Lecture 20: Groundwater Problems

Define Drawdown

The lowering of the water table from pumping

What forms in the water table as a result of drawdown?

A cone of depression

A circular area in the water table where there is a depression in water levels as a result of pumping

What may happen to the amount of discharge of groundwater to nearby streams close to a well?

Discharge would decrease

The water table lowers below the topography

What factors influence drawdown?

1. Extraction rate

2. Aquifer properties

   1. Soil permeability

   2. How high or low the saturated conductivity is

How would the shape of the cone of depression change if the same volume of water was extracted with a higher pumping rate?

Deeper and smaller radius

The faster pumping prevents the water from flowing outward, forming a smaller circle and depression.

Faster pumping also means the water level is reduced more quickly, increasing the depth

How would the shape of the cone of depression change if the same volume of water was extracted with a greater hydraulic conductivity?

Shallower and wider

Water can move through the soil more easily so shallower, larger depressions can form

What does groundwater depletion cause land subsidence?

Water in pores holds grains together

As water is extracted, there is less water to hold grains together

The air-filled pores compress and cause grains to pack together more tightly (reducing porosity)

The compaction of the grains causes the land to sink

What percent of land subsidence due to groundwater pumping occurs over croplands and urban regions?

70%

How much aquifer storage is being loss globally a year?

17 km³/year

What are Correlative Groundwater rights?

Water divided between overlying landowners

What are Appropriate Groundwater rights?

First in time, first in right

What are Absolute Groundwater rights?

If you can pump it, it's yours

What are Reasonable Groundwater rights?

IF you can pump it and use it reasonably, its yours

What are Restatement rules?

Don’t take too much or harm others

What are some relevant regulations?

Clean Water Act

National Environmental Policy Act (NEPA)

California Environmental Quality Act (CEQA)

What is California’s Sustainable Groundwater Management Act?

Passed in 2014

Each region in California is responsible for producing their own sustainable groundwater management plan

Goal: Reach sustainable groundwater management by 2042

Involves:

Monitoring of groundwater extraction and water table

Development of basin-specific management plans

Permits and restrictions (unpopular)

Define land water storage?

The amount of water stored above and underneath the surface of the Earth

Includes:

1. Groundwaters

2. Rivers

3. Soil Moisture

4. Lakes

5. Snow