Timber harvest planning—A combined optimization/simulation model

A special cascading fixed charge structure can be used to characterize a forest management planning problem in which the objectives are to identify the optimal shape of forest harvest cutting units and simultaneously to assign facilities for logging those units. We describe a four-part methodology that has been developed to assist forest managers in analyzing areas proposed for harvesting. This methodology performs an analysis of harvesting feasibility, computes the optimal solution to the cascading fixed charge problem, undertakes a GASP IV simulation to provide additional information about the proposed harvesting operation, and permits the forest manager to perform a time-cost analysis that may lead to a more realistic, and thus improved, solution.     

Does salt marsh fertilization enhance shellfish production? An application of flow analysis

The method of flow analysis, which is similar to economic input-output analysis, is presented as a means of making flow models of ecological systems more useful to environmental managers. This paper considers as an illustration the extent to which nitrogen fertilizer added toSpartina salt marsh sediments can enhance shellfish growth. Nitrogen flow models of both the Barataria Bay salt marsh complex of coastal Louisiana and the Sippewissett Marsh of western Cape Cod are analyzed. The analysis shows the transfer of added nitrogen to shellfish growth viaSpartina growth, decomposition, and detrital feeding to be considerably less efficient than its transfer toSpartina growth itself. These results are similar for both marsh systems, despite their great physical differences and despite the inclusion of considerably more microbial processing of nitrogen in the Barataria Bay model than in the Sippewissett models. The results suggest that the most efficient mechanism by which added nitrogen could enhance shellfish growth in salt marshes may have to bypass the route through theSpartina life cycle.     

WATER QUALITY PROJECTIONS: PREIMPOUNDMENT CASE STUDY1

ABSTRACT: Recent regulations require impact statements for major water development projects, including reservoirs that will be used for water supply, recreation, and pollution control. A water quantity/quality model was developed and used for making water quality projections of a proposed reservoir in Montgomery County, Maryland. The study area is uncommon in that there is an extensive water quality data base. The results indicate that land use changes will have a significant effect on water quality and that the proposed reservoir will improve the quality of the surface waters downstream from the reservoir. A major effect of land use changes is the increase in the variability of water quality.     

EFFECT OF URBANIZATION ON ALTERNATIVE FLOOD CONTROL STRATEGIES1

ABSTRACT: The effect of urbanization on alternative flood control strategies was investigated for a large developing watershed in Texas. Urban and rural areas were modeled separately using a geographically-referenced data base and the U.S. Corps of Engineers HEC-1 and HEC-2 programs, and results yielded a double-peaked hydrograph. Hydrograph input parameters were modified to predict the effects of a wide range of management alternatives including on-site storage, reservoirs, channelization, and development controls. Results indicated a combination of alternatives is required to protect existing and future developments.     

MODELING THE ENVIRONMENTAL EFFECTS OF A NAVIGATION CHANNEL IN A TIDAL BAY1

ABSTRACT: A circulation and salinity model was used to predict the effects of wind, fresh water inflow, and the construction of a navigation channel on Vermilion Bay, Louisiana. The model numerically solved continuity and motion equations and provided a time history and spatial distribution of tidal depths, flows, velocities, and salinity in two lateral dimensions. The model predicted that high south winds or high fresh water inflow would reduce average bay salinities, as would the construction of a channel through Vermilion Bay. The results suggested the main reason for this behavior is the presence of two bay outlets to the Gulf of Mexico.     

A DIGITAL MODEL APPLIED TO GROUND WATER RECHARGE AND MANAGEMENT1

ABSTRACT: Under Colorado's appropriative water right system, withdrawals by junior ground water rights must be curtailed to protect senior surface water appropriators sharing the same river system unless the ground water users replace the amount of their injury to the river under an approved plan for augmentation. Compensation of such injury with surface water may not only be expensive but unreliable in dry years. As an alternative, the curtailment of pumping may be obviated by recharging unused surface water into the aquifer when available and withdrawing it when needed. In order to manage such an operation, a practical tool is required to accurately determine that portion of the recharge water that does not return to the river before pumping for irrigation. A digital model was used for this purpose in a demonstration recharge project located in the South Platte River basin in northeastern Colorado. This paper summarizes the experiences gained from this project, the results of the digital model, the economic value of recharge, and the feasibility of the operation. It was determined through the use of the digital model that, with the given conditions in the area, 77 percent of the recharged water remained available for pumping. Economic analyses showed that water could be recharged inexpensively averaging about two dollars per acre foot.     

GEOMETRIC VARIATIONS IN RESERVOIR WATER QUALITY1

ABSTRACT: In developing water quality models for lakes and reservoirs, the assumptions of one-dimensionality (i.e., water quality changes are significant only in one dimension – usually depth), as well as two-dimensionality (considering the length and depth of the water body), have been utilized to predict water quality. In both caws, the assumption of lateral homogeneity is made. A field study was undertaken to determine the change of water quality in the lateral dimension. The main study reservoir was Center Hill Lake in Middle Tennessee. Data were also obtained for Cherokee Lake in East Tennessee. Several water quality parameters (temperature, dissolved oxygen, pH, conductivity, and oxidation reduction potential) were analyzed over the length, breadth, and depth of these reservoirs from pre-stratification through post-stratification. The statistical and theoretical three-dimensional analysis showed the expected variation for each water quality parameter in each direction. The influence of the lateral dimension on water quality management and modeling was found to be negligible.     

Planning future fuelbreak strategies using mathematical modeling techniques

Major drainage basins within the Angeles National Forest in southern California USA are aggregated into zones of homogeneous wildland fire damage-potential using multivariate statistical techniques. Mathematical models are utilized to examine the policy implications of ongoing and projected fuel management strategies in different Forest zones based on simulated impacts of fuelbreak construction and maintenance upon two proxies for future damage-potential: the expected area burned and an index of relative value used by Forest planners. Alternative strategies for future fuelbreak investments are evaluated based on model outcomes.     

Predicting the multiple pathways of plant succession

Classical concepts view succession as a deterministic, mechanistic regeneration of the disturbed community, and thus have limited applicability to fire-prone ecosystems, A recently developed multiple pathway succession model appears to have more realism and applicability in frequently disturbed ecosystems. It includes a set of species-specific attributes that are vital to reproduction and survival, and permits variable succession pathways depending on the stand's age (and thus species composition) when disturbed. Examples from Australia and the northern Rocky Mountains (USA) are presented, as are approaches to refining and improving the model.     

DISSOLVED OXYGEN MODEL OF A SHORT DETENTION TIME RESERVOIR WITH ANAEROBIC HYPOLIMNION1

ABSTRACT: A vertical dissolved oxygen model was calibrated and verified using independent field data sets from 1972 and 1973 in Lake Lyndon B. Johnson (LBJ), a short detention time reservoir with anaerobic hypolimnion. Ammonia, carbonaceous BOD, conductivity, and temperature were also simulated as state variables. The conductivity results provided a check on the mass balance and the method of entering the inflows to the reservoir model. Emphasis was placed on calculating the sinks of dissolved oxygen in the hypolimnion which could be useful in management decisions.