"STORMWATER DRAINAGE FLOOD PLAIN MANUAL"
S T O R M W AT E R D R A I N A G E AND F LO O D P L A I N MANUAL SHORT TIT LE: “ D R A I N A G E M A N U A L” J U LY 1 1 , 2 0 0 7 CIT Y OF IRV ING D E PA R T M E N T O F P U B L I C W O R K S 8 2 5 W I R V I N G B LV D IRV ING TX (972) 721-2611 INDEX TO DRAINAGE MANUAL 1. Design Storm Frequency 2. Determination of Design Discharge a. The Rational Method b. Unit Hydrograph Method 3. Open Channels a. Hydraulic Design b. Water Surface Profiles 4. Closed Conduits a. Design b. Velocity c. Manhole Location d. Minor Head Losses At Structures 5. Bridges and Culverts a. Hydraulic Design of Bridges b. Hydraulic Design of Culverts c. Discharge Velocities in Culverts 6. Permissible Spread of Water 7. Inlets a. Recessed inlets, where used, shall not interfere with the sidewalk. b. Design of inlets shall take into consideration pedestrian and bicycle traffic. 8. Off-site Drainage 9. Floodplain Reclamation a. Residential Construction b. Nonresidential Construction c. Mobile Homes d. Floodways (1) Encroachments (2) Placement of mobile home (3) Encroachment within a floodway e. Standards for areas of shallow flooding (AO and AH Zones) (1) All new construction and substantial improvements of residential structures shall have the lowest floor, including basement, elevated above the crown of the nearest street to or above the depth number or base flood evaluation specified on the FIRM; or (2) All new construction and substantial improvements of non- residential structures shall: (a) Have the lowest floor, including basement, elevated above the crown of the nearest street or above the depth number specified on the FIRM; or (b) Together with attendant utility and sanitary facilities, be completely flood-proof to or above that level so that any space below that level is watertight, with walls substantially impermeable to the passage of water and with structural components have the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy. (c) Certification (i) Elevation, in relation to mean sea level, of the lowest floor (including basement) of all proposed structures; (ii) Elevation, in relation to mean sea level, to which any non- residential structure shall be flood-proof; (iii) A certificate from a registered professional engineer that the non-residential flood-proof structure shall meet the flood- proofing criteria of section 47-14(2) of the City Code; (iv) Description of the extent to which any watercourse or natural drainage will be altered or relocated as a result of proposed development. 10. Federal Emergency Management Agency 11. 404 Permits a. Section 10 of the Rivers and Harbors Act of 1899 (33 U.S.C. 403) b. Section 404 of the Clean Water Act (33 U.S.C. 1344) City of Irving Public Works/Engineering Drainage Design Manual 1. Design Storm Frequency The Storm Frequency period to be used in determining the size and capacity of drainage structures and elements is as follows: TABLE 1 DESIGN STORM FREQUENCY Type of Description of Maximum Time Recommended Facility Area to be Drained of Concentration Design Frequency (Minutes) (Years) Storm Sewers* Residential, Commercial and Manufacturing 30 25 Culverts, Bridges, Any type of area less Channels & Creeks* than 100 acres 30 25 Culverts, Bridges, Any type of area greater Channels & Creeks* than 100 acres but less than 640 acres 45 50 Culverts, Bridges, Any type of area greater Channels & Creeks* than 640 acres No Limit 100 * When the maximum time of concentration of area to be drained is exceeded, the design shall be based on a 100 year frequency. 12. Determination of Design Discharge The Rational Method for computing storm water runoff is to be used for hydraulic design of facilities serving a drainage area of less than 300 acres. For drainage areas of more than 300 acres and less than 640 acres, the runoff shall be calculated by both the Rational Method and the Unit Hydrograph Method with the larger of the two values being used for hydraulic design. For drainage areas larger than 640 acres, the runoff shall be calculated by the Unit Hydrograph Method. July 11, 2007 Public Works / Engineering Page 4 of 24 Drainage Manual The Rational Method The Rational Method is an analysis of the runoff quantity for each individual drainage area along rational lines and includes the analysis of the flow of storm water runoff from the surface of the drainage area on which it falls to the receiving inlet which leads to the storm sewer system and then through the storm sewer system, culvert or channel to the point of disposal. As is the case in most empirical formulae, the accuracy of the calculations is dependent upon the values selected for the factors in the equation, and the manner in which the equation is applied. The total drainage area must be accurately determined. The runoff coefficient which is selected must reflect careful consideration of presently existing conditions as well as conditions which will exist after the drainage area is fully developed in a manner indicated by present zoning as well as foreseeable future changes in land use. The most demanding coefficient must then be applied in the formula. The intensity of rainfall must be based upon a time of concentration which is determined from consideration of the distance of runoff and the runoff velocity attained on the degree of slope of the runoff path. The basic equation of the rational method of runoff determination is: Q=CIA In which: Q = The quantity of water arriving at a given point measured in cubic feet per second (cfs). It is customary to use a subscript with the value Q to designate the frequency period for which it is calculated. For example Q50 indicates the quantity of water for a 50-year frequency rainfall. C = The runoff coefficient, or percentage of rainfall in an area which is not absorbed and which must be carried away, expressed as a decimal fraction. I= The intensity of rainfall for the selected period of time and frequency of return or recurrence in years as shown on the attached curve which complies with data published by the Weather Bureau, U.S. Department of Commerce on Technical Paper No. 25 (see Figure 1). Determination of the average runoff velocity for use in determining time of concentration shall be as follows: Public Works / Engineering July 11, 2007 Drainage Manual Page 5 of 24 Figure 1 July 11, 2007 Public Works / Engineering Page 6 of 24 Drainage Manual TABLE 2 AVERAGE RUNOFF VELOCITY Slope in Percent Description of ______________________(ft/sec)_______________________ Water Course 0-3% 4-7% 8-11% 12-15% Surface Drainage 5 ft/sec 10 ft/sec 14 ft/sec 16 ft/sec Channels Determine Velocity by Manning Formula Storm Sewer Determine Velocity by Manning Formula* * Manning Formula V = 1.486 R2/3 S1/2 n The average velocities shown in this table shall be used unless the designer submits calculations indicating that other velocities are appropriate for use in the area under study. By using the average velocity of runoff the calculation for time of concentration in minutes (T) shall be as follows: T = Inlet Time + ___L___ (V)(60) where L = Distance in feet from point of concentration to upper end of drainage system. V = Velocity in feet per second. Inlet Time = As indicated herein for various descriptions of areas. A = The area covered by the rainfall and which must be handled by the system under design, expressed in acres. This determination must include consideration of the present drainage divides as well as any future change in drainage divide resulting from planned street and area grading. An accurate map showing the drainage area shall be submitted as an integral part of any drainage plan. The values for runoff coefficient "C" and for the period of time for runoff to reach the first inlet of the drainage system (Inlet Time) based upon zoning and/or existing land use are as follows: Public Works / Engineering July 11, 2007 Drainage Manual Page 7 of 24 TABLE 3 RUNOFF COEFFICIENT AND INLET TIME Description of _______Range Coefficient "C"_____ Inlet Time Area Range Recommended (Minutes) Commercial, Shopping Centers 0.70-0.90 0.80 5 Parking Areas, Downtown Business, Paving Industrial, Manufacturing and 0.40-0.70 0.70 5 Warehouses - New Heavy Areas Industrial, Manufacturing and 0.40-0.70 0.70 10 Warehouses - New Light Areas Apartments 0.60-0.90 0.80 10 Duplexes 0.60-0.90 0.70 15 Residential R – 40 0.40-0.60 0.40 15 R – 15 0.40-0.60 0.45 10 R – 10 0.40-0.60 0.45 10 R - 7.5 0.40-0.60 0.50 10 R–6 0.40-0.60 0.50 5 R - 3.5, 2.5 0.40-0.60 0.60 5 Schools 0. 20-0.50 0.60 15 Parks 0.20-0.50 0.40 20 13. Open Channels In all instances, save and except where the width and/or size of the drainage channel renders it uneconomical and/or impractical as determined by the City Council, it is the policy of the City to have improved all drainage channels by owner installation of reinforced concrete pipe (RCP) or concrete lining. The final decision as to the size and/or type of channel improvements shall reside with the City Council. July 11, 2007 Public Works / Engineering Page 8 of 24 Drainage Manual c. Hydraulic Design The design water surface in an open channel is to be located a minimum of one foot below the top of the channel section to provide a margin of safety for channel obstructions and for flows which exceed the design storm frequency. Special care must be taken at entrances to closed conduits and culverts to provide for the headwater requirements. d. Water Surface Profiles Open channel flow in urban drainage systems is usually non-uniform because of bridge openings, curves and structures. This necessitates the use of backwater computations for all final channel design work. A surface water profile must be computed for all channels and shown on all final drawings. Computation of the water surface profile should utilize standard backwater methods or acceptable computer routines, taking into consideration all losses due to changes in velocity, drops, bridge openings and other obstructions. 14. Closed Conduits All storm drains shall be designed by the application of the continuity equation and Manning’s Equation either through the appropriate charts and nomographs or by direct solutions of the equations as follows: Q = AV, and Q = 1.486 AR2/3 Sf1/2 n Q = Pipe Flow (cfs) A = Cross sectional area of pipe (ft2) V = Velocity of flow (fps) n = Coefficient of roughness of pipe R = Hydraulic radius = A/W p (ft) Sf = Friction slope in pipe (ft/ft) W p = Wetted perimeter (ft) Public Works / Engineering July 11, 2007 Drainage Manual Page 9 of 24 There are several general rules to be observed when designing storm sewer runs. When followed, they will tend to alleviate or eliminate the common mistakes made in storm sewer design. These rules are as follows: • Select pipe size and slope so that the velocity of flow will increase progressively, or at least will not appreciably decrease, at inlets, bends or other changes in geometry or configuration. • Do not discharge the contents of a larger pipe into a smaller one, even though the capacity of the smaller pipe may be greater due to steeper slope. • At changes in pipe size, match the soffits of the two pipes at the same level rather than matching the flow lines. • Conduits are to be checked at the time of their design with reference to critical slope. If the slope of the line is greater than critical slope, the unit will likely be operating under entrance control instead of the originally assumed normal flow. • Conduit slope should be kept below critical slope if at all possible. This also removes the possibility of a hydraulic jump within the line. e. Design In the preliminary design, calculations made to select the pipe or channel size after the design flow is determined are based on calculating the approximate average velocity by use of Manning's Formula. This is a widely used formula that has been found to be reliable for designs of this nature. In order to apply this formula, however, it is necessary to take into consideration the roughness of the water carrying surfaces by the selection of an appropriate coefficient. Roughness coefficients used in the design are given as shown in Table 4. f. Velocity Storm sewers should operate within certain velocity limits to prevent excessive depositing of solids due to low velocities and to prevent invert erosion and undesirable outlet conditions due to excessively high velocity. A minimum velocity of 2.5 feet per second and a maximum velocity of 12 feet per second at the outfall shall be observed. g. Manhole Location Manholes shall be located at points where design indicates entrance into the conduit is desirable; however, in no case shall the distance between openings or entrances be greater than 1,200 feet. July 11, 2007 Public Works / Engineering Page 10 of 24 Drainage Manual TABLE 4 ROUGHNESS COEFFICIENTS Materials of Construction Concrete Pipe ...........................................................................0.013 Monolithic Concrete Structure...................................................0.015 Concrete Lining.........................................................................0.015 Earth Channel...........................................................................0.030 h. Minor Head Losses At Structures The following total energy head losses at structures shall be determined for inlets, manholes, wye branches or bends in the design of closed circuits. See Figures 2 and 3 for details of each case. Minimum head loss used at any structure shall be 0.10 foot, unless otherwise approved. The basic equation for most cases, where there is both upstream and downstream velocity, takes the form as set forth below with the various conditions of the coefficient Kj shown in Tables 5, 6 and 7. h= v22 - Kj v12 2g hj = Junction or structure head loss in feet. vI = Velocity in upstream pipe in fps. v2 = Velocity in downstream pipe in fps. Ki = Junction or structure coefficient of loss. Public Works / Engineering July 11, 2007 Drainage Manual Page 11 of 24 Figure 2 July 11, 2007 Public Works / Engineering Page 12 of 24 Drainage Manual Figure 3 Public Works / Engineering July 11, 2007 Drainage Manual Page 13 of 24 TABLE 5 JUNCTION OR STRUCTURE COEFFICIENT OF LOSS Case Reference Coefficient No. Figure Description of Condition Ki I 2 Inlet on Main Line* 0.50 II 2 Inlet on Main Line with Branch Lateral* 0.25 III 2 Manhole on Main Line with 45º 0. 50 Branch Lateral IV 2 Manhole on Main Line with 90º 0.25 Branch Lateral V 3 45º Wye Connection or Cut-in 0.75 VI 3 Inlet or Manhole at Beginning of Line 1.25 VII 3 Conduit on Curves for 90º** Curve Radius = Diameter 0.50 Curve Radius = (2 to 8) Diameter 0.40 Curve Radius = (8 to 20) Diameter 0.25 VIII 3 Bends Where Radius is Equal to Diameter 90º Bend 0.50 60º Bend 0.43 45º Bend 0.35 22½º Bend 0.20 Manhole on Line with 60º Lateral 0.35 Manhole on Line with 22½º Lateral 0.75 * Must be approved by Director of Engineering. ** Where bends other than 90º are used, the 90º bend coefficient can be used with the following percentage factor applied: 60º Bend – 85%; 45º Bend - 70%; 22½º Bend – 40%. In the case where the initial velocity is negligible, the equation for head loss becomes: hj = v22 2g July 11, 2007 Public Works / Engineering Page 14 of 24 Drainage Manual Short radius bends may be used on 24" and larger pipes when flow must undergo a direction change at a junction or bend. Reductions in head loss at manholes may be realized in this way. A manhole shall always be located at the end of such short radius bends. The values of the coefficient "Kj" for determining the loss of head due to obstructions in pipes are shown in Table 6 and the coefficients are used in the following equation to calculate the head loss at the obstruction: hj = Kj v22 2g TABLE 6 HEAD LOSS COEFFICIENTS DUE TO OBSTRUCTIONS A* Kj A* Kj A A 1.05 0.10 3.0 15.0 1.1 0.21 4.0 27.3 1.2 0.50 5.0 42.0 1.4 1.15 6.0 57.0 1.6 2.40 7.0 72.5 1.8 4.00 8.0 88.0 2.0 5.55 9.0 104.0 2.2 7.05 10.0 121.0 2.5 9.70 * A = Ratio of area of pipe to area of opening at obstruction. A The values of the coefficient "Kj" for determining the loss of head due to sudden enlargements and sudden contractions in pipes are shown in Table 7 and the coefficients are used in the following equation to calculate the head loss at the change in section: Hj = Kj v2 where v = velocity in smaller pipe 2g Public Works / Engineering July 11, 2007 Drainage Manual Page 15 of 24 TABLE 7 HEAD LOSS COEFFICIENTS DUE TO SUDDEN ENLARGEMENTS AND CONTRACTIONS D2 Sudden Enlargements Sudden Contractions D1 Kj Kj 1.2 0.10 0.08 1.4 0.23 0.18 1.6 0.35 0.25 1.8 0.44 0.33 2.0 0.52 0.36 2.5 0.65 0.40 3.0 0.72 0.42 4.0 0.80 0.44 5.0 0.84 0.45 10.0 0.89 0.46 >10.0 0.91 0.47 D2 = Ratio of larger to smaller diameter. D1 15. Bridges and Culverts d. Hydraulic Design of Bridges Wherever possible, the proposed bridge should be designed to span a channel section equal to the approaching channel section. If a reduction in channel section is desired, this should be accomplished upstream of the bridge and appropriate adjustments made in the hydraulic gradient. A distance of 2 feet between the maximum design water surface and the lowest point of the bridge stringers should be maintained, based on Irving's criteria. The quantity of flow which the structure must convey shall be calculated in accordance with the Procedure for Determination of Design Discharge. July 11, 2007 Public Works / Engineering Page 16 of 24 Drainage Manual e. Hydraulic Design of Culverts The function of a culvert or bridge is to pass storm water from the upstream side of a roadway to the downstream side without submerging the roadway or causing excessive backwater which floods upstream property. The Engineer shall keep head losses and velocities within reasonable limits while selecting the most economical structure. In general, this means selecting a structure which creates a headwater condition and has a maximum velocity of flow safely below the allowed maximum. The vertical distance between the upstream design water surface and the roadway elevation should be maintained to provide a safety factor to protect against unusual clogging of the culvert and to provide a margin for future modifications in surrounding physical conditions. In general, a minimum of two feet shall be considered reasonable when the structure is designed to pass a design storm frequency of 100 years calculated by Irving's criteria. Unusual surrounding physical conditions may be cause for an increase in this requirement. f. Discharge Velocities in Culverts Velocities in culverts should be limited to no more than 15 feet per second, but downstream conditions very likely will impose more stringent controls. Consideration must be given to the effect of high velocities and turbulence on the channel, adjoining property and embankment. Table 8 is a tabulation of maximum allowable velocities based on downstream channel conditions. The velocity of discharge from culverts should be limited as shown in Table 8. Consideration must be given to the effect of high velocities, eddies or other turbulence on the natural channel, downstream property and roadway embankment. TABLE 8 CULVERT DISCHARGE - VELOCITY LIMITATIONS Maximum Allowable Downstream Condition Discharge Velocity Earth ......................................................................... 6 fps Sod Earth .................................................................. 8 fps Shale....................................................................... 10 fps Paved or Riprap Apron............................................ 15 fps Rock........................................................................ 15 fps Public Works / Engineering July 11, 2007 Drainage Manual Page 17 of 24 16. Permissible Spread of Water The location of inlets and permissible flow of water in the street should be related to the extent and frequency of interference to traffic and the likelihood of flood damage to surrounding property. Interference to traffic is regulated by design limits on the spread of water into traffic lanes, especially in regard to arterials. The term spread of water as used in these design criteria refers to the amount of water that is allowed to collect in streets during the design storm with a 25-year frequency. The collection of storm water has been limited to the following: • Expressway - Eight feet (8') from face of curb • Major Thoroughfares (Divided) - One traffic lane on each side to remain clear • Secondary Thoroughfare (Not Divided) - Five inch (5”) depth of flow at curb • Secondary (Divided) - Five inch (5") depth of flow at curb • Residential - 36' FF five inch (5") depth of flow at curb • Residential - 30' FF five inch (5") depth of flow at curb 17. Inlets If, in the opinion of the Engineer, the flow in the gutter would be excessive under the conditions listed above, then consideration should be given to extending the storm sewer to a point where the gutter flow can be intercepted by more reasonable inlet locations. The primary purpose of storm drain inlets is to intercept excess surface runoff and deposit it in a drainage system, thereby reducing the possibility of surface flooding. The most common location for inlets (Figure 4) is in streets which collect and channelize surface flow, making it convenient to intercept. Because the primary purpose of a street is to carry vehicular traffic, inlets must be designed so as not to conflict with that purpose. July 11, 2007 Public Works / Engineering Page 18 of 24 Drainage Manual Figure 4 Public Works / Engineering July 11, 2007 Drainage Manual Page 19 of 24 The following guidelines shall be used in the design of inlets to be located in streets: c. When recessed inlets are used, they shall not interfere with the intended use of the sidewalk. d. Design and location of inlets shall take into consideration pedestrian and bicycle traffic. 18. Off-site Drainage In accordance with Irving City Code, under certain circumstances, the City will participate in the expense of storm sewer improvements designed for drainage originating off-site. 19. Floodplain Reclamation The City of Irving has adopted as part of its City Code, The Flood Insurance Study for the City of Irving, Dallas County, Texas, with accompanying Flood Insurance Rate Maps (FIRM) and Flood Boundary and Floodway Maps (FBFM) and any revisions thereof, as a basis for establishing the areas of special flood hazard. Within these areas of special flood hazard, the following provisions are required: f. Residential Construction New construction of any residential structure shall have the lowest floor, including basement, elevated to at least two feet (2’) above the base flood elevation. A registered professional engineer shall submit a certification to the director of public works that the standard of this subsection is satisfied. Further, once the above requirement has been met, the floor slab elevation of all new residential structures shall be no lower than the top of the street curb of the street on which the structure is located. g. Nonresidential Construction New construction of any commercial, industrial or other non-residential structure shall have the lowest floor, including basement, elevated to at least two feet (2’) above the level of the base flood elevation. A registered engineer shall submit a certification to the Director of Public Works that the standards of this subsection are satisfied. July 11, 2007 Public Works / Engineering Page 20 of 24 Drainage Manual h. Mobile Homes Other special and more detailed provisions apply to mobile homes and mobile home parks. These provisions are described in detail in the Irving City Code. i. Floodways Located within Special Flood Hazard Areas (SFHA) are zones designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of floodwaters which carry debris and potential projectiles and has a higher degree of erosion potential, the following provisions apply: (4) Encroachments, including fill, new construction, substantial improvements and other developments are prohibited if such encroachments will cumulatively increase the surface water elevation by more than one foot within the channel of a river or other watercourse and the adjacent land areas that must be re- served in order to discharge the base flood. (5) All new construction and substantial improvements permitted by this subsection shall comply with all applicable flood hazard reduction provisions of Section 47-14 of the Civil Code. (6) The placement of any mobile home, except in an existing mobile home park or subdivision, is prohibited. (7) A person proposing an encroachment within an area designated as a floodway shall provide to the Director of Public Works sufficient data, certified by a registered professional engineer, to establish that the proposed encroachment, together with a comparable encroachment, does not exist but is plausible, is not prohibited by paragraph (a) above and will not increase flooding or divert waters in such a way that any person's life or property will be endangered or subject to significant increased flooding. j. Standards for areas of shallow flooding (AO and AH Zones) Within the areas of shallow flooding, the following provisions apply: (3) All new construction and substantial improvements of residential structures shall have the lowest floor, including basement, elevated above the crown of the nearest street to or above the depth number or base flood evaluation specified on the FIRM; or (4) All new construction and substantial improvements of non- residential structures shall: Public Works / Engineering July 11, 2007 Drainage Manual Page 21 of 24 (d) Have the lowest floor, including basement, elevated above the crown of the nearest street or above the depth number specified on the FIRM; or (e) Together with attendant utility and sanitary facilities, be completely flood-proof to or above that level so that any space below that level is watertight, with walls substantially impermeable to the passage of water and with structural components have the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy. (5) A registered professional engineer shall submit a certification to the Director of Public Works that the standards of this section are satisfied. A plat is required to assure conformance with the provisions of the procedures for filling in a flood plain or floodway. This plat is issued by the Director of Public Works and must be obtained prior to the issuance of any building permit on property located in a special flood hazard area. Application for a plat shall be presented to the Director of Public Works on forms furnished by him, which forms may include, but not be limited to, plans in duplicate, drawn to scale, showing the location, dimensions and elevation of existing and proposed structures, and the location of the foregoing in relation to areas of special flood hazard. Additionally, the following information is required: 2. Elevation, in relation to mean sea level, of the lowest floor (including basement) of all proposed structures; 3. Elevation, in relation to mean sea level, to which any non- residential structure shall be flood-proof; 4. A certificate from a registered professional engineer that the non-residential flood-proof structure shall meet the flood- proofing criteria of section 47-14(2) of the City Code; 5. Description of the extent to which any watercourse or natural drainage will be altered or relocated as a result of proposed development. 20. Federal Emergency Management Agency The National Flood Insurance Program makes flood insurance available to property owners in communities that adopt and enforce flood plain management measures to reduce future flood losses. The Program provides flood hazard July 11, 2007 Public Works / Engineering Page 22 of 24 Drainage Manual maps (called “Flood Insurance Rate Maps, or FIRMs) and certain risk information upon which the communities base their local flood plain management program. One aspect of a sound flood plain management program is the maintenance of a floodway or channel, so as to assure that the elevations of future floods will not be increased significantly. The creation of a defined floodway preserves the conveyance cross-sectional area that is necessary for passage of floodwaters. By restricting certain actions, like filling the floodway, which would result in an increase in flood elevation, the impact of development is lessened. After a floodway is adopted, a community may encounter a compelling need to change the configuration of their floodway and therefore request a revision of the floodway map prepared by the Federal Emergency Management Agency (FEMA). There is no procedure whereby a floodway designation may be appealed by individuals at FEMA, since it is the community that selects and adopts the regulatory floodway. Thus, an individual should contact the community (the City of Irving) to appeal the floodway designation or seek amendments of the floodway maps. The community, in turn, may support the amendment request and forward the application to FEMA for revision of the FIRM. FEMA will review the request to ascertain that certain conditions are met before expending effort on the revision. It is recognized that while the floodway is adopted by a community, users of the Flood Insurance Study and FIRMs other than the community may request copies of the flood delineations. Therefore, in support of the community and other users, FEMA maintains a system for distributing floodway information and revision delineations as the need arises. When the revision is considered to be significant, FEMA will revise floodway maps and distribute them to recognized users. Significant floodway revisions are identified based on the size of area, as well as the number of interests affected by the revision. Public Works / Engineering July 11, 2007 Drainage Manual Page 23 of 24 21. 404 Permits The U.S. Army Corps of Engineers (Corps) has been regulating activities in the nation's waters since 1890. Until the 1960's, the primary purpose of the regulatory program was to protect navigation. Since then, as a result of laws and court decisions, the program has been broadened so that it now considers the full public interest for both the protection and utilization of water resources. The regulatory authorities and responsibilities of the Corps are based on the following laws: c. Section 10 of the Rivers and Harbors Act of 1899 (33 U.S.C. 403) prohibits the obstruction or alteration of navigable waters of the United States without a permit from the Corps. d. Section 404 of the Clean Water Act (33 U.S.C. 1344) prohibits the discharge of dredged or fill material into waters of the United States without a permit from the Corps. Laws that govern the Corps regulatory activities have been passed such that wetlands are now defined as waters of the United States. Wetlands are areas that are periodically or permanently inundated by surface or ground water and support vegetation adapted for life in saturated soil. Wetlands include swamps, marshes, bogs and similar areas. A significant natural resource, wetlands serve important functions relating to fish and wildlife, food chain production, habitat, nesting, spawning, rearing and resting sites for aquatic and land species, protection of other areas from wave action and erosion, storage areas for storm and flood waters, natural recharge areas where ground and surface water are interconnected, and natural water filtration and purification functions. Although individual alterations of wetlands may constitute a minor change, the cumulative effect of numerous changes often results in major damage to wetland resources. The review of applications for alteration of wetlands will include consideration of whether the proposed activity is dependent upon being located in an aquatic environment. If property that is being considered for development contains areas to be altered in the course of development that may be classified as wetlands, the Corps should be contacted to determine the extent of their jurisdiction and the possible need for obtaining a Section 404 Permit. July 11, 2007 Public Works / Engineering Page 24 of 24 Drainage Manual