Use of Hydro-meteorological Data in Watershed Planning
Hydro-meteorological data is an important hydrologic data. It includes data on precipitation, abstractions of precipitation and other meteorological parameters which influence the watershed management. Depending on the objectives of watershed planning, the hydro-meteorological data requirement will be different. The watershed planning and management may generally have any one or more of the following objectives along with any one of the following listed features [as given in Table 8.1]:
Table 8.1. Watershed planning objectives and the features associated with them
Watershed planning objective Associated features
1. Hydrological characterization: a) Watershed planning,
b) General water balance;
2. Flood management and control: a) Structures [i.e., dams, river training etc.],
b) Flood forecasting & warning,
c) Flood plain zoning & flood frequency estimation,
d) Coastal inundation;
3. Irrigation and drainage: a) Supply,
b) Demand scheduling;
4. Groundwater planning: a) Recharge,
b) Flooding management;
5. Water quality management: a) Pollution control,
c) Salinity & sedimentation management;
6. Fisheries and eco-conservation: a) Hydro-ecology,
According to the purpose as well as the associated feature, the hydro-meteorological data requirement will be as listed in Table 8.2:
Table 8.2. Watershed planning objective, feature(s) and relevant hydro-meteorological data required
Watershed planning Hydro-meteorological data requirement Objective & feature
as given in Table 8.1
1 a. and 1 b. Precipitation, temperature, humidity, wind speed.
2 a. Precipitation, temperature, humidity, wind speed & direction.
2 b. Precipitation, temperature, evapo-transpiration, synoptic information, forecasts & alerts, medium & long range forecasts.
2 c. Precipitation, temperature, evapo-transpiration, synoptic information.
2 d. Wind speed & direction, synoptic information, forecasts & alerts.
3 a. and 3 b. Precipitation, temperature, humidity, wind speed, medium & long range forecasts.
4 a and 4 b. Precipitation, temperature, humidity, wind speed, medium & long range forecasts.
5 a., 5 b. and 5 c. Precipitation, temperature, humidity, wind speed, forecasts & alerts.
6 a. and 6 b. Precipitation, temperature, humidity, wind speed, medium & long range forecasts.
Use of Hydro-Meteorological Data in Hydrological Characterization
The primary concern of a water management agency is with rainfall, river flow and groundwater, and the focus of their activity will be the measurement and analysis of these variables. Historically the main climate variable collected by a water management agency is rainfall, as this, even in the absence of water management or catchment models, will provide an intuitive, subjective or qualitative assessment of the interaction between rainfall, river and groundwater. For the most part, rainfall data are widely available on a daily basis, and can be agglomerated into 10-day, monthly, seasonal values, etc.
The climate data items used are: precipitation, temperature and evaporation, either in conjunction with, or drivers for, hydrological and hydro-geological variables. Evaporation data are produced by measurement using evaporation pans or evaporimeters, or estimated as evapo-transpiration. The most widely used method for the latter is by the Penman-Monteith Equation, which requires measurement of air temperature, humidity (as vapour pressure), solar radiation or duration of sunshine, wind speed and length of day.
The most basic level of providing data for catchment planning is through a “catalogue” approach, where statistics related to locations and areas are presented. However, there are few instances outside of the more developed countries, e.g. USA, Australia, New Zealand, of comprehensive visualization of data-sets. Their establishment requires a lead agency to host the site and have the responsibility for a range of decisions on what the system will provide, including:
Maintenance of the website
Regularity of updating
Content and format of presentation
Control of access, e.g. user controlled, open public access
Management of queries.
In the tactical role, a water balance or catchment model needs to be periodically updated on a scale of weeks to consider such requirements as releases for irrigation and power scheduling, and thus the component data has to be regularly updated. Updated data in these applications are often part of a more complex decision support framework, which may involve critical actions outside the immediate brief of the collection agency. The time frame for accessing data may well be at different time intervals than regular processing and publication procedures employed by data collection agencies, which are mostly monthly. The present widespread use of data-logging instruments allows data access and processing to be flexible.
In the operational role data feeds for similar applications as those of a tactical nature may be necessary at short intervals, of a few days or daily. It is more common for water management agencies to collect climate data for their own requirements, than for climate agencies to collect their own hydrological data.
A significant data item in water balance activities is the estimation of evapo-transpiration (ET) as a major component of losses on a range of spatial and temporal scales. Estimation of ET in practical terms has always been a problematic topic. ET requires the measurement of:
All of which require integration over a daily period.
Use of Hydro-Meteorological Data in Flood Management and Control
The responsibilities for planning and design of flood management can fall within the brief of planning and infrastructure agencies, whereas operations for major flood defence, which includes such measures as flood forecasting and warning may be the responsibility of water management or meteorological agencies. Catchment management covers dams, diversion structures, river bank and infrastructure protection. Apart from the usual data mentioned in Table 8.2, the following data is also needed:
Sub-daily rainfall, at least hourly,
Wind velocity and direction.
Daily and sometimes sub-daily rainfall are variables collected by both climate and water management agencies, and the greater density of rain gauges in networks used by water management agencies may reduce the need for data from climate agencies.
Wind velocity and direction are most important for dam design, where wind set-up for wave protection is required, but may apply to exposed sections of river embankments. Wind set-up requires information on mean wind speed, duration of winds above certain thresholds, persistent direction and maximum gust velocity.
For flood forecasting and warning, radar measurement of rainfall, weather satellite information, numerical weather prediction and quantitative precipitation forecasting are required. In flood frequency estimation, maximum river levels and discharges are required as part of the extrapolation of the more extreme events. The effects of catchment structure, antecedent conditions and statistical methods may assume that a flood of a given probability is produce by a rainfall of lesser probability. The estimation of probable maximum precipitation (PMP) is a special aspect of flood frequency analysis.
The aim of flood plain zoning is to identify parts of the flood plain, with different categories of risk for planning and development purposes, broadly to define which parts are subject to more frequent flooding. Therefore it has to be avoided for domestic habitation and critical infrastructure.
Coastal flooding, which may also include flooding in estuary areas, can be caused by range of conditions relating to tide, wind speed and direction and atmospheric pressure. Areas showing particular physical structures, including narrowing coastal bays and shelving sea-bed, can be particularly susceptible to a combination of meteorological conditions, defined as a storm surge. The principal observations involved, wind speed and direction, atmospheric pressure and tides, are generally the responsibility of meteorological services, but coastal flood warning operations are often shared between the meteorological and water management agencies.
Use of Hydro-meteorological Data in Irrigation and Drainage
At the highest, strategic, level irrigation and drainage require consideration in terms of long-term national planning, and involve many more bureaucratic operators than just the meteorological and water management agencies. However, as data providers, these two rank in importance alongside the agricultural agency. Tables of daily data are published that include the full range of variables for the calculation of potential evapo-transpiration and a 24-hour measurement of evaporation is included for most stations.
The supply sources for irrigation and drainage can come from surface water and groundwater, and the overall management of these are the responsibility of a water management agency. However, the day-to-day operations will be done by the irrigation managers, based on resource availability, demand and constraints put in place by general water and environmental management. Managing the supply on a small, individual abstraction, or for a major system, requires some information on meteorological forecasts, mostly in the medium term (days and months) and in the longer term, (years or longer) where planning and strategy have to be considered.
Meteorological services could perhaps provide enhanced information for demand scheduling by making available observations from a national or regional network of automatic weather stations (AWS). The latest versions of AWS have sophisticated software for the estimation of evapo-transpiration.
Use of Hydro-meteorological Data in Groundwater Planning
In arid and semi-arid climates, given suitable geological conditions, it can provide the only reliable, large volume source. Its management is a sub-division of the overall brief for water management, and in many countries is done on a departmental basis within the water management agency.
Groundwater is usually characterized by an annual cycle of drawdown and recharge, and its use as a water supply depends on its management within this cycle. There are also cases, due either to the configuration or type of aquifer, or major cyclical climate patterns, e.g. El Nino-La Nina, that cycles over more than one year can occur. Confined aquifers, where recharge is delayed, can show response to rainfall conditions weeks or even months later. Large artesian basins, such as those in the interior eastern areas of Australia and the eastern Sahara, can have responses to seasonal rainfall patterns in peripheral mountains, lagged by several years.
Groundwater recharge takes place during rainy seasons, e.g. monsoon seasons in the tropics, winter in temperate latitudes. When rainy conditions begin to predominate, it is first necessary for the soil moisture deficit (SMD) to be replenished. The magnitude of SMD prior to recharge is a function of evapo-transpiration, vegetation and soil type. Groundwater management is done by reference to known trigger levels, which may be particular aquifer water or storage level, or demand criteria.
Groundwater flooding chiefly occurs when aquifer water levels (water table) rise to above ground level, a situation brought about by high rainfall quantities over extended periods. Because of the delayed response in vertical and horizontal flow in aquifers, flooding often takes place sometime after the causative rainfall events, and may persist for some time (days, weeks), as outflow is also controlled by the aquifer characteristics.
Use of Hydro-meteorological Data in Water Quality Management
The catchment management to maintain water quality in rivers, lakes and groundwater is primarily a function of the water management agency. The maintenance of quality is implemented through complex legislation covering chemical, biological and physical characteristics, and a broad range of users, e.g. agriculture, industry, municipalities all have controls under which they must operate. The need for quality maintenance is becoming more stringent, as national and international targets for ecological and conservation measures are put into place.
Incidents of water pollution arise for several reasons, and response to these incidents can often have a dependence on meteorological conditions for their management and restoration of normalcy. A particular issue for the short-term management of sewage is the risk of combined sewer overflows (CSOs). Combined sewers, where foul water and surface water are carried in the same system are widespread in many countries, and when heavy rainfall occurs, rapid surcharge of the system will result in spillage of untreated sewage. It is important for sewer management to be able to identify the types of conditions that cause CSOs.
Dilution is a key method for permitting the discharge of waste which may, even after treatment, still contain some impurities. Depending on the regime of the receiving water, usually a river or a lake, there are obviously advantages to the management and control from a forecast or projection of meteorological conditions, either incidence of rain, or the duration of dry weather. Information on immediate or protracted elevated temperatures is also important, as these can affect the status of the receiving waters.
Problems of salinity and sedimentation are most directly the result of droughts, and in markedly seasonal climates are of greater or lesser significance in most dry seasons. Thus meteorological information on the extent of dry conditions is of considerable importance. Salinity build up in the soils of irrigated areas results from excessive evaporation from water in the top surface of the soil, which brings up salts that have been previously leached, often by over-application of water, or maintaining drainage water levels to high.
Use of Hydro-meteorological Data for Fisheries and Eco-Conservation
Fisheries within rivers and lakes are highly dependent on the maintenance of the required water quality to support the whole of the aquatic environment. The hydro-meteorological information requirements for temperature monitoring and drought forecasting are equally relevant here. In addition, high temperatures can be critical for some fishes. In combination with water quality especially under low flow conditions, they can produce stress or death of fish stocks.
Conservation is a very complex topic, and in the water sector concerns complex physical and biological relationships in water-bodies and wetlands. Water management may be affected by catchment-wide initiatives, or by site-specific interventions. Conservation agencies can operate on a range of levels, from international bodies such IUCN (the International Union for the Conservation of Nature), WWF (World Wildlife Fund), to national and local conservation bodies. These two organizations have become increasingly involved in decision-making on water resources on several levels.
8.2 Use of Physiographical Data in Watershed Planning
Physiographical data broadly includes topographic data, land use-land cover data and soil data. In this section, we shall discuss its utility in watershed planning.
Utility of Topographical Data in Watershed Planning
Topographical data involves data on physical/ natural features of the watershed, watershed boundaries, floodplains in the watershed, wetlands and water bodies etc. Depending upon the purpose and the features of watershed planning as listed in Table 8.1, the utility of the topographical data will vary. In many cases, the data on either the spatial variation or the spatio-temporal variation of the topographical data parameters listed below are required.
For hydrological characterization, the data on slope, permeability of the ground surface, roughness of the ground surface, obstructions like buildings or other manmade infrastructure or hills or depressions is required. For flood management and control, the data on wetlands and water bodies, channel cross sections, other natural and artificial flood mitigation structures is required. For irrigation and drainage, data on optimum water table depth, canal linings, canal flow capacity, crop type, crop area are necessary.
For groundwater management, the data on annual changes in water table depth, crop root zone depths, wetlands and water bodies is needed. For water quality management, the locations of point and non-point pollution sources, total maximum daily loads (TMDLs), spatio-temporal variations in pH, turbidity, total suspended solids, total dissolved solids, biochemical oxygen demand (BOD) etc. may be needed. For fisheries and eco-conservation, the data on dissolved oxygen, spatio-temporal variations in aquatic plants and animals having eco-conservation capabilities is required.
Utility of Land Use/ Land Cover (LULC) Data in Watershed Planning
LULC data consists of data on forests, grass/ range lands, cultivated lands, orchards, wildlife reservations, recreation areas, urban/ rural areas, water bodies, eroded areas etc. Depending upon the purpose and the features of watershed planning as listed in Table 8.1, the utility of the LULC data in watershed planning varies. In most of the cases, the data on either the spatial variation or the spatio-temporal variation of the LULC data is required to carry out watershed planning.
LULC influences practically all the processes of hydrologic cycle like interception, infiltration, surface runoff, surface storage, groundwater runoff, groundwater storage, evapo-transpiration (ET). LULC also influences meteorological parameters such as temperature, humidity and wind velocity, which in turn impact the estimation of ET. Therefore especially the purposes of watershed planning like hydrological characterization, flood management and control, groundwater planning in a watershed get affected significantly. Thus LULC data has a great utility in watershed planning.
An improved model performance plays a vital role in achieving the watershed planning objectives. Hence, appropriate values of the lumped and/or distributed model parameters need to be assigned in the model, based on the accurate analysis by experts of the spatio-temporal variations in the watershed LULC data.
Utility of Soil Data in Watershed Planning
Soil data can be an important factor in determining the amount of erosion and storm water runoff that occurs in the watershed of interest. It can enable the estimation of water retained within the soil, analyze the slope stability or the flow of groundwater through the soil pores. Data on the types of soils in the watershed and their characteristics helps us to identify the areas that are prone to erosion or sedimentation as well as the areas which are more likely to experience runoff.
Keywords: Hydro-meteorological data utility, Physiographical data utility, Precipitation data utility, Topographical data utility, Land use land cover data utility, Soil data utility.