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Ripairian Ecology
University of Montana - Spring 2009 - Riparian Ecology
| Question | Answer |
|---|---|
| What are the five primary characteristics of the natural flow regime as defined by LeRoy Poff (1997)? | Magnitude - rate discharge, Frequency - Any flood over certain threshold, Flow duration, Timing and rate, Base flow vs Stream flow. |
| How is flow magnitude defined and measured, and does it vary along a river channel? | Magnitude -- Rate of discharge (Volume/Time) (Velocity x Cross Sectional Area FT^3/sec |
| How do we express the frequency of flood flows? | Any floods that are over a certain threshold. Calculated in exceedance probability (P). The probability that a flow will be equaled or exceeded. P = M//(N+1) M = rank Recurrence interval (T). T=1/p(years) ex. 5%=1/20 T=20yrs. |
| What is the relationship between the exceedance probability of a flood event and its recurrence interval? | They are inverses of each other. |
| What is the difference between the flood exceedance probabilities calculated from an annual flood series and a partial duration series? | Annual flood probability is that annual peak flow (flood) in any one year will exceed or equal a specified value. Where as partial duration is the probability that any flood event will exceed or equal a specified value. |
| What information does a flow duration curve provide? | The flow duration curve shows variability or flashiness of flows. In other words it shows how stable a flow is. |
| What is baseflow? | The flow between storm events maintained by ground water discharge. |
| What is the primary hydrologic difference between perennial, ephemeral and intermittent streams? | Perennial flows all year long. Ephemeral flows only during storm events. Intermittent streams have characteristics of both. |
| What are the primary factors that control the size and timing of the streamflow hydrograph? | Slope steepness, watershed sizes, storm characteristics and watershed characteristics. |
| Describe three ways in which rainfall can affect the stormflow hydrograph. | Watershed shape, human impacts, slope steepness, |
| Describe four ways in which the topographic characteristics of a watershed can affect the stormflow hydrograph. | Steepness, shape, aspect relative to storm, and size of drainage. |
| What are the dominant runoff processes that deliver water to streams during storm events and where would you expect a particular runoff process to be dominant? | Hortonian overland flow, groundwater flow, subsurface storm flow, saturation overland flow, macropore flow. |
| How can humans alter the dominant runoff processes in a watershed, and what is the overall effect on the stormflow hydrograph? | Urbanized landscapes (Hortonian flow)and forest harvest (infiltration excess). |
| What is bankfull flow and how frequently does it occur a) as the annual flood and b)as any flood event? | When a stream meets and exceeds the upper limit of stream bank and flows into flood plain. The occurance interval is inverse of probability or 1.5 years for annual flood or .92 years for any flood event. |
| What is the ecological significance of baseflow? | Groundwater supply for riparian vegetation. Also maintains minimum for low flows. |
| What is the ecological significance of small floods (within the channel banks)? | Maintains structure by transfering sediment down stream. |
| What is the ecological significance of moderate floods (overbank but near the stream)? | These are annual - decedal events. They are important for nutrient cycling. They scour and deposit sediment on flood plain. Seedling establishment. Provides benthic habitat. |
| What is the ecological significance of large floods (floods that cover most of the valley floor)? | These events isolate the stream from the flood plain (promote succession). They help maintain geomorphic landscape. |
| What is hotonian overland flow? | This flow happens when rainfall exceeds the soil infiltration cap. This happens most frequently in deserts. It also happens in parking lots. |
| What is groundwater flow? | This flow happens when their are slower base flows between storms. It also happens frequently in forested settings. |
| What is subsurface storm flow? | This happens when water moves through soil, but does not reach ground water. Not as rapid Hortonian flow. This happens in the Rocky Mountains. |
| What is macropore flow? | This happens when conduits for H2O flow (root channels, burrows created by small mammals). Can be very significant in forested systems. |
| What are the factors that determine the magnitude and timing of groundwater recharge from hillslopes to riparian zone? | Hillslope inputs, floodwater recharge, storm recharge stream water inputs. Steeper more confined slopes will recharge quicker than flatter less confined slopes. |
| Under what conditions would you expect the floodplain water table to be primarily controlled by a) hillslpe recharge and b) stream - groundwater interactions? | A)Wetter year round percipitation. Steeper more confined areas with courser (higher K) soils and a continous aquifer. B)Arid climate, less confined topography, areas with low conductivity. |
| Under what conditions would you be most likely to encounter a gaining dominated stream channel? | In a wetter steeper confined envirnment. |
| Under what conditions would you be most likely to encounter a losing dominated stream channel? | In an arid climate with a flatter landscape. |
| Under what conditions would you be most likely to encounter a disconnected dominated stream channel? | In a desert climate. |
| Under what conditions would you be most likely to encounter a underflow dominated stream channel? | In a topographically steep climate. |
| What factors determine the effect of stream - groundwater interactions on floodplain water table levels? | The hillslope adds water into the groundwater via run off introductions. The permiability of flood plain sediment by magnitude of the stage (hieght of river) changes, magnitude of hillslope inputs. |
| What is the hyporheic zone and where is it most likely to occur? | It is the zone of mixing of surface and ground water. It is the zone in which the stream water temperarily flows in the subsurface. |
| Give three examples of hyporheic flow in different riverine geomorphic envirnments. | Ripples on stream bed. Step pool streams. Meander bends. |
| What is the ecological significance of a) floodplain water table levels and b) hyporheic exchange? | A)Groundwater supply to phreatophytes. B)Nutrient exchange. |
| What is a phreatophyte? | Any plant species that obtains a significant portion of the water that it needs to survive from the zone of saturation or the capillary fringe above the zone of saturation. |
Created by:
JGILL40167
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