THE WATERSHED IN PRINCIPLE1

Three fundamental concepts linking drainage basin characteristics, stream behavior, and management of watersheds are deduced from field data and observations. An electrical analogy of a watershed clarifies definitions and broadens understanding of this complex natural resource. The three basic principles deal with (1) the interrelationships of watershed morphology, constitution, and appearance; (2) the nature of the control man can exert over runoff-influencing forces, and (3) the efficiency of watershed management efforts. Recognition of these principles can assist educators, managers, planners and researchers to more fully inform students and to more effectively guide and evaluate management decisions.     

GENERATING FARM DESCRIPTIONS IN A WATERSHED FROM INCOMPLETE DATA USING SIMULATED ANNEALING1

ABSTRACT: A fundamental problem faced in developing spatially explicit, simulation‐based analyses of watershed management and policy options is determining the distribution and spatial location of agricultural resources within a watershed based on incomplete information. This paper describes the use of simulated annealing, a heuristic scheduling process, to generate an assignment of all livestock and agricultural fields in a watershed to hypothetical farms such that the combined distribution of farm types, livestock, and farmland within the watershed is a reasonable representation of watershed‐level data. Compared to a manual method using GIS‐based analysis and data from aerial photography, the heuristic method was more likely to generate realistic spatial characterizations of the distribution of agricultural resources and practices in a watershed. Also compared to the manual method, the heuristic process was considerably more efficient and could more easily accommodate multiple criteria and modifications to those criteria.     

CLIMATIC CHANGE AND U.S. WATER RESOURCES: FROM MODELED WATERSHED IMPACTS TO NATIONAL ESTIMATES1

ABSTRACT: Water is potentially one of the most affected resources as climate changes. Though knowledge and understanding has steadily evolved about the nature and extent of many of the physical effects of possible climate change on water resources, much less is known about the economic responses and impacts that may emerge. Methods and results are presented that examine and quantify many of the important economic consequences of possible climate change on U.S. water resources. At the core of the assessment is the simulation of multiple climate change scenarios in economic models of four watersheds. These Water Allocation and Impact Models (Water‐AIM) simulate the effects of modeled runoff changes under various climate change scenarios on the spatial and temporal dimensions of water use, supply, and storage and on the magnitude and distribution of economic consequences. One of the key aspects and contributions of this approach is the capability of capturing economic response and adaptation behavior of water users to changes in water scarcity. By reflecting changes in the relative scarcity (and value) of water, users respond by changing their patterns of water use, intertemporal storage in reservoirs, and changes in the pricing of water. The estimates of economic welfare change that emerge from the Water‐AIM models are considered lower‐bound estimates owing to the conservative nature of the model formulation and key assumptions. The results from the Water‐AIM models form the basis for extrapolating impacts to the national level. Differences in the impacts across the regional models are carried through to the national assessment by matching the modeled basins with basins with similar geographical, climatic, and water use characteristics that have not been modeled and by using hydro‐logic data across all U.S. water resources regions. The results from the national analysis show that impacts are borne to a great extent by nonconsumptive users that depend on river flows, which rise and fall with precipitation, and by agricultural users, primarily in the western United States, that use a large share of available water in relatively low‐valued uses. Water used for municipal and industrial purposes is largely spared from reduced availability because of its relatively high marginal value. In some cases water quality concerns rise, and additional investments may be required to continue to meet established guidelines.     

APPLICATION OF THE RHESSys MODEL TO A CALIFORNIA SEMIARID SHRUBLAND WATERSHED1

ABSTRACT: Distributed hydrologic models which link seasonal streamflow and soil moisture patterns with spatial patterns of vegetation are important tools for understanding the sensitivity of Mediterranean type ecosystems to future climate and land use change. RHESSys (Regional Hydro‐Ecologic Simulation System) is a coupled spatially distributed hydroecological model that is designed to be able to represent these feedbacks between hydrologic and vegetation carbon and nutrient cycling processes. However, RHESSys has not previously been applied to semiarid shrubland watersheds. In this study, the hydrologic submodel of RHESSys is evaluated by comparing model predictions of monthly and annual streamflow to stream gage data and by comparing RHESSys behavior to that of another hydrologic model of similar complexity, MIKESHE, for a 34 km² watershed near Santa Barbara, California. In model intercomparison, the differences in predictions of temporal patterns in streamflow, sensitivity of model predictions to calibration parameters and landscape representation, and differences in model estimates of soil moisture patterns are explored. Results from this study show that both models adequately predict seasonal patterns of streamflow response relative to observed data, but differ significantly in terms of estimates of soil moisture patterns and sensitivity of those patterns to the scale of landscape tessellation used to derive spatially distributed elements. This sensitivity has implications for implementing RHESSys as a tool to investigate interactions between hydrology and ecosystem processes.     

A CRITICAL APPROACH TO THE CALIBRATION OF A WATERSHED MODEL1

ABSTRACT: A complex watershed-scale water quality simulation model, the Hydrological Simulation Program-FORTRAN (HSPF) model, was calibrated for a 16 km² catchment. The simulation step size was 0.33 hours with predicted and recorded hydrologic flows compared on an annual and monthly basis during a total calibration period of four years. Unguided numerical optimization when applied alone did not yield a model parameter set with acceptable predictive capability; instead, it was necessary to apply a critical process that included sensitivity analysis, numerical optimization, and testing of derived model parameter sets to evaluate their performance for periods other than those for which they were determined. Using this critical calibration process, the model was proven to have significant predictive capability. Numerical optimization is an aid for model calibration, but it must not be used blindly.     

THE WESTERN WATER COMMISSION: WATERSHED MANAGEMENT RECEIVES THE AVI'ENTION OF A NEW GENERATION1

ABSTRACT: Our nation periodically reviews national water policy and considers its directions for the future. The most recent examination was directed at the western United States and the role of the federal agencies in meeting its needs. The West is no longer the frontier, but rather contains vibrant cities and booming centers of international trade, as well as tourism, mineral, and oil and gas development, agricultural, and other development. In this changing environment, federal water policies need to consider the long term sustainability of the West, provide justice to Indian tribes, protect the rivers and ecosystems on which natural systems depend, balance the needs of newcomers with those of agricultural users and communities, and meet a myriad of other demands. The Western Water Policy Review Advisory Commission has just concluded its review of these issues and issued its report. Key among the recommendations is the need to coordinate federal agencies at the basin and watershed level and make government more responsive to local needs, but within a framework that includes national mandates. The Commission's recommendations are presented here, along with some of the issues that surrounded the operations of the Commission.     

A CRITIQUE OF WATERSHED MANAGEMENT EFFORTS IN THE LOWER MISSISSIPPI ALLUVIAL PLAIN1

ABSTRACT: Integrated watershed management in the Lower Mississippi Alluvial Plain (Delta) requires blending federal, state, and local authority. The federal government has preeminent authority over interstate navigable waters. Conversely, state and local governments have authority vital for comprehensive watershed management. In the Delta, integrating three broad legal and administrative regimes: (1) flood control, (2) agricultural watershed management, and (3) natural resources and environmental management, is vital for comprehensive intrastate watershed, and interstate river basin management. Federal Mississippi River flood control projects incorporated previous state and local efforts. Similarly, federal agricultural programs in the River's tributary headwaters adopted watershed management and were integrated into flood control efforts. These legal and administrative regimes implement national policy largely in cooperation with and through technical and financial assistance to local agencies such as levee commissions and soil and water conservation districts. This administrative infrastructure could address new national concerns such as nonpoint source pollution which require a watershed scale management approach. However, the natural resources and environmental management regime lacks a local administrative infrastructure. Many governmental and non governmental coordinating organizations have recently formed to address this shortcoming in the Delta. With federal and state leadership and support, these organizations could provide mechanisms to better integrate natural resources and environmental issues into the Delta's existing local administrative infrastructure.     

A STRATEGY FOR IMPLEMENTING BMPs FOR CONTROLLING NONPOINT SOURCE POLLUTION: THE CASE OF THE FEI‐TSUI RESERVOIR WATERSHED IN TAIWAN1

ABSTRACT: This paper describes a concerted effort by the Taiwan Water Resources Bureau, the City of Taipei, and the Bureau of Fei‐tsui Reservoir Management to protect the water quality in the Fei‐tsui Reservoir.The reservoir is the major source of water supply for over two million people in the metropolitan area of Taipei. Over the years the reservoir has suffered from siltation and more recently eutrophication. The sources of the pollution are traced to the hundreds of tea gardens, rice fields and other agricultural areas in the watershed and to urban sources such as construction sites. Large amounts of nutrients enter the reservoir by way of storm water runoff during storm or typhoon events. Since 1999, various agencies have worked to initiate an effort to reduce nonpoint pollution in the Fei‐Tsui Reservoir watershed. Practices being considered include nonstructural measures such as nutrient management, and structural measures such as swales, detention basins, and wetlands, in addition to erosion and sediment control methods. A number of field tests have been completed on the performance of selected best management practices (BMPs). A strategy for implementing the BMPs at the watershed scale has been developed based on a total maximum daily load (TMDL) analysis that is reported in this paper.     

DRY AND WET WEATHER FLOW NUTRIENT LOADS FROM A LOS ANGELES WATERSHED1

Effective watershed management requires an accurate assessment of the pollutant loads from the associated point and nonpoint sources. The importance of wet weather flow (WWF) pollutant loads is well known, but in semi‐arid regions where urbanization is significant the pollutant load in dry weather flow (DWF) may also be important. This research compares the relative contributions of potential contaminants discharged in DWF and WWF from the Ballona Creek Watershed in Los Angeles, California. Models to predict DWF and WWF loads of total suspended solids, biochemical oxygen demand, nitrate‐nitrogen, nitrite‐nitrogen, ammonia‐nitrogen, total Kjeldahl nitrogen, and total phosphorus from the Ballona Creek Watershed for six water years dating from 1991 to 1996 were developed. The contaminants studied were selected based on data availability and their potential importance in the degradation of Ballona Creek and Santa Monica Bay beneficial uses. Wet weather flow was found to contribute approximately 75 percent to 90 percent of the total annual flow volume discharged by the Ballona Creek Watershed. Pollutant loads are also predominantly due to WWF, but during the dry season, DWF is a more significant contributor. Wet weather flow accounts for 67 to 98 percent of the annual load of the constituents studied. During the dry season, however, the portion attributable to DWF increases to greater than 40 percent for all constituents except biochemical oxygen demand and total suspended solids. When individual catchments within the watershed are considered, the DWF pollutant load from the largest catchment is similar to the WWF pollutant load in two other major catchments. This research indicates WWF is the most significant source of nonpoint source pollution load on an annual basis, but management of the effects of the nonpoint source pollutant load should consider the seasonal importance of DWF.     

THE (POLITICAL) SCIENCE OF WATERSHED MANAGEMENT IN THE ECOSYSTEM AGE1

ABSTRACT: Ecosystem management has become an important unifying theme for environmental policy in the past decade. Whereas the science of ecosystem dynamics suggests that it will remain difficult to define ecosystem borders and all of the natural and anthropogenic effects that influence them, the politics of ecosystem management require that a national ecosystem delineation standard be adopted. Moreover, a political framework for ecosystem management decision making must be designed in such a way as to complement the hierarchical, interrelated nature of ecosystems generally. This paper advocates that a watershed-based ecosystem delineation standard is the most politically suitable because it will be easily understood by the public and watersheds have a long history as a medium of environmental policy. The paper then proposes that the political framework for watershed-based ecosystem management must depend heavily on state and local autonomy, subject to federally prescribed standards and goals. The Coastal Zone Management Act provides a model for how a national ecosystem management policy can work within state and local watershed cultures and economies.     

FOREST HYDROLOGY ISSUES FOR THE 21ST CENTURY: A CONSULTANT'S VIEWPOINT1

ABSTRACT: Forest hydrology should be a mature science with routine use of hydrological procedures to evaluate the effect of past, current and proposed harvesting practices on water resources. It is not. However, water users are pressuring forest managers to exercise their role in managing forested watersheds for water supply. Most forest managers are poorly equipped to carry out this role. Forestry schools need to ensure that their graduates, whether employed in forest management positions or as specialists in watershed management, understand that all forestry operations may affect instream or downstream water users. Specialists in forest hydrology should be fully aware of the following: (1) climate and watershed characteristics influence streamflow in separate ways; (2) forestry practices produce changes in water yield and quality, and that only these changes need to be evaluated to estimate their effects; (3) watershed storage is a critical factor in evaluating the effects of harvesting on streamflow; and (4) the effect of harvest on one watershed cannot be extrapolated to another without consideration of the processes affected. Research is needed to assist watershed managers in applying models to watersheds for which climate and streamflow data are insufficient. Research is also needed to incorporate climate, streamflow and other data for hydrological models into geographic information systems. Joint research projects are needed to develop physical relationships between stream channel characteristics of importance to fisheries biologists and streamflow characteristics affected by forest harvest.     

LAND USE AND AQUATIC BIOINTEGRITY IN THE BLACKFOOT RWER WATERSHED,MONTANA1

ABSTRACT: Benthic macroinvertebrate samples representing 151 taxa were collected in August 1995 to examine the linkage between land use, water quality, and aquatic biointegrity in seven tributaries of the Blackfoot River watershed, Montana. The tributaries represent silvicultural (timber harvesting), agricultural (irrigated alfalfa and hay and livestock grazing), and wilderness land uses. A 2.4 km (1.5 mile) reach of a recently restored tributary also was sampled for comparison with the other six sites. A geographic information system (GIS) was used to characterize the seven subwatersheds and estimate soil erosion, using the Modified Universal Soil Loss Equation, and sediment delivery. The wilderness stream had the highest aquatic biointegrity. Two agricultural streams had the largest estimated soil erosion and sediment delivery rates, the greatest habitat impairment from nonpoint source pollution, and the most impoverished macroinvertebrate communities. The silvicultural subwatersheds had greater rates of estimated soil erosion and sediment delivery and lower aquatic biointegrity than the wilderness reference site but evinced better conditions than the agricultural sites. A multiple-use (forestry, grazing, and wildlife management) watershed and the restored site ranked between the silvicultural and agricultural sites. This spectrum of land use and aquatic biointegrity illustrates both the challenges and opportunities that define watershed management.     

THE POTENTIAL FOR WATER YIELD AUGMENTATION FROM FOREST MANAGEMENT IN THE ROCKY MOUNTAIN REGION1

With the exception of the Sierra-Cascade mountain ranges, the Rocky Mountain chain is the only portion of the western United States that consistently yields more than 3 cm of flow annually. Ten to 15 percent of the land mass in the region produces the majority of the total flow. This paper addresses the opportunities for increasing flow through forest manipulation, and summarizes the research base that has yielded the current “state of the art” understanding of how snow pack and vegetation management can influence water yield. The optimal harvest design appears to consist of small openings, irregularly shaped, and about 3 to 8 tree heights in width parallel to the wind.     

APPLICATION OF THE BASINS DATABASE AND NPSM MODEL ON A SMALL OHIO WATERSHED1

ABSTRACT: The purpose of this study was to evaluate the Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) watershed management system. BASINS data were used with the NPSM model to predict discharge and sediment concentrations at the outlet of a 103 km² Ohio watershed. It was concluded that the NPSM model should always be calibrated but only a few of the parameters provided with BASINS needed to be calibrated. For a three‐year study period, there was a 2 percent underestimation of discharge using area weighted precipitation values and a 25 percent overestimation using the single station data in BASINS. A comparison of observed and predicted monthly discharge resulted in an r² of 0.86 with area‐weighted precipitation and an r² of 0.74 with the single station data. Calibrating the model to substantially improve sediment predictions was unsuccessful and we concluded that a calibration period of one year was too short. For the three‐year study period, the r² for sediment was 0.36 with a slope of 0.37 and an intercept of 18.8 mg/l. The mean observed and predicted sediment concentrations were 27.1 mg/l and 22.6 mg/l, respectively.     

A PARTICIPATORY APPROACH TO WATERSHED MANAGEMENT: THE BRAZILIAN SYSTEM1

ABSTRACT: Brazil is currently facing the challenge of implementing a new water resources management system to promote the rational and sustainable use of the country's waters. This system is based on the following principles of water management: (2) stakeholders' participation; (2) the watershed as the planning and management unit; and (3) the economic value of water. Stakeholders' participation and the involvement of civil society in the decision making process is guaranteed by permanent seats in the watersheds' management committees. These committees are the highest decision level for the establishment of water policy and for planning its use. The executive branch of the committees is the watershed agency or the water agency. This paper presents the recently approved Brazilian water resources management system and discusses the participatory approach followed to validate and to ensure prompt response to decisions regarding water use by all stakeholders. The formulation of the National Water Law (January/1998) was also supported by extensive consultation with civil society, professional associations, state and municipal governments as well as with federal governmental agencies and private sector organizations. It also presents an overview of the formulation of the National Water Law. Finally, as watershed committees have been created and are already operating in a limited number of watersheds, some of the major obstacles to the success of the new system are discussed along with alternatives for overcoming such obstacles.     

USE OF SOIL AND WATER PROTECTION PRACTICES AMONG FARMERS IN THE NORTH CENTRAL REGION OF THE UNITED STATES1

ABSTRACT: Data were collected in the fall of 1998 and the winter of 1999 from 1,011 land owner‐operators within three watersheds in the North Central Region of the United States to assess adoption of soil and water protection practices. Farm owner‐operators were asked to indicate how frequently they used 18 different agricultural production practices. Many farmers within the three watersheds had adopted conservation protection practices. However, they also employed production practices that could negate many of the environmental benefits associated with conservation practices in use. Comparison of adoption behaviors used in the three watersheds revealed significant differences among the study groups. Respondents in the Iowa and Ohio watersheds reported greater use of conservation production systems than did farmers in Minnesota. However, there were no significant differences between Ohio and Iowa farmers in terms of use of conservation production practices. This was surprising, since farmers in the Ohio watershed had received massive amounts of public and private investments to motivate them to adopt and to continue using conservation production systems. These findings bring into serious question the use of traditional voluntary conservation programs such as those employed in the Ohio watershed. Study findings suggest that new policy approaches should be considered. It is argued that “whole farm planning” should be a significant component of new agricultural conservation policy.     

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.