pond - usdaefotg.sc.egov.usda.gov/references/public/mw/md378_00.pdf · 2002. 7. 17. · peak breach...

Pond MD-378-1

NRCS - MARYLAND JANUARY 2000

USDANATURAL RESOURCES

CONSERVATION SERVICEMARYLAND

CONSERVATION PRACTICESTANDARD

POND

CODE 378(Reported in No.)

DEFINITION

A water impoundment made by constructing adam or an embankment or by excavating a pitor dugout.

In this standard, ponds constructed by the firstmethod are referred to as embankment ponds,and those constructed by the second methodare referred to as excavated ponds. Pondsconstructed by both excavation and the em-bankment methods are classified as embank-ment ponds if the depth of water impoundedagainst the embankment at the principal spill-way storm design high water elevation is 3feet or more (See Table 1).

This 3 feet shall be measured from the lowpoint on the upstream toe of the embankmentto the design high water.

PURPOSE

To provide water for livestock, fish and wild-life, recreation, fire control, crop and orchardspraying, and other related uses, and to main-tain or improve water quality. This standardalso applies to stormwater managementponds.

CONDITIONS WHERE PRACTICEAPPLIES

General - This practice applies where it is

determined that stormwater management,water supply, or temporary storage is justifiedand it is feasible and practicable to build apond which will meet local and state law re-quirements.

This standard establishes the minimum ac-ceptable quality for the design and construc-tion of ponds if:

1. Failure of the dam will not result in loss oflife; in damage to homes, commercial orindustrial buildings, main highways, orrailroads; or interruption of the use orservice of public utilities.

2. The product of the storage times the ef-fective height of the dam is less than3,000. Storage is the volume, in acre-feet,in the reservoir below the elevation of thecrest of the emergency spillway.

The effective height of the dam is the dif-ference in elevation, in feet, between theemergency spillway crest and the lowestpoint on a profile taken along the center-line of the dam, excluding the cutofftrench. If there is no emergency spillway,the top of the dam becomes the upperlimit for determining the storage and theeffective height.

3. For dams in rural areas, the effectiveheight of the dam (as defined above) is 35feet or less and the dam is hazard class”a”. For dams in urban areas, the effec-tive height of the dam is 20 feet or lessand the dam is hazard class ”a”.

Ponds exceeding any of the above conditionsshall be designed and constructed accordingto the requirements of Technical Release 60.

Exemptions - Soil Conservation District smallpond approval is not required for small class“a” structures where the following exists:

1. Ponds or other structures have less thanfour (4) feet of embankment, or

2. The storage at emergency spillway design

Conservation practice standards are reviewed periodically, and updated if needed. To obtain the current version of this standard,contact the Natural Resources Conservation Service

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high water elevation according to Table 1does not exceed 40,000 cubic feet, and theheight of the embankment is 6 feet or less.

The height of the embankment shall be meas-ured from the top of the dam to the lowestpoint of excavation, excluding the cutofftrench, along the centerline of the dam.

In addition, an embankment pond that meetsthe criteria below shall be considered an exca-vated pond and is also exempt from smallpond approval.

1. The calculation of 10H+20=L, whereH=height from the pond bottom to the topof the dam, is provided, and

2. The projection of L horizontally down-stream from the pond bottom is below theexisting or proposed ground, and

3. The existing or proposed downstreamground slope within the projection of L isless than 10% at any point.

The review and design of such class “a”structures shall be based on sound engineeringjudgment assuring a stable outfall for the ten(10) year, 24-hour storm event.

Site Conditions - Site Conditions shall besuch that runoff from the design storm can besafely passed through (1) a natural or con-structed emergency spillway, (2) a combina-tion of a principal spillway and an emergencyspillway, or (3) a principal spillway.

Drainage Area - The drainage area above thepond must be protected against erosion to theextent that expected sedimentation will notshorten the planned effective life of the struc-ture.

For ponds whose primary purpose is to trapsediment for water quality, adequate storageshould be provided to trap the projectedsediment delivery from the drainage area forthe life of the pond.

If the intent is to maintain a permanent pool,the drainage area should be at least 4 acres foreach acre-foot of permanent storage. Theserecommendations may be reduced if a de-

pendable source of ground water or divertedsurface water contributes to the pond. Thewater quality shall be suitable for its intendeduse.

Soils Investigation - A soils investigation isrequired on all ponds. As a minimum it shallinclude information along the centerline of theproposed dam, in the emergency spillway lo-cation, and the planned borrow area. Thetype of equipment used and the extent of theinvestigation will vary from site to site. Allinvestigations shall be logged using the Uni-fied Soil Classification System.

Road Embankments - Where road embank-ments are being designed to impound a spe-cific volume of water, either as a permanentpool or temporary stormwater storage, specialdesign and evaluation criteria may be requiredas determined by Appendix B.

CONSIDERATIONS

Water Quantity - The following items shouldbe considered for water quantity:

1. Effects upon components of the waterbudget, especially effects on volumes andrates of runoff, infiltration, evaporation,transpiration, deep percolation, andground water recharge.

2. Variability of effects caused by seasonal orclimatic changes.

3. Effects on the downstream flows or aqui-fers that could affect other water uses orusers.

4. Potential for multiple use.

5. Effects on the volume of downstream flowto prohibit undesirable environmental, so-cial or economic effects.

Water Quality - The following items shouldbe considered for water quality:

1. Effects on erosion and the movement ofsediment, pathogens, and soluble andsediment attached substances that are car-ried by runoff.

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2. Effects on the visual quality of on-site anddownstream water resources.

3. Short-term and construction-related ef-fects of this practice on the quality ofdownstream water courses.

4. Effects of water level control on the tem-peratures of downstream waters to pre-vent undesired effects on aquatic andwildlife communities.

5. Effects on wetlands and water-relatedwildlife habitats.

6. Effects of water levels on soil nutrientprocesses such as plant nitrogen use ordenitrification.

7. Effects of soil water level control on thesoil chemistry, soil water, or downstreamwater.

8. Potential for earth moving to uncover orredistribute sulfidic bearing soils.

CRITERIA

Embankment Ponds

Structure Hazard Classification - Docu-mentation of the classification of dams is re-quired. Documentation is to include but is notlimited to location and description of dam,configuration of the valley, description of ex-isting development (houses, utilities, high-ways, railroads, farm or commercial buildings,and other pertinent improvements), potentialfor future development, and recommendedclassification. It is also to include results ob-tained from breach routings, if breach routingsare used as part of the classification process.The class (“a”, “b”, and “c”) as contained inthis document is related to the potential haz-ard to life and property that might result froma sudden major breach of the earth embank-ment. Structure classification and land use forrunoff determination must take into consid-eration the anticipated changes in land usethroughout the expected life of the structure.The classification of a dam is the responsibilityof the designer, and subject to review andconcurrence of the approving authority.

The classification of a dam is determined onlyby the potential hazard from failure, not by thecriteria. Classification factors in the NationalEngineering Manual, as supplemented, aregiven below:

Class “a” - Structures located in rural, ag-ricultural or urban areas dedicated to re-main in flood tolerant usage where failuremay damage non-inhabited buildings, agri-cultural land, floodplains or county roads.

Class “b” - Structures located in rural, ag-ricultural, or urban areas where failuremay damage isolated homes, main high-ways or minor railroads or cause interrup-tion of use or service of relatively impor-tant public utilities.

Class “c” - Structures located where fail-ure may cause loss of life or serious dam-age to homes, industrial and commercialbuildings, important public utilities, mainhighways, or railroads.

“Rural areas” is defined as those areas inwhich residents live on farms, in unincorpo-rated settlements, or in incorporated villagesor small towns. It is where agriculture, in-cluding woodland activities, and extractiveindustries, including seafood harvesting, pro-vides the primary employment base for resi-dents and where such enterprises are depend-ent on local residents for labor.

Non-rural areas shall be classified as urban.

Peak Breach Discharge Criteria - Breachroutings are used to help delineate the areapotentially impacted by inundation should adam fail and can be used to aid dam classifi-cation. The breach hydrograph is the outflowhydrograph attributed to the sudden release ofwater in reservoir storage. This is due to adam breach during non-storm conditions.

Stream routings made of the breach hydrog-raph are to be based upon topographic dataand hydraulic methodologies mutually con-sistent in their accuracy and commensuratewith the risk being evaluated.

The minimum peak discharge of the breachhydrograph, regardless of the techniques used

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to analyze the downstream inundation area, isas follows:

Qmax = 3.2 Hw2.5 where,

Qmax = the peak breach discharge, cfs.

Hw = depth of water at the dam at the timeof failure, feet. This is meas-ured to the crest of the emer-gency spillway or to designhigh water, if no emergencyspillway exists. Use “non-storm” conditions downstreamof the dam.

Where breach analysis has indicated that onlyovertopping of downstream roads will occur,the following guidelines will be used:

Class Depth of Flow(d) ft.

“a” d<1.5“b” & “c” d>1.5

Use and importance of the roadway shall beconsidered when making a classification.

Hydrology - Principal and emergency spill-ways will be designed within the limitationsshown on TABLE 1. The storm durationused shall be 24 hours except where TR-60 isspecified. The pond shall be designed tosafely pass the base flow along with volumeand peak rates of runoff from design storms,specified in Table 1. All storm water man-agement ponds shall be designed using urbancriteria. This can be done by using principaland emergency spillways. The following shallbe used to determine runoff rates and vol-umes:

1. NRCS “Engineering Field Handbook, Part650” or;

2. NRCS, NEH, Section 4, Hydrology” or;

3. NRCS, TR-55, “Urban Hydrology forSmall Watersheds” or;

4. NRCS, TR-20, “Computer Program forProject Formulation” or,

5. Computer programs using NRCS hydrol-ogy methods with identifiable inputs andoutputs as approved by the reviewingagency.

Earth Embankment

Top Width - The minimum top width of thedam is shown in Table 2. When the embank-ment top is to be used as a public road, theminimum width is to be 16 feet for one-wayand 26 feet for two-way traffic. If the em-bankment is to be used for infrequent vehiclecrossings, the minimum top width shall be 10feet. Guardrails or other safety measures areto be used where necessary and are to meetthe requirements of the responsible roadauthority.

Side Slopes - The combined upstream anddownstream side slopes of the settled em-bankment shall not be less than five horizontalto one vertical (5:1) with neither slope steeperthan 2:1. If the dam is used as a road crossingwith a top width greater than 26 feet, then thecombined side slopes of the settled embank-ment shall not be less than 4 horizontal to onevertical (4:1) with neither slope steeper than2:1. Slopes must be designed to be stable inall cases, even if flatter side slopes are re-quired.

Earth Cuts - If cuts in an existing fill or innatural ground are required for the rehabilita-tion of an existing pond spillway or the con-struction of a new pond, the slope of thebonding surfaces between the existing mate-rial in place and the fill to be placed shall notbe steeper than a ratio of two horizontal toone vertical (2:1).

Foundation Cutoff - A cutoff trench of rela-tively impervious material shall be providedunder the entire length of the dam and shall belocated at or upstream from the centerline ofthe dam. The cutoff trench shall have a bot-tom width adequate to accommodate theequipment used for excavation, backfill andcompaction operations, with the minimumwidth being 4 feet, and shall have side slopesno steeper than one horizontal to one vertical.Minimum depth shall be 4 feet.

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Impervious Core - Any impervious corewithin the embankment shall be located at orupstream from the centerline of the dam, andshall extend up the abutments to the 10-yearwater surface elevation. The impervious coreshall extend vertically from the cutoff trenchup to the 10-year water surface elevationthroughout the embankment.

Seepage Control - Seepage control is to beincluded: (1) if pervious layers are not inter-cepted by the cutoff; (2) if seepage from theabutments may create a wet embankment; (3)if the phreatic line intersects the downstreamslope; or (4) if special conditions requiredrainage to insure a stable dam. The phreaticline shall be drawn on a 4:1 slope starting onthe inside slope at the normal pool elevation.For stormwater management ponds, normalpool shall be considered as the 10-year watersurface elevation.

Seepage may be controlled by (1) foundationabutment or embankment drains; (2) reservoirblanketing; or (3) a combination of thesemeasures. Foundation drains may controlseepage encountered in the cutoff trench dur-ing construction. These drains must be lo-cated downstream of the dam centerline andoutside the limits of the proposed cutofftrench. All drains must be designed accordingto the section Principal Spillway, ConduitPiping and Seepage Control.

Wave Erosion Protection - Where needed toprotect the face of the dam, special waveprotection measures such as a bench, rockriprap, sand-gravel, soil cement or specialvegetation shall be provided. (ReferenceNRCS Technical Releases 56 & 69)

Freeboard - The top elevation of the settledembankment shall be determined in accor-dance with minimum criteria established inTable 1

Allowance for Settlement - The design heightof the dam shall be increased by the amountneeded to insure that the design top of fill ele-vation will be maintained after all settlementhas taken place. This increase shall not beless than 5 percent, except where detailed soiltesting and lab analyses indicate a lesseramount is adequate.

Principal Spillway

Capacity - A conduit, with needed appurte-nances, shall be placed under or through thedam, except where a weir type structure isused. The minimum capacity of the principalspillway shall be that required in Table 1.

Crest Elevation of Inlet - The crest elevationof the principal spillway shall be no less than1.0 foot below the crest of the emergencyspillway. The crest elevation is the invert ele-vation of the lowest opening 6 inches or largerin any direction.

The inlet or riser size for the pipe drops shallbe such that the flow through the structuregoes from weir-flow control to pipe-flowcontrol without going into orifice-flow controlin the riser. The inlets and outlets shall bedesigned and analyzed to function satisfacto-rily for the full range of flow and hydraulichead anticipated.

The riser shall be analyzed for flotation as-suming all orifices and pipes are plugged. Thefactor of safety against flotation shall be 1.2or greater.

Pipe Conduits - Pipe conduits under orthrough the dam shall meet the following re-quirements:

1. All pipes shall be circular in cross sectionexcept for cast-in-place reinforced con-crete box culverts.

2. Pipe shall be capable of withstanding theexternal loading without yielding, buck-ling, or cracking.

3. Pipe strength shall be not less than thoseshown on Tables 3, 4 and 5 for corrugatedsteel, aluminum, and plastic pipes and ap-plicable ASTM’s for other materials.

4. Where inlet or outlet flared sections areused, they shall be made from materialscompatible with the pipe.

5. All pipe joints shall be made watertight bythe use of flanges with gaskets, couplingbands with gaskets, bell and spigot ends

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with gaskets, or by welding. See Con-struction Specifications for details.

6. The joints between sections of pipe shallbe designed to remain watertight afterjoint rotation and elongation caused byfoundation consolidation.

The capacity of the pipe conduit shall be ade-quate to discharge long duration, continuousor frequent flows without flow through theemergency spillway. The diameter of the pipeshall be not less than 6 inches.

For dams 20 feet or less in effective height,the following pipe materials are acceptable:cast-iron, ductile iron, steel, corrugated steelor aluminum, concrete with rubber gaskets,plastic, and cast-in-place reinforced concretebox culverts. Plastic pipe that will be exposedto direct sunlight should be made of ultravio-let resistant materials and protected by coatingor shielding. Connections of pipe to lessflexible pipe or structures must be designed toavoid stress concentrations that could rupturethe pipe.

For dams over 20 feet in effective height,conduits are to be reinforced concrete pipe,cast-in-place reinforced concrete box culverts,corrugated steel, ductile iron, welded steel oraluminum pipe. The maximum height of fillover any principal spillway steel, aluminum, orplastic pipe must not exceed 25 feet.

Concrete pipe shall have a concrete cradleextending up the sides of the pipe at least 50%of its outside diameter with minimum thick-ness of 6 inches. Where a concrete cradle isnot needed for structural reasons, flowable fillmay be used as described in theCONSTRUCTION SPECIFICATIONS sec-tion of this standard. Gravel bedding is notpermitted. Cantilever outlet sections, if used,shall be designed to withstand the cantileverload. Pipe supports shall be provided whenneeded. Other suitable devices such as plungebasin, stilling basin, impact basin, or rockriprap spreader should be used to provide asafe outlet. Cathodic protection is to be pro-vided for welded steel and corrugated steelpipe where the need and importance of thestructure warrant. Cathodic protection shouldnormally be provided for corrugated steel pipe

where the saturated soil resistivity is less than4,000 ohms-cm or the pH is lower than 5.The National Handbook of ConservationPractices, Irrigation Water Conveyance, SteelPipeline Standard (430-FF), provides criteriafor cathodic protection of welded steel pipes.

Multiple Conduits - Where multiple conduitsare used, there shall be sufficient space be-tween the conduits and the installed anti-seepcollars to allow for backfill material to beplaced between the conduits by the earthmoving equipment and for easy access byhand operated compaction equipment. Thisdistance between conduits shall be equal to orgreater than half the pipe diameter but not lessthan 2 feet.

Conduit Piping and Seepage Control - Seep-age along pipe conduit spillways extendingthrough the embankment shall be controlledby use of (1) anti-seep collars, or (2) filter anddrainage diaphragm. Seepage control will notbe required on pipes 6 inches in diameter orless.

Anti-seep collars shall be installed around allconduits through earth fills according to thefollowing criteria:

1. Sufficient collars shall be placed to in-crease the seepage length along the con-duit by a minimum of 15 percent of thepipe length located within the saturationzone.

2. The assumed normal saturation zone shallbe determined by projecting a line at aslope (4) horizontal to (1) vertical fromthe point where the normal water eleva-tion meets the upstream slope to a pointwhere this line intersects the invert of thepipe conduit or bottom of the cradle,whichever is lower. For StormwaterManagement ponds, the phreatic linestarting elevation shall be the 10-year wa-ter elevation.

3. Maximum collar spacing shall be 14 timesthe required projection above the pipe.The minimum collar spacing shall be 5times the required minimum projection.

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4. Anti-seep collars should be placed withinthe saturated zone. In cases where thespacing limit will not allow this, at leastone collar will be in the saturated zone.

5. All anti-seep collars and their connectionsto the conduit shall be watertight andmade of material compatible with the con-duit.

6. Collar dimensions shall extend a minimumof 2 feet in all directions around the pipe.

7. Anti-seep collars shall be placed a mini-mum of two feet from pipe joints exceptwhere flanged joints are used.

8. For pipes with concrete cradles, the pro-jection shall be measured from the cradle.

Filter and drainage diaphragms are alwaysrecommended, but are required when the fol-lowing conditions are encountered:

1. The pond requires design according toTR-60.

2. Embankment soils with high piping poten-tial such as Unified Classes GM, SM, andML.

Filter and drainage diaphragms shall be de-signed in accordance with procedures fromNRCS TR-60, Earth Dams and Reservoirs,Section 6, Principal Spillways, as describedbelow.

The drainage diaphragm shall usually consistof sand, meeting the fine concrete aggregaterequirements (ASTM C-33). A design analy-sis shall be made using Part 633 of the Na-tional Engineering Manual, Chapter 26, Gra-dation Design of Sand and Gravel Filters.

The drainage diaphragm shall be a minimumof 3 ft thick and extend vertically upward andhorizontally at least three times the conduitoutside diameter or the width of the cradle,whichever is greater except that:

1. The vertical extension need be no higherthan the maximum potential reservoir waterlevel, and

2. The horizontal extension need be no fur-ther than 5 feet beyond the sides and slopes ofany excavation made to install the conduit.

3. The minimum soil cover over any portionof the filter-drainage diaphragm measurednormal to the nearest embankment surfaceshall be at least 2 feet.

It shall extend vertically downward at least 2ft beneath the conduit outside diameter orbottom of the cradle, whichever is greater.The drainage diaphragm shall be located im-mediately downstream of the cutoff trench,approximately parallel to the centerline of thedam but no further upstream than the center-line of the dam.

The drainage diaphragm shall outlet at theembankment downstream toe, preferably us-ing a drain backfill envelope continuouslyalong the pipe to where it exits the embank-ment. Protecting drain fill from surface ero-sion will be necessary.

It is required that the outlet for the filter dia-phragm is sized to safely discharge the designflow. Where a drain backfill envelope is usedas the outlet, it is recommended that it be de-signed so the hydraulic head does not exceedthe depth of the drain outlet. The exposedarea of the drain outlet must also be protectedfrom external attack such as surface erosionand slope instability due to horizontal seepagepressures. A weighted toe cover such asriprap can be effective if protected with aproperly designed filter between the sanddrain material and the riprap cover.

If pipe drain outlets are used, considerationmust be given to the structural design of theconduit in resisting external loading and thedesign life of the pipe must be consistent withthe design life of the dam and physical condi-tions of the site. Also, the pipe must be de-signed for capacity and size of perforations asoutlined in NEH Part 633, Chapter 26 andSoil Mechanics Note 3. If the pipe corrodes,is crushed by exterior loading, or is otherwisedamaged, the outlet of the filter diaphragm islost and a piping failure may occur.

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The design quantity (Q) used to size the outletcan be calculated by Darcy's Law, Q = kiAwhere:

k = permeability of the embankment or drainoutlet material (ft/day)

i = hydraulic gradient where i = h/l

h = head differential (ft)

l = seepage path (ft)

A = area of flow (diaphragm or outlet) (ft2)

Anti-vortex Devices - Drop inlet spillways areto have adequate anti-vortex devices. Splittertype anti-vortex devices shall be placed in linewith the barrel. An anti-vortex device is notrequired if weir control is maintained in theriser through all flow stages.

Trash Racks - All pipe and inlet structuresshall have a trash rack. Openings for trashracks shall be no larger than 1/2 of the barrelconduit diameter, but in no case less than 6inches.

Flush grates for trash racks are not accept-able. Inlet structures that have flow over thetop shall have a non-clogging trash rack suchas a hood-type inlet extending a minimum of 8inches below the weir openings, which allowspassage of water from underneath the trashrack into the riser.

For inlet structures with solid covered tops,the bottom of the cover slab must be set at anelevation to prevent orifice flow control be-fore pipe flow control governs.

Low stage releases, where the opening islarger than 6 inches, shall have a non-cloggingtrash rack with openings no larger than halfthe low flow dimension.

For all low stage releases 6 inches or smallerin any direction, the emergency spillway de-sign storm shall be routed assuming the re-lease has failed, using storage and dischargeonly above the elevation of the next openinglarger than 6 inches in all directions. This de-sign storm routing shall not overtop the dam.

Drain Pipe - A pipe with a suitable valve shallbe provided to drain the pool area, whereneeded for proper pond management. Theprincipal spillway conduit may serve as a ponddrain, when so located, to accomplish thisfunction.

Water Supply Pipes or Utilities - All pipesthrough the dam shall have an inside diameterof not less than 1 1/4 inches. Pipes / utilitiesnot parallel to the axis of the dam shall meetall principal spillway requirements (i.e. filterdiaphragm, embankment soils, etc.). Pipes /utilities parallel to the axis of the dam shall beconstructed with no granular bedding.

Earth Emergency Spillways

Emergency spillways are provided to conveylarge flood flows safely past earth embank-ments. An emergency spillway must be pro-vided for each dam, unless the principal spill-way is large enough to pass the routed designhydrograph peak discharge and any trashwithout overtopping the dam. The only de-sign that may be utilized without an emer-gency spillway is: a principal spillway with across-sectional area of 3 square feet or moreand an inlet that will not clog, such as a hood-type inlet which allows passage of water fromunderneath the trash rack into the riser.

Capacity - The minimum capacity of emer-gency spillways shall be that required to passthe peak flow expected from a design stormof the frequency and duration shown in Table1 less any reduction creditable to conduit dis-charge and detention storage.

The emergency spillway shall (1) safely passthe storm design peak or (2) the storm runoffshall be routed through the reservoir. Therouting shall start with the water surface atthe elevation of the crest of the principalspillway, or at the water surface after 10 daysdrawdown, whichever is higher. The 10-daydrawdown shall be computed from the crestof the emergency spillway or from the eleva-tion that would be attained had the entire de-sign storm been impounded, whichever islower. Emergency spillways are to providefor passage of the design flow at a non-erosive velocity to a point downstream wherethe dam will not be endangered.

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Component Parts - Earth spillways are openchannels and usually consist of an inlet chan-nel, level section, and an exit channel. Theminimum difference in elevation between thecrest of the emergency spillway and the set-tled top of dam shall be 2.0 feet.

Cross-Section - Earth spillways shall betrapezoidal and shall be located in undisturbedearth. The side slopes shall be stable for thematerial in which the spillway is to be con-structed, but not steeper than 2:1. The emer-gency spillway shall have a bottom width ofnot less than 8 feet.

The inlet channel may be curved to fit existingtopography; however, it should be flared toallow unrestricted flow to the level section.The level section should be located as near thecenterline of dam as possible. The level sec-tion shall be 25 feet in length, and shall berectangular or square.

Exit channel centerline shall be perpendicularto the level section downstream edge andmust be straight for a distance beyond thedownstream toe, so that discharges will notreach the earth embankment. The grade ofthe exit channel shall fall within the range es-tablished by discharge requirement and per-missible velocities.

The crest of any “token” spillway will be lo-cated at or above the 100-year storm eleva-tion in undisturbed earth and have a minimumdepth of one foot and bottom width of 8 feet.

Permissible Velocities - Earth spillways shallbe designed for non-erosive velocities throughthe control section and to a point downstreamwhere the dam will not be endangered. Themaximum permissible velocity for the grassand grass mixture to be used shall be selectedfrom Table 6. Velocities exceeding these val-ues will require use of linings other thanvegetation.

Infiltration / Water Quality Basins – Ponds,either excavated or embankment, that are de-signed solely for infiltration or as water qual-ity basins will have an emergency spillway.The capacity of the spillway will be deter-mined by the following procedure:

Pass the routed 100-Year Storm with 1 footof freeboard to the top of dam elevation.Routing will begin at the emergency spillwaycrest.

Structural Emergency Spillways

Chutes or drops, when used for principalspillways or principal-emergency or emer-gency spillways, shall be designed in accor-dance with the principals set forth in the Na-tional Engineering Handbook, Section 5 “Hy-draulics”; Section 11 “Drop Spillways”; andSection 14 “Chute Spillways”. The minimumcapacity of a structural spillway shall be thatrequired to pass the peak flow expected froma design storm of the frequency and durationshown in Table 1 less any reduction creditableto conduit discharge and detention storage.

Visual Resource Design

The visual design of ponds shall be carefullyconsidered in areas of high public visibilityand those associated with recreation. Theunderlying criterion for all visual design is ap-propriateness. The shape and form of ponds,excavated material, and plantings are to relatevisually to their surroundings and to theirfunctions.

The embankment may be shaped to blend withthe natural topography. The edge of the pondshould be shaped so that it is generally curvi-linear rather than rectangular. Excavatedmaterial shall be shaped so that the final formis smooth, flowing, and fitting to the adjacentlandscape rather than angular geometricmounds. If feasible, islands may be added forvisual interest and to attract wildlife.

Trees and Shrubs

Non-Roadway Embankments - Trees and/orshrubs will not be allowed on any embank-ment, will not be allowed within the bufferzone (15 feet from the toe of the dam), andwill not be allowed within a 25-foot radiusaround the inlet structure.

Roadway Embankments - Trees and/orshrubs will not be allowed on any embank-ment, except for dry stormwater management

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structures that will be utilized as a roadwayunder all the following conditions:

1. Plantings may only be on top of the damalong the roadway and/or sidewalks.

2. The top of the dam shall have a minimumof 50-foot top width.

3. Plantings will not be allowed on the sideslopes of the embankment.

4. Plantings will not be allowed within thebuffer zone (15 feet from the toe of thedam).

5. Plantings will only be shallow rooted(roots less than 3’ deep) trees or shrubs.

6. The pond is a “dry” structure (normalpool not exceeding 18 inches).

7. A landscape plan showing type and loca-tion of planting must be prepared by aLandscape Architect certifying shallowrooted plants (roots less than 3’ deep) un-der mature conditions.

8. A minimum of 3 feet freeboard above the100-year water surface elevation must bemaintained.

9. The structure is a low hazard (Class “a”)pond.

Safety

Special considerations should be made forsafety and access during the design of a pond.Measures to be considered may include fenc-ing, slope benching, access roads, flattenedside slopes, etc. When fencing a structure, thefence will be located so it will not interferewith the operation of the emergency spillway.

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Excavated Ponds

General - Excavated ponds that create a fail-ure potential through a constructed or createdembankment will be designed as embankmentponds. Excavated ponds that include a pipeor weir outlet control system for urbanstormwater management shall be designedusing the principal and emergency spillwayhydrologic criteria for Embankment Ponds,Table 1.

Side Slopes - Side slopes of excavated pondsshall be such that they will be stable and shallnot be steeper than 1 horizontal to 1 vertical.Flatter slopes are to be utilized where safetyfor children, livestock watering, etc. is a de-sign factor.

Perimeter Form - Where the structures areused for recreation or are located in high pub-lic view, the perimeter or edge should beshaped to a curvilinear form.

Inlet Protection - When the excavated pondis a bypass type and water is being divertedfrom a stream, the minimum size inlet lineshall be a 4-inch diameter pipe. All state lawsconcerning water use and downstream rightsshall be strictly adhered to.

Where surface water enters the pond in anatural or excavated channel, the side slope ofthe pond shall be protected against erosion.

Outlet Protection – An excavated pond witha low embankment (combination excavation /embankment pond) shall be designed to en-sure a stable outfall for the 10-year, 24-hourfrequency storm.

Placement of Excavated Material - The ma-terial excavated from the pond shall be placedin one of the following ways so that its weightwill not endanger the stability of the pond sideslopes and where it will not be washed backinto the pond by rainfall:

1. Uniformly spread to a height not exceed-ing 3 feet with the top graded to a con-tinuous slope away from the pond;

2. Uniformly placed or shaped reasonablywell with side slopes no steeper than 2 to

1. The excavated material will be placedat a distance equal to the depth of thepond, but not less than 12 feet from theedge of the pond;

3. Shaped to a designed form that blendsvisually with the landscape;

4. Used for low embankment and leveling; or

5. Hauled away.

Reservoir Area for Wet Ponds

For most ponds, the topography of the siteshall permit storage of water at a depth andvolume that ensures a dependable supply,considering beneficial use, sedimentation, sea-son of use, and evaporation and seepagelosses. Soils in the reservoir shall be impervi-ous enough to minimize seepage losses orshall be of a type that sealing is practical.Excavation and shaping required to permit thereservoir area to suitably serve the plannedpurpose shall be included in the constructionplans.Reservoirs designed specifically for fish pro-duction or wildlife management shall followdesign criteria in the standards and specifica-tions for Fish Pond Management (MD-399)and Wildlife Wetland Habitat Management(MD-644), as appropriate.

Pond MD-378-12


TABLE 1

HYDROLOGIC CRITERIA FOR PONDS

Spillway Capacity5

Principal2 Emergency3, 4 Freeboard6StructureClass

StorageHeight

Product1

WatershedArea

(Acres)

Height ToEmergencySpwy Crest

(Feet)

NormalSurface

Area(Acres) Rural Urban Rural Urban Rural & Urban

“c” & “b” Any Any Any Any TR 60 TR 60 TR 60 TR 60 TR 60

“a” 3,000 ormore

Any Any Any TR 60 TR 60 TR 60 TR 60 TR 60

320 >20 - 35 >12 25 YR TR 60 100 YR 100 YR

Less and <20 >12 10 YR 25 YR 100 YR 100 YR

Larger <15 <12 5 YR 10 YR 50 YR 100 YR

2.0’ above E.S.Design Storm

100 >20 - 35 >12 10 YR TR 60 100 YR 100 YR 2.0’ above E.S.Design Storm

“a” than to <20 >12 5 YR 10 YR 50 YR 100 YR 1.0’ above E.S.Design Storm

320 <15 <12 2 YR 5 YR 25 YR 100 YR 1.0’ above E.S.Design Storm

Less >20 - 35 >12 5 YR TR 60 50 YR 100 YR

3,000 Than <20 >12 2 YR 5 YR 25 YR 100 YR

100 <15 <12 10% of25 YRPeak

5 YR 25 YR 100 YR1.0’ above E.S.Design Storm

NOTES

1) The storage is defined as the original capacity of the reservoir in acre-feet at the elevation of the crest of the emergencyspillway. The effective height is the difference in elevation in feet between the emergency spillway crest and the lowest point on aprofile taken along the centerline of the dam, excluding the cutoff trench. If there is no emergency spillway, this height shall be tothe top of the dam.

2) Principal - minimum storm to be contained below the crest of the emergency spillway including any combination of temporarystorage and principal spillway discharge.

3) Emergency - minimum storm used to proportion the emergency spillway to meet the limitations for shape, size, velocity andexit channel. This storm can be handled by any combination of principal spillway discharge, emergency spillway discharge andstorage.

4) For ponds without a separate emergency spillway, the principal spillway functions as the emergency spillway. In this situa-tion, the principal spillway must comply with the emergency spillway hydrologic criteria.

5) All ponds, which are being designed to meet local stormwater requirements, will be required to use the urban criteria. Stormduration used shall be 24 hours except where TR-60 is specified.

6) For ponds without a functioning open channel emergency spillway, minimum freeboard will be 2 feet.

Pond MD-378-13


TABLE 2

TotalHeight Of Embankment(Feet)

MinimumTop Width

(Feet)10 or less 611 - 14 815 - 19 1020 - 24 1225 - 34 1435 or more 15

TABLE 31,2

MINIMUM GAGES

CORRUGATED STEEL PIPE2 - 2/3 inches x 1/2 inch Corrugations

Fill Height Pipe Diameter in InchesOver Pipe 24 &(Feet) Less 30 36 42 481 - 15 16 16 14 10 1015 - 20 16 12 10 * *20 - 25 16 10 * * *

CORRUGATED STEEL PIPE3 inches x 1 inch or 5 inch x 1 inch Corrugations

Fill Height Pipe Diameter (Inches)Over Pipe Flowable Fill(Feet) 36 42 48 543 603 663 723

1 - 15 16 16 16 14 14 14 1415 - 20 16 16 12 14 14 14 1420 - 25 14 14 10 14 14 14 14

* Not Permitted.

TABLE 41,2

MINIMUM GAGES

CORRUGATED ALUMINUM PIPE2 - 2/3 inches x 1/2 inch Corrugations

Fill Height Pipe Diameter in InchesOver Pipe 21 &(Feet) Less 24 301 - 15 16 14 1015 - 20 12 10 *20 - 25 10 * *

CORRUGATED ALUMINUM PIPE3 inches x 1 inch Corrugations

Fill Height Pipe Diameter in InchesOver Pipe(Feet) 30 36 42 48 543

1 - 15 16 16 14 10 1415 - 20 16 12 * * *20 - 25 12 * * * *

* Not Permitted.

1 Coatings for corrugated metal shall be as specified by the MD-378 Construction Specifications.2 Tables 3 and 4 were developed using the modified Spangler equation. Sizes other than those shown

above are not permitted.3 Must use flowable backfill as specified by the MD-378 Construction Specifications and the pipe must be

bituminous coated.

Pond MD-378-14


TABLE 5

ACCEPTABLE PLASTIC PIPE FOR USE INEARTH DAM1, 2

Nominal PipeSize (inches)

Schedule or StandardDimension Ratio

(SDR)

MaximumDepth

of Fill Over 3

6 - 24 PVC Schedule 40 106 - 24 PVC Schedule 80 156 – 24 PVC SDR 26 106 - 24 Corrugated HDPE 10

1 See Specifications, Plastic Pipe2 All designs based on Technical Release 77, Refer-ence 20. Other diameters and / or fill heights may beused that meet all the requirements of TR-77.3 larger fill heights may be permitted when usingflowable fill.

TABLE 6

Permissible Velocities (Ft/Sec)For Emergency Spillways Lined with Vegetation

Slope Of Exit Channel

Type of Cover 0 - 5% 5 - 10%

Bermudagrass 6 5

Reed Canarygrass 5 4

Tall Fescue 5 4

Kentucky Bluegrass 5 4

Grass-legume mixture 4 3

Pond MD-378-15


CONSTRUCTION SPECIFICATIONS

These specifications are appropriate to allponds within the scope of the Standard forpractice MD-378. All references to ASTMand AASHTO specifications apply to the mostrecent version.

Site Preparation

Areas designated for borrow areas, embank-ment, and structural works shall be cleared,grubbed and stripped of topsoil. All trees,vegetation, roots and other objectionable ma-terial shall be removed. Channel banks andsharp breaks shall be sloped to no steeper than1:1. All trees shall be cleared and grubbedwithin 15 feet of the toe of the embankment.

Areas to be covered by the reservoir will becleared of all trees, brush, logs, fences, rub-bish and other objectionable material unlessotherwise designated on the plans. Trees,brush, and stumps shall be cut approximatelylevel with the ground surface. For drystormwater management ponds, a minimum ofa 25-foot radius around the inlet structureshall be cleared.

All cleared and grubbed material shall be dis-posed of outside and below the limits of thedam and reservoir as directed by the owner orhis representative. When specified, a suffi-cient quantity of topsoil will be stockpiled in asuitable location for use on the embankmentand other designated areas.

Earth Fill

Material - The fill material shall be taken fromapproved designated borrow areas. It shall befree of roots, stumps, wood, rubbish, stonesgreater than 6”, frozen or other objectionablematerials. Fill material for the center of theembankment, and cut off trench shall conformto Unified Soil Classification GC, SC, CH, orCL and must have at least 30% passing the#200 sieve. Consideration may be given tothe use of other materials in the embankmentif designed by a geotechnical engineer. Suchspecial designs must have construction super-vised by a geotechnical engineer.

Materials used in the outer shell of the em-bankment must have the capability to supportvegetation of the quality required to preventerosion of the embankment.

Placement - Areas on which fill is to beplaced shall be scarified prior to placement offill. Fill materials shall be placed in maximum8 inch thick (before compaction) layers whichare to be continuous over the entire length ofthe fill. The most permeable borrow materialshall be placed in the downstream portions ofthe embankment. The principal spillway mustbe installed concurrently with fill placementand not excavated into the embankment.

Compaction - The movement of the haulingand spreading equipment over the fill shall becontrolled so that the entire surface of eachlift shall be traversed by not less than onetread track of heavy equipment or compactionshall be achieved by a minimum of four com-plete passes of a sheepsfoot, rubber tired orvibratory roller. Fill material shall containsufficient moisture such that the required de-gree of compaction will be obtained with theequipment used. The fill material shall containsufficient moisture so that if formed into a ballit will not crumble, yet not be so wet thatwater can be squeezed out.

When required by the reviewing agency theminimum required density shall not be lessthan 95% of maximum dry density with amoisture content within ±2% of the optimum.Each layer of fill shall be compacted as neces-sary to obtain that density, and is to be certi-fied by the Engineer at the time of construc-tion. All compaction is to be determined byAASHTO Method T-99 (Standard Proctor).

Cut Off Trench - The cutoff trench shall beexcavated into impervious material along orparallel to the centerline of the embankmentas shown on the plans. The bottom width ofthe trench shall be governed by the equipmentused for excavation, with the minimum widthbeing four feet. The depth shall be at leastfour feet below existing grade or as shown onthe plans. The side slopes of the trench shallbe 1 to 1 or flatter. The backfill shall be com-pacted with construction equipment, rollers,or hand tampers to assure maximum densityand minimum permeability.

Pond MD-378-16


Embankment Core - The core shall be paral-lel to the centerline of the embankment asshown on the plans. The top width of thecore shall be a minimum of four feet. Theheight shall extend up to at least the 10 yearwater elevation or as shown on the plans.The side slopes shall be 1 to 1 or flatter. Thecore shall be compacted with constructionequipment, rollers, or hand tampers to assuremaximum density and minimum permeability.In addition, the core shall be placed concur-rently with the outer shell of the embankment.

Structure Backfill

Backfill adjacent to pipes or structures shallbe of the type and quality conforming to thatspecified for the adjoining fill material. Thefill shall be placed in horizontal layers not toexceed four inches in thickness and com-pacted by hand tampers or other manually di-rected compaction equipment. The materialneeds to fill completely all spaces under andadjacent to the pipe. At no time during thebackfilling operation shall driven equipmentbe allowed to operate closer than four feet,measured horizontally, to any part of a struc-ture. Under no circumstances shall equipmentbe driven over any part of a concrete structureor pipe, unless there is a compacted fill of 24”or greater over the structure or pipe.

Structure backfill may be flowable fill meetingthe requirements of Maryland Department ofTransportation, State Highway AdministrationStandard Specifications for Construction andMaterials, Section 313 as modified. Themixture shall have a 100-200 psi; 28 day un-confined compressive strength. The flowablefill shall have a minimum pH of 4.0 and aminimum resistivity of 2,000 ohm-cm. Mate-rial shall be placed such that a minimum of 6”(measured perpendicular to the outside of thepipe) of flowable fill shall be under (bedding),over and, on the sides of the pipe. It onlyneeds to extend up to the spring line for rigidconduits. Average slump of the fill shall be 7”to assure flowability of the material. Ade-quate measures shall be taken (sand bags,etc.) to prevent floating the pipe. When usingflowable fill, all metal pipe shall be bituminouscoated. Any adjoining soil fill shall be placedin horizontal layers not to exceed four inchesin thickness and compacted by hand tampers

or other manually directed compactionequipment. The material shall completely fillall voids adjacent to the flowable fill zone. Atno time during the backfilling operation shalldriven equipment be allowed to operate closerthan four feet, measured horizontally, to anypart of a structure. Under no circumstancesshall equipment be driven over any part of astructure or pipe unless there is a compactedfill of 24” or greater over the structure orpipe. Backfill material outside the structuralbackfill (flowable fill) zone shall be of the typeand quality conforming to that specified forthe core of the embankment or other em-bankment materials.

Pipe Conduits

All pipes shall be circular in cross section.

Corrugated Metal Pipe - All of the followingcriteria shall apply for corrugated metal pipe:

1. Materials - (Polymer Coated steel pipe) -Steel pipes with polymeric coatings shallhave a minimum coating thickness of 0.01inch (10 mil) on both sides of the pipe.This pipe and its appurtenances shallconform to the requirements of AASHTOSpecifications M-245 & M-246 with wa-tertight coupling bands or flanges.

Materials - (Aluminum Coated Steel Pipe)- This pipe and its appurtenances shallconform to the requirements of AASHTOSpecification M-274 with watertight cou-pling bands or flanges. Aluminum CoatedSteel Pipe, when used with flowable fill orwhen soil and/or water conditions warrantthe need for increased durability, shall befully bituminous coated per requirementsof AASHTO Specification M-190 TypeA. Any aluminum coating damaged orotherwise removed shall be replaced withcold applied bituminous coating com-pound. Aluminum surfaces that are to bein contact with concrete shall be paintedwith one coat of zinc chromate primer ortwo coats of asphalt.

Materials - (Aluminum Pipe) - This pipeand its appurtenances shall conform to therequirements of AASHTO SpecificationM-196 or M-211 with watertight coupling

Pond MD-378-17


bands or flanges. Aluminum Pipe, whenused with flowable fill or when soil and/orwater conditions warrant for increased du-rability, shall be fully bituminous coatedper requirements of AASHTO Specifica-tion M-190 Type A. Aluminum surfacesthat are to be in contact with concreteshall be painted with one coat of zincchromate primer or two coats of asphalt.Hot dip galvanized bolts may be used forconnections. The pH of the surroundingsoils shall be between 4 and 9.

2. Coupling bands, anti-seep collars, endsections, etc., must be composed of thesame material and coatings as the pipe.Metals must be insulated from dissimilarmaterials with use of rubber or plastic in-sulating materials at least 24 mils in thick-ness.

3. Connections - All connections with pipesmust be completely watertight. The drainpipe or barrel connection to the riser shallbe welded all around when the pipe andriser are metal. Anti-seep collars shall beconnected to the pipe in such a manner asto be completely watertight. Dimplebands are not considered to be watertight.

All connections shall use a rubber or neo-prene gasket when joining pipe sections.The end of each pipe shall be re-rolled anadequate number of corrugations to ac-commodate the bandwidth. The followingtype connections are acceptable for pipesless than 24 inches in diameter: flanges onboth ends of the pipe with a circular 3/8inch closed cell neoprene gasket, pre-punched to the flange bolt circle, sand-wiched between adjacent flanges; a 12-inch wide standard lap type band with 12-inch wide by 3/8-inch thick closed cell cir-cular neoprene gasket; and a 12-inch widehugger type band with o-ring gasketshaving a minimum diameter of 1/2 inchgreater than the corrugation depth. Pipes24 inches in diameter and larger shall beconnected by a 24 inch long annular cor-rugated band using a minimum of 4 (four)rods and lugs, 2 on each connecting pipeend. A 24-inch wide by 3/8-inch thickclosed cell circular neoprene gasket willbe installed with 12 inches on the end of

each pipe. Flanged joints with 3/8 inchclosed cell gaskets the full width of theflange is also acceptable.

Helically corrugated pipe shall have eithercontinuously welded seams or have lockseams with internal caulking or a neoprenebead.

4. Bedding - The pipe shall be firmly anduniformly bedded throughout its entirelength. Where rock or soft, spongy orother unstable soil is encountered, all suchmaterial shall be removed and replacedwith suitable earth compacted to provideadequate support.

5. Backfilling shall conform to “StructureBackfill”.

6. Other details (anti-seep collars, valves,etc.) shall be as shown on the drawings.

Reinforced Concrete Pipe - All of the fol-lowing criteria shall apply for reinforced con-crete pipe:

1. Materials - Reinforced concrete pipe shallhave bell and spigot joints with rubbergaskets and shall equal or exceed ASTMC-361.

2. Bedding - Reinforced concrete pipe con-duits shall be laid in a concrete bedding /cradle for their entire length. This bed-ding / cradle shall consist of high slumpconcrete placed under the pipe and up thesides of the pipe at least 50% of its out-side diameter with a minimum thickness of6 inches. Where a concrete cradle is notneeded for structural reasons, flowable fillmay be used as described in the “StructureBackfill” section of this standard. Gravelbedding is not permitted.

3. Laying pipe - Bell and spigot pipe shall beplaced with the bell end upstream. Jointsshall be made in accordance with recom-mendations of the manufacturer of thematerial. After the joints are sealed forthe entire line, the bedding shall be placedso that all spaces under the pipe are filled.Care shall be exercised to prevent any de-viation from the original line and grade of

Pond MD-378-18


the pipe. The first joint must be locatedwithin 4 feet from the riser.



Plastic Pipe - The following criteria shall ap-ply for plastic pipe:

1. Materials - PVC pipe shall be PVC-1120or PVC-1220 conforming to ASTM D-1785 or ASTM D-2241. CorrugatedHigh Density Polyethylene (HDPE) pipe,couplings and fittings shall conform to thefollowing: 4” – 10” inch pipe shall meetthe requirements of AASHTO M252 TypeS, and 12” through 24” inch shall meet therequirements of AASHTO M294 Type S.

2. Joints and connections to anti-seep collarsshall be completely watertight.

3. Bedding -The pipe shall be firmly anduniformly bedded throughout its entirelength. Where rock or soft, spongy orother unstable soil is encountered, all suchmaterial shall be removed and replacedwith suitable earth compacted to provideadequate support.



Drainage Diaphragms - When a drainagediaphragm is used, a registered professionalengineer will supervise the design and con-struction inspection.

Concrete

Concrete shall meet the requirements ofMaryland Department of Transportation,State Highway Administration StandardSpecifications for Construction and Materials,Section 414, Mix No. 3.

Rock Riprap

Rock riprap shall meet the requirements ofMaryland Department of Transportation,State Highway Administration StandardSpecifications for Construction and Materials,Section 311.

Geotextile shall be placed under all riprap andshall meet the requirements of Maryland De-partment of Transportation, State HighwayAdministration Standard Specifications forConstruction and Materials, Section 921.09,Class C.

Care of Water during Construction

All work on permanent structures shall be car-ried out in areas free from water. The Con-tractor shall construct and maintain all tempo-rary dikes, levees, cofferdams, drainage chan-nels, and stream diversions necessary to pro-tect the areas to be occupied by the permanentworks. The contractor shall also furnish, in-stall, operate, and maintain all necessarypumping and other equipment required forremoval of water from various parts of thework and for maintaining the excavations,foundation, and other parts of the work freefrom water as required or directed by the en-gineer for constructing each part of the work.After having served their purpose, all tempo-rary protective works shall be removed orleveled and graded to the extent required toprevent obstruction in any degree whatsoeverof the flow of water to the spillway or outletworks and so as not to interfere in any waywith the operation or maintenance of thestructure. Stream diversions shall be main-tained until the full flow can be passedthrough the permanent works. The removalof water from the required excavation and thefoundation shall be accomplished in a mannerand to the extent that will maintain stability ofthe excavated slopes and bottom required ex-cavations and will allow satisfactory perform-ance of all construction operations. Duringthe placing and compacting of material in re-quired excavations, the water level at the lo-cations being refilled shall be maintained be-low the bottom of the excavation at such lo-cations which may require draining the watersumps from which the water shall be pumped.

Stabilization

Pond MD-378-19


All borrow areas shall be graded to provideproper drainage and left in a sightly condition.All exposed surfaces of the embankment,spillway, spoil and borrow areas, and bermsshall be stabilized by seeding, liming, fertiliz-ing and mulching in accordance with theNatural Resources Conservation ServiceStandards and Specifications for Critical AreaPlanting (MD-342) or as shown on the ac-companying drawings.

Erosion and Sediment Control

Construction operations will be carried out insuch a manner that erosion will be controlledand water and air pollution minimized. Stateand local laws concerning pollution abatementwill be followed. Construction plans shalldetail erosion and sediment control measures.

Pond MD-378-20


OPERATION AND MAINTENANCE

An operation and maintenance plan in accor-dance with Local or State Regulations will beprepared for all ponds. As a minimum, thedam inspection checklist located in AppendixA shall be included as part of the operationand maintenance plan and performed at leastannually. Written records of maintenance andmajor repairs needs to be retained in a file.The issuance of a Maintenance and RepairPermit for any repairs or maintenance thatinvolves the modification of the dam or spill-way from its original design and specificationsis required. A permit is also required for anyrepairs or reconstruction that involve a sub-stantial portion of the structure. All indicatedrepairs are to be made as soon as practical.

Pond MD-378-21


SUPPORTING DATA ANDDOCUMENTATION

Field Data and Survey Notes

The following is a list of the minimum dataneeded:

1. Profile along centerline of structure.

2. Profile along centerline of principal spill-way.

3. Profile along centerline of emergencyspillway.

4. Survey of storage area to develop topog-raphy and storage volumes.

5. Soil investigation logs and notes.

Design Data

Record on appropriate engineering paper.The following is a list of the minimum re-quired design data:

1. Determine pond class and list appropriatespillway design criteria, including map.

2. Determine peak runoff from the contrib-uting area for the design storms selected,including topo map.

3. Develop a stage-storage/discharge curvefor the site.

4. Determine the pipe spillway by stormrouting using the procedure in the SWMPond Design Manual; Chapter 11, EFH;Chapter 6, TR-55; or TR-20.

5. Design emergency spillway using EFH 11-61.

6. Drawings should show the following as aminimum: profile along centerline of dam;profile along centerline of emergencyspillway; cross section through dam atprincipal spillway; cross section throughemergency spillway; plan view; and con-struction details & notes and soil logs.

7. Compute earth fill (if needed).

8. Special design feature details; watering,fire hydrants, fish management, irrigation,outfall stabilization, etc.; structural detailswith design loadings, if applicable, shouldbe shown on the drawings.

9. Complete data required on MD-ENG-14.

10. Record seeding plan on drawings or MD-CONS-10.

11. A written Operation and MaintenancePlan.

Construction Check Data/As-built

Record on survey note paper, SCS-ENG-28.Survey data for ponds will be plotted in red.All construction inspection visits shall be re-corded on the CPA-6 or appropriate docu-mentation paper. The documentation shallinclude the date, who performed the inspec-tion, specifics as to what was inspected, allalternatives discussed, and decisions made andby whom. The following is a list of the mini-mum data needed for As-Builts:

1. A profile of the top of the dam.

2. A cross-section of the emergency spillwayat the control section.

3. A profile along the centerline of the emer-gency spillway.

4. A profile along the centerline of the prin-cipal spillway extending at least 100 feetdownstream of the fill.

5. The elevation of the principal spillwaycrest.

6. The elevation of the principal spillwayconduit invert (inlet and outlet).

7. The diameter, length, thickness and typeof material for the riser.

8. The diameter, length, and type of materialfor the conduit.

9. The size and type of anti-vortex and trashrack device and its elevations in relation tothe principal spillway crest.

Pond MD-378-22


10. The number, size and location of the anti-seep collars.

11. The diameter and size of any low stageorifices or drain pipes.

12. Show the length, width, and depth ofcontours of the pool area so that designvolume can be verified.

13. Notes and measurements to show that anyspecial design features were met.

14. Statement on seeding and fencing.

15. Notes on site clean up and disposal.

16. Sign and date check notes to includestatement that practice meets or exceedsplans and specifications.

Pond MD-378-23


REFERENCES

1. AWWA Standards, American WaterWorks Association, Denver, Colo-rado.

2. ASTM Standards, American Societyfor Testing and Materials, Philadel-phia, Pennsylvania.

3. Engineering Field Handbook, Part650, USDA, Soil Conservation Serv-ice.

4. Handbook of PVC Pipe Design andConstruction, First Edition, Uni-BellPlastic Pipe Association, Dallas,Texas, 1980.

5. Handbook of Steel Drainage andHighway Construction Products,Third Edition, American Iron andSteel Institute, Washington, D.C.,1983.

6. Maryland Dam Safety Manual,Maryland Department of Natural Re-sources, Water Resources Admini-stration, Annapolis, Maryland, June1993.

7. Maryland Technical Guide, SectionIV, Standards and Specifications,USDA, Natural Resources Conserva-tion Service.

8. National Engineering Handbook,Section 4, Hydrology, USDA, NaturalResources Conservation Service,March 1985.

9. National Engineering Handbook,Section 5, Hydraulics, USDA, NaturalResources Conservation Service,August 1956.

10. National Engineering Handbook,Section 11, Drop Spillways, USDA,Natural Resources ConservationService, April 1968.

11. National Engineering Handbook,Section 14, Chute Spillways, USDA,

Natural Resources ConservationService, October 1977.

12. National Handbook of ConservationPractices, USDA, Natural ResourcesConservation Service.

13. Standard Specifications for Materialsand Methods of Sampling and Test-ing, Nineteenth Edition, American As-sociation of State Highway and Trans-portation Officials, Washington D.C.,1998.

14. Standard Specifications for Construc-tion and Materials, Maryland De-partment of Transportation, StateHighway Administration, Baltimore,Maryland, October 1993.

15. Technical Release No. 20, ComputerPrograms for Project FormulationHydrology, USDA, Natural ResourcesConservation Service, 1992.

16. Technical Release No. 55, Urban Hy-drology for Small Watersheds, USDA,Natural Resources ConservationService, 1986.

17. Technical Release No. 56, A Guide forDesign and Layout of VegetativeWave Protection for Earth Dam Em-bankments, USDA, Natural ResourcesConservation Service, 1974.

18. Technical Release No. 60, EarthDams and Reservoirs, USDA, NaturalResources Conservation Service,1985.

19. Technical Release 69, Riprap forSlope Protection Against Wave Ac-tion, USDA, Natural Resources Con-servation Service, 1983.

Pond MD-378-24


20. Technical Release No. 77, Design andInstallation of Flexible Conduits,USDA, Natural Resources Conserva-tion Service, 1990.

21. National Engineering Handbook, Part633, Chapter 26, Gradation Design ofSand and Gravel Filters, USDA,Natural Resources ConservationService, October 1994.

Pond MD-378-25


APPENDIX A

Pond MD-378-26


Pond MD-378-27


Pond MD-378-28


APPENDIX B

ROADWAY EMBANKMENTDESIGN CRITERIA

HW - TW > 10'* AND HW/D > 2,OR PERMANENT POOL > 3' OR

PROPOSED RISER

MEETS SMALL POND CRITERIA, ANDCLASS "A"

8:1 PROJECTION LINE INTERSECTSDOWNSTREAM SLOPE OF THE

EMBANKMENT

MD 378Design

Yes

Yes

Yes

NO SPECIALDESIGN

MDE DAM SAFETYREVIEW

SPECIALEMBANKMENT

DESIGN

Use any nonorganic soils for theembankment, elimination of the cut-off trench and core based on ap-proval of geotechnical engineer andacceptable to local jurisdictions.

Filter diaphragm is required.

All other MD 378 criteria apply.

No

No

No

pond - usdaefotg.sc.egov.usda.gov/references/public/mw/md378_00.pdf · 2002. 7. 17. · peak breach...

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