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Hydrology is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and drainage basin sustainability. A practitioner of hydrology is called a hydrologist. Hydrologists are scientists studying earth or environmental science, civil or environmental engineering, and physical geography. Using various analytical methods and scientific techniques, they collect and analyze data to help solve water related problems such as environmental preservation, natural disasters, and water management.
In physical geography and hydrology, a channel is a landform on which a relatively narrow body of water is situated, such as a river, river delta or strait. While channel typically refers to a natural formation, the cognate term canal denotes a similar artificial structure.
A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second . Hydrographs often relate changes of precipitation to changes in discharge over time. It can also refer to a graph showing the volume of water reaching a particular outfall, or location in a sewerage network. Graphs are commonly used in the design of sewerage, more specifically, the design of surface water sewerage systems and combined sewers.
Drainage density is a quantity used to describe physical parameters of a drainage basin. First described by Robert E. Horton, drainage density is defined as the total length of channel in a drainage basin divided by the total area, represented by the following equation:
Infiltration is the process by which water on the ground surface enters the soil. It is commonly used in both hydrology and soil sciences. The infiltration capacity is defined as the maximum rate of infiltration. It is most often measured in meters per day but can also be measured in other units of distance over time if necessary. The infiltration capacity decreases as the soil moisture content of soils surface layers increases. If the precipitation rate exceeds the infiltration rate, runoff will usually occur unless there is some physical barrier.
The United States Environmental Protection Agency (EPA) Storm Water Management Model (SWMM) is a dynamic rainfall–runoff–subsurface runoff simulation model used for single-event to long-term (continuous) simulation of the surface/subsurface hydrology quantity and quality from primarily urban/suburban areas.
Surface runoff is the unconfined flow of water over the ground surface, in contrast to channel runoff. It occurs when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the soil is saturated by water to its full capacity, and the rain arrives more quickly than the soil can absorb it. Surface runoff often occurs because impervious areas do not allow water to soak into the ground. Furthermore, runoff can occur either through natural or human-made processes.
Streamflow, or channel runoff, is the flow of water in streams and other channels, and is a major element of the water cycle. It is one runoff component, the movement of water from the land to waterbodies, the other component being surface runoff. Water flowing in channels comes from surface runoff from adjacent hillslopes, from groundwater flow out of the ground, and from water discharged from pipes. The discharge of water flowing in a channel is measured using stream gauges or can be estimated by the Manning equation. The record of flow over time is called a hydrograph. Flooding occurs when the volume of water exceeds the capacity of the channel.
Baseflow is the portion of the streamflow that is sustained between precipitation events, fed to streams by delayed pathways. It should not be confused with groundwater flow. Fair weather flow is also called base flow.
An hydrological transport model is a mathematical model used to simulate the flow of rivers, streams, groundwater movement or drainage front displacement, and calculate water quality parameters. These models generally came into use in the 1960s and 1970s when demand for numerical forecasting of water quality and drainage was driven by environmental legislation, and at a similar time widespread access to significant computer power became available. Much of the original model development took place in the United States and United Kingdom, but today these models are refined and used worldwide.
The HBV hydrology model, or Hydrologiska Byråns Vattenbalansavdelning model, is a computer simulation used to analyze river discharge and water pollution. Developed originally for use in Scandinavia, this hydrological transport model has also been applied in a large number of catchments on most continents.
Geographic information systems (GISs) have become a useful and important tool in the field of hydrology to study and manage Earth's water resources. Climate change and greater demands on water resources require a more knowledgeable disposition of arguably one of our most vital resources. Because water in its occurrence varies spatially and temporally throughout the hydrologic cycle, its study using GIS is especially practical. Whereas previous GIS systems were mostly static in their geospatial representation of hydrologic features, GIS platforms are becoming increasingly dynamic, narrowing the gap between historical data and current hydrologic reality.
Groundwater models are computer models of groundwater flow systems, and are used by hydrologists and hydrogeologists. Groundwater models are used to simulate and predict aquifer conditions.
HydroGeoSphere (HGS) is a 3D control-volume finite element groundwater model, and is based on a rigorous conceptualization of the hydrologic system consisting of surface and subsurface flow regimes. The model is designed to take into account all key components of the hydrologic cycle. For each time step, the model solves surface and subsurface flow, solute and energy transport equations simultaneously, and provides a complete water and solute balance.
A hydrologic model is a simplification of a real-world system that aids in understanding, predicting, and managing water resources. Both the flow and quality of water are commonly studied using hydrologic models.
The following outline is provided as an overview of and topical guide to hydrology:
Vflo is a commercially available, physics-based distributed hydrologic model generated by Vieux & Associates, Inc. Vflo uses radar rainfall data for hydrologic input to simulate distributed runoff. Vflo employs GIS maps for parameterization via a desktop interface. The model is suited for distributed hydrologic forecasting in post-analysis and in continuous operations. Vflo output is in the form of hydrographs at selected drainage network grids, as well as distributed runoff maps covering the watershed. Model applications include civil infrastructure operations and maintenance, stormwater prediction and emergency management, continuous and short-term surface water runoff, recharge estimation, soil moisture monitoring, land use planning, water quality monitoring, and water resources management.
SHETRAN is a hydrological modelling system for water flow, solute and sediment transport in river catchments. SHETRAN is a physically based, distributed model (PBDM) that can simulate the entire land phase of the hydrologic cycle including surface water flow and groundwater flow. The plan area of the catchment in SHETRAN is usually in the range of one to a few thousand square kilometres and the horizontal depth of the subsurface is usually less than 100m.
The Water Erosion Prediction Project (WEPP) model is a physically based erosion simulation model built on the fundamentals of hydrology, plant science, hydraulics, and erosion mechanics. The model was developed by an interagency team of scientists to replace the Universal Soil Loss Equation (USLE) and has been widely used in the United States and the world. WEPP requires four inputs, i.e., climate, topography, soil, and management (vegetation); and provides various types of outputs, including water balance, soil detachment and deposition at points along the slope, sediment delivery, and vegetation growth. The WEPP model has been improved continuously since its public delivery in 1995, and is applicable for a variety of areas.
DPHM-RS is a semi-distributed hydrologic model developed at University of Alberta, Canada.
References
- ↑ Downer, C.W., and F.L. Ogden, 2004, GSSHA: A model for simulating diverse streamflow generating processes, J. Hydrol. Engrg., 9(3):161-174.
- ↑ WMS
- ↑ Downer, C.W., and F.L. Ogden, 2004, GSSHA: A model for simulating diverse streamflow generating processes, J. Hydrol. Engrg., 9(3):161-174.
- ↑ Downer, C.W., F.L. Ogden, J. M. Niedzialek, and S. Liu, 2006, Gridded Surface/Subsurface Hydrologic Analysis (GSSHA) Model: A Model for Simulating Diverse Streamflow Producing Processes, p. 131-159, in Watershed Models, V.P. Singh, and D. Frevert, eds., Taylor and Francis Group, CRC Press, 637 pp.
- ↑ Downer, C.W., and F.L. Ogden, 2006, Gridded Surface Subsurface Hydrologic Analysis (GSSHA) User's Manual, Version 1.43 for Watershed Modeling System 6.1, System Wide Water Resources Program, Coastal and Hydraulics Laboratory, U.S. Army Corps of Engineers, Engineer Research and Development Center, ERDC/CHL SR-06-1, 207 pp.
- ↑ Julien, PY; Saghafian, B. 1991. CASC2D Users Manual - A Two Dimensional Watershed Rainfall-Runoff Model. Civil Engr. Report, CER90-91PYJ-BS-12. Colorado State University, Fort Collins. 66 pp.
- ↑ Ogden, F.L., and P.Y. Julien, 2002, Distributed model CASC2D, in Mathematical Models of Small Watershed Hydrology, Vol 2, V.P. Singh, R. Frevert, and D. Meyers eds., Water Resources Publications, ISBN 1-887201-35-1, 972 pp.
- ↑ Ogden, F.L., and B. Saghafian, 1997, Green and Ampt Infiltration with Redistribution, J. Irrigation and Drainage Engineering, 123(5):386-393.
- ↑ Kilinc, M. Y., and Richardson, E. V. (1973). "Mechanics of soil erosion from overland flow generated by simulated rainfall". Hydrology Papers No. 63, Colorado State University, Fort Collins, CO.
- ↑ Englund, F., and E. Hansen, A Monograph on Sediment Transport in Alluvial Streams, 62 pp., Teknisk Vorleg, Copenhagen, Denmark, 1967.