Modes of Sustainability Definition

In text

In aquifer-storage terms

In water-budget terms

In physical changes at the river (natural side)

Sustainability – in text

Indicators and Metrics

An indicator is a system characteristic that can be used to assess resource condition or change. Characteristic may be biological, physical, chemical, socioeconomic, etc.

A metric is a specific value or range of values of an indicator that can be used in assessment or management of a resource

Some examples from hydrology:INDICATOR ASSOCIATED METRIC

Concentration of a dissolved constituent in water

A maximum concentration level recommended of a specific use

Seven-day low-flow at a streamgaging station

A specific discharge below which fish may not be able to spawn

The annual rate of land subsidence caused by extraction of ground water

A maximum subsidence rate allowed to prevent subsidence-related problems

Cautions Regarding Indicators and Metrics

Indicators and metrics are by nature simple. They can sometimes oversimplify conditions and effects, especially when taken individually. Some examples are

• In many USGS ground-water appraisal reports, authors compute the volume of ground water in storage down to some depth below land surface. This leaves open some questions such as—Is it physically and economically possible to extract water uniformly to that depth?—What unintended consequences would happen if water were extracted to that depth?

• In many areas, “safe yield” of an aquifer is considered to be the average annual recharge. This ignores spatial effects of withdrawal patterns as well as the effect of capturing all of the outflow.

• In some states, ground-water withdrawals are said to impair surface water resources if X percent of extraction at time Y is depletion of surface water. Values “X” and “Y” are arbitrary.

Consideration of Time in Use of Metrics

Response from development of surface water can occur immediately

Hydrologic response can keep pace with gradual land use changes such as urbanization, deforestation, etc.

Response from development of ground-water can range from immediate to long-term

i.e., if metric is tied to slower responses, may always be playing catch-up…

Hydrologic response to human activities can take place over a variety of time scales:

Sustainability – regional aquifer indicators

Responses of water levels (red-green map)

Changes in gravity (aquifer storage)

Both are spatially distributed

Both are affected by natural and human factors

Figure 7. Changes in ground-water levels, 2001 to 2006, in the Sierra Vista Subwatershed, Upper San Pedro Basin, Arizona.

Sustainability – in water budget terms

A function of human and natural factors

Natural Recharge (total natural inflow) +

Active management measures +

Incidental/Urban Enhanced Recharge +

Natural Discharge (total) -

Stream base flow -

Evapotranspiration -

Ground-water underflow -

Net Pumping -

Annual Deficit =

Sustainability – physical changes

Water needs study allows qualitative or quantitative (x2) definition

Quantitative – relation of hydrology to ecology

Quantitative – riparian ET need

condition class:

Stream divided into riparian condition classes by study sites. Classes were determined by using biological indicator variables (not hydrologic variables). See table 34 from water needs study.

Study sites of each class were compared to hydrologic variables (see table 37).

Class 3 (wettest) sites have highest streamflow permanence and shallowest ground water. Conversely, class 1 (driest) sites have lowest permanence and deepest groundwater. However, some riparian properties correlate to streamflow permanence (most related to herbaceous species) while others relate more closely to depth to ground water (most related to woody species).

The Water Needs study provides tools to define sustainability for the river

Prediction of sustainability

Ground-water model provides predictive tool to link to responses at river. Model calculates: Hydraulic head (water levels) – changes in head

are more reliable Flux (recharge and discharge)

Model stress period = two annually

Condition class scoring

Condition classes defined by ecology and related to hydrology

Science to Management

Condition classes defined by ecology and related to hydrology

The classes provide definition to the management goals

Relation of riparian condition class to hydrologic parameters

Predict streamflow permanence?

Not easily – model temporal resolution insufficient

Difficult to relate permanence at a site to long-term gage record owing to site-specific effects WY2002 July depth to ground water vs WY2002 permanence

R2 = 0.5973

0

20

40

60

80

100

120

-1.00 -0.50 0.00 0.50 1.00 1.50 2.00 2.50 3.00

Depth to water relative to thalweg (m)

Stre

amflo

w p

erm

anen

ce

Modes of Sustainability Definition

In text

In aquifer-storage terms

In water-budget terms

In physical changes at the river (natural side)

Application to 321?

Step 1: define sustainability (natural),for example:

Relative to condition classes – no hydrology How do you deal with natural variability?

Condition classes including depth to water/permanence

Condition classes, hydrology, ET How does estimated ET relate to sustainability?

Accretion of storage/rise of regional WLs Where spatially?

Water budget

Application to 321

Step 2: Determine the indicator(s),for example:• ground-water levels, storage change• condition classes• stream lowflow, permanence• water budget• other?

Step 3: Determine the metric(s)