Click to edit Master title style

Click to edit Master title style
11 Streams and Flood Processes Hyndman/Hyndman Natural Hazards and Disasters, 3rd Edition

Too Close to a River Disaster relief coordinator of Plains, Montana built new house on floodplain, 10 m back from banks of Clark Fork River Spring runoff eroded bank until house was undercut and ground was too unstable to move house Local authorities burned house before it fell into river

Stream Flow and Sediment Transport
River is not fixed structure Subject to natural processes Changes course, floods River is complex network of interconnected channels Many small tributaries flowing to few large streams, flow to one major river Valleys are eroded over thousands  millions of years Respond to changes in: Climate Amount and variability of flow Size and amount of sediment particles supplied to channels

Stream Flow Streams collect water and carry it across land to ocean
In humid regions, streams collect most water from groundwater seepage Flow increases in downstream direction Additional flow from tributary streams and groundwater enters channel Streams accumulate surface water from watershed (drainage basin): upstream area from which surface water will flow toward channel

Figure 11-1 WATERSHED OF A STREAM
The watershed of this stream near Boise, Idaho, is outlined in blue. This area includes all of the slopes that drain water to feed the stream. Fig. 11-1, p. 316

Stream Flow Discharge: volume of water flowing per unit of time
Average water velocity multiplied by cross-sectional area of stream Point velocities measured at equal intervals and depths across channel Acoustic doppler current profiler: measures water velocity at hundreds of locations based on shift in sound frequencies due to moving particles

Sediment Transport and Stream Equilibrium
Streams carry sediment downstream, eroding material in one place and depositing it in another Graded stream changes to maintain dynamic equilibrium Inflow and outflow of sediment is in balance Cross section of stream adjusts to accommodate flow, sediment volume and grain sizes Geometry of cross section is controlled by flow velocities and stream’s ability to carry sediment Stream flowing through easily eroded sand and gravel at low flow: steep banks and broad, flat bottom Stream flowing through resistant bedrock or fine silt and clay: narrow and deep channel

Figure 11-2 MEASURING STREAM FLOW
A. The cross-sectional area of a simple stream channel can be approximated by dividing it into a rectangular grid. With individual velocity measurements for each such box, the total flow would be the sum of V1 x A1 + V2 x A , where A1 and V2 are the areas of individual boxes. B. Stream flow through the San Joaquin River in California was measured using an acoustic doppler current profiler. The stream flow is then c alculated by summing the velocity of each cell by the cross-sectional area of that cell. Fig. 11-2, p. 317

Streams carry sediment downstream, eroding material in one place and depositing it in another Graded stream changes to maintain dynamic equilibrium Inflow and outflow of sediment is in balance Cross section of stream adjusts to accommodate flow, sediment volume and grain sizes

Geometry of cross section is controlled by flow velocities and stream’s ability to carry sediment Stream flowing through easily eroded sand and gravel at low flow: steep banks and broad, flat bottom Stream flowing through resistant bedrock or fine silt and clay: narrow and deep channel Streams adjust gradient (slope) in response to: Water velocity Sediment grain size Total sediment load Adjustments allow stream to transport supplied sediment over time

Total Flow of Stream Q = VA
Flow is average water velocity multiplied by cross-sectional area through which it flows: Q = VA where: Q = discharge or total flow (m3/sec) V = average velocity (m/sec) A = cross-sectional area = width x depth (m2)

Streams begin high in drainage basin Harder rocks, steeper slopes Coarser grain sizes Steeper gradient or faster water to move sediment Downstream Gradient decreases Sediment is worn down to smaller sizes Larger flow transports particles on gentler slope Eventually stream reaches lake or ocean: base level below which stream cannot erode

Stream descends from steeper mountainous gradient onto broad valley bottom Local base level Rapid decrease in gradient causes stream to change from erosional mode to depositional mode Forms alluvial fan: broad fan-shaped deposit Stream reaches base level of lake or ocean Abrupt drop in velocity causes sediments to sink down Forms delta (underwater alluvial fan)

Sediment Load and Grain Size
Streams can be provided with particles of any size from mud to giant boulders Volume and velocity of flow limit size and amount of sediment that stream can carry Coarser particles provide greater friction, slow water velocity along base of stream Limit exists to amount of sediment (load) stream can carry Large volumes of sediment from easily eroded source can overwhelm stream’s carrying capacity Excess sediment is deposited in stream channel Floodwaters carry more sediment

Streams can be provided with particles of any size from mud to giant boulders Volume and velocity of flow limit size and amount of sediment that stream can carry Coarser particles provide greater friction, slow water velocity along base of stream Limit exists to amount of sediment (load) stream can carry Large volumes of sediment from easily eroded source can overwhelm stream’s carrying capacity Excess sediment is deposited in stream channel

Figure 11-4 STREAM VELOCITY AND EROSION
This diagram shows the approximate velocity required to pick up (erode) and transport sediment particles of various sizes. Note that both axes are log scales, so the differences are much greater than it seems on the graph. Fig. 11-4, p. 318

Flooding is natural part of process of moving sediment and maintaining equilibrium Increased water velocity and water depth of flood means Significant turbulence increases erosive power of stream Increase size and volume of sediment which can be carried Break up of coarser particles into smaller ones

Velocity in Channel V n = 1.49 R2/3 s1/2
Velocity multiplied by channel roughness is proportional to average water depth of channel multiplied by square root of slope: V n = 1.49 R2/3 s1/2 where: n = Manning roughness coefficient (0.03 to 0.15) R = hydraulic radius (proportional to water depth) s = slope of channel

Carrying Capacity of a Stream
Carrying capacity is proportional to discharge: L a Qn where: L = suspended load transport rate (cm3/sec) Q = discharge (cm3/sec) n = exponent between 2.2 and 2.5

Channel Patterns The way in which streams pick up and deposit sediment determines pattern of channel, determines the way channel moves over time and the type of characteristic flooding for type of stream Meandering streams are most common Braided streams are less common and straight streams are rare Bedrock streams occur in mountainous areas of solid rock

Meandering Streams Any irregularity that diverts water toward one bank helps erode that bank Thalweg: deep and highest-velocity part of stream Streams preferentially erode outside of meander bends Sediment deposited as point bar along inside of bend

Figure 11-7 PATTERNS OF EROSION AND DEPOSITION IN A MEANDERING STREAM
A. The Carson River in Nevada illustrates the eroding cut bank on the outside of meanders and the depositional gravelly point bar on a meander’s inside. Flow is toward the right. B. Cross sections of a typical meandering stream channel from a riffle at A, downstream through pools at B and C, then finally through a riffle at D. Note that the river erodes on the outside of the meander bends where it has a deep channel, and it deposits on the inside of bends where it has a shallow channel. C. Deepwater channels on outside of meander bends and prominent point bar deposits on the inside of meander bends along Beaver Creek, north of Fairbanks, Alaska. Fig. 11-7, p. 320

Riffle D Pool Deposition Pool C Erosion Deposition Pool Riffle B
FIGURE 11-7 PATTERNS OF EROSION AND DEPOSITION IN A MEANDERING STREAM A. The Carson River in Nevada illustrates the eroding cut bank on the outside of meanders and the depositional gravelly point bar on a meander’s inside. Flow is toward the right. B. Cross sections of a typical meandering stream channel from a riffle at A, downstream through pools at B and C, then finally through a riffle at D. Note that the river erodes on the outside of the meander bends where it has a deep channel, and it deposits on the inside of bends where it has a shallow channel. C. Deepwater channels on outside of meander bends and prominent point bar deposits on the inside of meander bends along Beaver Creek, north of Fairbanks, Alaska. A Riffle Deposition Stepped Art Fig. 11-7, p. 320

Figure 11-8 OXBOW LAKE Meanders in this river near Houston, Texas, eroded the outsides of bends and migrated until one meander bend spilled over to one farther d ownstream, leaving an abandoned o xbow lake in the center of the photo. Fig. 11-8, p. 320

Relative Proportions of Meandering Streams
Meander wavelength ~ 12 x channel width or 1.6 x meander belt width or 4.5 meander radius of curvature Meander width ~ 2.9 x meander radius of curvature

Meandering Streams Meanders can come closer and closer together until floodwater breaks through neck between them, creating cutoff straight channel and oxbow lake in abandoned meander Erosion and deposition of meanders over long term moves river back and forth to create broad valley bottom: floodplain

Figure 11-9 FLOODPLAIN The darker floodplain of this northern Great Plains river was carved out as shifting meanders of the stream gradually widened the floodplain. A major flood would fill the floodplain wall-to-wall. Fig. 11-9, p. 321

Braided Streams Do not meander, instead form broad, multi-channel paths Overloaded with sediment that is deposited in islands between small channels Promoted by dry climate with little vegetation protecting slopes from erosion Characterized by eroding banks, steep gradient, abundant stream bedload Form alluvial fan where braided stream lowers gradient Particularly dangerous flood areas

Figure 11-10 BRAIDED RIVERS
A. This braided river channel of the Wairou River is southwest of Blenheim, New Zealand. B. The strikingly braided Tanana River near Fairbanks, Alaska. Fig , p. 322

Figure 11-12 HAZARD AREAS OF ALLUVIAL FANS
The highest hazard area is at the apex of the fan, where the flow concentrates. The hazard becomes less as the flow spreads out, decreasing in depth and intensity downslope. However, the path of the flow may change to concentrate on different parts of the fan as it finds the easiest way down the slope. Shown here is Copper Canyon, Death Valley. Fig , p. 322

Bedrock Streams Develops when stream erodes down to resistant bedrock
Abrupt change in gradient (knickpoint) from bedrock section to braided or meander section of stream High-gradient channels Deep, narrow cross-sections Carry turbulent, highly erosive flood flows Vortices or whirlpools can form and drill potholes in bedrock

Figure 11-13 BEDROCK STREAMS
A. The turbulent, high-energy Colorado River in Grand Canyon, Arizona. B. A steep, bedrock channel of the Shotover River in New Zealand cleans out any loose material during every flood. Fig , p. 323

Figure POTHOLES Potholes in the streambed of McDonald Creek in Glacier National Park were probably formed by rocks and boulders transported during a flood. Fig , p. 323

Groundwater, Precipitation, and Stream Flow
Some of the precipitation in an area percolates through soil to become groundwater and is collected by rivers and streams Gaining streams are fed by groundwater Losing streams lose water into the ground

Figure 11-15 GAINING AND LOSING STREAMS
In wet climates, groundwater flows into gaining streams, ensuring year-round flow. In dry climates, water from streams feeds the groundwater. These losing streams may dry up between rainstorms. Fig , p. 324

Groundwater, Precipitation, and Stream Flow
Areas of moderate to high annual rainfall: Groundwater continuously feed streams Changes in precipitation result in changes to groundwater levels, but stream inflow is generally constant Semi-arid to arid regions: Water from losing streams sinks into ground and streams may dry up between storms Flash floods can occur after any major or prolonged rainfall

Precipitation and Surface Runoff
Some precipitation flows as surface runoff during torrential rainfall Rapid runoff is overland flow Ability of ground to absorb rainwater depends on Rate of precipitation Permeability of soil Extent of prior saturation Whether ground is frozen Some regions are more prone to heavy rainfall Weather patterns such as major storm systems Higher elevations and heavy snowfall

Flooding Processes Bankfull level: level at which water spills over banks Streams generally reach bankfull every years Increase in discharge during flood involves increase in water velocity, water depth and stream width

Figure 11-16 STREAM CHANNEL AT VARIOUS FLOWS
The shape of a channel changes with the level of flow. The greater the flow, the more erosion occurs to deepen the channel and increase its capacity. Fig , p. 326

Channel erosion during bankfull stage
Low flow: 95% of time Floodplain Mean annual flow: 30% of time Bankfull flow: 2 times in 3 years on average Channel erosion during bankfull stage FIGURE STREAM CHANNEL AT VARIOUS FLOWS The shape of a channel changes with the level of flow. The greater the flow, the more erosion occurs to deepen the channel and increase its capacity. Moderate flood: every 10 years on average Channel erosion during moderate flood Stepped Art Fig , p. 326

Changes in Channel Shape during Flooding
Channel scour: depth of sediment eroded during floods Flood increases water velocity  increases frictional drag on stream bottom  causes more erosion Waning flow as flood declines  coarser material in suspension drops out  deposition raises streambed Slow water velocity at edge of deeper channel forms natural levee of sediments Nearly continuous low ridge along edge of channel May keep small floods within channel

Figure 11-17 CHANNEL CHANGES DURING FLOODING
On September 9, 1941, the San Juan River near Bluff, Utah, was at its normal depth. With early water rise (September 15), sediment from upstream deposited to raise the channel bottom. As water rose further to the maximum level (October 14), the channel eroded to its deepest point. As the flood level waned (October 26), sediment again deposited to raise the channel bottom. Fig , p. 326

Figure 11-18 NATUREAL LEVEES
A. The main channel of a river has the coarsest gravels at the bottom, grading to finer grains above; the natural levees are still finer grains settled out in shallower water; the floodplain consists of very fine-grained muds that settled out from almost still water during floods. B. Houses built on natural levees along a channel and floodplain in the Mississippi River delta. Fig , p. 327

Drag on Stream Bottom to a v2
Drag on stream bottom is proportional to velocity squared: to a v2 where: to = friction v = velocity

Flood Intensity Intensity of flood depends on discharge of floodwater and rate of rise of water Varies with time according to rate of runoff, shape of channel, distance downstream, number of tributaries Floods in small, narrowly confined drainage basins tend to be more violent

Rate of Runoff Floods more common after prolonged soaking of ground by rainfall or snowmelt More rapid transfer of water to stream can be caused by urbanization or deforestation Use hydrograph to plot volume of water over period of time, depict flood intensity graphically Discharge rises steeply to flood crest (peak discharge), falls gently

Figure 11-19 URBANIZATION AND FLOODING
This hydrograph is a plot of stream discharge versus time for a similar eighteen-hour rainfall event for the same area before and after urbanization. Note that the area under the two curves is similar, that is, approximately the same total volume of water for both floods. Actually, because less water infiltrates, the flood volume after urbanization will be a little larger. Fig , p. 327

Rate of Runoff Flash flood is flood with very steep hydrograph
Appear unexpectedly Water levels rise dangerously Highest flash-flood danger in semiarid, mountainous areas Floodwaters may rush down channel from distant storm

Figure 11-20 FLASH-FLOOD HAZARD
Regions of the United States with higher numbers (orange areas) are most susceptible to flash floods. Notice that flash floods are most severe in the driest regions of the country. Fig , p. 328

Stream Order Stream order: number of tributaries to stream
First-order streams: small, lack tributaries First-order streams join to form second-order streams, etc. Low-order streams: Water travels short distance to stream Flood rapidly in storms Less flood warning time Higher-order streams: Flood peak begins later, lasts longer Flood warning time is longer

Stream Order Storm in headwaters area may cause flooding in several first-order streams Flood crest for each stream moves downstream, arrives at second-order stream, with staggered timing in different streams Upstream: higher flood peak, shorter lag time Downstream: lower flood peak, longer lag time, longer flood duration

Figure 11-22 DOWNSTREAM FLOODING
A. Localized afternoon rainfall over Tucson, Arizona. B. Storm rainfall entering a stream precedes the flood crest that it causes. The flood hydrograph nearest the rainfall area is highest and narrowest. Farther downstream at location B, the flood hydrograph crests at a lower level but lasts longer. Still farther downstream at C, the flood crests at an even lower level and lasts longer. Fig , p. 329

Downstream Flood Crest
Flood intensity and lag time between storm and resulting flood depend on: Slope steepness Basin area and shape Spacing of drainage channels Vegetation cover Soil permeability Land use Flood hazards are more concerned with height of flood crest than timing

Flood Frequency and Recurrence Intervals
Flood frequency recorded as recurrence interval Average time between floods of given size Larger flood discharges on given stream have longer recurrence intervals between floods

100-year Floods and Floodplains
100-year flood used by U.S. Federal Emergency Management Agency (FEMA) to establish regulations for building near streams 100-year flood has 1% chance of happening in any given year (including year after similar event) 100-year floodplain is area likely to be flooded by largest event in 100 years (on average) Based on extrapolation from few large recorded events Does not account for probable changes from upstream alterations to drainage basin, human activities

Recurrence Intervals and Discharge
Statistical average number of years between flows of certain discharge is recurrence interval Inverse of recurrence interval is probability that certain discharge will be exceeded in any given year Calculated recurrence interval depends on total number of years in flood record and rank of flood in question Any new larger flood reduces rank, reduces recurrence interval

Figure 11-23 FLOOD FREQUENCY
The flood frequency plot for Squaw Creek, a tributary of the Mississippi River at Ames, Iowa, is plotted for before and after the largest flood of historical record in The recurrence interval (plotted at top) and exceedence probability (plotted at bottom) are shown. Fig , p. 330

Recurrence Intervals and Discharge
Statistical average number of years between flows of certain discharge is recurrence interval Inverse of recurrence interval is probability that certain discharge will be exceeded in any given year Calculated recurrence interval depends on total number of years in flood record and rank of flood in question Any new larger flood reduces rank, reduces recurrence interval

Recurrence Intervals T = (n+1)/m
For given-size flood, recurrence interval is: T = (n+1)/m where T = recurrence interval n = total number of years in record m = rank of flood (largest flood = 1; second-largest flood = 2; etc.)

Recurrence Intervals Example:
If largest flood on river at single location was in 1997  m1997 = 1 And have 87 years of records  n = 87 Then recurrence interval for 1997 flood is T1997 = (87+1)/1 = 88 years (average)

Recurrence Intervals Example: If in 2007 slightly larger flood occurs,
m2007 = 1 and m1997 = 2 Corrected recurrence interval for 1997 flood is T1997 = (97 + 1)/2 = 98/2 = 49 years (average) If in 2011 slightly larger flood occurs, m2011 = 1, m2007 = 2 and m1997 = 3 T1997 = ( )/3 = 102/3 = 34 years (average) Dramatic changes in calculated recurrence interval for same 1997 flood, from 88 years to 34 years

Table 11-1, p. 331

Paleoflood Analysis Short record of stream flow data is major problem
Use physical evidence of past flooding that is preserved in geologic record to reconstruct approximate magnitude and frequency of major floods Estimate paleoflood magnitude or flood height Critical information on minimum hazard of past flood

Paleoflood Analysis Early post-flood evidence: Paleoflood markers
Nature and magnitude of flood most obvious immediately afterward Useful features indicating height, velocity and size of flood: High-water marks Cross-sectional area Mean flood depth Estimated water velocity Mean flow velocity Discharge

Paleoflood Analysis Tree ring damage Slack-water deposits
Trees may preserve effects of damage from flood and indicate numbers of years since damage Height on tree indicates minimum height of flood Slack-water deposits Silt and fine sand deposited on sheltered parts of floodplains, mouths of tributaries, shallow caves, downstream from major bedrock obstructions Organic material can be dated with radiocarbon methods to indicate dates of floods Boulders often deposited where flood velocity decreases, for minimum height of flood

Problems with Recurrence Intervals
Data for recurrence interval must cover interval long enough to be representative Assumes that upstream conditions were similar through time Climate changes Human impacts (urbanization, channelization, dikes and dams, deforestation, overgrazing All floods plotted should originate from similar causes for random distribution of flood sizes

Figure 11-29 EFFECT OF URBANIZATION ON FLOOD PATTERNS
The 100-year flood for Mercer Creek, Washington, near Seattle, i ncreased dramatically following rapid urbanization from 1977 to 1994. Fig , p. 334

Mudflows, Debris Flows, and Other Flood-Related Hazards
Proportion of sediment increases to more than 20%: hyper-concentrated flow Proportion of sediment increases to more than 47%: debris flow Mud or clay dominates sediments: mudflow Volcanic material dominates sediments: lahar Solids more abundant, coarser, variable in size: debris flow

Mudflows and Lahars Tiny pore spaces and low permeability of mud slurries retain water, keep mud mobile Active volcanoes spur lahars of volcanic ash (mud-size material) Contain rocks and boulders Volcano weather produces rain for lahars

Figure LAHAR This is the flow front of one of the many fast-moving lahars racing right to left down a valley from Mount Pinatubo in the Philippines. Note that the surface of the flow is covered with rocks and pebbles, especially in the nose of the cresting flow. Fig , p. 336

Debris Flows Common and widespread
Extremely dangerous: begin without warning, move quickly Most common in mountainous areas, along active faults, empty onto alluvial fans High density of debris flows allows them to pick up large objects, move at higher velocity Base of flow can scour material from channel

Debris Flows Commonly begin with heavy rainfall or rapid snowmelt – raises pore pressure to set mass in motion, especially if disturbed by earthquake, strong wind Tend to move in surges, with boulders moved to sides and front of flow Movement slows when water drains from between fragments Long periods may pass before canyon accumulates enough debris for another debris flow to occur

Debris Flows Evidence of former debris flows:
Boulders too large for current stream to move Levees of coarse, angular material next to stream Deep, narrow channels in levees Fan-shaped deposits with coarser material around edges Rocks lodged against trees, in tree branches, in bark Bark scars high on trees Lobes of younger vegetation Drainage basin with large, actively eroding areas Active faulting, supplying broken rock

Figure 11-33 DISTRIBUTION OF SEDIMENT
A. A schematic diagram shows the distribution of grain sizes and water in a debris flow. B. The steep, bouldery snout of a debris flow that flowed from upper right to left. East of Tuscon, Arizona. Note geologists at right, for scale. Fig , p. 337

Glacial Outburst Floods: Jokulhlaups
Toe of glacier: meltwater feeds stream with occasional, sudden, catastrophic floods Glacial-outburst floods from collapse of glacial ice dam or glacial tunnel Ponding of meltwater under glacier During last ice age, huge glacial meltwater floods from continental ice sheets

Figure ICE DAM An ice jam built up at a river constriction threatens a bridge at Gorham, New Hampshire. The power shovel tries to get the river flowing again. Fig , p. 340

Ice Dams Sudden warm spell can melt and break up ice to dam a channel where it is constricted (such as bridge) North-flowing rivers have upstream thaw before downstream thaw, sending meltwater into ice dam

Other Hazards Related to Flooding
Torrential rain from hurricanes or thunderstorms Heavy rains initiated from volcanic eruption can produce mudflows Wildfires denude slopes of vegetation, increase runoff and increase likelihood of debris flows Floods increase rate of erosion

Heavy Rainfall on Near-Surface Bedrock Triggers Flooding: Guadalupe River Upstream of New Braunfels, Texas, 2002 Typical Texas summer storm stalled over central Texas for one week, dumped more than ¾ m of rain on thin soils Storm flow raised reservoir level 12 m in four days, overtopping spillway Flood gouged down Guadalupe River, reaching New Braunfels six hours after topping dam

A Flash Flood from an Afternoon Thunderstorm: Big Thompson Canyon, Northwest of Denver
July 31, 1976: Beginning of three-day celebration of Colorado’s centennial More than 3,500 people in sparsely populated canyon Thunderstorms stationary over Big Thompson Canyon, dumping 30 cm of rain (3/4 of typical annual total) in four hours Rapid runoff from mountain slopes became flash flood, 6 m deep wall of water moving through canyon at more than 22 km/hr Highway road washed out, 139 people in cars died and more than 600 others were never accounted for

A. Water recedes in the 2002 Guadalupe River flood below Canyon Lake after washing out this bridge. B. A kitchen submerged during the 2002 flood retained heavy deposits of mud. p. 341

Desert Debris Flows and Housing on Alluvial Fans: Tucson, Arizona, Debris Flows, 2006
Heavy rain on July 31, after four days of saturating rain More than 600 slope failures on Santa Catalina Mountains and adjacent ranges Severely eroded roads, clogged culverts, buried roads and small buildings

Intense Storms on Thick Soils: Blue Ridge Mountains Debris Flows
Hurricane Camille in 1969 dumped 71 cm of rain on Virginia in eight hours More than 1,100 slopes slid Intense storm stalled in 1995, dumping more than 76 cm of rain in sixteen hours Triggered more than 1,000 debris flows Included one landslide that developed into 2.5-km-long debris flow, moving at 8-20 m/s

Spring Thaw from the South on a North-Flowing River: The Red River, North Dakota – 1997 and 2009
Heavy snowstorms in winter of In spring, Red River thaws first in North Dakota while still frozen farther north, causing widespread flooding In 1997, Red River broke its 100-year record at 6.9 m above flood level Damage and cleanup more than $1 billion Floods more frequent and larger in future

A. The Red River flows north along the border of North Dakota and Minnesota, through southern Manitoba, and into Lake Winnipeg. The extent of Glacial Lake Agassiz, about 9,800 years ago, controlled the area of the 1997 flood. Water draining northeast on a gentle slope was dammed by the south edge of the continental ice sheet. B. This hydrograph shows the flood level for the Red River at Fargo, North Dakota. p. 346

Click to edit Master title style

Similar presentations

Presentation on theme: "Click to edit Master title style"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Click to edit Master title style

Similar presentations

Presentation on theme: "Click to edit Master title style"— Presentation transcript:

Similar presentations

About project

Feedback