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OCR for page 137
1 APPENDS C Other Tend Use Change Effects on Recharge Several changes in land use due to natural and human-induced causes other than mining alter the landscape water budget and change recharge. Removal of forest vegetation leads to an increase in streamflow, as documented by Douglass and Swank (1972) for four watershed study sites in the Appalachian Highlands. The greater the proportion of forest removal, the greater the increase in streamflow during the first year after clearing (Figure C.1~. This increase in streamflow occurred mainly during the late summer and autumn at the Coweeta site in North Carolina (Figure C.2) and was attributed to the reduction in transpiration that increased both stormflow (Hewlett and Helvey, 1970) and baseflow. The increase in baseflow is a good indication of greater recharge. Similar results occurred in a watershed in West Virginia where deforestation of half of the watershed changed the stream from intermittent to perennial flow (Patric and Reinhart, 1971~. Surface disturbance by logging operations can reduce infiltration and increase runoff (Lull and Reinhart, 1972) and can lead to large increases in stream turbidity (Packer, 19679. Stoeckeler (1959) demonstrated that infiltration rates of forest soil declined by 10 to 20 times with woodland grazing. Such grazing has been shown to increase overland -137-

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-138- ~ i- I 1 1 ~ ~ ~ ~ r- ~ 1 16 ;~14 ~~ 12 ~ _ s~ 10 C owttta o ,llNOW x LI&OINC 110~. HUB.~BO .~c ~ /~_. _ .' -X ~ ~~ 0 10 _' o X ~ 1 1 1 ~ I . 20 30 do so do To So 90 t so REDUCTION IN FOREST STAND BASAL AREA (PERCENT1 FIGURE C.1 Relationship between streamflow increase the year after forest removal and the percentage reduction in forest stand. SOURCE: Douglass and Swank (1972~.

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-139- 5 2 1 ,~ [3 ~~N FLOW _ COWEETA WATERSHED 17 -OIL WATERYEAR a INCtIAS ~ 1.32 .35 ~ ~ 1 0. ~= JUNE JULY AUG. SEPT. OCT. NOV. OEC. JAN. FEB. EAR. APR. FIGURE C.2 Timing of mean flow before treatment and the average increase in flow produced by a Coweeta watershed which was clearcut and recut annually for 7 years. SOURCE: Douglass and Swank (1972) .

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-140- flow, and the frequency and magnitude of peak stre~mflow (Johnson, 1952~. These studies have relevance to land use during and after reclamation of surface mining. Compaction caused by grazing of surface-mined areas reclaimed as pastureland may reduce recharge by causing less infiltration and more surface runoff. Conversion of forest land to crop or pasture land use usually leads to less evapotranspiration, and recharge would be expected to increase. Short vegetation often has less interception and a more shallow root system than does forest. These effects could lead to greater soil water drainage and enhanced ground water recharge. However, infiltration can be less in croplands favoring greater overland flow than in forests (Hobbs, 1946).