Lecture Notes Review: Hydrology and Water Resources

Flashcards generated from lecture notes covering hydrology, water quality, and erosion control for exam preparation.

What is a watershed, and why is topography crucial for its boundary?

A watershed is the land area that drains water, sediment, and dissolved materials to a common outlet; boundaries are set by topographic divides that control where water flows.

How do management priorities differ between headwaters and lowland reaches based on the erosion–transition–deposition framework?

Headwaters (upper, high-gradient zones) are dominant sources of flow and sediment routing, requiring protection of infiltration and baseflow; lowland depositional zones need floodplain/storage protection and sediment management.

If a county increases impervious area through development, what hydrologic changes would you expect in the watershed?

More runoff, less infiltration and evapotranspiration (ET), higher and quicker stream peaks, and reduced storage (ΔS).

What are two ways an unsaturated air mass can become saturated, and which lifting processes are associated with them?

Cooling (e.g., frontal or orographic lift) and moisture addition; lifting cools air to its saturation vapor pressure (SVP), triggering clouds/precipitation.

Compare cold and warm fronts in terms of typical rainfall intensity and its impact on runoff.

Cold fronts usually bring higher-intensity rain (leading to flashier runoff), while warm fronts bring lower-intensity, longer-duration rain (offering more infiltration potential).

Explain the difference in precipitation patterns between the windward and leeward sides of a mountain range.

Air is forced up on the windward side, causing cooling, condensation, and precipitation; descending air on the leeward side is drier, creating a rain shadow.

What is the watershed ET balance equation, and name a land-use change that affects ET at the basin scale?

ET = P − Q − ΔS − Δl; changing vegetation/land cover (e.g., deforestation/afforestation) alters ET by changing energy, canopy, and water availability.

Define Potential Evapotranspiration (PET) and Actual Evapotranspiration (AET), and explain why AET is often less than PET.

PET is atmospheric demand with unlimited water; AET is actual water loss and is limited by soil moisture, vegetation, and energy.

How does the ratio of ET to Precipitation (ET/P) vary between dry and humid climates, and what are the implications for water storage?

Dry climates have higher ET/P (leaving less for storage/runoff); humid climates have lower ET/P (allowing for more soil/groundwater storage and runoff).

Distinguish between infiltration capacity and infiltration rate, and what occurs when rainfall surpasses the capacity.

Infiltration capacity is the maximum possible entry rate; infiltration rate is what actually enters. When rainfall exceeds capacity, the excess becomes surface runoff.

Rank sands, loams/silts, and clays by their typical infiltration rate from highest to lowest, and explain why.

Sand > loam/silt > clay; larger pores in coarse soils transmit water faster.

Provide two mechanisms through which litter and organic matter enhance infiltration.

Litter/OM adds roughness/a barrier to sealing and builds structure/macropores via humus and soil fauna.

List three stormflow pathways and one baseflow pathway, describing their typical speeds.

Channel interception (instant), overland/surface runoff (fast), subsurface stormflow (intermediate); baseflow from groundwater (slow, sustained).

According to the Variable Source Area Concept, how do source areas change during a prolonged storm?

Saturated zones near the channel expand upslope as rainfall continues; after long/wet periods, large portions (even whole watershed) can contribute to runoff.

How do urbanization and forest cover influence hydrograph peaks and timing?

Urbanization raises peaks and shortens lag time (making it flashier); forests lower/flatten peaks and lengthen response time through increased infiltration and ET.

In which geographical regions is baseflow usually a greater proportion of annual streamflow, and what is the reason?

In humid regions with higher groundwater storage, as more recharge sustains streams between storms.

What is the central goal of the Clean Water Act (CWA), name one regulatory tool it established, and one remaining limitation?

Goal: “fishable and swimmable” waters; tool: NPDES permits for point discharges; limitation: nonpoint pollution remains a major challenge.

Provide an example of point source pollution and nonpoint source pollution, and explain why nonpoint sources are more challenging to regulate.

Point: factory pipe; Nonpoint: farm fields/roads. Nonpoint is diffuse and variable in time/space, making permitting/monitoring harder.

Outline the process of eutrophication from nutrient loading to dissolved oxygen (DO) depletion, and name the associated lake trophic classes.

Nutrient loading fuels algal growth; decay increases oxygen demand, lowering DO and harming biota; trophic states: oligotrophic, mesotrophic, eutrophic.

Describe two natural patterns of dissolved oxygen (DO) variation and one biological impact of low DO.

DO varies with season/temperature and depth/day-night; low DO stresses or kills aquatic life and shifts community structure.

What two factors influence specific conductivity, and what is a typical reference range for unpolluted rivers in Michigan?

Influenced by geology and groundwater vs. surface water inputs (also temperature, salts); ~100 µS/cm (UP) to ~300 µS/cm (LP).

Arrange splash, sheet, rill, and gully erosion in their likely sequence along a hillslope during intensifying storm conditions.

Splash (raindrop detachment) → sheet (thin removal) → rill (small channels) → gully (large channels).

List three site factors that contribute to increased water-driven surface erosion.

Higher rainfall/runoff amounts/intensity, steeper/longer slopes (higher velocity), and low vegetative cover; more erodible soils also increase risk.

Define slope failure in terms of forces involved, and describe one role vegetation plays in slope stability.

Failure occurs when shear stress exceeds shear strength; removing forest vegetation reduces root strength and transpiration, destabilizing slopes.

Describe two effects of sediment on water quality and aquatic life, and indicate when suspended sediment typically peaks on a hydrograph.

Increases turbidity and buries habitat; suspended sediment peaks on the rising limb of a hydrograph.

What are the five core principles for controlling erosion and sediment during construction?

Minimize disturbed area; stabilize ASAP; keep velocities low; divert runoff from bare soil; trap sediment onsite.

For Michigan Part 91, when is a permit required for earth changes, and who is responsible for enforcement?

Earth changes ≥1 acre or within 500 ft of water require a permit; counties/MEAs/APAs enforce with EGLE oversight.

For no-till/conservation tillage, what primary erosion/sediment mechanism does it target?

Maintains residue, reduces raindrop impact and detachment.

For cover crops, what primary erosion/sediment mechanism do they target?

Protects soil in the off-season, reduces bare soil exposure.

For contour strips, what primary erosion/sediment mechanism do they target?

Shorten flowpaths, slow runoff, increase infiltration.

For terraces/diversions, what primary erosion/sediment mechanism do they target?

Reduce slope length, control and route runoff.

For grassed waterways, what primary erosion/sediment mechanism do they target?

Safely convey flow, prevent gully formation.

For vegetated filter strips, what primary erosion/sediment mechanism do they target?

Promote infiltration and trap sediment before channels.

What specific hydrograph changes would you anticipate after implementing diversion terraces on cropland?

Lower and delayed peak discharge due to reduced slope length and controlled runoff routing.

What is one impact unique to accelerated (human-caused) erosion rates that is relevant to water resources planning?

Rapid loss of infiltration capacity and increased sediment delivery reduce channel/reservoir capacity and raise flood/siltation risks.