Laserfiche WebLink
<br /> <br />the ground-water system by an unsaturated zone, <br />Where the stream is disconnected from the <br />ground-water system by an unsaturated zone, the <br />water table may have a discernible mound below <br />the stream (Figure 10) if the rate of recharge <br />through the streambed and unsaturated zone is <br />greater than the rate of lateral ground-water flow <br />away from the water-table mound, An important <br />feature of streams that are disconnected from <br />ground water is that pumping of shallow ground <br />water near the stream does not affect the flow of <br />the stream near the pumped wells, <br />In some environments, streamflow gain or <br />loss can persist; that is, a stream might always <br />gain water from ground water, or it might always <br />lose water to ground water, However, in other <br /> <br />DISCONNECTED STREAM <br /> <br />Flow direction <br /> <br /> <br />Unsaturated <br />zone <br /> <br />----------~ <br /> <br />Water table <br />--____1___________ <br /> <br />"" <br /> <br />.... <br /> <br />Figure 10. Disconnected streams are separated from <br />the ground-water system by an unsaturated zone, <br /> <br />environments, flow direction can vary a great <br />deal along a stream; some reaches receive ground <br />water, and other reaches lose water to ground <br />water, Furthermore, flow direction can change <br />in very short timeframes as a result of individual <br />storms causing focused recharge near the stream- <br />bank, temporary flood peaks moving down the <br />channel, or transpiration of ground water by <br />streamside vegetation, <br />A type of interaction between ground water <br />and streams that takes place in nearly all streams <br />at one time or another is a rapid rise in stream <br />stage that causes water to move from the stream <br />into the streambanks, This process, termed bank <br />storage (Figures 11 and 12B), usually is caused by <br />storm precipitation, rapid snowmelt, or release of <br /> <br />BANK STORAGE <br /> <br />Flow direction <br /> <br /> <br />i7 <br />, <br /> <br />-r-r- <br />if f r r <br /> <br />-----------~:: <br />r- <br />Water table <br />during base flow <br /> <br />Figure 11, If stream levels rise higher than adjacent <br />ground-water levels, stream water moves into the <br />stream banks as bank storage, <br /> <br />"Streams interact with ground water <br />in three basic ways: streams gain <br />water from inflow of ground water <br />through the streambed (gaining stream), <br />they lose water to ground water by outflow <br />through the streambed (losing stream), or <br />they do both, gaining in some reaches <br />and losing in other reaches" <br /> <br />l <br /> <br />10 <br />