Lecture 16

Question 1

Groundwater layers

Answer 1

• unconfined aquifers
• impermeable rock (aquiclude)
• confined aquifer
• impermeable rock (aquiclude)

Question 2

Aquifers

Answer 2

-porous rock units that have enough permeability to supply water at a rate useful to humans

Question 3

Aquiclude

Answer 3

A unit with permeability low enough to form a barrier to flow

Question 4

Unconfined aquifer

Answer 4

• has a water table everywhere

- upper surface of aquifer is water table

Question 5

Confined aquifer

Answer 5

Bounded above by an aquiclude

Question 6

Wells in unconfined aquifers

Answer 6

-if rate of withdrawal (pumping) exceeds rate of local groundwater flow, can get cone of depression in the water table surrounding the well

Question 7

Wells in confined (artesian) aquifers

Answer 7

• water table only in recharge area
• water within aquifer is under pressure
• water level in lower well rises due to hydraulic head

Question 8

Solution and mineral precipitation from groundwater

Answer 8

• solution by groundwater
• caves, sinkholes, and karst
• deposition from groundwater
  - stalagmites, stalactites
  - cement

Question 9

Solution by groundwater

Answer 9

• depends on water chemistry, especially pH, groundwater may dissolve minerals
• CO2 dissolved in rain water makes it slightly acidic
• calcite (main constituent of limestone) is particularly soluble in acidic water

Question 10

Caves, sinkholes, and karst

Answer 10

• groundwater solution creates distinctive landscape features in limestone and other soluble rock types
• caves are very large pore spaces formed by solution
• sinkholes form where the roof of a cave collapses
• karst is characterized by numerous sinkholes and/or pillars of rock isolated by solution

Question 11

Deposition from groundwater

Answer 11

-dissolved mineral ions may be deposited in response to:

1. Evaporation of groundwater in caves
2. Other changes in chemistry

Question 12

Stalagmites, stalactites

Answer 12

• mineral deposits (typically calcite) form in air filled portions of caves
• stalactites resemble icicles hanging from ceiling
• stalagmites are corresponding pillars growing from cave floor

Question 13

Cement

Answer 13

• more abundant than stalagmites and stalactites
• are mineral deposited in small pore spaces
• cement may convert:

1. Loose hand into hard sandstone
2. An aquifer into an aquiclude
3. A potential oil reservoir into a non porous non reservoir

Huge economic significance

Question 14

Overland flow and stream flow

Answer 14

• rainfall and melt-water flow down slope under gravity
• initial sheet-like overland flow
• erosion creates channels in which flow is concentrated

Question 15

Stream flow

Answer 15

• base flow (fed by groundwater)
  
  • no base flow=ephemeral
  • with base flow=perennial
• storm flow (overland flow into channel from precipitation)

Question 16

Characteristics of stream systems

Answer 16

• streams are organized in river systems
• small streams (tributaries) typically merge downstream
• area drained by a major river and its tributaries is a drainage basin
• drainage basins are separated by drainage divides