Revised Data FOURMILERUN LOCAL FLOOD PROTEGTION CITY OF ALEXANDRIA & ARLINGTON COUNTY, VIRGINIA

SUPPLEMENT TO FINAL ENVIRONMENTAL STATEMENT

Prepared by U.S. Army Engineer District, Baltimore

March 1974 REVISED DATA TO THE SUPPLEMENT TO FINAL ENVIRONMENTAL STATEMENT

FOURMILE RUN LOCAL FLOOD PROTECTION CITY OF ALEXANDRIA AND ARLINGTON COUNTY, VIRGINIA

Prepared by: US ARMY ENGINEER DISTRICT, BALTIMORE BALTIMORE, MARYLAND

March 1974 REVISED DATA TO THE SUPPLEMENT TO FINAL ENVIRONMENTAL STATEMENT FOURMILE RUN LOCAL FLOOD PROTECTION CITY OF ALEXANDRIA AND ARLINGTON COUNTY, VIRGINIA Table of Contents Page INTRODUCTION ~I I. PROJECT DESCRIPTION A. GENERAL 2 1. Project Purpose 2 2. Location 2 3. Benefit-Cost Ratio 2 B. SPECIFIC PROJECT CHANGES 2 1. Flood Channel Capacities 4 2. Levees and Walls 4 3. Bridge Modifications 5 4. Slope Protection 5 5. Disposal of Material 5 6. Recreation 6 7. Construction Sedimentation Control 6 8. Additional Terms of Local Cooperation 6 II. ENVIRONMENTAL SETTING WITHOUT THE PROJECT 7 III. ENVIRONMENTAL IMPACT OF THE PROPOSED ACTION Should The project be implemented 7 A. GENERAL 7 B. IMPACTS OF SPECIFIC MODIFICATIONS 7 1. Mouth of Fourmile Run Upstream to Route 1 7 2. Route 1 Bridge Complex Upstream 8 to Mt. Vernon Avenue 3. Mt. Vernon Avenue Upstream to Long Branch 9 4. Long Branch Upstream to West Glebe Road Bridge 10 5. West Glebe Road Bridge Upstream to Shirley Highway 10 6. Watershed Management for the Basin 11 Page IV. ADVERSE ENVIRONMENTAL EFFECTS WHICH CANNOT BE AVOIDED SHOULD THE PROPOSAL BE IMPLEMENTED 13 A. GENERAL 13 B. AESTHETICS 13 C. SOCIAL 13 D. ECONOMIC 14 E. PHYSICAL 14 F. ECOLOGICAL 14 V. THE RELATIONSHIP BETWEEN LOCAL SHORT-TERM USES OF MAN'S ENVIRONMENT AND THE MAINTEXAnCE AnB ENHANCEMENT OF LONG-TERM PRODUCTIVITY 14

PLATES

1. Location Map 2. Existing Conditions 3. Existing Conditions 4. Project for Which Supplement was Prepared 5. Project for Which Supplement was Prepared 6. Project Proposed Under Present Authorization 7. Project Proposed Under Present Authorization 8. Project Proposed Under Present Authorization 9. Project Proposed Under Present Authorization 10. Proposed Recreation Plan 11. Proposed Recreation Plan 12. Proposed Recreation Plan 13. Proposed Recreation Plan REVISED DATA TO THE SUPPLEMENT TO FINAL ENVIRONMENTAL STATEMENT

FOURMILE RUN LOCAL FLOOD PROTECTION CITY OF ALEXANDRIA AND ARLINGTON COUNTY, VIRGINIA

INTRODUCTION The final Fourmile Run Environmental Statement, dated 24 September 197C, was filed with the Council on Environmental Quality on 20 October 1970. The final Environmental Statement was prepared for the pre­ authorization study which responded to a resolution by the Committee on Public Works of the House of Representatives on 5 October 1966. The resolution requested a review of the report on the Potomac River and Tributaries and others with a view to determining if improvements in the interests of flood control are advisable at this time, with par­ ticular reference to Holmes Run, Fourmile Run, and other streams that flow through the City of Alexandria, Virginia. Following sub­ mission of the study report, the Fourmile Run project was authorized under Section 201 of the 1965 Flood Control Act (Public Law 89-298) by resolutions of the Committees on Public Works of the United States Senate and House of Representatives dated 25 June and 14 July 1970, respectively. Subsequent to authorization of the project and the accompanying final Environmental Statement, a post-authorization study indicated that design changes were necessary. As a result, a Supplement to the final Environmental Statement was prepared to outline the changes from the authorized plan and describe the resulting environmental impact changes. The Supplement, dated April 1973, was coordinated and then filed with CEQ on 24 April 1973. In addition, response to EPA’s comments of 4 June 1973 on the Supplement were forwarded to CEQ for filing with the Supplement. Subsequent to the formulation of the postauthorization project for which the Supplement was prepared, increased costs for the Federal interests indicated that re-authorization was necessary. As a result of current Congressional re-authorization, design modifications have been made to the local flood protection project to make the present project conform with the conditions of re-authorization. The information provided in this report describes the current project and revises the pertinent in­ formation provided in the Supplement. The modifications required by current authorization have been made to reduce costs and consideration has been given to the positions taken by various agencies which commented on the earlier Statements and Supplement. This report incorporates the response to EPA comments, dated 4 June 1973, which have been previously furnished the Council. This information described all the modifications of the project since the Supplement was filed and the resulting changes in environmental impacts. I. PROJECT DESCRIPTION A. General. 1. Project Purpose. The purpose of the proposed project remains unchanged. The flood control works will protect against a fluvial flood of 27, 000 cubic feet per second (c.f. s.) on Fourmile Run having a frequency occurrence of once in 100 years. Refined engineering studies at this stage, however, have resulted in changes in channel capacity at specific areas within the project as will be described in paragraph B-l. The basic configuration of the project remains unchanged, but construction elements of the specific areas have been altered as a result of the changes in channel capacities. 2. Location. The location of the project remains unchanged, extending from the Potomac River upstream along Fourmile Run to 1-95, Shirley Highway. 3. Benefit-Cost Ratio. The project has a benefit-cost ratio of 1.4 to 1.0, based on July 1973 prices and a 100-year project life at 5 5/8 percent interest rate for both Federal and non-Federal investme nt costs. B. Specific Project Changes. Changes to the project from that described in the Supplement to the final Environmental Statement include flood channel capacities; revisions to channels, walls and levee dimensions and configuration; revised interior drainage facilities; revision to spoil disposal plans; bridge modifications; revisions to the recreation plan; and potential restoration of sedimentation from construction. Additions to the project include additional terms of local cooperation. Comparative data for the project described in the supplement and the presently authorized project are presented in Table 1 and in the following paragraphs. Existing conditions are showm on Plates 2 and 3. The project for which the Supplement was prepared is shown on Plates 4 and 5. The project proposed under present authorization is shown on Plates 6 and 7. TABLE 1 COMPARISON OE PLAN FOR WHICH SUPPLEMENT WAS PREPARED AND PROJECT UNDER PRESENT AUTHORIZATION FOURMILE RUN FLOOD CONTROL PROJECT

Project (EIS Present Item Supplement) Project

Design Discharge, Ft Per Second Fourmile Run 27, 000 27,000 Long Branch 4, 700: 4, 700 Potomac River Design Stage*, msl 11.2 11.2 Length of Improved Channel, Feet Fourmile Run 1 1, 880 11,880 Long Branch 280 400 Length of Levee, Feet Fourmile Run 2, 250 000 Long Branch 100 GOG Flood/Retaining Wall Fourmile* Run 3, 145 3, 833 Long Branch 000 890 Interior Drainage Facilities No. Pumping Station 1 000 Ponding Area, Acre-Feet 000 000 Bridge Modifications No New Highway Bridges 2 2 No. New Railroad Bridges 4 4 No. Modified Existing Highway Bridges 2 1 Drop Structures Fourmile Run 1 000 Long Branch 1 1

-This figure was incorrectly presented in the Supplement to the final Environmental Statement as 4, 100 cfs. 1. Flood Channel Capacities Compared to the previous plan, channel bottom widths have been gen­ erally decreased from station 474+50 (at the downstream end of the pollution control plant) upstream to tne upstream limit of the project at Shirley Highway. The amount of decrease varies. From the pollution control plant upstream to Mt. Vernon Bridge, the proposed channel is reduced 25 feet in width from the earlier plan; from Mt. Vernon Bridge upstream to Long Branch, the proposed channel is reduced 50 feet from the earlier plan; from Long Branch upstream to West Glebe Road, the proposed channel is reduced by 55 feet; from West Glebe Road upstream to Shirley Highway, the amount of decrease varies from 0 feet up to 85 feet. However, in most cases, the reduction in channel capacity represented by reduced channel bottom widths has been com­ pensated for by changes in dimension and configuration of walls and side slopes of the channel as described in rhe following paragraph. The areas where this is not the case include the portion from Shirley Highway downstream to Long Branch, except for the immediate West Glebe Road bridge vicinity, and from Mt. Vernon Avenue Bridge down­ stream to the pollution control plant. It is expected that some increase in overbank flooding will occur at these points during major floods than would have occurred under the original plan. Flows in excess of 16-18, 000 c.f. s. will leave the channel in the vicinity of West Glebe Road, flow down old South Glebe Road (now a residential access road) and return to Fourmile Run through South Glebe Road. Entrance and exit structures will be provided for this flow. In addition to the changes in channel bottom widths, the channel bottom gradient from Shirley Highway downstream to near West Glebe Road bridge has been increased from gradients of 0.005 and 0.00519 to a gradient of 0.00662. This increase in gradient is the result of elimi­ nating a proposed drop structure from the earlier plan. 2. Levees and Walls. a. Levees. As shown on Table 1 and on the plates, the presently authorized plan has deleted 2, 250 linear feet of levee and the associated pumping station located in the vicinity of Mt. Vernon Avenue in Alexandria. In lieu of the levee, local interests will insure that new construction in the area that would have been protected by the levee will be controlled below the 100 year flood elevation. In addition, the 100 linear feet of levee originally proposed along Long Branch has been replaced with 890 linear feet of flood wall varying from O' to 6' in height above existing ground level. The wall with a top elevation of 24' above mean sea level will prevent peak flow from cutting through an existing low swale on the east bank of Long Branch. b. Walls. In addition to the wall along Long Branch, the amount of channel wall required in the project along Fourmile Run has increased by 688 linear feet. The top of the walls are one to two feet higher than the former walls due to higher water surface ele­ vations caused by reduced channel widths. Not only has the amount and height of the wall increased, the purpose of the walls has changed from purely earth retaining structures incorporated as a part of the channel banks to overbank flood walls. Except for the wall in the immediate vicinity of West Glebe Road bridge and immediately upstream of Mt. Vernon Avenue Bridge, which will remain a vertical bank re­ taining wall and simply be increased in height, all walls will be con­ structed at the top of gabion protected side slopes. The top elevations of the walls will be from 1' to 4' above existing ground levels. Re­ grading of the ground surface on the landward side for drainage and landscape enhancement will, however, reduce the height of the visible wall. 3. Bridge Modification. An additional span for the West Glebe Road Bridge proposed in the earlier plan will not be constructed in the currently proposed project. 4. Slope Protection. The plan for which the Supplement was prepared included provision of riprap channel bank protection to the design flood elevation for the entire length of the channel improvement. The current plan provides for a combination of grass slopes, gabions and riprap as shown on Plates 6 and 7. 5. Disposal of Material. Plans for disposal of dredged material remains essentially unchanged from the previous plan with the exception of the material which will be excavated from the stream channel at the mouth of Fourmile Run. The material, contaminated with nutrients, heavy metals, volatile solids and organic carbon, was to be placed in a diked disposal area on low quality wetland adjacent to Federal Aviation Administration owned land near the mouth of the stream. The area was to be allowed to settle, be covered with topsoil and landscaped to a park-like appear­ ance. In the current plan, the material will be placed on a dry land site on the National Airport property. The wetland at the mouth of Fourmile Run that was to be the spoil area will remain unchanged. 6. Recreation. The concept plans for recreation presented in the Supplement to the Environmental Statement have been detailed and are presented on Plates 10through 13. In the design process several changes have taken place although the concept remains essentially unaltered. A separate addi­ tional bridge across the mouth of Fourmile Run which was to be con­ structed as emergency access to Federal Aviation Administration boating facilities from National Airport was also to serve the National Park Service hiking-biking trail along the Potomac River. The emer­ gency access is no longer necessary, therefore, the separate bridge will be consolidated into the George Washington Memorial Parkway bridge as a separated bridge but constructed upon the Parkway bridge piers and abutments. The only additional significant change which affects recreation is the elimination of the levee in the vicinity of the Mt. Vernon Avenue bridge. The levee which would have required filling a portion of the adjacent marshland has been eliminated. The routing of the hiking-biking trail which used the levee as a base has there­ fore, been moved back from the marshland and the required filling significantly reduced. 7. Construction Sedimentation Control. A matter of concern that has been raised since the Supplement was filed is the potential for sedimentation of the Fourmile Run channel and Potomac River estuary downstream of the mouth of the stream. Control of sedimentation over the life of the project is subject to local control in the upper watershed and will be studied as a portion of local interest's land management process. However, regarding sedi­ mentation of the estuary at the mouth of Fourmile Run resulting from construction, the Corps will make pre-construction surveys of the area and any deposition of sediments as a result of construction will be removed. 8. Additional Terms of Local Cooperation. In addition to terms of local coordination involving cost sharing and maintenance responsibilities, the current legislation requires that appropriate non-Federal interests agree to: a. develop a land management planning process to insure that future development in the basin will not result in increased runoff which would impair the effectiveness of the flood control improvement; and; b. develop a land use management planning process which will insure that future development will not be permitted in flood prone areas unless suitable structural or non-structural flood control mea­ sures are first undertaken by non-Federal public or private interests at no expense to the Federal Government. II. ENVIRONMENTAL SETTING WITHOUT THE PROJECT Existing conditions in the project area have not changed significantly since the development and coordination of the Supplement to the En­ vironmental Statement. That document generated and presented data describing the existing and expected future conditions without the pro­ ject. The purpose of this document is to present an analysis and eval­ uation of the impacts and resulting effects of the described design modi­ fications. Therefore, new descriptive data has not been generated. Pertinent description of existing conditions may be found in the Supple­ ment. III. ENVIRONMENTAL IMPACT OF THE PROPOSED ACTION SHOULD THE PROJECT BE IMPLEMENTED A. General. The purpose of this section is to present an analysis and evaluation of the impacts of the described project changes upon the pertinent aes­ thetic, social, economic, physical and ecological conditions of the area. The following analysis of impacts will discuss each of the project changes and will cover the project area proceeding from the mouth of Fourmile Run upstream to Shirley Highway. B. Impacts of Specific Modifications 1. Mouth of Fourmile Run Upstream to Route 1. a. Change in Disposal Area. The only change in the plan for disposing of excavated material is a change in location of the spoil area for the toxic material to be dredged from underwater at the mouth of Fourmile Run. Instead of being placed in a diked disposal area on a 3. 6 acre portion of wetland of delta sediments at the mouth of Fourmile Run, the material will be placed on FAA property at National Airport. The National Airport site is a low swale which is presently used for location of landing signals and lights. The area is a dry land site and has been used previously as a spoil area. The channel bottom material will be mixed with dry bank excavation and placed in the spoil area. The area will then be graded and seeded. The impact upon the airport site will be beneficial in the sense that the area will be more useful and more attractive than at the present time. The impact upon the wetland will be beneficial in an ecological sense in that 3. 6 acres of wetland will not be disturbed. At the same time, however, the opportunity for use of the area for actual recreation will not be developed. Aesthetically, the area will remain as intermittantly inundated wetland with its characteristic vegetation and animal popu­ lation, rather than landscaped park land. b. Bridge Changes. The consolidation of the Potomac hiking-biking trail bridge into the Parkway supports, even though it will remain separate by function, will impact upon the user experience. Users of the trail will be closer in proximity to the noise, odor and visual effects of automobile traffic. Fr om a contrasting aesthetic view­ point, however, the stream will appear to have one less bridge crossing and therefore appear more natural. The connection of the Potomac trail with a Fourmile Run trail pass mg under the bridge complex and proceeding around the marsh to the upstream end of the project will be maintained. c. Slope Protection. The dimensions of the channel in this area, the reshaping of the banks, and the use of berms and landscaping remain unchanged. The slope protection, however, will become gabions rather than riprap except at the railroad bridges and U.S. Route 1 bridge. Aesthetically, it is expected that this will be an im­ provement. Although the material will still be rock, the dimensions of the stones will be smaller resulting in more compatable scale. In addition, stones in the top and outer layers of the gabion baskets will be hand placed, presenting a more pleasing appearance. It is also ex­ pected that low ground cover, grass and native vegetation, will naturally vegetate into the crevices making the side slopes more natural and attractive than would be the case with large riprap stones. Periodic maintenance will insure that large woody plant materials do not become established, but smaller plant material should soften the outlines of the slopes and make the channel more natural appearing. 2. Route 1 Bridge Complex Upstream to Mt. Vernon Avenue. a. Changes in Channel Bottom Width. The channel bottom width in this portion of the project is reduced by twenty-five feet. This will make the channel appear slightly narrower than was proposed in the earlier plan. Slightly more stream side land will remain. Some slight increase in overbank flooding will occur in this area under peak floods. Although the Pollution Control Plant grounds may have addi­ tional flooding, the plant will remain operable to the design flow. b. Slope Protection. The slope protection in this portion of the project will become a combination of gabions and grass slopes. Approximately 4430 feet of sideslope, more than half of the slopes, will be seeded. This includes the slopes along the right bank adjacent to the marshland and much of the left bank along the sewage treatment plant. The remainder will be gabion surfaced. The grass and gabion slopes will not only make the channel more visually natural but the grass slopes will preserve the edge of the marsh in its more char­ acteristic ecological state. Seeding of the slope along the marsh will be less destructive to the marsh during construction than placing gabions or riprap. c. Recreation. During the engineering design phase, (since the Supplement was filed), recreational development in the project has decreased slightly in scope and type. The trail system, which is the spine of the proposed recreation system, remains along with light­ ing, signing, fountains, picnic areas, open field space and associated landscaping. However, some auxilliary facilities such as play lots and play grounds, secondary foot paths, and weather shelters have been de­ leted. This will result in the recreation areas being slightly more passive in nature than under the previous plan. The trail system will be rerouted in the vicinity of the previous levee as discussed in the following para­ graph. d. Elimination of Levee. A modification from the plan des­ cribed in the Supplement is the elimination of 2, 250 linear feet of levee and the associated pumping station located in the vicinity of Mt. Vernon Avenue in Alexandria. Aesthetically, the elimination of the levee will preserve a more natural appearing river bank configuration, although the river bank use may appear more urban because the blockage of view of existing buildings by the levee will be eliminated. Deletion of the levee will however provide more area for landscaping, aesthetic treat­ ment and preservation of existing marshland. Much of the original levee was located in the marshland and no plants other than grass would have been allowed on the levee. The bicycle-hiking trail has been realigned in this section and a 100 foot distance has been maintained between the existing buildings and the path. Ecologically the levee's elimination will preserve natural drainage in the area and will preserve much more of the limited woody vegetation of the marshland than under the previous plan. From a land use standpoint, new construction in the area will be restricted below the 100 year flood elevation. Under the current plan without the levee a few apartments in the Bruce Street area in the vicinity of Mt. Vernon will not be provided 100 year protection and will have to be flood proofed to the 100-year level. 3. Mt. Vernon Avenue Upstream to Long Branch. a. Changes in Channel Bottom Width. The channel bottom width in this reach of the stream is reduced 50 feet from the earlier plan. However, the stream may not visually appear narrower in width or smaller in scale. The type of bank protection for most of this reach has been changed from vertical bank retaining wall to a gabion pro­ tected sideslope with a flood wall on the top of the bank. Therefore the top-of-bank to top-of-bank width remains essentially the same as under the earlier plan. b. Side Slopes. Aesthetically this change in side slopes will make the gabion protected slopes much more natural in appearance, especially if low vegetation succeeds on the slopes. However, much of the stream will be less visible because of the flood walls which will vary in this reach from two to four feet above the existing ground sur­ face. Regrading and landscaping measures for public use may amelio­ rate much of this effort. c. Long Branch Flood Wall. Under the previous plan, protection along Long Branch consisted of 100 linear feet of levee across a low swale in the vicinity of the east bank apartment complex. Under the existing plan, approximately 890 linear feet of flood wall will be required to an elevation of 24.0 msl. The wall is required because of insufficient space to construct a levee of the necessary dimensions between Long Branch and the previously mentioned apart­ ment complex. The wall may reduce the natural appearance of the small stream valley and the paralleling Long Branch Park, even though land­ scaping and aesthetic measures to fit the wall into the setting will be utilized. d. Recreation Plan. Under the previous plan, the trail along Fourmile Run was proposed to pass under the South Glebe bridge at Long Branch via a new bridge span and then tie into the pedestrian trail along Long Branch. Due to the side slopes required for the Fourmile Run channel at the mouth of Long Branch however, it is not feasible to ramp the trail connection down the slope and under the bridge. Any connection with the Long Branch trail will therefore, have to be on-grade across South Glebe Road. 4. Long Branch Upstream to West Glebe Road Bridge. a. Channel Width. The channel width has been reduced by 55 feet; the side slope protection changed from riprap to gabions. Therefore, this portion will be more natural in appearance. No struc­ tural changes are contemplated for the West Glebe Road bridge as pro­ posed under the previous plan. 5. West Glebe Road Upstream to Shirley Highway. a. Channel Width. Portions of this reach have been nar­ rowed by as much as 85 feet. While this means a less visible stream and the preservation of more land adjacent to the channel, it also reduces the proposed stream capacity. Although the presently existing wall will be raised 1 to 2 feet above existing ground levels, it is expected that under peak floods, water wrill leave the channel at this point, flow across West Glebe Road, down old South Glebe Road which is now a residential access road, and into Long Branch. This will mean slight flooding, i. e. less protection, of lower elevations in the residential area of Arna Valley on the north bank of Fourmile Run. Even though the area will have more protection than under existing conditions, as compared to the earlier proposed plan, the current plan will entail disruption to traffic and full use of the area during peak floods and clean-up and restoration in the overbank area following the peak floods, i. e. sixty year frequency and greater. b. Slope Protection. All of the sideslopes which arc not already retaining wall or presently ripraped will be surfaced with gabions with the resulting change in visual appearance. c. Channel Gradient. The gradient of the channel bottom in this reach will be increased to 0.00662 to grade the proposed channel back to existing grade. This is required due to the elimination of a planned drop structure. As a result, the stream will have naturally appearing bottom surface, but velocities in this section will be greater. Although the Supplement pointed out that low flows severely limit the value of any fishery resource in the non-tidal portion, the elimination of the drop structure eliminates an artificial channel barrier from the stream channel. 6. Watershed Management for the Basin. Throughout the environmental statement coordination process there has been much concern regarding the need for basin-wide planning of non-structural as well as structural solutions to flood problems result­ ing from the development trends in the basin. In response to the 4 June 1973 comments of the Environmental Protection Agency, the following discussion of the status of local comprehensive planning for flood control in effect at that time was presented. The four local jurisdictions in the Fourmile Run basin include the Cities of Alexandria and Falls Church, and Arlington and Fairfax Counties. Three of the four municipalities. Falls Church excluded, are actively participating in the National Flood Insurance Program, which requires them to adopt and enforce stringent flood plain management regulations. Falls Church is presently in the process of preparing a Flood Plains District Ordinance. Flood Plain Information Studies were prepared by the Baltimore District, Corps of Engineers, for the City of Alex­ andria and Arlington County, Fourmile Run, in October 1968. A Flood Insurance Study was prepared for the Federal Insurance Administration by the Baltimore District for Alexandria, Virginia, in 1970. The City of Alexandria and Arlington County, which bound on the project area, currently have flood plain zoning ordinances which apply to the 100-year flood plain. These ordinances prohibit construction of struc­ tures within the 100-year flood plain which would be subject to damage by a 100-year flood. They also require all additions to existing buildings be provided flood protection to the level of the 100-year flood. In addition, Alexandria and Arlington County have agreed to incor­ porate flood proofing of existing structures to the project 100-year design level into their land use planning for the project area.

Since* the completion and filing of the Supplement to the* Environmental Statement, representatives of the Corps <>f Engineers, the* Cities of Alexandria and Calls Church, and Counties of Arlington and Eairfax, the Northern Virginia Planning District Commission, and the Virginia State W ater Control Board have conforred on several < ' easie-ns con­ cerning current watershed management laws and practices and means of strengthening and expanding such efforts.

The efforts are concerned with land use planning as il relates to flood damage reduction. All four local jurisdictions have agreed to work with the Corps of Engineers to develop and implement a program to assure that the total land use development of each jurisdiction will not result in aggravating the flood producing character ist its of the basin.

Subsequent to and derived directly from these efforts, current authori­ zation has included additional terms of local cooperation which require development of such management programs. As a result, the* Northern Virginia Planning District Commission acting as agent for the four concerned political jurisdictions has initiated a study for tin* develop­ ment of a land management planning process which will be concerned with programs in water* quality, hydraulic and hydrologic work, runoff control, erosion control, flood control, and public involvement.

W’hile it is difficult to qualify the exact effect at this point in time, implementation of a land management planning process for the basin should have desirable long-term eeononiic, social and ecological con­ sequences. It is also impossible at this time to predict accurately what implementation procedures will be developed and the resulting environmental impacts whichthe implementation might cause.

Bv insuring that the* project docs not become less functional over time by development in the upstream watershed and by development on lands adjacent to the protection, the need for future structural solutions on Fourmile Kun may be avoided. Flood protection in the future will therefore become more a preventive technique than a reactive techni­ que. As stated in responses in the Supplement to the Environmental Statement, however, significant reductions in downstream flood stages by on-site retention of storm water runoff is generally limited to smaller floods and will have little reduction on the magnitude of the 100-year flood. Therefore, it is not considered feasible* to reduce the size of the proposed structural measures. IV. ADVERSE ENVIRONMENTAL EFFECTS WHICH CANNOT BE AVOIDED SHOuED~THE PROPOSAL BE IMPLEMENTED'----- A. General. Most of the modifications to the project under the current plan will result in beneficial impacts. This includes the impacts of structural changes such as the change in the downstream spoil disposal plan, the reduction in channel dimensions, the change of much of the side slope protection to gabion or grass surfaces, and the elimination of the levee and pumping station. It is also expected that non-structural changes, i. e. the development of land management programs, will result in long-term beneficial impacts. There are, however, certain impacts from project changes that are potentially adverse even though the scope of such potential adverse impacts may be relatively small. There are also certain changes which represent tradeoffs, i.e. the change displays both potential beneficial and adverse impacts. The following section elaborates on the potential adverse impacts and the potential tradeoff impacts. B. Aesthetics. The addition of flood walls in some reaches of the stream will reduce the naturalness of stream banks and the visibility of the stream from certain areas along the stream bank despite the inclusion of project measures aimed at integrating the walls into public use areas and archi­ tectural treatments for beautification and enhancement of the walls. Changing the downstream spoil area will represent a tradeoff in aes­ thetics. The area will remain a natural tidal area rather than a land­ scaped park area. Consolidation of the trail bridge adjacent to the GWMP bridge will visually reduce the number of separate bridge crossings of Fourmile Run, but will also slightly alter the recreational experience. C. Social. The alterations to the recreation plan will change the orientation of the public use by orienting the development more towards passive use than under the earlier plan. From a recreation standpoint, this re­ duces the degree and diversity of the user experience. From an eco­ logical standpoint, it may represent a beneficial impact to the degree that it reduces active public use and potentially damaging uses adjacent to the marshland. D. Economic. The minor overbank flooding which would have occurred under the earlier plan will increase slightly. To the degree that this is a constraint upon the use of the flooded area temporarily, it must be termed an adverse impact. It may represent temporary traffic constraints and open space constraints along the South Glebe Road in the Arna Valley vicinity during peak floods. It will also mean greater flooding of the grounds of the Water Pollution Control plant even though the plant will remain operable to the design flood. If this slight reduction in access is viewed as serious, it would be an adverse impact of the current plan. E. Physical. There are no significantly greater adverse impacts under the current plan than under the previous flood control plan. F. Ecological. Ecologically, the significant changes are beneficial rather than ad­ verse. Specifically regarding the marshland along Fourmile Run, some minor changes have occurred as a result of continuing engineering studies. Deletion of the remaining portions of levee and the associated pumping station near Mt. Vernon Avenue will allow the preservation of slightly more marshland (one acre approximately) than had been anticipated. Although the increase in size of marshland preserved is relatively small, it maintains essentially unaltered the higher eleva­ tions of the marshland, the natural tree edges, and the existing drainage patterns into the marshland. The trail system will be relocated from the levee to firm land along the periphery of the marshland. The 3. 6 acres of wetland at the mouth of Fourmile Run which was proposed to be used as a diked disposal area will remain as it is presently. V. THE RELATIONSHIP BETWEEN LOCAL SHORT-TERM USES OF MAN'S ENVIRONMENT AND THE MAINTENANCE AND ENHANCEMENT OF LONG-TERM PRODUCTIVITY Two issues concerning the relationship of short-term versus long-term uses of the environment are affected by the current modifications in the project. The following comments elaborate upon the continuing concern with these two issues. The Environmental Protection Agency and the Bureau of Sport Fisheries and Wildlife have both at various times expressed concern over the use of marshland in the project formulation. The concern of both agencies in regard to the 3. 6 acres of wetland at the mouth of Fourmile Run should be satisfied with the present plan to place the spoil material on a contained dryland site. Careful engineering speci­ fications should satisfy the remaining concern as to the minimization of the effects of the construction process. In response to EPA concern with the remaining effects of the project on the marshland along Four­ mile Run, it must be stated that the program for providing recreation, public use, and visual enhancement in conjunction with flood control in the Fourmile Run project was the result of close coordination with the local jurisdictions involved. In addition to an examination of the Alexandria and Arlington County Master Plans, local recreation sup­ ply and demand, and the role of the stream valley in the community, much consideration was given to the value of the marshland from an ecological and a public use standpoint. The purpose of the marshland filling is not solely to provide cheap recreation land; rather, the pur­ pose was to determine a land use plan which would provide opportunities for people to use the marshland as an educational and aesthetic re­ source, at the same time insure its preservation by institutionalizing its maintenance, and also ameliorate the effects of some demands that are already being placed on the edges of the marshland by public util­ ities, residential and recreational uses. The District is cognizant of the environmental impacts of the utilization of these lands and as engineering design continues for the subject project efforts to amelio­ rate these impacts will also continue. The second main issue concerns the desire that the structural flood control measures proposed by the Corps be incorporated into a com­ prehensive plan for managing urban storm water run-off that relates to other needs such as open space, erosion and sediment control and water quality. It is believed that a process (previously discussed) is well underway which can meet this concern.