A CASE STUDY OF SHALLOW FLOW PATHS IN A STEEP ZERO-ORDER BASIN1

ABSTRACT: Soil water potentials, slope throughflow, runoff chemistry, and isotopic composition were monitored in a 97 m² zero-order basin within the Maimai 8 watershed on the South Island of New Zealand, for a natural rain storm and two artificial water applications. Contrary to results previously reported for other portions of the Maimai catchment, much of the runoff occurred as a shallow subsurface organic layer flow. For the 47 mm natural rain event, pre-storm soil matric potential ranged from ?60 to ?150 cm H₂O. No saturation was produced within the profile, and the majority of storm runoff emanated from flow within the organic horizon perched on the mineral soil surface. Hillslope applications corroborated this interpretation by showing >90 percent new water flushing with negligible mineral soil moisture response. Although the mechanisms cited in the text are not representative of the entire catchment, the study demonstrates: (1) the value of a combined physical-chemical-isotopic approach in quantifying slope processes, and (2) the heterogeneous nature and diversity of slope runoff pathways in a relatively homogeneous catchment.     

ANALYSIS AND MODELING OF LONG-TERM STREAM TEMPERATURES ON THE STEAMBOAT CREEK BASIN,OREGON: IMPLICATIONS FOR LAND USE AND FISH HABITAT1

ABSTRACT: Steamboat Creek basin is an important source of timber and provides crucial spawning and rearing habitat for anadromous steelhead trout (Oncorhynchus mykiss). Because stream temperatures are near the upper limit of tolerance for the survival of juvenile steelhead, the possible long-term effect of clear-cut logging on stream temperatures was assessed. Twenty-year (1969–1989) records of summer stream temperature and flow from four tributaries and two reaches of Steamboat Creek and Boulder Creek (a nearby unlogged watershed) were analyzed. Logging records for the Steamboat Creek basin and air temperature records also were used in the analysis. A time-series model of the components of stream temperature (seasonal cycle of solar radiation, air temperature, streamflow, an autoregressive term of order 1, and a linear trend variable) was fitted to the water-temperature data. The linear trend variable was significant in all the fitted models except Bend Creek (a tributary fed by cool ground-water discharge) and Boulder Creek. Because no trends in either climate (i.e., air temperature) or streamflow were found in the data, the trend variable was associated with the pre-1969 loss and subsequent regrowth of riparian vegetation and shading canopies.     

WATER TABLE INDUCED SHRUB-HERBACEOUS ECOTONE: HYDROLOGIC MANAGEMENT IMPLICATIONS1

ABSTRACT: Environmental factors were investigated across a shrub-herbaceous ecotone (sharp zone of change) on a sloping site underlain by shallow groundwater on the arid floor of Owens Valley, California. Dominant plant species were salt rabbitbrush (Chrysothamnus nauseosus ssp. consimilis [E. Greene] Hall and Clements) and saltgrass (Distichlis spicata var. stricta EL.] E. Greene); typical of many similar habitats across the Great Basin. Historic air photographs were analyzed, and soil properties, water table levels and shrub and herbaceous cover were measured at discrete sample points. To investigate soil and vegetation spatial properties, sample points were apportioned on both sides of the ecotone. Land management practices and fire were ruled out as causal factors for the ecotone which remained stable through a 45-year period of air photo record. Soil textural, chemical and hydraulic properties were similar across the ecotone and were uniform throughout the site. Only depth to the water table changed significantly in a gradient perpendicular to the ecotone. The shrub-herbaceous ecotone was located where the water table depth fluctuated periodically between 0.8 and 1.2 m; deeper water tables than this range favors shrub cover while shallower depths favors meadow vegetation. When extrapolated to hydrologic management such as groundwater pumping, such a shallow depth and a narrow range of amplitude could restrict options for water development if maintenance of meadow vegetation is a goal.     

EFFECTS OF BASIN-SCALE TIMBER HARVEST ON WATER YIELD AND PEAK STREAMFLOW1

ABSTRACT: Streamflow changes resulting from clearcut harvest of lodgepole pine (Pinus contorta) on a 2145 hectare drainage basin are evaluated by the paired watershed technique. Thirty years of continuous daily streamflow records were used in the analysis, including 10 pre-harvest and 20 post-harvest years of data. Regression analysis was used to estimate the effects of timber harvest on annual water yield and annual peak discharge. Removal of 14 million board feet of lodgepole pine (Pinus contorta) from about 526 hectares (25 percent of the basin) produced an average of 14.7 cm additional water yield per year, or an increase of 52 percent. Mean annual daily maximum discharge also increased by 1.6 cubic meters per second or 66 percent. Increases occurred primarily during the period of May through August with little or no change in wintertime streamflows. Results suggest that clearcutting conifers in relatively large watersheds (> 2000 ha) may produce significant increases in water yield and flooding. Implications of altered streamflow regimes are important for assessing the future ecological integrity of stream ecosystems subject to large-scale timber harvest and other disturbances that remove a substantial proportion of the forest cover.     

SNOWPACK CHANGES RESULTING FROM TIMBER HARVEST INTERCEPTION,REDISTRIBUTION, AND EVAPORATION1

ABSTRACT: Three processes were examined as causing snowpack changes in forest clearings. Two of the three contribute to increases and one counteracts by reducing snowpack. The two that increase snowpack are redistribution and decreased loss to interception. Snow evaporation from a clearing counteracts snowpack increases. Research has indicated that as vegetation density increases, so too does the loss to interception. As snow in the canopy reaches the limit that the canopy can hold (the threshold amount) evaporation increases. Aerodynamics of the forest canopy were studied as well. As timber is cut, wind patterns are disturbed, creating disruptions in the wind velocity gradient depositing snow in openings. This redistribution leads to an increased snow water equivalent and augments runoff. Snow evaporation was shown to increase proportionally with opening size. Evaporation offsets the water yield gains derived from forest cut. It was found that this offset is inclusive to the measurements of water yield changes in experimental forests. An optimal size of harvest block may be five tree heights in width as suggested by numerous studies.     

TEMPORAL AND GEOMORPHIC VARIATIONS OF STREAM STABILITY AND MORPHOLOGY: MAHOGANY CREEK,NEVADA1

ABSTRACT: Detailed studies of long-term management impacts on rangeland streams are few because of the cost of obtaining detailed data replicated in time. This study uses government agency aquatic habitat, stream morphologic, and ocular stability data to assess land management impacts over four years on three stream reaches of an important rangeland watershed in northwestern Nevada. Aquatic habitat improved as riparian vegetation reestablished itself with decreased and better controlled livestock grazing. However, sediment from livestock disturbances and road crossings and very low stream flows limited the rate of change. Stream type limited the change of pool variables and width/depth ratio, which are linked to gradient and entrenchment. Coarse woody debris removal due to previous management limited pool recovery. Various critical-element ocular stability estimates represented changes with time and differences among reaches very well. Ocular stability variables tracked the quantitative habitat and morphologic variables well enough to recommend that ocular surveys be used to monitor changes with time between more intensive aquatic surveys.     

A WATERSHED APPROACH TO ECOSYSTEM MONITORING IN DENALI NATIONAL PARK AND PRESERVE,ALASKA1

ABSTRACT: The National Park Service and the National Biological Service initiated research in Denali National Park and Preserve, a 2.4 million-hectare park in southcentral Alaska, to develop ecological monitoring protocols for national parks in the Arctic/Subarctic biogeographic area. We are focusing pilot studies on design questions, on scaling issues and regionalization, ecosystem structure and function, indicator selection and evaluation, and monitoring technologies. Rock Creek, a headwater stream near Denali headquarters, is the ecological scale for initial testing of a watershed ecosystem approach. Our conceptual model embraces principles of the hydrological cycle, hypotheses of global climate change, and biological interactions of organisms occupying intermediate, but poorly studied, positions in Alaskan food webs. The field approach includes hydrological and depositional considerations and a suite of integrated measures linking key aquatic and terrestrial biota, environmental variables, or defined ecological processes, in order to establish ecological conditions and detect, track, and understand mechanisms of environmental change. Our sampling activities include corresponding measures of physical, chemical, and biological attributes in four Rock Creek habitats believed characteristic of the greater system diversity of Denali. This paper gives examples of data sets, program integration and scaling, and research needs.     

INTEGRATED RIVER BASIN OPTIMIZATION: MODELING ECONOMIC AND HYDROLOGIC INTERDEPENDENCE1

ABSTRACT: This paper presents an integrated optimal control model that optimizes economic performance of reservoir management in watersheds in which there are significant economic and hydrologic interdependencies. The model is solved using the General Algebraic Modeling System (GAMS). Results show that application of this model to New Mexico's Rio Chama basin can increase total system benefits over historical benefits by exploiting complementarities between hydroelectricity production, instream recreation, and downstream lake recreation.     

HYDROLOGIC LANDSCAPES ON THE DELMARVA PENINSULA PART 2: ESTIMATES OF BASE-FLOW NITROGEN LOAD TO CHESAPEAKE BAY1

ABSTRACT: Base-flow samples were collected from 47 sampling sites for four seasons from 1990–91 on the Delmarva Peninsula in Delaware and Maryland to relate stream chemistry to a “hydrologic landscape” and season. Two hydrologic landscapes were determined: (1) a well-drained landscape, characterized by a combination of a low percentage of forest cover, a low percentage of poorly drained soil, and elevated channel slope; and (2) poorly drained landscape, characterized by a combination of an elevated percentage of forest cover, an elevated percentage of poorly drained soil, and low channel slope. Concentrations of nitrogen were significantly related to the hydrologic landscape. Nitrogen concentrations tended to be higher in well-drained landscapes than in poorly drained ones. The highest instantaneous nitrogen yields occurred in well-drained landscapes during the winter. These yields were extrapolated over the part of the study area draining to Chesapeake Bay in order to provide a rough estimate of nitrogen load from base flow to the Bay and its estuarine tributaries. This estimate was compared to an estimate made by extrapolating from an existing long-term monitoring station. The load estimate from the stream survey data was 5 ± 10⁶ kg of N per year, which was about four times the estimate, made from the existing long-term monitoring station. The stream-survey estimate of base flow represents about 40 percent of the total nitrogen load that enters the Bay and estuarine tributaries from all sources in the study area.     

HYDROLOGIC LANDSCAPES ON THE DELMARVA PENINSULA PART 1: DRAINAGE BASIN TYPE AND BASE-FLOW CHEMISTRY1

ABSTRACT: The relation between landscape characteristics and water chemistry on the Delmarva Peninsula can be determined through a principal-component analysis of basin characteristics. Two basin types were defined by factor scores: (1) well-drained basins, characterized by combinations of a low percentage of forest cover, a low percentage of poorly drained soil, and elevated channel slope; and (2) poorly drained basins, characterized by a combinations of an elevated percentage of forest cover, an elevated percentage of poorly drained soil, and low channel slopes. Results from base-flow sampling of 29 basins during spring 1991 indicate that water chemistry of the two basin types differ significantly. Concentrations of calcium, magnesium, potassium, alkalinity, chloride, and nitrate are elevated in well-drained basins, and specific conductance is elevated. Concentrations of aluminum, dissolved organic carbon, sodium, and silica are elevated in poorly drained basins whereas specific conductance is low. The chemical patterns found in well-drained basins can be attributed to the application of agricultural chemicals, and those in poorly drained basins can be attributed to ground-water flowpaths. These results indicate that basin types determined by a quantitative analysis of basin characteristics can be related statistically to differences in base-flow chemistry, and that the observed statistical differences can be related to major processes that affect water chemistry.     

LONG-TERM AQUATIC HABITAT RESTORATION: MAHOGANY CREEK,NEVADA, AS A CASE STUDY1

ABSTRACT: We compared the recovery from abusive grazing of aquatic habitat due to different range management on two geomorphically similar rangeland streams in northwest Nevada. Managers excluded livestock from the Mahogany Creek watershed from 1976 to 1990 while allowing rotation of rest grazing on its tributary Summer Camp Creek. Bank stability, defined as the lack of apparent bank erosion or deposition, improved through the study period on both streams, but periodic grazing and flooding decreased stability more on Summer Camp Creek than flooding alone on Mahogany Creek. Pool quantity and quality on each stream decreased because of coarse woody debris removal and sediment deposition during a drought. Fine stream bottom sediments decreased five years after the removal of livestock, but sedimentation increased during low flows in both streams below road crossings. Tree cover increased 35 percent at both streams. Thus, recovery of stability and cover and decreased sedimentation are compatible with rotation of rest grazing on Summer Camp Creek. Width/depth ratio and gravel/cobble percent did not change because they are inherently stable in this stream type. Management activities such as coarse woody debris removal limited pool recover and road crossings increased sedimentation.     

HYDRODYNAMIC CONTROL OF AN EMERGENT AQUATIC PLANT (SCIRPUS ACUTUS) IN OPEN CHANNELS1

ABSTRACT: Control of emergent aquatic plants such as tule (Scirpus acutus Muhl.; Bigel.) is of direct interest to managers of surface waters in Western North America. Where conditions of water velocity and depth occur that permit this and similar species to colonize and grow, their clonal habit may restrict, or even block, open channels within several seasons after their establishment. Fortunately, sufficient flow depth and velocity naturally prevent these plants from growing into and blocking channels. We investigated physical constraints for tule stem growth with the ultimate intent to apply this knowledge in rehabilitating 60 miles of the diverted Owens River in Eastern California, presently choked with emergent growth. Bending stress resulting from hydrodynamic drag on tule stems was found to induce lodging; permanent deformation and consequent loss of function. The depth-velocity envelope describing this process (at 95 percent confidence) is uD/d= 12.8 where u = average velocity acting upon the stem (m/s), D = local depth of flow (m), and d = tule stem diameter at the point of attachment (m). Maintaining a discharge or reconfiguring a channel so this critical depth-velocity-stem diameter envelope is exceeded (predictable using flow models) through the summer growing period should prevent encroachment into an active channel.     

SPATIALLY OPTIMIZING FOREST MANAGEMENT SCHEDULES TO MEET STORMFLOW CONSTRAINTS1

ABSTRACT: A spatial optimization model is developed and used to limit cumulative effects resulting from storm events by strategically arranging and scheduling forest treatments to meet peak storm-flow constraints. A mixed integer forest management scheduling formulation is used to select the location and timing of forest treatments. The approach includes simulated spatial routing of storm-flows imbedded as hydrologic process constraints (in a nested schedule) within longer-term forest management planning periods in the mathematical programming model. Although difficult to solve, the model shows promise for further research.