ROLE OF CARBONATE ROCKS IN MODIFYING FLOOD FLOW BEHAVIOR1

ABSTRACT. The interrelationships between the runoff characteristics of watersheds (expressed as the mean annual flood), standard basin parameters (area, drainage properties, and relief), and the parameters which describe the solutional modification of the basins (carbonate rock fractions, sinkhole development, and measures of internal drainage) were used to group 62 carbonate watersheds. Simple binary correlations were obtained by direct plotting of the data. This was followed by multivariate analyses: factor and cluster analyses. Following the cluster analysis, which separated the basins into three groups, the variance within each group was examined again by binary correlations and by factor analysis. Prediction equations for those basins underlain by dolomite rock [QBAR = 12.4 TOT^1.01] and for those basins underlain by carbonate rock with very little surface expression [QBAR = 43.5 TOT^0.87] were proposed. Basins underlain by karstic limestone had a large amount of variance within the data set; therefore no prediction equation could be obtained. (QBAR = mean annual flood, cfs; TOT = total length of all blue lines shown on topographic maps, miles.)     

WATERSHEDS AS THE BASIC ECOSYSTEM: THIS CONCEPTUAL FRAMEWORK PROVIDES A BASIS FOR A NATURAL CLASSIFICATION SYSTEM1

ABSTRACT: A scheme is outlined to classify watersheds as ecosystems, based on their natural attributes. Two physical factors of the environment, climate and geology, are selected as state factors. Climate is the master factor that supplies energy and water to all ecosystems; geologic structure supplies the materal from which the forces of climate carve landforms to establish ecosystems. At the next lower level, soil and vegetation interact in a succession of transactions to produce a mosaic of tesseras within each watershed. It is these interacting tesseras that moderate climate and store energy within the ecosystem that influences the embedded stream. At the bottom of the scale is the stream with its passive role and inability to interact with the higher factors of the ecosystem. Thus, we have a controlling force consisting of two elements (climate and geology), a reacting force (soil and vegetation) that responds by circular conditioning to controlling forces, and at the lowest level, the stream which responds to all factors of the living system within its watershed.     

Brushland fire-management policies: A cross-impact simulation of southern California

A cross-impact simulation computer language, UW-KSIM, is presented as a potentially useful technique for assessing the consequences of resource policies. Cross-impact simulation is used to estimate trends in a set of variables that result from interactions produced from hypothesized relationships among the members of the set. This technique is illustrated with an example that simulates the likely impacts of a 20-year rotation burn policy in southern California's brushland watersheds and that compares the results to a simulated representation of the observed effects of the fire-exclusion policy. Simulated losses under the fire-exclusion policy were up to 300% higher than those produced by the rotation burn policy. Similarly, the simulated average area burned per year was reduced from 5.6% of the study area under the fire-exclusion policy to 2% of the study area under the rotation burn policy. A corresponding reduction in simulated appropriations for fighting wildfires was also demonstrated.     

STATE VARIABLE MODEL FOR URBAN RAINFALL-RUNOFF PROCESS1

ABSTRACT: A nonlinear hydrologic system model has been developed for analyzing the urban rainfall-runoff process. The model is formulated as a state variable model consisting of several parameters. A search technique is employed to find the set of parameters for which the model's response best fits observed data. The model could be used in either a simulation or forecasting mode. The model is applied to observed data for the Waller Creek Watershed in Austin, Texas, to develop the model parameters for various levels of urbanization of the watershed. The trend of each parameter with respect to levels of urbanization is examined.     

CONNECTING GROUND WATER INFLUXES WITH FISH SPECIES DIVERSITY IN AN URBANIZED WATERSHED1

ABSTRACT: Valley Creek watershed is a small stream system that feeds the Schuylkill River near Philadelphia, Pennsylvania. The watershed is highly urbanized, including over 17 percent impervious surface cover (ISC) by area. Imperviousness in a watershed has been linked to fish community structure and integrity. Generally, above 10 to 12 percent ISC there is marked decline in fish assemblages with fish being absent above 25 percent ISC. This study quantifies the importance of ground water in maintaining fish species diversity in subbasins with over 30 percent ISC. Valley Creek contains an atypical fish assemblage in that the majority of the fish are warm‐water species, and the stream supports naturally reproducing brown trout, which were introduced and stocked from the early 1900s to 1985. Fish communities were quantified at 13 stations throughout the watershed, and Simpson's species diversity index was calculated. One hundred and nine springs were located, and their flow rates measured. A cross covariance analysis between Simpson's species diversity index and spring flow rates upstream of fish stations was performed to quantify the spatial correlation between these two variables. The correlation was found to be highest at lag distances up to about 400 m and drop off significantly beyond lag distances of about 800 m.     

AUTUMN CHEMISTRY OF OREGON COAST RANGE STREAMS1

ABSTRACT: During an autumn runoff event we sampled 48 streams with predominantly forested watersheds and igneous bedrock in the Oregon Coast Range. The streams had acid neutralizing capacities (ANC) > 90 μeq/L and pH > 6.4. Streamwater Na ⁺, Ca^{2 +}, and Mg^{2 +} concentrations were greater than K ⁺ concentrations. Anion concentrations generally followed the order of Cl^- > NO₃^- > SO₄^2-. Chloride and Na ⁺ concentrations were highest in samples collected in streams near the Pacific Ocean and decreased markedly as distance from the coast increased. Sea salt exerted no discernible influence on stream water acid-base status during the sampling period. Nitrate concentrations in the study streams were remarkably variable, ranging from below detection to 172 μeq/L. We hypothesize that forest vegetation is the primary control of spatial variability of the NO₃^- concentrations in Oregon Coast Range streams. We believe that symbiotic N fixation by red alder in pure or mixed stands is the primary source of N to forested watersheds in the Oregon Coast Range.     

WATERSHEDSS: A DECISION SUPPORT SYSTEM FOR WATERSHED-SCALE NONPOINT SOURCE WATER QUALITY PROBLEMS1

ABSTRACT: A significant portion of all pollutants entering surface waters (streams, lakes, estuaries, and wetlands) derives from non-point source (NPS) pollution and, in particular, agricultural activities. The first step in restoring a water resource is to focus on the primary water quality problem in the watershed. The most appropriate NPS control measures, which include best management practices (BMPs) and landscape features, such as wetlands and riparian areas, can then be selected and positioned to minimize or mitigate the identified pollutant(s). A computer-based decision sup. port and educational software system, WATERSHEDSS (WATER, Soil, and Hydro-Environmental Decision Support System), has been developed to aid managers in defining their water quality problems and selecting appropriate NPS control measures. The three primary objectives of WATERSHEDSS are (1) to transfer water quality and land treatment information to watershed managers in order to assist them with appropriate land management/land treatment decisions; (2) to assess NPS pollution in a watershed based on user-supplied information and decisions; and (3) to evaluate, through geographical information systems-assisted modeling, the water quality effects of alternative land treatment scenarios. WATERSHEDSS is available on the World Wide Web (Web) at http://h2osparc.wq.ncsu.edu .     

SEDIMENT,NITRATE, AND AMMONIUM IN SURFACE RUNOFF FROM TWO TAHOE BASIN SOIL TYPES 1

ABSTRACT: Few studies have addressed the natural pollution potential of pristine subalpine forested watersheds on a site-specific basis. Consequently, specific source and amounts of nutrient discharge to tributaries of the Tahoe Basin are difficult to identify. The sediment content and nitrate and ammonium levels in surface runoff from two soil types (Meeks and Umpa), four plot conditions (wooded natural and disturbed, open natural and disturbed), and three slopes (gentle, moderate, and steep) were studied using rainfall simulation that applied a 9 cm h¹, 1-h event. A significant (P ≤ 0.005) two-way interaction between soil type and plot condition affected runoff nitrate concentration. Runoff from natural or disturbed open plots contained significantly (P = 0.05) greater nitrate than wooded plots. Peak concentrations of nitrate commonly occurred during early runoff, suggesting that peak nitrate discharge to Lake Tahoe tributaries can be expected during early runoff from snowmelt and summer precipitation events. The highest nitrate runoff concentration and 1-h cumulative loading from the 0.46 m² plots were 6.7 mg L-¹ (Umpa, open natural, 15–30 percent slope), and 0.7 mg (Umpa, open natural, ≥ 30 percent slope), respectively. Ammonium in surface runoff was generally below detection limits (≤ 0.05 μg L^?1). No statistical relationship between runoff nitrate and sediment discharge was detected.     

ALAWAT: A spatially allocated watershed model for approximating stream,sediment, and pollutant flows in Hawaii,USA

The Ala Wai Canal Watershed Model (ALAWAT) is a planning-level watershed model for approximating direct runoff, streamflow, sediment loads, and loads for up to five pollutants. ALAWAT uses raster GIS data layers including land use, SCS soil hydrologic groups, annual rainfall, and subwatershed delineations as direct model parameter inputs and can use daily total rainfall from up to ten rain gauges and streamflow from up to ten stream gauges. ALAWAT uses a daily time step and can simulate flows for up to ten-year periods and for up to 50 subwatersheds. Pollutant loads are approximated using a user-defined combination of rating curve relationships, mean event concentrations, and loading/washoff parameters for specific subwatersheds, land uses, and times of year. Using ALAWAT, annual average streamflow and baseflow relationships and urban suspended sediment loads were approximated for the Ala Wai Canal watershed (about 10,400 acres) on the island of Oahu, Hawaii. Annual average urban suspended sediments were approximated using two methods: mean event concentrations and pollutant loading and washoff. Parameters for the pollutant loading and washoff method were then modified to simulate the effect of various street sweeping intervals on sediment loads.     

RED ALDER LEAF LITTER AND STREAMWATER QUALITY IN WESTERN OREGON1

ABSTRACT: Streamside red alder (Alnus rubra Bong.) stands are common in western Oregon, and they have been suspected of causing water quality problems in domestic supplies during autumn leaf fall. Studies in the Seaside municipal watershed showed potential water quality effects (particularly increased color) from alder leaves, but stream sampling during 1981–82 revealed no chronic problems. The few observed short-term increases in water color occurred near the onset of storm flows, which suggested a flushing of organic matter storage sites. An extended period of unusually low flows and high leaf fall are probably necessary to produce significant water quality problems in this stream system. Laboratory leaching of alder leaves in filtered stream water indicated a fairly constant release of colored organic matter over time, and running water leached this matter more efficiently than still water. Water color increased linearly with increasing leaf mass added to still water, and for a given leaf mass there appeared to be a limit to the amount of colored matter that could be removed in the first 48 hours of leaching. Other laboratory tests showed that ultraviolet absorbance (254 mm) may provide a reasonable estimate of dissolved organic carbon concentrations in systems dominated by alder leaf inputs.