Stormflow Volume Research Articles

EFFECTS OF FOREST HARVESTING BEST MANAGEMENT PRACTICES ON SURFACE WATER QUALITY IN THE VIRGINIA COASTAL PLAIN

Three small watersheds located in Westmoreland County, Virginia, were monitored to evaluate the impact offorest clearcutting on surface water quality and to evaluate the effectiveness of forestry best management practices(BMPs) for minimizing hydrologic and water quality impacts associated with timber harvesting. One watershed (7.9 ha)was clearcut without implementation of BMPs, one watershed (8.5 ha) was clearcut with the implementation of BMPs anda third watershed (9.8 ha) was left undisturbed as a control. Forest clearcutting without BMP implementation reducedstorm runoff volume and did not significantly change peak flow rates. Following site preparation, both storm flowvolumes and peak flow rates decreased significantly. For the watershed with BMP implementation, storm flow volumedecreased significantly following harvest, while peak flow increased. Site preparation did not change storm flow volumesover post-harvest conditions, but did significantly reduce storm peak flow rates. Disruptions in subsurface flow pathwaysduring harvest or rapid growth of understory vegetation following harvest could have caused these hydrologic changes.Harvest and site preparation activities significantly increased the loss of sediment and nutrients during storm events.Storm event concentrations and loadings of sediment, nitrogen, and phosphorus increased significantly following forestclearcutting and site preparation of the No-BMP watershed. Both the BMP watershed and the Control watershed showedfew changes in pollutant storm concentrations or loadings throughout the study.<br><br>Results of this study indicate forest clearcutting and site preparation without BMPs can cause significant increases insediment and nutrient concentrations and loadings in the Virginia Coastal Plain. However, these impacts can be greatlyreduced by implementing a system of BMPs on the watershed during harvesting activities.

Rainfall-runoff Responses and Roles of Soil Moisture Variations to the Response in Tropical Rain Forest, Bukit Tarek, Peninsular Malaysia

Field observations were conducted at Bukit Tarek Experimental Watershed in Peninsular Malaysia to investigate the relationship between rainfall-runoff responses and variation in soil moisture in a tropical rain forest. Stormflow depended strongly on the antecedent wetness as represented by the initial runoff rate. Though heavy rains fell in almost every month, the soil moisture decreased when fair weather was sustained. The soil moisture depleted and became dry at 160 cm depth during occasional dry spells. During dry conditions, streamflow responded quickly to rain events but declined rapidly after the rain stopped, and the soil moisture of surface soil (≤20 cm) increased but remained dry at lower depths (≥80 cm). This suggests that the rain water was mostly retained in the soil and only small proportions appeared as stormflow. As soil moisture conditions became wetter, the recession limb of the storm hydrograph was more gradual. Stormflow volume increased with increasing soil moisture. During wet conditions, the soil profile was moist at all parts of the slope. The hydraulic gradient was around 1.0 and there was downward soil water flux, which followed the pressure gradient. This suggests that subsurface flow from the upper part of the slope might also be important for stream-flow production. Positive pressures were observed at 10 cm and 160 cm depths during large storms. The behavior of the subsurface flow might be an important determinant of stormflow.

The Effects of Riparian Clearing and Clearfelling of an Indigenous Forest on Streamflow, Stormflow and Water Quality

SYNOPSIS The paired catchment method was used to measure the effects of riparian zone clearing and clearfelling on streamflow, stormflows and water quality. The forested riparian zone of a 39,6 ha, humid Northern Province catchment, amounting to 10 % of the catchment area, was cleared and kept clear of vegetation. Two years later the entire catchment was cleared by bulldozing and burning its cover of indigenous evergreen forest and scrub forest, and replanted to Eucalyptus grandis seedlings. The riparian clearing resulted in a small 55 mm (9 %) increase in streamflow in the first year, and mean increases per storm in quickflow volume of 2,32 mm (71 %), in stormflow volume of 4,60 mm (76 %) and in storm response ratio by 2,37 % (a 50 % increase). By the second year these effects were diminished, and total flow was reduced by 56 mm (19 %) below expected flow. Clearfelling and replanting of the catchment had similarly small effects on streamflow and stormflows. This could be ascribed partly to a serious drought at the time of the treatment. Only the total streamflow could be shown to have changed significantly after the clearfelling. In the first year after clearing total flow increased by 27 mm (35 %), but by the second year the rapid establishment of the eucalypt crop and a dense cover of weeds had resulted in a small decrease in total flow of 12 mm (6 %). There was no significant response in total suspended sediment (TSS) concentrations to the riparian clearing. In total the sediment loss from the catchment was 0,186 t/ha in the first and 0,046 t/ha in the second year after the riparian treatment. In the first year after the clearfelling and afforestation of the whole catchment, the only water quality variables to change significantly were K+, NO3-N, PO4 3,-P and Si. In the second year after clearfelling there were changes in TSS, K+, TP, Si, NO3-N, and PO4 3,-P. Sediment losses amounted to only 0,022 and 0,028 t/ha in the first and second years respectively. None of the concentrations in stormflow showed significant changes. Most concentration levels, and especially that of sediment, were lower during the period of the drought. We conclude that: 1. indigenous evergreen forest is a relatively conservative user of water and that the quality of water from such catchments is high; 2, clearing of riparian and other indigenous forest and scrub vegetation is not a practical means of augmenting streamflow in this region; 3. the apparently extreme treatments applied did not disturb the soil mantle enough, or for long enough, to change the mode of streamflow generation in this catchment; 4. although the extreme clearfelling treatment had a statistically significant effect on a few water quality variables, concentrations never exceeded levels acceptable for aquatic life in river water; and 5. the minimal effects of the treatments may in part be due to the below average rainfall experienced during the experiment.

Occupation des sols et régimes hydrologiques : les enseignements des bassins versants guyanais

The effect of land use and vegetal cover changes on runoff regimes is taken as one of the most typical effects of mon activity on the hydrological cycle. A presentation of the available methods and tools used by the hydrologist to assess these effects (such as the paired watershed approach), shows that even if these impacts do exist, it might be very difficult to quantify them. The data collected on ten small watersheds during the Ecerex experiment in French Guyana is taken as a case study. According to the watershed and to the hydrological parameter considered (annual runoff, peak flow), the hydrological effects of land use changes were assessed with high accuracy and quantified with a very low statistical risk, but for some of the experiments, the uncertainty was much wider and the outcome is more a presumption than a scientific proof. The major issue for evaluating the effects of any treatment is the capacity of the hydrologist to predict the hydrological behaviour which would have been observed on a specifie treated watershed under the same climatic conditions, if the treatment would not have been applied. The Ecerex experiment started with a 2-year calibration period, which has shown a wide range of runoff under natural forest : for a similar amount of rainfall, the variation of runoff within the set of the ten watershed was in a range of 1 to 5, Le. stormflow volumes varied from 7 % to 54 % of the rainfall, according to soil characteristics. The initial treatment (logging followed by mechanised land clearing) has created bare soil conditions for seven of the watersheds. The increase of stormflow during the first year after the treatment was very high (+ 228 mm to + 714 mm, or + 66 % to + 199 % in relative terms). The highest relative increases were observed for the watersheds having the lowest flows in natural conditions. The treatments applied include natural regrowth of the forest, fast-growing tree plantation (pine, eucalyptus), fruit trees plantation, grazing, traditional slash-and-burn agriculture. The effects on annual stormflow and on peak discharges were quantified for the first years after the application of the treatments.

Water balance and hydrologic characteristics of a rain forest catchment in the Central Amazon Basin

The water balance and hydrologic characteristics of streamflow and subsurface outflow were measured for a first‐order catchment draining a 23.4‐ha stand of undisturbed terra firme rain forest in the central Amazon Basin over a 1 year period. Total rainfall during the study period, representing a 1 in 10 wet year, was 2870 mm of which 1650 mm and 42 mm respectively were exported from the catchment as streamflow and subsurface outflow. A hydrograph separation technique applied to the entire streamflow record distinguished 173 storms. The storm flow volume was 88 mm, which represented only 5% of overall streamflow and less than 3% of the rainfall. The 20% of least frequent, large‐volume storms accounted for 75% of the rainfall volume and 80% of the storm flow volume. The fraction of the catchment that could account for the volume of storm flow runoff in a given storm as overland flow never exceeded 4%, even for the largest storms. The change in soil water storage from the previous year was equivalent to about 57 mm of water. Evapotranspiration, estimated as the water balance residual, was equivalent to 1120 mm per year with an uncertainty, estimated by propagating measurement errors, of ±16–21%. Evapotranspiration is significantly less than values previously reported from catchment‐scale water balance studies in the central Amazon, and is slightly lower than recent estimates derived from micrometeorologieal techniques, though differences in the latter case are within measurement error.

HYDROLOGIC EFFECTS OF CLEARCUTTING AND STRIPCUTTING LOBLOLLY PINE IN THE COASTAL PLAIN1

ABSTRACT: Harvesting 29‐year‐old loblolly pine (Pinus taeda L.) plantations on six small catchments in the Coastal Plain of west Tennessee caused variable but generally minor increases of storm‐flow volumes during the four years following harvest. The increases were primarily associated with decreases of rainfall interception rather than with soil disturbance. Harvesting had no effect on stormflow volumes in six nearby catchments of 37‐year‐old loblolly pine to which the same treatments were applied. Postharvest increases of flow‐weighted sediment concentrations averaged higher for the catchments with greater flows at both locations. During the fourth through eighth years after harvest, average sediment concentrations for harvested catchments at each location approximated closely the base rate of 62 mg L‐1 previously defined for undisturbed pine types. Thus, relatively minor postharvest increases of stormflow volumes in the six 29‐year‐old plantations and increases of sediment concentrations in all 12 catchments were limited to about four years. Nevertheless, because of potential channel erosion, the findings confirm the need to extend stream management zones well up into drainages with intermittent and ephemeral flows wherever water quality is a concern. Despite certain undesirable effects of logging (baring of mineral soil, decreased weight and depth of forest floor, increased soil bulk density), the results demonstrate the high resilience developed by pine planted on severely eroded sites in the southern Coastal Plain.

Stormflow Production in a Headwater Basin Swamp

Summer stormflow from a 1.57 km2 headwater basin in southern Ontario, Canada, which contained a 0.31 km2 valley-bottom, treed spring-fed swamp, was examined in 1987 and 1988. A large and annually constant groundwater flux emerged in the swamp, producing permanent saturated areas and a series of surface streamlets. The streamlets play a significant role in the production of an overland flow component of storm runoff. Stormflow volume produced by the basin was very small (runoff coefficients less than 0.01), but because of the well developed surface ‘streamlet’ system stormflow response and recession were rapid. Stormflow yield was equivalent to the depth of precipitation incident on the surface streamlets and stormflow volume was directly proportional to the volume of rain, indicating the size of the saturated zone was constant and not influenced by the storm rainfall. There was no evidence of groundwater being a major contributor to storm runoff. However, because groundwater controls the development of the surface streamlets and swamp saturation, seasonal groundwater hydrology and storm surface hydrology are inseparable.

A Rationale for Old Water Discharge Through Macropores in a Steep, Humid Catchment

Simultaneous observations of rapid preferential flow through macropores and isotopically “Old” water displacement remain unresolved in the Maimai (M8) catchment. Continuous, three‐dimensional soil moisture energy conditions were monitored in two discrete catchment positions for a series of storm events in 1987. Tensiometric response was related to the soil water characteristic curve, hillslope throughflow, and total catchment runoff. For events yielding ≪2 mm hr−1 peak runoff, near‐stream valley bottom groundwater systems discharged water volumes sufficient to account for storm period streamflow. This process was assisted by regular low (&lt;−40 cm H2O) matric potential conditions and rapid filling of available soil water storage. For events yielding &gt;2 mm hr−1 peak storm flow, hillslope hollow drainage into steeply sloping first‐order channels dominated old water production and most of the catchment storm flow. Highly transient macropore‐driven processes of crack infiltration (bypass flow), slope water table development, and lateral pipe flow enabled large volumes of stored water to be delivered to the first‐order channel bank at the appropriate time to satisfy catchment storm flow volumes and water isotopic and chemical composition.

Source areas contributing to the episodic acidification of a forested headwater stream

A study was initiated on the Leading Ridge Experimental Watersheds in central Pennsylvania to investigate the extent to which episodic depressions of streamwater pH result from direct channel interception of acidified rainwaters and from rapid subsurface stormflow. During a 4.78-cm rainfall event on June 6, 1986, stream pH declined from 5.93 to 5.46. Analysis of the storm hydrograph indicated that direct channel interception accounted for only 2.8% of the total stormflow volume but contributed 40% of the total increase in the concentration of H +. At peak flow, channel interception accounted for 5.7% of the stormflow volume and 72% of H +. Large increases in the height of the saturated soil zone and coinciding increases in H + concentrations in soilwater were measured at a number of soilwater observation wells. These fluctuations occurred almost simultaneously with measured fluctuations in both streamflow and streamwater H + concentrations, indicating direct interactions between saturated soilwater and the storm discharge. These results indicate that cathcments in which soil macropores permit rapid subsurface flow could be especially susceptible to stream acidification.

Subsurface stormflows in the highly permeable forested watersheds of southwestern British Columbia

Most forested watersheds in southwestern British Columbia are characterized by steep slopes, shallow but highly permeable soils peak flows occurring mainly in the fall-winter period in response to major rainstorms with prolonged duration of 24 hours of greater. A comparison of rainfall intensities with soil hydrologic characteristics, hydrograph analyses and field observations strongly suggest that rapid subsurface flows through macropores and/or the soil matrix play a dominant role in contributing to stormflow volumes and peaks of forested watersheds in this coastal region. Two mechanisms observed in field studies and considered to be at least partly responsible for the fast response of subsurface stormflows are (1) an effective flow delivery system associated with the expanding stream channels during a storm and (2) the rapid transmission of flow through macropores with low resistance. The contribution to stormflow volume and magnitude from the “new water” of current storms relative to that from the downslope displacement of the pre-storm “old water”, i.e. antecedent watershed moisture, requires close examination locally, but, as indicated by available electrical conductivity data, probably is positively related to the stormflow size. Implications of the study results are discussed with regard to peak flow estimation, landslide initiation, logging impact assessment and the movement of nutrients and contaminants.

INFLUENCE OF SMALL MAMMALS ON STORMFLOW RESPONSES OF PINE‐COVERED CATCHMENTS1

ABSTRACT: The relative abundance of small mammals in five forest land cover types on the upper Coastal Plain of north Mississippi was determined. Burrowing mammals accounted for one‐half of the total captures; one shrew species that accounted for over one‐fourth of the total captures had a strong affinity for well‐stocked pine plantations. The opportunity for detention and retention of rainfall was enhanced by burrowing activity. Reductions of stormflow volumes 12 to 15 years after replacing poor quality, upland hardwoods with loblolly pine were only partially explained by increased interception of rainfall; much of the residual reductions are postulated to be due to small mammal burrows. Small mammal activity deserves further study as an important aspect of forest land hydrology.

Changes in storm hydrographs after clearcutting at a small hardwood-forested watershed in Central Taiwan

Changes in storm hydrographs after clearcutting were determined for a small hardwood-forested watershed in central Taiwan. Skyline yarding was used to minimize soil disturbance in the watershed. Based on paired watershed regression analysis, the results indicated that neither the stormflow volume nor the response factor (ratio of stormflow volume to the gross precipitation) had been affected after the clearcutting. Median value of the peak discharge, however, was increased by 48%. The magnitude of increases diminished as the storm size increased. Initial discharge also increased after the cutting, which indicated that water stored in the soil mantle had increased as a result of vegetation removal. The increase in initial discharge also showed a similar trend of diminishing as storm size increased. The ability of a forested watershed to retain infiltrated rainwater is limited under heavy rainfall storms during the wet season. From the point of view of increasing flooding caused by timber harvesting, there was only a minor impact from clearcutting of the studied watershed.

The dependence of storm flows on rainfall intensity and vegetal cover in South Africa

Analysis of 1546 storm flows from eight small basins in South Africa provides new evidence that hourly rainfall intensity, and consequently overland flow, play a minor role in flood production in many source areas. Regressed against gross storm rainfall and maximum hourly rainfall intensities, storm-flow volumes showed: (1) decreasing sensitivity to rain intensity on high response basins; and (2) decreasing sensitivity as rainstorm size increases on the same basin. In other words, small channel-source storm flows respond to hourly intensity, but large storm flows from expanded source areas do not. Afforestation of a 195-ha basin with Pinus patula produced a detectable but unimportant decrease in storm flows and peak flows, while periodic burning of grass veld ( Themeda grasses) showed no detectable change in storm flows or peak flows. Results are consistent with previous analyses of actual data from a number of drainage basins large enough to contain perennial streams.

Estimation of stormflow volumes from small semi-arid catchments using the R-index method

Abstract The R -index method for calculating stormflow volumes was intended for use on forested and wildland catchments in the eastern U.S.A. This method is tested on data from three semi-arid catchments in South Africa and the model parameters and accuracy of the method are evaluated. Four procedures for representing catchment antecedent moisture conditions in the model are investigated and the effects on model calibration of two events of extreme magnitude are dealt with briefly. The results indicate that the R -index method is suitable for stormflow estimates in these semi-arid catchments. Parameter values for the model differ markedly to those in humid and sub-humid catchments and the effect of antecedent moisture conditions on stormflow volumes in these catchments is shown to be generally unimportant particularly for the larger events.

Effects of clearcutting and site preparation on stormflow volumes of streams in Pinus elliottii flatwoods forests

Three operational-sized watersheds in pine flatwoods of the Lower Coastal Plain in north Florida were isolated and continuously monitored for 3 1 2 years. Recording flumes assessed quantity of runoff water. After 1 year of calibration monitoring, two of the watersheds were, harvested, site-prepared, and planted under distinct harvest and regeneration practices. Minimum practices, imposed on one watershed, consisted of manual shortwood harvest of pinelands, roller drum chopping of harvest residues and residual understory, bedding, and planting. Maximum practices, imposed on another, consisted of tree-length logging of pinelands with heavy equipment, extraction of lightwood stumps, burning and windrowing of logging residue and residual understory, harrowing, bedding, and planting. Both silvicultural systems increased stormflow volumes; maximum practices moreso. Under both systems stormflow volumes apparently increased immediately following tree harvests. The increase persisted through site preparation, planting, and subsequently for 1 1 2 years without further detectable change. Results of this and two earlier reports on the effects of silviculture on hydrologic regimes of flatwoods forests are reviewed and summary conclusions drawn.

ASPEN CLEARCUTTING INCREASES SNOWMELT AND STORM FLOW PEAKS IN NORTH CENTRAL MINNESOTA1

ABSTRACT: Clearcutting aspen from the upland portion of an upland peatland watershed in north central Minnesota caused snowmelt peak discharge to increase 11 to 143 percent. Rainfall peak discharge size increased as much as 250 percent during the first two years after clearcutting, then decreased toward precutting levels in subsequent years. Storm flow volumes from rain during the first two years increased as much as 170 percent but declined to preharvest volumes in the third year. Snowmelt volumes did not significantly change. Snowmelt peak discharge occurred about four to five days earlier after clearcutting, but the timing of storm flow from rainfall was not changed.Snowmelt peaks remained above precut size for nine years after clearcutting on an area undergoing natural regeneration to aspen saplings. Partial cutting ‐ up to approximately one‐half of the watershed ‐ reduced peak snowmelt discharge because melt was desynchronized in cleared and forested parts. Clearing more than 2/3 of the watershed caused snowmelt flood peak size to double during years with snow packs in excess of seven inches of water that remained until a day when maximum air temperatures exceeded 60d̀F.

An assessment of the R-index method for calculating stormflow volumes in Natal, South Africa

The R-index method was developed in the eastern U.S.A. for calculating stormflow volumes and peak discharge rates from small forested and wildland catchments. The purpose of this study is to assess the possible adaptation of this method for calculating stormflow volumes from small catchments in Natal, South Africa. Following a description of the R-index method, procedures for testing the model on selected catchments in Natal are outlined. Initial flow rate and a seasonal variable are given as alternative indices for estimating antecedent moisture conditions for the R-index method, procedures which are unsuitable for the widespread use of this method in Natal. An attempt is made to replace these indices by a measure of antecedent rainfall without incurring substantial losses in model accuracy. Results are presented and discussed and areas of future research identified.

ASSESSING THE EFFECT OF SPATIAL PATTERN OF PRECIPITATION IN MODELING STREAM FLOW HYDROGRAPHS1

ABSTRACT: In most approaches to modeling the rainfall/runoff process, a spatially lumped description of precipitation has been assumed adequate for modeling the important characteristics of catchment response. However, theories of catchment hydrology as well as some re cent modeling studies suggest that spatial variability in precipitation may be important in determining the characteristics of stream flow hydrographs. Data from two intensive rainfall recording experiments in Illinois have been used to examine the effects of rainfall pattern on stream hydrographs for summer convective storms. A threshold analysis was introduced to distinguish storms of markedly different pattern. A mixed deterministic/stochastic modeling procedure was used to generate hydrographs resulting from storms of different patterns. It was found that differences in peak timing resulting from different patterns were highly significant, differences in the distributions of peak flow were significant and differences in the distributions of storm flow volumes were insignificant even given a long period of synthetic record. Rainfall pattern per se seems to have only a second order effect on hydrograph characteristics. Assessing the correct volume of input in a highly spatial variable pattern is far more important in predicting stream hydrographs.

EFFECT OF SURFACE MINING ON STORM FLOW AND PEAK FLOW FROM SIX SMALL BASINS IN EASTERN KENTUCKY1

ABSTRACT: Hydrologic records from six small Eastern Kentucky watersheds were analyzed to determine the effect of surface mining on storm flows and peak flows. Average storm flow volumes were not changed by surface mining, whereas average peak flows were increased 36 percent. Peak flow increases were only in the summer. Smaller peak flows are doubled; moderate ones are increased by about a third; peak flows around 100 csm seem to be largely unaffected; and the larger peak flows may have been reduced by surface mining. The maximum annual storm flows, usually in winter or spring, appeared slightly reduced. No time trend in either storm flows or peak flows could be detected in five years of postmining record. Surface mining is not a serious floodwater discharge problem.

Aqueous‐ and Sediment‐Phase Nitrogen Yields from Five Southern Pine Watersheds

AbstractNitrogen (N) in solution and associated with suspended sediments in stormflow from five reforested watersheds (1.5–2.8 ha) in northern Mississippi was determined during the 1975 water year. Samples were collected using Coshocton wheel samplers set below 0.91‐m H‐flumes. Mean yearly solution NH4‐N and NO3‐N concentrations, 0.20 and 0.01 mg/liter, respectively, did not differ among watersheds. Sediment‐N concentrations ranged from 2,410 to 6,080 µg/g and were 5.4 to 10.0 times those in the watershed soils. The N enrichment of sediment relative to soil was attributed to selective erosion of fine sediments (clay) and/or deposition of coarse sediments in transport. Significant differences in sediment N yields among the five watersheds were related to stormflow volume, sediment concentration, and sediment N concentration. Nitrogen was transported from the watersheds about equally in the sediment and solution phases. Mean solution NH4‐N and NO3‐N yields for the water year were 422 and 28 g/ha, respectively, for the five watersheds; mean sediment N yield was 395 g/ha. For the year, 8–17% of the precipitation was measured as stormflow; the remainder was deep seepage and evapotranspiration since there was essentially no baseflow.