World Deltas: HNRS 2010 Midterm Prof Hiatt

a delta is

a landform created by the deposition of sediment as a river flows into a larger body of water, such as an ocean, lake, or another river. These wetlands form when the sediment input from the river exceeds the dispersal processes of the drainage basin. Deltas have developed over the past several thousand years under stable sea levels and predictable material inputs from both the river and the sea, functioning as highly open systems.

deposit

the accumulation of sediment in the receiving basin

receiving basin

the region downstream of the mouth of the river

distributary channels

carry water and sediment throughout the delta plain and to the receiving basin

delta floodplain or delta plain

the subaerial (i.e., above water) low-lying land mass that is part of the deposit

channel mouths

the part of a river where the river flows into another river, a lake, a reservoir, a sea, or an ocean.

mouth bars

At the channel mouths water slows down and sediment forms

bifurcation

channel splits due to mouth bars

prodelta

is farther offshore and deeper below the influence of waves or tides. Here, sediment deposition is slowest and consists of the finer and lighter particles deposited from the river.

delta front

is the sloped portion of the deposit that is below the water level.

delta lobes

the different regions of land formed by water and sediment carried by the distributary channels. The river changes course over time and creates new lobes, and abandons old lobes.

natural levees

areas of high elevation next to the channel caused by depositing sediment during periods of high river flow.

river avulsions

a natural process in which a river abruptly changes its course, leaving its current channel and forming a new one.

source to sink

rivers carry sediment from the watershed to the delta

source

erosion from slopes and migrating river channels generate a lot of sediment

transport

rivers move sediment downstream

sink

sediment is deposited across natural rivers and floodplains

tributaries

small river or stream that flows in to a larger river or stream; a branch of the river

distributary

a branch of a river that flows away from the main stream

type of sediment

one factor that helps to determine the shape of the delta

River-dominated deltas attain a "bird-foot" morphology because

dominance of fluvial over marine fluxes enables mouth bar formation and maintenance of multiple distributary channels

fluvial

pertaining to a river

Bird Foot Morphology

type of river delta shape that resembles the outstretched claws of a bird's foot. This occurs when sediment deposition is concentrated along several narrow, elongated channels extending outward from the river's mouth. It typically forms in areas where river currents dominate over tidal or wave action, allowing the sediment to build up in finger-like projections

as the moons position changes

the tide rises and falls in response, with high tide staying in relation to the moon

perigean spring tide

occurs when the moon is either new or full and closest to Earth.

ebb curretn

moves water away from shore as the tide falls

flood current

brings water towards the shore as water rises

Primary factors influencing delta formation

relative influence of sediment supply, river fluxation, tidal energy flux, and wave energy flux.

tides create

funnel-shaped distributary channels and clear islands parallel to the flow direction

surface waves

are created by the friction between wind and surface water

Intertropical Convergence Zone (ITCZ)

The latitude that receives the most intense sunlight, which causes the ascending branches of the two Hadley cells to converge

Most delta area and delta population are in the

tropical zone

Almost all roads in south Louisiana (that are not built on raised structure) are on

old river channels of the Mississippi River

Why are sediment deposition events important for deltas

Because deltas are sinking due to the compaction of sediments. (subsidence)

To survive Relative Sea Level Rise due to subsidence and sea level rise, they must grow

upwards

what percent of the world's population inhabits deltas?

7%

tide dominated deltas result in

estuarine

wave-dominated deltas result in an

cupsate shaped deltas

river dominated deltas result in an

elongated delta shape

river/wave dominated deltas result in a

lobate delta shape

processes influencing delta evolution

River: Sediment Supply
Ocean: Erosion and Sediment Transport (tides, waves, currents, including hurricanes)
Local: Subsidence/dewatering/compaction, Plant growth
Global: Sea Level Change

Stream power, ability to carry sediment, is proportional to

velocity

most sediment is carried by the

core of the plume, and most is deposited there

Coarse sediment deposits

first and closest

Extensive subaqueous delta/clinoform extends

offshore below depth of wave influence

arctic ice is an important factor, especially regarding

waves

active delta leads to an (stage 1) an erosional headland with flaking barriers through

abandonment

an erosional headland with flaking barriers leads to (stage 2) transgressive barrier arch through

submergence

transgressive barrier arch leads to (stage 3) inner shelf shoal through

submergence

inner shelf shoal leads to and active delta through

reoccupation

Fundamental morphodynamics

the study of how landforms evolve over time through the interaction of physical processes, such as water flow and sediment transport, shaping landscapes like rivers and coastlines.

Lacustrine

deltas formed where a river meets a lake, depositing sediment in the lake basin.

bay head

deltas at the head of a bay, where a river enters and deposits sediment.

shelf delta

deltas that extend onto a continental shelf, where sediment spreads across shallow waters.

retreating headland

eroding coastal headlands where sediment is redistributed, often forming beaches or spits.

Barrier island/subsiding bay

coastal features where barrier islands form, and bays behind them subside, trapping sediments.

submerged shoal

underwater sandbanks formed by sediment deposition in shallow coastal waters.

During flooding, greatest volumes and coarsest grains are deposited

closest to the channel

Over multiple flood events,

higher ground builds next to the river

wind pressures

•Positive (pushing)
•Negative (pulling)
•Exerted on surface
•Create loads in structure
•Loads need pathway

A properly installed sealed roof deck

reduces water entry by 95%.

An unsealed roof deck allows

up to 60% of the rain that lands on an exposed area to enter the attic

flood risk =

flood probability x consequences

FORTIFIED roof, silver, and gold

reduce wind risk significantly

NNBF (Natural and Nature-Based Features) is a

community-scale mitigation option

the Nile delta is classified as

Primarily wave-dominated, with some influence from tides and rivers. arcuate (arc-like) shape

over ________ live near the nile basin

257 million people or ~20% of African continent's population

the nile basin covers over

11 countries: Burundi, DR Congo, Egypt, Eritrea, Ethiopia, Kenya, Rwanda, South Sudan, Sudan, Tanzania, Uganda

The Nile Delta itself is

only a small portion of the Nile River's run

the nile is estimated to be around

30 million years old

The Nile's longevity in essentially the same path is sustained by the persistence of

a stable topographic gradient, which in turn is controlled by deeper mantle processes.

First recorded exploration for river source occurred with Romans in 66 A.D. when

Emperor Nero launched a failed expedition up White Nile.

White Nile and Blue Nile are

the nile's major tributaries

The two rivers meet at the

Sudanese capital of Khartoum.

Blue Nile begins

at Lake Tana in Ethiopia and flows into Sudan from southeast

White Nile begins

begins at Lake Victoria and flows through Uganda and South Sudan

the sudd is

one of the largest wetlands in the world. It forms in the floodplains of the White Nile River and is characterized by its dense vegetation and floating mats of aquatic plants.

ancient Egyptian agriculture was

timed after summer floods of Nile and improved by the fertile nile soils

the aswan high dam

controlled flooding, generated hydroelectric power, supported agriculture, and created Lake Nasser, but reduced nutrient transport, harmed fisheries, and increased coastal erosion due to decreased silt deposition.

the nile is currently facing two major issues,

erosion and pollution

Aswan High Dam construction caused

serious reductions in the delivery of sediment

Coastal resilience means

building the ability of a community to "bounce back" after hazardous events

Structural designs to decrease erosion or reduce coastal risks inclde

Levees, Storm Surge Barriers, Breakwaters

Non-Structural alternatives to reduce exposure to coastal hazards include

Floodplain Policy and Management, Flood preparedness planning, Relocations

Nature-Based measures influenced by same process as natural features, but created by design to provide services include

Marsh creation, Barrier island restoration, Living shoreline protection (oyster reef)

Diversity of Scale of Coastal Resilience Efforts

Individual or household-level, Community-level, State or regional-level

TEK stands for Traditional Ecological Knowledge refers to the

understanding, practices, and beliefs developed by indigenous and local communities over generations through direct interaction with their environment.

a wetland is an area

saturated with water, either permanently or seasonally, with distinct ecosystems and hydric soils.

Hydric soil is soil that is

permanently or seasonally waterlogged, leading to anaerobic conditions.

Wetlands store carbon due to

slow decomposition in waterlogged, anaerobic soils, reducing carbon release

Wetlands play a major role in the global carbon cycle by

sequestering carbon in waterlogged soils, where slow decomposition traps organic matter. This helps reduce greenhouse gas emissions, mitigating climate change.

Wetlands help with water quality improvement by

filtering pollutants, trapping sediments and nutrients.

Wetland restoration typically involves reintroducing water to

reestablish natural hydrology, which supports the recovery of ecological functions like habitat creation, water filtration, and carbon storage.

Anerobic soil conditions =

slow decomposition

What Prevents O2 from getting into the soil?

As O2 moves into the soil, the microbes quickly consume it. the diffusion of O2 in water is 10,000 times slower than in air

A fishery is an area or industry focused on

catching, processing, and selling fish and other aquatic species or wild habitats like oceans and rivers or managed environments such as fish farms.

deltas support a diverse range of fish such as

fresh, saltwater, and brackish species

The challenges with Maximum Sustainable Yield (MSY) include

variable fish populations, limited sampling, difficulty in estimation, yearly fluctuations, social pressures to exceed MSY, and the disconnect between catch and actual abundance.

future challenges for fisheries include

climate change, habitat degration, bycatch

The delta has developed over thousands of years through

processes driven by the river's flow, which carries and deposits sediment in a fan-shaped pattern at its mouth. (Sediment, Transport, Sediment Deposition, Channel Migration, Flooding, Natural Compaction)