Hydroguide….a series of topics, and questions to assist students understand
hydrology and water resources management module…GES 410 . Students are
expected to read more on suggested topics and concepts and their applications. This
is only a guide providing basics to areas and issues involved in the module.
C R Mutsiwegota
What is hydrology…study of occurrence, distribution, movement, and quality of water in
the atmosphere, earth’s surface and its subsurface, and in the ground (underground)
Hydrologic data: precipitation (including snow, etc) dam level, river flow, evaporation,
soil moisture, water quality; any information about water in its different forms of
existence.
Classification: Hydrological data has three different uses and therefore 3 classifications:
a. Planning: used for the long term
b. Management: short/medium projects
c. Research: good quality data
Sources of data: Gvt agents responsible for water
Private projects using water
Schools, Farms, and Research projects,
Own generated data
Hydrometric network:
A network for collecting specific or group of related information in hydrology
Network considerations: topography, areal extent, land use, ecological regions.
What is an ideal hydrometric network?
The Hydrologic Cycle…movement/existence of water through the atmosphere, oceans,
earth’s surface and in the ground. Can be representned by the Hydrologic equation:
P-R-E-T-G= S (change in storage) P=precip. E=Evapo. T=Transp. G=g/water and
S=change in storage.
This equation can be used to determine the water budget of the world or of a place.
What is the global water balance? Where is the world’s most and least water?
How can the water budget of Gweru be determined?
What are the problems of using the Hydro equation for determining water budgets?
Where have these been successful and why?
What is hydrometeorology?
What are the various methods used to measure each component of the hydrologic
equation? Give at least two. Consider G as soil moisture.
The hydro. Components have two aspects: at a point/place or over a given area. For each
aspect, consider/study at least two methods that can be used to measure the component
under consideration.
What are the factors influencing areal differences of each component in a country and in
Zimbabwe?
What is the importance of understanding each one of these hyro. components at a place or
in an area in agric. and reservoir building activities ?
…An 800 sq miles watershed received 20 ins o precipitation in one year. Annual
streamflow was 5000 cfs Calculate ET. Qualify answer.
…During a given month lake of surface area 350 acres has inflow of 20 cfs, an outflow of
18 cfs, total seepage of 1 in. and monthly precip of 1.5 in. Estimate change in storage.
The hydrologic equation can be represented by a flow chart. Draw one.
Discuss the difference between Hortonian and Surface Overland flow.
Flow Analysis
The following concepts explain the types of waterflow in the hydrologic process:
Streamflow, overland flow, hortonian flow, groundwater flow, surface overland flow (see
Chorley in Fluvial Processes)
Nature of waterflow :
Uniform, nonuniform, steady, nonsteady, laminar, critical, turbulent. What factors
create each characteristic nature of flow? How is each nature of flow determined?
Flow measurement: Most surface flow is measured in streams and rivers. It is what is left
after abstractions on and under the ground surface. This is normally referred to as
streamflow. Water running in a river is measured as runoff or discharge. It is measured
in volume…..cubic metres per second (cumecs) or cms, cubic feet per second (cusecs) or
cfs, etc. This is the volume of water passing through a cross-section of stream/river
where measurements are being made…..it is the volume of water passing through that
point…different at any other points/sections of the same river. Why?
Measurements are taken per second. How do you get daily monthly and annual flows of
the river at a section?
The velocity of water (its) speed at a cross-section is not uniform..at the bed of the river,
along its channels, and at the middle of the water flow. How is river flow velocity
distributed from the bottom of the river to its top? What affects this flow profile? How do
you get the velocity of the river flow?
Measuring velocity…..How is this done?
The important measurement in streamflow or runoff is discharge…volume per unit time.
Methods of flow measurement: VAM and its variations, current metres, stage/discharge
relationships, automatic river gauges. What does each of these methods measure and how
do you get volume of flow?
What other methods exist for measuring flow in the field? What do they measure and
how do you get flow volume?
Flumes and weirs are also used to measure river/stream flows. How do these work and
where are they most appropriate?
The hydrograph represents flow of water in a stream. What is it and how does this
measure flow? What are its components and what do they represent? Describe situations
represented by different shapes of hydrographs. Explain the various uses of a hydrograph.
Explain mean daily, monthly, and annual flows. When is it appropriate to use each of
these flows. Daily, monthly and annual flows. How do you get these?
Coefficient of variation in streamflow. What is it? What is its importance? The return
interval and its significance? Flow duration curve …how is it developed? What is its
importance?
Time series analysis. What does this show? On selected flow data or even precipitation
data conduct time series analysis.
What is the use of a moving average on a set of flow data? What are the advantages and
disadvantages? Show this on selected data.
What is the use of the return interval in flood management?
Rainfall/runoff relations
There is an obvious relationship between rainfall and runoff as the latter is usually the
result of the former. However, the relation is not always obvious. Why?
Explain factors affecting this relation starting with rain and water flow on a concrete
catchment. Draw hypothetical graph relations and eleborate.
What factors affect this relationship and how do you handle them in trying to determine a
proper relation?
On a selected catchment, how do you show the relationship between rainfall and runoff.?
What is a unit hydrograph? How does it show the relationship between rainfall and
runoff? Given a set of hydrologic data for a selected catchment, develop a unit
hydrograph of the catchment.
The time area method…How does it show rainfall/runoff relations?
Missing data…a stream may have missing flow records or may not have any records at
all. How do you generate data for a much needed project?
Explain the following in generating or extending missing records:
Moving average, correlations, direct transfer, models, serial correlation.
Field activities.
Groundwater
Two major zones of groundwater; the aeration and the saturation zones. Describe and
characterize these zones and relate them to rainfall, land use, and runoff.
What is specific yield and what is its significance if g/water? What determines specific
yield?
Volume of water in the ground is related to geology of ground water basin, bedrock
areas, hydrologic characteristics of rocks. Explain.
Describe geologic formations likely to contain water in the ground. Give examples of
such formations in Zimbabwe.
What factors influence the level of water in the ground at any time? Give details.
What is water table? How does it relate to groundwater zones? Why is water table
highest under the highest surface? What is head? Why is it important? What causes its
fluctuations?
Groundwater flow
Discuss Darcy’s Law
What is the relationship between Darcy’s law and Reynold”s number?
An important aspect in groundwater flow is permeability. It is represented by hydraulic
conductivity. What is the relationship and why use hydraulic conductivity insteady of
permeability.
Well hydraulics:
A well is a hole in the ground producing water. It can be shallow, medium or very deep.
A well has three elements: the hole, the pump, and discharge mechanisms or pump.
Draw two well in an aquifer (a) unpumped (b) pumped. Explain the differences. (c)
What has happened if a well stop producing water? D) What is happeing if a well
produces water contously? What are the equations describing the flow of water in an
unconfined aquifer and a confined aquifer?
Show Darcy’s law on flow of water towards a well.
Boundary conditions: What are these and giving real life examples, explain how they
affect flow of water in the g round. What problems can emanate from these problems?
How can boundary conditions be artificially created?
Pollution
Discuss types of g/water pollution, their sources, measurement and monitoring,
abatements and control. Discuss two cases of known g/water pollution indicating source
and impacts and control measures taken.
Boreholes are being suggested to overcome water shortages in Gweru or Senga in
particular. What are the pros and cons? What is the official position on drilling boreholes
in high density areas of urban areas? What is your position? Medium and deep well water
is often considered safe in rural areas. Comment.
Sediment transport
Describe the following terms or concepts of sediment movement: total sediment yield,
sediment sample , sediment discharge; and out line factors influencing total sediment
yield.
Read on components of sediment transport and their characteristics and measurement.
Sediment measurement relates to soil erosion. Samples are used to estimate materials
being washed away by water on the catchment. The sampling is done at a particular
cross section of the river. The samples refer to erosion above the measuring point.
Sources of sediment are many and varied. They include; river channel, different land-use
areas of the catchment, tributaries to the river, etc. The difficulty is determineing sources
contributing most sediment to this measuring section. Methods of sampling therefore
have to be carefully chosen depending on problem at hand.
Sampling methods:
Erosion is the removal of soil from the earth’s surface either by wind or running water.
The most important erosion agent in Zimbabwe is erosion, influenced by several factors.
This eroded material contributes to sediment in rivers. However, in many cases eroded
materials do not readily reach rivers, depending on size of material and nature of surface
on which material is carried. There is recognition of the fact erosion rates are not the
same as sedement transport rates on the river. Therefore measurements of erosion
methods are directed towards specific land-use and type of areas.
Erosion methods:
Catch pits, airphoto interpretation, dam/lake/resrvoir layers, universal soil eqation, soil
loss equation for Southern Africa.