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Regional GW Flow
examining regional flow patterns
| Question | Answer |
|---|---|
| Recharge areas | • flow directed downward at the water table • occurs under topographic highs (hills) • generally larger than discharge areas |
| Discharge areas | • flow directed upward at the water table • generally higher flux than recharge areas • occurs under topographic lows (valleys) |
| Hinge line | separates recharge areas from discharge areas |
| What are the tree major influences of regional groundwater flow patterns? | 1. Topographic driving forces (water table configuration) 2. Basin geometry (ratio of depth to lateral extent) 3. Basin geology (variations in K from heterogeneity and anisotropy [due to layering]) |
| Influence of Topography | undulating water table results in complex flow patterns having multiple recharge and discharge areas; occurs below undulating terrain creates local, intermediate, and regional flow systems |
| What controls the depth of local flow systems? | amplitude of water table undulations |
| Stagnation points | location of very low flow develop where 3 flow systems intersect |
| Influence of basin geometry | shallow vs deep |
| Influence of heterogeneity | GW wants to preferentially flow along high K layers (less resistance to flow) and across low K layers |
| Influence of Anisotropy | in anisotropic materials flow lines are generally not perpendicualr to equipotentials. When Kx>>Kz, the flow paths tend to be shallower |
| GW & SW | streams, rivers, wetlands, & lakes are connected to GW, w/ GW entering into or seeping out of the surface water body |
| Efffluent | gaining stream |
| Influent | losing stream |
| What are the important ecological functions of GW in realtion to streams? | 1. It maintains the baseflow during dry periods. 2. It regulates the temperature of water around springs. 3. It brings nutrients (carbon, nitrogen, etc.) into the stream. 4. It supports stream-side (riparian) vegetation. |
| Explain hyporheic exchange | localized recharge and discharge; associated w/ changes in streambed topography or meandering streams; results in zone of increased chemical & microbiological activity near streams & rivers |
| Baseflow | groundwater discharge to the stream that sustains flow between precipitation events |
| Direct Pricipitation | rain falling directly on the stream |
| Horton overland flow | occurs when precipitation rate exceeds the infiltration capacity of the soil; occurs only during very intense storms or when the soil is saturated or frozen; more common in urban areas |
| Interflow | water that infiltrates vertically and then moves laterally in the vadose zone ( due to low K layer) |
| Throughflow | similar to interflow except that it emerges as seepage on the surface before entering the stream |
| Bank storage | water flow from the stream into the subsurface along the banks of the stream; caused by stream level rising during rainfall event, reversing gradients |
| when is GW discharge to lakes greatest? | near shore |
| where do subaqueous springs result from? | Flow and discharge through high K layers |
| How can discharge be measured directly? | seepage meter |
| How do wetlands form? | areas of gw discharge; occur due to complex local & regional flow systems, along gw springs that form near topographic breaks, adjacent to streams, or as a result of precipitation & runoff in closed topographic depressions |
| What is depression focused recharge? | "prairie potholes" water table is inverted due to interactions w/ SW hummocky glacial terrain resuts in closed drainage basins; preicipitation collects in these depressions creating series of disconnected ponds or sloughs source of gw recharge |
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700827381589447
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