Geography 2412

Lecture Notes: Chap. 12: Hydro Environment
Sections: 12.1; 12.2; 12.4; 12.6; 12.7; 12.9; 12.10

Basic hydro cycle (12.1 and lecture material)

–Evaporation and transpiration (ET)

–Precip (P)

–Runoff (Ro)

–Infiltration (I)

–Ground Water

 Some key human interventions in the hydro cycle (also the subject of this week’s recitations):

Purposeful Interventions

–       Evaporation and transpiration (ET): remove vegetation (burning, spraying; etc.)

–       Precip (P): cloud seeding

–       Runoff (Ro): stormwater drains; dams/reservoirs

–       Infiltration (I): plowing; impermeable covers; GW injection/recharge

–       Ground Water: pumping to sfc/discharge

  • Evaporation and transpiration (ET): remove vegetation (burning, spraying; etc.) : farmers kills weeds sometimes because they compete with crops for soil moisture, that they then ET to the atmosphere. Some resource managers argue that we should cut down more trees to increase water runoff into reservoirs..
  • Precip (P): cloud seeding is the chief technical intervention here, it is founded on the the notion that rain and snow are often limited by the concentrations of condensation nuclei, not just be water vapor, and if you add more, you’ll get more precip. Example: cloud seeding project in Florida to make thunderstorm produce more rain; Denver Water board paid for a private contractor to seed snowstorms last winter in the mts. Results: in my view, pretty uncertain, hard to prove an effect.
  • Runoff (Ro): stormwater drains move runoff fast thru citites and into stream networks to prevent urban flooding; ; reservoirs intercept and at least temporarily store runoff.;
  • Infiltration (I) [please note, the terms infiltration and percolation are the same process: water being absorbed into the ground rather than running off). plowing: farmers sometimes plow to help rain and snow melt get into the soil; impermeable covers are sometimes used to reduce infiltration into soils where we do not want them to get wet, e.g., around buildings like houses; also that may cause landslides when they get saturated. GW injection is used sometimes to recharge aquifers, store water, or dispose of waste water.
  • Ground Water: pumping to sfc: the most obvious intervention into the ground water.

Inadvertent or Unintended Interventions

–       Evaporation and transpiration (ET): deforestation; sfc water storage

–       Precip (P): air pollution, global warming

–       Runoff (Ro): paving and structures 

–       Infiltration (I): soil compaction

–       Ground Water: fill wetlands; water-logging

  • Evaporation and transpiration (ET): deforestation reduces ET; sfc water storage increase ET, which isb bad if you want to keep the water.
  • Precip (P): some forms of air pollution may enhance precip by providing more condensation nuclei; global warming surely affects the whole hydro cycle, including ET and P.
  • Runoff (Ro): paving and structures of all sorts increase runoff by reducing infiltration.
  • Infiltration (I): soil compaction by many types of human activities from farming to hiking and mt biking, can decrease I.
  • Ground Water: filling wetlands for development educes the recharge of aquifers; water-logging occurs as ground water tables rise due to over-irrigation.

Streamflow and Floods (Sec. 12.4)

Changes in flow pattern (hydrograph) due to land use development in a watershed: more flood prone or "flashy" (Fig. 12.11). For a given amount of input (P) the runoff pattern changes to more peaked.

Changes in flow due to dams (see pp. 259-260): reduced peak flows; altered seasonal and total discharge; reduced sediment; reduced temp in many parts of the world (like western US); de-watering. All of this leads to altered biota: some species reduced, some increased (e.g., because dams in the western US create clear, cold conditions downstream, warm-water fish disappear and coldwater fish (e.g., sporfish like trout) either diffuse in or are planted. .

Ground Water: a key resource in most parts of the US and the world. One problem is that aquifers are often over-pumped, meaning that discharge thru pumping is greater in time and volume than recharge; that is, pumping to sfc; often exceeds recharge (above "safe aquifer yield"). This is true for the Ogallala Aquifer labeled on the map (Fig. 12.16), where farmers use ground water for irrigation. As the text point out, this aquifer is recharged slowly (if at all under current climate conditions) and the water being pumped has been in the aquifer for hundreds and maybe thousands of years). Local note: some of the porous sandstones that hold the Ogallala actually tilt up to the surface here at the edge of the Rockies including the Flat Irons—so this could be considered a recharge zone). Programs to reduce pumping rates have succeeded in reducing over-draft in many parts of the Ogallala region.

Wetlands: areas of land often with standing, shallow surface water, water-loving vegetation, and important wildlife habitat; important habitat and recharge areas for aquifers; wetlands also: act as fish nurseries on the coasts; help clean water by straining out sediment; and act as flood buffers along streams and rivers.

Wetlands have experienced a net decline with land development in US and world—simply put, we need to drain wetlands for agriculture and settlement. Some protections in federal and state law, some artificial additions, but by most assessments probably a net loss still on-going, and the habitat quality of anthropogenic wetlands remains to be seen.

Water resources: main uses (Table 12.3)

  • Domestic/municipal
  • Industrial
  • Agriculture
  • Power generation (cooling)

Consumptive vs. non-consumptive uses: irrigation consumes thru ET more than 50% of water used; most industrial and domestic/municipal uses consume 10-20 % (so, your household water use, except for watering lawns and washing cars) most goes back into Boulder Creek via the wastewater system---it is put back in at the treatment plant out by my house at Jay Rd and 75th street—worth a visit to see where your water goes after it goes down the drain!

Degrading uses: most human uses degrade water at least somewhat, with:

  • Sediment: erosion from agricultural lands
  • Biological agents: pathogens in sewage
  • Chemical pollutants: wastes of all sorts, from industries, households, and urban stormwater runoff (e.g., crankcase oil from roadways);
  • Thermal pollution: especially from power plants cooling water
  • Reduced flows" that reduce the stream habitat quality and ability to dilute other pollutants.

Some of these degradations are reduced in waste water treatment, but others, like ag and urban runoff are not captured for treatment, but may be diluted as they flow into drainage networks.

Allocation: Water is something of a “Common Property” resource---like air, wildlife, it moves around, who can “capture” and use it?

•        Allocation in US:

–       Riparian: adjacent land owners use water

–       Prior appropriation: water is owned as property, can be moved around.

–       Also: treaties: with Mexico on Colorado

•        But how d we “allocate” to the environment? Very difficult for a resource people want to extract and use. Common approach is: Instream flow: allocate enough to meet ecological uses and services, but who allocates and who loses water for these “uses”?