Hydrologic and Water Quality Integration Tool: HydroWAMIT

Abstract: A spatially distributed and continuous hydrologic model focusing on total maximum daily load ͑TMDL͒ projects was developed. Hydrologic models frequently used for TMDLs such as the hydrologic simulation program-FORTRAN ͑HSPF͒, soil and water assessment tool ͑SWAT͒, and generalized watershed loading function ͑GWLF͒ differ considerably in terms of spatial resolution, simulated processes, and linkage flexibility to external water quality models. The requirement of using an external water quality model for simulating specific processes is not uncommon. In addition, the scale of the watershed and water quality modeling, and the need for a robust and cost-effective modeling framework justify the development of alternative watershed modeling tools for TMDLs. The hydrologic and water quality integration tool ͑HydroWAMIT͒ is a spatially distributed and continuous time model that incorporates some of the features of GWLF and HSPF to provide a robust modeling structure for TMDL projects. HydroWAMIT operates within the WAMIT structure, developed by Omni Environmental LLC for the Passaic River TMDL in N. J. HydroWAMIT is divided into some basic components: the hydrologic component, responsible for the simulation of surface flow and baseflow from subwatersheds; the nonpointsource ͑NPS͒ component, responsible for the calculation of the subwatershed NPS loads; and the linkage component, responsible for linking the flows and loads from HydroWAMIT to the water quality analysis simulation program ͑WASP͒. HydroWAMIT operates with the diffusion analogy flow model for flow routing. HydroWAMIT provides surface runoff, baseflow and associated loads as outputs for a daily timestep, and is relatively easy to calibrate compared to hydrologic models like HSPF. HydroWAMIT assumes that the soil profile is divided into saturated and unsaturated layers. The water available in the unsaturated layer directly affects the surface runoff from pervious areas. Surface runoff from impervious areas is calculated separately according to precipitation and the impervious fractions of the watershed. Baseflow is given by a linear function of the available water in the saturated zone. The utility of HydroWAMIT is illustrated for the North Branch and South Branch Raritan River Watershed ͑NSBRW͒ in New Jersey. The model was calibrated, validated, and linked to the WASP. The NPS component was tested for total dissolved solids. Available weather data and point-source discharges were used to prepare the meteorological and flow inputs for the model. Digital land use, soil type datasets, and digital elevation models were used for determining input data parameters and model segmentation. HydroWAMIT was successfully calibrated and validated for monthly and daily flows for the NSBRW outlet. The model statistics obtained using HydroWAMIT are comparable with statistics of HSPF and SWAT applications for medium and large drainage areas. The results show that HydroWAMIT is a feasible alternative to HSPF and SWAT, especially for large-scale TMDLs that require particular processes for water quality simulation and minor hydrologic model calibration effort

Development and application of the Riparian Mapping Tool to identify priority rehabilitation areas for nitrogen removal in the Tully-Murray basin, Queensland, Australia

One feature of riparian zones is their ability to significantly reduce the nitrogen loads entering streams by removing nitrate from the groundwater. A novel GIS model was used to prioritise riparian rehabilitation in catchments. It is proposed that high-priority areas are those with a high potential for riparian denitrification and have nearby land uses that generate high nitrogen loads. For this purpose, we defined the Rehabilitation Index, which is the product of two other indices, the Nitrate Removal Index and the Nitrate Interception Index. The latter identifies the nitrate contamination potential for each raster cell in the riparian zone by examining the extent and proximity of agricultural urban land uses. The former is estimated using a conceptual model for surfacegroundwater interactions in riparian zones associated with middle-order gaining perennial streams, where nitrate is removed via denitrification when the base flow interacts with the carbon-rich riparian sediments before discharging to the streams. Riparian zones that are relatively low in the landscape, have a flat topography, and have soils of medium hydraulic conductivity are most conducive to denitrification. In the present study, the model was implemented in the Tully - Murray basin, Queensland, Australia, to produce priority riparian rehabilitation area maps

Waste assimilative capacity of coastal waters along Mumbai mega city, west coast of India using MIKE-21 and WASP simulation models

Coastal waters are the ultimate receivers of the organic waste materials generated by upstream cities and towns. This waste can cause dissolved oxygen depletion due to increased oxygen demand, affecting the natural ability of water bodies to withstand certain amount of pollution - the Waste Assimilative Capacity. The pollution load (Biochemical Oxygen Demand) calculated using the Population Equivalent value of 0.225 m3/day for the present Mumbai population of 13 million is 731,250 kg/day. Simulations using MIKE-21 and WASP models along with the observed water quality data as well as current meter data indicated that the coastal waters can withstand the present pollution load since the simulated Biochemical Oxygen Demand was with in the range of 0.2-1.5 mg/L, the National Standard limits. A projected population increase exceeded the target BOD value of 2 mg/L, indicating the deterioration of ambient quality of coastal waters. Waste Assimilative Capacity studies are crucial in the present-day regional, as well as global issues, such as population explosion, water shortage and climate change