Earth Science Exam 2: Rivers

What is topography?

• Shapes & features of the land surface 

  • landforms (hills & valleys, etc.) & elevations 

  • rivers, lakes, & land cover 

What is drainage basin?

• Area that supplies water to a river

What is drainage divide?

• A boundary that separates neighboring drainage basins

What is a river?

• A flow of water in a channel

  • confined by banks

  • transports water + sediments + ions

What are perennial rivers?

• A year round flow

What are intermittent rivers?

• A seasonal flow

What are ephemeral rivers? 

• An event driven flow (after rain or snowmelt and dry the rest of the time) 

What is the first variable for the manning equation?

• V = velocity (m/s or ft/s); average water velocity

What is the second variable for the manning equation?

• R = hydrologic radius (m or ft)

  • A = cross sectional area of flow

  • P = wetted perimeter

What is the third variable for the manning equation?

• S = channel slope ( gradient along channel)

What is the fourth variable for the manning equation? 

• n = manning number 

  • rouge = larger

  • smooth = smaller

How does water velocity control the grain size and amount of erosion?

• faster flow moves larger sediment (higher competence)

• faster flow moves more sediment- more bed and bank material eroded (higher capacity)

How does erosion and deposition vary across a river bend and how does this relate to the development of cutbacks and point bars?

• outside of bend = faster flow (erosion of cutbank)

• Inside bend = slower flow (deposition of point bar)

How respectively do oxbow lakes develop?

• erosion and deposition at bends

How do gorges develop?

• when river is high above base level

How do waterfalls develop?

• strong bedrock will erode

What are sediment loads of rivers, and how does bed load change during transport?

• Dissolved load = ions

• Suspended load = silt & clay

• Bed load gets rounder & smaller as transported

What is a floodplain of a river?

flat area beside a river that gets flooded - usually dry land - sediment deposited during floods - builds higher near channel 

What is a delta of a river? 

forms when flow slows at river mouth - front slowly advances 

What may happen soon along the lower Mississippi River in Louisiana and why?

• it could attempt a natural avulsion, breaking out of its current channel to flow along the shorter, steeper Atchafalaya river route

• this could significantly alter the rivers course

What are the two types of food and what are their general characteristics?

• Regional: main stem rivers - large area and long duration

• Flash: headwater tributaries - small area & short duration - rapid onset, deep and fast flow, over quickly

How do rainfall intensity and topographic focusing affect the severity of flash flood?

• Typically 3+ inches per hour rate, sustained 1+ hours - thunderstorms

• In narrow valleys increasing flood height

When during the year are rivers in central NY at their seasonal highest and when lowest? 

high in winter and spring 

low in late summer and fall

When during the year and for what reasons do floods happen in central NY?

anytime

hurricane rainfall (intense) - worse if slow-moving

warm rain on wet snow

ice jams

mid-latitude cyclones

How do deforestation and urbanization affect the size and onset speed of floods?

• deforestation increases peak river discharge

• urbanization increases peak river discharge even more

What happens during lithification of sediment to sedimentary rock?

Sediments are compacted and cemented together

Why does foliation develop in many metamorphic rocks? 

It develops when stress causes minerals to recrystalize in a single orientation 

Which one of these topographic or geologic factors at a hillside will increase the chance of a mass wasting event?

A road cut has removed mass from the base of the slope

What happens on the outside of a river bend?

erosion here will cause development of a cutbank

What is the lower Mississippi River currently threatening to do in Louisiana?

Divert into the Atchafalaya river and take a different route to the ocean