INTRODUCTIONThis design covers the principles of hydraulic design and Analysis of the more usual Flood Control Structures found in Civil Engineering practice. These include the design of Dams, Embankments, Channels, Revetments and Spurdikes

T0PIC CONTENTSDESIGN DATA REQUIRED 1. OUTLINE DESIGN DATA REQUIRED A. Field Survey Information B. Hydrologic Data 2. SUMMARY REQUIRED DESIGN DATAII. DESIGN CRETERIA AND STANDARDS 1. OUTLINE DESIGN CRITERIA AND STANDARDS 2. DESIGN OF EMBANKMENT 3. DESIGN OF CHANNELS 4. DESIGN OF REVETMENTS 5. DESIGN OF SPURDIKES 6. DETAIL DESIGN CRITERIA AND STANDARDS III. DESIGN PROCEDURES IV. DESIGN REVISION

A. Field Survey Information 1. Topographic Survey 2. Hydrographic Survey 3. Soils Subsurface and Surface Exploration

B. Hydrologic Data

1. Precipitation2. River Stage3. Discharge4. Sediment Transport

1. OUTLINE DESIGN DATA REQUIRED

1. Topographic map of the proposed project area with 0.50 m contour interval at a scale of 1:10,000 m.2. Ground profiles along the banks at horizontal and vertical scales of 1:1,000 m and 1:100 m respectively.3. Water surface profile indicating maximum experienced flood level, design water level, and minimum water level at horizontal and vertical scales of 1:1,000 m. 1:100 m respectively.4. Profile of the riverbed along the centerline of the river channel at horizontal and vertical scales of 1:1,000 and 1:100 m respectively.5. Cross-sections facing downstream at 100 meters interval for straight and uniform section, 25 meters for river bends and 20 meters for sharp bends, indicating thereon the

2. SUMMARY REQUIRED DESIGN DATA

proposed structures, maximum experienced flood level and ordinary water level as well as design water level and character of bank and river bed material.6. Soil investigation data and analysis.7. Hydrologic and hydraulic design analysis supported by topographic map showing the watershed area and point of interest.

II. DESIGN CRITERIA AND STANDARDS1. OUTLINE DESIGN CRITERIA And STANDARDSDams are hydraulic structures constructed to controlAnd/or conserve water.

A. Location and AlignmentB. FreeboardC. SlopeD. HeightE. Top WidthF. Easement

2. DESIGN OF EMBANKMENTSA ridge constructed of earth, stone, or other material toPrevent water from passing beyond desirable limits.Also known as bank.

A. Location and AlignmentB. FreeboardC. SlopesD. HeightE. Top WidthG. Berms

3. DESIGN OF CHANNELSA natural or artificial waterway connecting two bodies of water or containing moving water.

A. AlignmentB. FreeboardC. Slope

4. DESIGN OF REVETMENTSRevetments are flood control structures constructed alongriver banks subjected to direct attack of the river flowand along second dike slopes for protection againstscouring and wave wash.

A. Location and AlignmentB. FreeboardC. SlopeD. Height

5. DESIGN OF SPURDIKESSpurdikes are river training structures constructed along the banks of rivers and flood dikes to deflect or repelthe flow for the purpose of training the course of theriver channel and to protect the banks from scouringby inducing siltation in the area.

A. Location and AlignmentB. LengthC. SlopesD. HeightE. Top WidthF. Spacing

6. DETAIL DESIGN CRITERIA AND STANDARDSDesign of DamsLocation and Alignment

1. For earth fill, rock fill and low gravity dams can be built on gravel foundation.2. For gravity dams these can be built on earth foundation; and their height in this case is limited to 20.0 meters.

B. Freeboard

Freeboard which is one of the elements for deciding the dam crest elevation.

C. Slope

1. Earth fill Dam

Upstream Slope = 3:1 (3 hor. 1ver.) Downstream Slope = Previous zone embankment

2. Rock fill Dam

Upstream Slope = 0.5:1 Downstream Slope = 1:1.3

3. Concrete Dam

Upstream Slope = Vertical Downstream Slope = 0.7:1

D. Height

Dam Crest Elevation = Design Flood Water Level(DFWL) + Hf (free board)E. Top Width

The width of dam crest shall be determined considering the minimum required width forconstruction and utilization as road afterconstruction, etc. The recommended width isas follows:

W > 0.2H + 3.0 where:W = Width of dam crest mH = Dam height, m

F. EasementThe banks of rivers and streams and the shoresof the seas and lakes throughout their entire Length and within a zone of three (3) metersIn Urban areas, twenty (20) meters in agricultureAreas and forty (40) meters in forest areas, alongTheir margins, are subject to the easement of public use in the interest of recreation, navigation,Floatage, fishing and salvage.

2. Design of Dikes/Embankments/Levees The term dike/levee is an embankment constructed parallel to the banks of a stream, river, lake or other body of water for the purpose of protecting the landside from inundation by floodwater, or to confine the stream flow within its regular channel.

a) Types of Levee 1. Urban Levees - Levees that are constructed to provide protection of the densely populated communities, including their industrial, commercial, and residential facilities against flooding.

2. Agricultural Levees - Levees that provide protection from flooding in lands used for agricultural purposes.

b. Classification of Levees According to Use. 1. Mainline and Tributary Levees Levees that lie along a mainstream and its tributaries, respectively. 2. Ring Levees Levees that completely encircle or ring an area subject to inundation from all directions. 3.Setbacks Levees Levees that are built landward of existing levees that have suffered distress or are in some way being endangered, as by river migration.

Location and Alignment

Embankment should be located along high ridges or natural banks where materials for construction of same are available.2. Embankment should not be close to the river banks otherwise it will be in danger of beingundermined by the caving of the river bank.3. The embankment should be well away from the estimated meander belt of the meandering river.4. The alignment should be as straight as possible,as sharp curves are subject to direct attack from flow and should be avoided.

B. FreeboardThe freeboard allowance corresponding to theDesign flood discharge

DESIGN DISCHARGE, Q (M3 /S) FREEBOARD, Hf (m)Less than 200 0.60200 to less than 500 0.80500 to less than 2000 1.002000 to less than 5000 1.205000 to less than 10,000 1.50More than 10,000 2.00

Top width of the embankment may not be of special importance if ample freeboard and side slopes are already provided. However, adequate widths of the top embankment may be required to serve as a road for facilitating the transport of materials during the construction stage and maintenance operations. Below are the recommended top widths for the given design discharges.

C. Top width

D. Slope

1. The normal side slopes on both landside and riverside of the embankment are 2:1 for low embankment (4). 2. A side slope of 4:1 is usually used for embankment consisting of sand and shall be protected by providing a cover of good soil sodded at least 500 mm thick. 3. For landside side slope, the coarser or more permeable the material is, the flatter would be the side slope.

E.Height The height of the embankment is reckoned from the design flood elevation plus an additional freeboard allowance depending on design discharge as shown in Table 3.1.

D.Slopes

F. Berm Berm are provided along the slopes of high embankments as an erosion control measure and also to improve the stability of the side slopes: 1. Riverside When the crest height from river bed is more than 6.00 metres, berms shall be provided at every 3.00 to 5.00 metres in height from crest elevation with a width of 1.00 metre or more.

2. Landside When the crest height from existing ground is more than 4.00 metres, berms shall be provided at every 2.00 metres to 3.00 metres in height from crest elevation with a width of 3.00 metres or more. 3. Masonry dike may have a minimum berm width of 1 metre when necessary, for stability purposes.

3. Design of ChannelNatural channel refer to all channels which have been developed by natural processes and have not been significantly improved by humans. Artificial channel includes all channels which have been developed by human effort.

Prismatic - has both a contrast cross-sectional shape and bottom slope. Channel which do not meet this criterion are termed a non-prismatic.Canal - refers to a rather long channel of mild slope. These channels may be either unlined or lined with concrete, cement, grass, wood, bituminous material, on an artificial membrane.Flume - refers to a channel built above the ground surface to convey a flow across a depression. It is usually constructed of wood, metal, masonry or concrete.Chute and Drop - a chute is a channel having a steep slope. A drop channel also has a steep slope. Drop channel also has a steep slope but is much shorter than a chute.Culvert - a culvert only partially full is an open channel primarily used to convey a flow under highways, railroad embankments, or runways.

A. Location and Alignment 1.Regulation works should aim at stabilization of sand bars and shallows in the inner banks and this can be obtained by giving the low water channel an S-shaped alignment with appropriate radii of bends.2.The minimum angle of 500 curvature is acceptable to obtain a fully developed helical flow which will stabilize and sand bank in the inner bend.3. Short cutting of a sharp bend in a meandering river channel in alluvial flood plain by a cut-off channel will avoid bar formation of curved flows, reduce flood levels in the upper reaches and accelerate flood discharges.4. The alignment of cut-off channels should be such that at both ends the cut is tangential to the main direction of river flow.5. The entrance to the cutoff channel should be bell mouthed.

a) Rectangular Channel1. A freeboard of 0.60 metre for velocities of 10 m/s or less. For curve alignment, the wall height must be at least 0.30 m above the superelevated water surface.2.A freeboard 0.90 metre for velocities higher than 10 m/s. For curve alignment, the wall height must be at least 0.60 m above the superelevated water surface.3.If the flow is supercritical, the wall height shall be equal to the sequent depth but not less than the heights required in items 1 and 2 above. Special consideration shall be given to additional freeboard if the channel is not designed to reduce or eliminate the formation of waves.

B. Freeboard

Channel freeboard shall be provided by an additional wall height above the design flood level. This freeboard shall be based on the following criteria:

b) Trapezoidal Channel1. A freeboard of 0.80 metre for velocities of 10 m/s or less. For curve alignment, the wall height must be at least 0.30 metre above the superelevated water surface.2. A one (1) metre freeboard for velocities higher than 10 m/s. For curve alignment, the wall height shall be at least 0.60 metre above the superelevated water surface.3. If the flow is supercritical, the wall height shall be equal to the sequent depth but not less than the heights required under Items 1 and 2 above. Special consideration shall be given to additional freeboard if the channel in not designed to reduce or eliminate the formation of waves. Roadside drainage channels used for diverting or removing surface water from the highway right-of-way shall be designed for a ten (10) year storm with a freeboard of at least 0.15 m. Channels not included in the above categories shall be designed for a ten (10) year storm with sufficient freeboard to contain a storm of 50 years frequency.

C.Slope The longitudinal slope is governed by topography, the non-scouring and non-silting velocity requirements in the channel, or it may depend on the purpose of the channel. The side slopes of the channel depend on the kind of stream bank materials as shown in Table 3.7. Table 3.7 Recommended Channel Side Slopes

A. Location and alignment1. Along meander bends of the river.2.At downstream and upstream of hydraulic and other related structures where turbulent flow usually occurs.3. It should be smooth to prevent formulation of vortices and dead water zones.4. Along side slopes of irrigation canals to prevent loss of water due to percolations. Figure 3.5 Location of Revetment of River Bend4. Design of Revetment

B. FreeboardGenerally, a minimum free board allowance of 0.60 m above the maximum experienced flood level or design flood level, as the case may be, is provided for revetments confining flood flows. C. Slope Slope of revetment will depend on the kind of materials used and protection works required for the structures. Table 3.3 shows the recommended slopes of revetment with respect to the kind of materials to be used in the construction of said structure.

Heights of revetment will depend on the maximum experienced flood level or design flood level. For other cases when combined with flood control works such as levee/embankment, the height of the revetment is up to the designed height of the structures due to the possibility of the occurrence of floodwaters that may exceed the design flood level or the crest of the dike. If the height of revetment is more than 5.0 meters, berm must be provided in order to separate the revetments into segments, as well as in consideration of site and geological condition and structural stability of the revetment. Berms shall be at least 1.0 meter in width for maintenance purposes.

Figure 3.6 a H < 5 metersFigure 3.6 b H >5 metersD. Height

E.. Depth of Foundationa. For a narrow river (less than 50 meters in width) the minimum depth of revetment foundation should be 1.0 meter below the deepest elevation of the original or design riverbed, where soil materials are subject to erosion/scouring. b.For a wide river (more than 50 meters in width) and subjected to river bed degradation, more than 1.0-meter depth of revetment foundation should be considered. In case of a wide river where the velocity is generally mild and when the mainstream course is fixed and flowing more than 20 meters away from the bank, the foundation may be placed 1.0 meter below the existing toe of the bank. If the mainstream course has a tendency to change, the foundation depth should be determined.c. If the construction of the revetment foundation below the original or designed riverbed is not possible due to high water level, the used of sheet piles or other types of revetment should be considered.

Figure 3.7 Depth of Revetment Foundation

F. Segment LengthThe length of one segment of revetment along the longitudinal direction should not be more than 50 meters in order to prevent damage on the adjoining section of the revetment once it collapses. Edge of the segment shall be provided with end protection and adequately filled with joint filler or sealer to connect with the adjoining section. G. ThicknessThe thickness of revetment is generally based on the flow velocity, sediment runoff, topography, geological conditions, scouring and degradation and soil and groundwater pressure at the back of revetment and other factors. Minimum thickness should be 300 mm for all types of revetment, except for reinforced concrete type.

H. WeepholesRevetment should be provided with weepholes ranging from 50 75 mm in diameter PVC pipes spaced at 2.00 meters on center and staggered. Pervious materials consisting of graded gravel or geo-textile is placed between the revetment and original ground. I. End Protection Works Revetments should be provided with end protection works to prevent scouring at the upstream and downstream ends. The scouring causes the escape of backfill materials resulting to the gradual damage of the revetment. A transition structure like gabions/boulders should be provided on both ends of the revetment.

Figure 3.8 End Protection Works

5. Design of SpurdikesSpurdikes are river training structures constructed along the banks of rivers and flood dikes to deflect or repel the flow for the purpose of training the course of the river channel and to protect the banks from scouring by inducing siltation in the area.A spurdike is classified into two types, namely: 1. The permeable type allows the water to flow through and reduces the velocity by its resistance in order to induce sedimentation thereat. 2. The impermeable type tends to deflect the flow away from the bank.

A. Location and Alignment1. Spurdikes are designed either perpendicular to the bank or deflected upstream or downstream, making a deflection angle of 10 to 15 degrees with the line perpendicular to the bank at straight sections and 5 to 10 degrees and 0 to 10 degrees for concave and convex sections, respectively.2.The abutment of spurdikes should be protected with revetment to prevent scouring when the spurdike is overtopped.3.Spurdikes deflected upstream will deflect the flow towards the center of the river with scouring at the tip and silting at the downstream side of the abutment, thus protecting the bank from scouring.4.The right angle spurdike is usually adopted because it gives the average effects of the deflected spurdikes but scouring at the tip can not be avoided.

Figure 3.9 Spurdike Alignment and Area of Scouring and Sedimentation

B.LengthSpurdikes should have lengths from 10 to 15 percent of the width of the river or channel but not to exceed 100 metres.

Figure 3.10 Dimensions of Spurdike

C. SpacingThe distance between spurdikes should be as follows:1. For concave sections, 1.5-2.0 times the length of spurdikes.2. For straight sections, 2.0-2.5 times the length. 3. For convex sections, 3.0-4.0 times the length. D.Slopes1. The longitudinal slope of the spurdike should be 1/20 to 1/100 toward the center of the river.2. The side slopes shall depend on the quality of the subsoil, groundwater flow and the type of structure. Underwater slopes are between 1:2-1/2 and 1:3-1/2 while slopes to be constructed in dry land are somewhat steeper.

E. Top WidthUsually, the top width of spurdikes ranges from 1 to 2 metres.F. Height Height should be at least one (1) metre above the normal or ordinary water level and at the location of the maximum velocity of flow to serve its purpose of inducing siltation along the bank.G. Toe Protection WorksProvide protection works at the toe of spurdike to prevent scouring and its collapse/damage.

Figure 3.11 Toe Protection of Spurdike H. Depth of Embedment1.For concrete and masonry type of spurdike, a minimum embedment depth of 0.5 m is recommended. For the permeable type (i.e., pile-type, crib-type, etc.), an embedment depth of 2/3 the pile length is recommended.2. For gabion, boulder, and concrete block type spurdikes, provision of 0.2 metre layer of gravel before placing the main body is recommended.

III. DESIGN PROCEDURESFor Dikes/Embankment/leveesFrom the location or topographic map of the project area, establish the alignment of the embankment (s) considering the present course and probable meander of the river.

2. For confining dikes, the width of the floodway or distance between parallel dikes shall be determined with due consideration to non-silting and/or non-scouring velocity in the channel.

3. Then, establish the design flood level at a particular section, using the Stage Discharge Relationship or Rating Curve, if available, or by the Mannings Formula.

4. Select the most suitable type of dike or embankment to be adopted based on the field conditions and available materials at the project site.

5. Establish an appropriate section for the dike based on the design criteria.

6. Determine the stability of the embankment slopes by the Swedish Slip-Circle Method, and check if the factor of safety is within acceptable limits.

7. Check if protection works are needed, and so, determine the appropriate type to be provided.

For RevetmentsGather all survey and hydrologic information needed for the design of revetments.

2. Compute the velocity of flow based on the design flood discharge and the river profile and the cross- section using the Mannings formula.

Determine the type of revetment to be adopted based on the design flood level and the quality and quantity of available construction materialsat the project area.

For dry boulders riprap, the size of boulders to beused can be determined from the graph (show Fig.4.2).

5. Determine by backwater analysis the design flood level along the banks to be protected.

6. Determine the kind and extent of foundation works that would be needed such as cut-off walls, sheet piles, boulder aprons, or other foot protection works, based on the maximum probable depth of scour as determine from field conditions.

For Spur DikesGather the information on design flood level, ordinary water level and river behavior.

2. From the location map of the river showing the extent of erosion and scouring establish the positions and locations of the proposed spur dikes.

3. Determine the type of spur dike to be used depending upon the available construction materials at the project area.

Determine the section, longitudinal slope, height, aswell as the length and spacing based on the design criteria.

For DamsDetermine the type of dam to be adopted based on topography of the area and kind of foundation and the available materials at, or in the vicinity of the project site.

2. Establish a trial section of the dam and compute for all forces acting on the dam based on the unit length of the dam.

Determine the location of the resultant force andcheck the stability of the trial section against overturning by computing the corresponding factor of safety and find out if they are within acceptable limits.

4. For concrete gravity dams, compute the maximum compressive and shearing stresses and check if they are within the maximum allowable values for concrete.

5. For earth dams, draw the line seepage or phreatic line on the dam body to check against piping of the embankment material as well as seepage through the same and underneath the embankment.

6. Check for possible settlement of the dam by analyzing the bearing capacity of the foundation and comparing it with the bearing stress on the same as caused by the dam.

7. If the design requirements are not completely satisfied modify and compute repeatedly the trial section until all design requirements are complied with.

For Channel ImprovementCollect all necessary information needed for the design of channels.

2. For the given material forming the channel body, estimate the roughness coefficient n, side slopes and the maximum and or minimum permissible velocity, for non-scouring or non-silting requirement as the case may be.

3. Express the hydraulic radius R in terms of the bottom width, b and depth of flow, y, by the Mannings formula.

4. Compute the water area required by the given design flood discharge and the permissible velocity, or A = Q/V

5. Compute the wetted perimeter, or P = A/R

6. Using the expressions for A and P, solve simultaneously for b and y.

7. Add a proper free board, and modify the section for practicability.

8. Long channels are usually divided into several reaches. The discharge for each is computed considering the total tributary area. The channel section is then designed to carry this discharge following the above procedures.

IV. DESIGN REVISIONThis design revision involves:

When there is modification, corrections improvement, and alterations of the project plans, as well as the quality of plans and

b) When there is a variation orders (change orders, extra work orders, supplemental agreements) of work changes. The Bureau of Design (BOD) prepared checklist of requirements for the review and evaluations of plans and variation orders for reference and guidance.

1. REQUIREMENTS FOR QUALITY OF PLANSAll the sheets in a set of plans should be uniform and of one standard size.

2. Draftsmanship should be a professional quality. Drafting and lettering works should be done in ink and with the use of technical pens and Leroy or similar lettering.

3. All words on the plans should be correctly spelled and grammatically errors in the various texts of the General Notes should be locked after.

4. The meaning and intent of the provision and/or specifications under the General Notes should be made clear and specific and leave no room for misinterpretations that may lead to Variation Orders later on.

5. Revised or new plans for specific structures and other items of work should be prepared in standard sheets and properly authenticated with signatures of concerned DPWH officials and/or consultants.

6. All plans should be prepared using good quality tracing paper preferably Mylar and half-ruled or full-ruled cross-section paper.

7. All sheets of the set of plans should be neat and clean and without any crossed-out or avoided portion thereon.

8. The title block should be made an integral part of the sheet of plan and not merely patched-up thereon.

2. REQUIREMENTS FOR REVIEW OF DETAILED ENGINEERING PLANS. 1. General plans (location plan; schematic diagram for water supply; vicinity map; legends and symbols; abbreviations; and general notes including design criteria)

2. Hydrologic and hydraulic design analysis supported by topographic map showing the watershed area and point of interest.

3. Topographic map of service area (for water supply).

4. Oceanographic investigations and analysis for shore protection works.

5. Soil investigation data and analysis.

6. Structural/stability analysis of proposed structures in SI units.

7. Profile along both banks and channels centerline and cross-sections indicating the proposed structures, maximum experienced flood control level and ordinary water level as well as as design water level.

8. Typical sections of proposed works.

9. Detailed quantity calculations.

3. REQUIREMENTS FOR REVIEW OF AS-STAKED PLANSWhen there are changes, original plan, profile and cross-section superimposed on the As-Staked plans.

2. Detailed quantity calculations of all the items of work involved.

3. Technical justifications with design analysis and computations for the proposed changes.

4. Copy of complete set of the approved original plans.

5. Copy of complete design analysis (Structural, hydrologic and hydraulic) if it will involve major revision of structures/bridges.

4. REQUIREMENTS FOR EVALUATION OF CHANGE ORDERS, EXTRA WORK ORDERS, AND SUPPLEMENTAL AGREEMENTS1. Duly signed/approved plans for the proposed changes.

2. Technical justifications for the proposed changes.

3. Design analysis and computations (in SI units) and quantity calculations for the proposed changes.

4. Copy of the complete set of the approved original plans.

5. Copy of prior clearance/authority to issue the proposed variation order.

6. Comments/recommendations of DPWH officials (Regional Director, Project Director/Manager and Project Consultant concerned.

7. Copy of approved contract and previously approved variation order(s).

NOTE: Where substitution of materials is involved, the following requirement shall be submitted:Certification on the non-availability of the specified materials by three (3) leading manufacturers or suppliers.

2. Technical specifications of the original and substitute materials.

5. REQUIREMENTS FOR EVALUATION OF FINAL CHANGE ORDERSCopy of complete set of As-Built plans duly approved by Head of Implementing Office.

2. Technical justifications for the proposed changes.

3. Design analysis and computations (in SI units) and quantity calculations for the proposed changes.

4.Copy of the complete set of the approved original plans.

5. Copy of prior clearance/authority to issue the proposed variation order.

6. Comments/recommendations of DPWH officials (regional Director, Project Director/Manager) and Project Consultants concerned.

7. Copy of approved contract and previously approved variation order(s).

Engr. AVENIDO

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