameda County Flood Control and Water Conservation District indicated its concurrence with the general plan of improvement and its willingness and ability to meet the requirements of local cooperation.

79. The State of California, in 1945, adopted a water-resources policy under which the State will pay for the cost of lands, easements, and rights-of-way required by Federal flood-control projects when such projects are recommended by the water resources board and approved by the legislature. It is considered highly probable that, under this policy, the State of California will participate in the project proposed for the improvement of San Lorenzo Creek to the extent of providing the lands, easements, and rights-of-way required. It is the opinion of the district engineer, therefore, that local interests are willing and able to meet the requirements of local cooperation.


ALLOCATION OF COSTS

80. The cost for the proposed improvement was allocated in accordance with section 3 of the Flood Control Act of 1936, as amended. In addition, local interests have been required to contribute in cash, or perform equivalent construction in lieu thereof toward the cost of the project. The requirements of local cooperation under the flood-control acts are that for the type of project being proposed in this report for San Lorenzo Creek local interests shall provide without cost to the United States all lands, easements, and rights-of-way required for the project, and maintain and operate the improvements after completion. The costs of modifying or replacing the public vehicular bridges and of such relocation or modification as may be required for any public utilities are allocated to local interests as a part of the cost of rights-of-way. These items are estimated to cost $535,000. Because of the local benefits which are expected to result from the construction of the project, it is considered proper to require local interests to bear a part of the construction costs in addition to the minimum required by present flood-control acts. The principal benefit from the project, $179,200, would result from the reduction in flood damages. Additional benefits, which are local in nature, would be $11,000 from higher land utilization and $3,000 from replacement of 2 obsolete highway bridges. Since the bridges are to be replaced whether the project is constructed or not, the benefits, and costs, would not enter into the cost allocations. On the basis of the remainiag evaluated benefits, it has been determined that local interests should be required to participate in the project to the extent of an additional $96,000. The derivation of this figure is given in appendix IV [not printed]. The total cost to local interests will be $631,000, or 14.8 percent of the total project cost.


COORDINATION WITH OTHER AGENCIES

81. With the initiation of the investigation upon which this report is based, a public hearing was held by the district engineer on April 23, 1946, at Hayward, Calif., to afford all interested parties an opporturnity to present data relative to flood control and related problems on San Lorenzo Creek and opinions on possible solutions of those problems. The public hearing was attended by representatives of the Department of the Interior, the Department of Agriculture, the State of California, and local agencies, as well as individual local residents and property owners. Throughout the progress of the investigation, pertinent information was made available to the several Federal and State agencies. Advance copies of the report were furnished to various Federal agencies, the California State director of public works, and the Alameda County Flood Control and Water-Conservation District. The comments of these agencies are presented in appendix V [not printed]. None of the agencies were opposed to the improvements recommended in this report. Continued coordination will be required, however, with such agencies as the United States Fish and Wildlife Service and the United States Soil Conservation Service during the planning and design stage for the project.


DISCUSSION

82. San Lorenzo Creek drains an area of 61 square miles situated on the east side of San Francisco Bay. The stream flows through the city of Hayward and through recently developed urban areas adjacent to the bay. In its upper reaches, the flood-carrying capacity of the stream is adequate for most flood flow; however, it decreases progressively downstream to the extent that just prior to entering the bay the channel is poorly defined and capable of carrying only very low flows.

83. Residential, commercial, and agricultural developments are subject to frequent damage from floods on San Lorenzo Creek. If flood-control works are not constructed, it is estimated that future flood damages will average $180,500 annually. These damages are concentrated principally in the area extending downstream from B Street in Hayward to the mouth of the creek. Damages in the upstream part of this area result primarily from bank erosion, while damages in the lower part result from inundation. Outside of this area, a small amount of local damage occurs periodically in Castro Valley; however, this may be prevented by installation of an adequate local storm drainage system. Such a system is now under consideration by local interests; but it has local opposition by occupants of the flood plain of San Lorenzo Creek because of the possibility that it would aggravate the flood problem in the lower basin. Also, improvements of drainage in small adjacent areas by diversion of storm runoff into San Lorenzo Creek have met with opposition for the same reason.

84. The critical need for water conservation in this basin has been alleviated for the present by the services provided by two large municipal water systems which have their source of supply outside of the area. However, in view of the continuing need for water for irrigation, it is planned to provide openings in the bottom of the proposed channel paving which would permit water to percolate to the aquifers underlying the channel. Power development on San Lorenzo Creek is infeasible due to the small drainage area and intermittent flow. Recreational areas, such as those provided by reservoirs, are in great demand in the vicinity of the heavily populated San Francisco Bay area; however, the water surface in a possible multiple-purpose reservoir on San Lorenzo Creek would fluctuate to the extent that its recreational value would be negligible.

85. Preliminary studies indicate that control of floods by multiple- or single-purpose reservoirs would be infeasible because reservoirs at the available sites would not control enough of the drainage area to prevent flood flows in the downstream channel. The cost of a reservoir plus the necessary downstream channel works would exceed the benefits that might accrue from such a plan. The best plan of improvement, which would provide protection against both erosion and overflow damage, consists of constructing an enlarged and riprapped channel and levees below a point about 1,600 feet downstream from Lorenzo Avenue Bridge and a concrete-lined channel from that point to Foothill Boulevard, and improvement of the channel from Foothill Boulevard to B Street by clearing the channel and revetting wIth sacked concrete those portions of the banks most vulnerable to erosion. Under this plan, all flood flows up to, and including, the standard project flood would be confined. Since the standard project flood is a very rare flood which is not expected to occur more than once in several hundred years, the project can be considered as providing complete protection against damages from floods. Three public vehicular bridges and one railroad bridge would be modified or replaced. One farm bridge would be abandoned.

86. Average annual benefits estimated at $193,200 would result from the proposed improvement, the first cost of which is estimated at $4,275,000 with total annual charges estimated at $165,700. The resulting benefit-cost ratio is 1.17 to 1. In addition to the tangible benefits, there would also be the intangible benefits resulting from eliminating the present opposition to drainage improvements in areas undergoing urbanization, such as Castro Valley and adjacent minor watersheds, from making available potential convenient housing areas, and from removal of the fear of floods.

87. Construction of the proposed improvements would be contingent upon local interests providing assurances satisfactory to the Secretary of the Army that they would (a) provide without cost to the United States, all lands, easements, and rights-of-way required for the project, now estimated to cost $264,000; (b) hold and save the United States free from damages due to the construction of the improvements; (c} modify or replace the existing public vehicular bridges over San Lorenzo Creek at Lorenzo Avenue, Hesperian Boulevard, and East 14th Street, now estimated to cost $269,000 according to plans approved by the Chief of Engineers; (d) make minor alterations and relocations of utilities, required for construction of the proposed improvements, now estimated to cost $2,000, in accordance with plans approved by the Chief of Engineers; (e) contribute in cash an amount now estimated at $96,000, or in lieu thereof perform additional construction for the project equivalent to the amount of the cash contribution in accordance with plans approved by the Chief of Engineers; (f) operate and maintain the project after completion; and (g) prevent any encroachment in the project channels which might interfere with their proper functioning for flood control. The total cost to local interests is estimated at $631,000 for initial construction and $14,500 annually for maintenance and operation. The total non-Federal annual charge, including maintenance, operation, interest on the non-Federal initial cost, and amortization of that cost in 50 years is estimated at $36,700. The remainder of the initial cost of the improvements, or $3,644,000, would be borne by the United States. The Federal annual charge for interest and amortization over a 50-year period would be $128,500. In addition there has been included a Federal annual cost of $500 for periodic inspections of the completed works. Local interests favor the proposed improvement and have indicated a willingness to meet the responsibilities of required local cooperation. The existing Alameda County Flood Control and Water ConservatIon District is a properly constituted public body legally empowered to assume such responsibilities.


CONCLUSIONS

88. The district engineer concludes:

(a) That damages from floods in the San Lorenzo Creek Basin are largely concentrated in the heavily populated flood plain downstream from B Street in Hayward, and that future floods will, unless protective measures are taken, cause damages estimated at $180,500 per year.

(b) That possible reservoirs which might be constructed in the drainage basin would effect only a low degree of flood control and that the cost of such reservoirs would exceed, by a wide margin, the prospective benefits, whether they be operated for flood control alone or for multiple uses.

(c) That a high degree of flood control could be effected by improving the channel of San Lorenzo Creek by clearing the channel, revetting the banks with sacked concrete, and constructing sills across the channel bottom as required to prevent bank erosion and channel degradation in the reach from B Street to Foothill Boulevard; paving the channel with reinforced concrete from Foothill Boulevard to a point 1,600 feet below Lorenzo Avenue; and riprapping the channel and constructing confining levees from that point to San Francisco Bay, all at an estimated initial cost of $4,275,000 and an estimated annual cost of $15,000 for maintenance and operation.

(d) That Federal and non-Federal annual charges, including interest, amortization, maintenance, and operation, would total $165,700.

(e) That the construction of the proposed improvements would produce annual benefits estimated at $193,200 arising principally from the prevention of flood damages but including minor benefits from making possible a higher type of land utilization, and from the replacement of obsolete vehicular bridges.

(f) That the evaluated annual benefits from the construction of the proposed improvements would exceed the estimated annual charges by a substantial amount and that the project is economically justified.


RECOMMENDATIONS

89. The district engineer recommends:

(a) Adoption by the United States of a project for the improvement of San Lorenzo Creek in Alameda County, Calif., for flood control by clearing the channel, revetting the banks and constructing sills across the channel bottom as required to prevent bank erosion and channel degradation between B Street and Foothill Boulevard; lining the channel with reinforced concrete between Foothill Boulevard and a point 1,600 feet below Lorenzo Avenue; and riprapping the channel and constructing confining levees between that point and San Francisco Bay, all at an estimated Federal first cost of $3,644,000 and an estimated non-Federal first cost of $631,000, for a total proJect first cost of $4,275,000, and an estimated non-Federal annual cost of $14,500 for maintenance, operation, and replacements, and a Federal annual cost of $500 for periodic inspections.

(b) That construction of the improvements recommended above be subject to such reasonable modification as, in the discretion of the Chief of Engineers, may be advisable at the time of construction, and subject also to the condition that local interests give assurances satisfactory to the Secretary of the Army that they will:

(1) Provide without cost to the United States the lands, easements, and rights-of-way required for construction of the recommended improvements, now estimated to cost $264,000.

(2) Modify or replace the existing vehicular bridges at Lorenzo Avenue, Hesperian Boulevard, and East 14th Street, now estimated to cost $269,000, in accordance with plans approved by the Chief of Engineers.

(3) Make minor alterations and relocations of utilities, now estimated to cost $2,000, in accordance with plans approved by the Chief of Engineers.

(4) Contribute in cash an amount now estimated at $96,000, or in lieu thereof perform an additional construction for the project equivalent to the amount of the cash contribution, in accordance wIth plans approved by the Chief of Engineers.

(5) Maintain and operate the project after completion in accordance with regulations to be prescribed by the Secretary of the Army, estimated to cost $14,500 annually; hold and save the United States free from damages due to the construction of the project; and prevent encroachment on the project channels which might interfere with their proper functioning for flood control.

(c) That of the total of $3,644,000 allocated to the United States for construction of the recommended project, an initial allotment of $2,500,000 be made available for the first-year construction funds.

HENRY WALSH,
Colonel, Corps of Engineers,
District Engineer.


[First endorsement]

SOUTH PACIFIC DIVISION,
CORPS OF ENGINEERS, UNITED STATES ARMY,
San Francisco 4, Calif., March 14, 1953.

To: Chief of Engineers, Department of the Army, Washington 25, D.C.

I concur in the conclusions and recommendations of the district engineer.

P. D. BERRIGAN,
Colonel, Corps of Engineers,
Division Engineer.


LIST OF APPENDIXES MADE IN CONNECTION WITH THE DISTRICT REPORT

(Not printed)

I. Geology
II. Hydrology
III. Flood damages and flood-control benefits
IV. Bases for design and cost estimates
V. Comments of other agencies


LIST OF ILLUSTRATIONS MADE IN CONNECTION WITH THE REPORT OF THE DISTRICT ENGINEER

(Profiles and details map not printed)

File No. 62-52-1. General map of basin (enclosure 1)
File No. 62-39-4. Plan of improvement (enclosure 2, sheet 1)
File No. 62-39-4. Profiles and details (enclosure 2, sheet 2)


Original document scanned by
Friends of San Lorenzo Creek
Nov. 21, 2004