Hydrology in Civil Engineering: Measuring Flow and Base Flow

This report provides a comprehensive overview of hydrology within the context of civil engineering. It begins by examining the impact of the water cycle on the environment, addressing issues such as pollution by chemicals and biological agents, as well as the effects of chemical weathering. The report then delves into various methods for measuring flow rates in natural watercourses, including velocity-area methods (stationary meter and ADCP), volumetric methods, tracer dilution techniques, and the use of hydraulic structures and indirect discharge methods. A significant portion of the report focuses on the separation of base flow from stream hydrographs, explaining the importance of this analysis and detailing several techniques, such as the smoothed-minimum method, half linear-minimum/maximum methods, and the efficient sub-surface method. The conclusion acknowledges the inherent inaccuracies in base flow separation, emphasizing the arbitrary nature of the exercise. The report highlights the importance of understanding hydrological processes for effective civil engineering practices and environmental management.

HYROLOGY IN CIVIL ENGINEERING
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Abstract
The main aim of this study-work is to discuss how water-cycle has impacted on the environment,
various methods for measuring flow-rate and usage as well the separation of base-flow from
hydrograph. Water is a basic component of human life and a better part of the earth's surface is
occupied by water. Therefore, stream-flow hydrograph analysis is necessary to help in the
understanding of base flow can be separated from the hydrograph stream's discharge.
Introduction
From previous research and findings, it is believed that the earth surface is covered by water
which constitutes about 70%. The hydrological cycle is a process that involves continuous-
circulation of water on earth surface. The formation of water includes evaporation, transpiration,
condensation, precipitation, and run-off. Evaporation is the process by which the heated water
surface is lost into the atmosphere (Marsalek et al., 2014) This water mass lost turns into gaseous
state and condenses (process of condensation) back in liquid form, that raindrops (process of
precipitation) and eventually to running floods (surface run-off).
Impact of water-cycle to the environment
Human-population has been rapidly increasing and this has exerted a lot of pressure on the
earth's surface resources. Further, the need for many countries across the world to be heavily
industrialized also significantly affects the environment, for example, poor methods of disposing
of industrial wastes have led to water pollution.
There has been a lot of debate about the changing climatic situation or patterns caused by the
emission of greenhouse gases into the atmosphere as well as deforestation acts which have
facilitated the problem of desertification. This has led to high temperatures hence global

warming and land encroachment leaving no forest cover that acts as water catchment areas. In
general, these issues have a reciprocating effect on the hydrological water cycle (Jiang,
Hendrickson and VanBriesen, 2014).
The following factors have a great influence on water-quality thereby impacting on the
environment.
Pollution by chemicals
Even though there is a growing need for industries across the world, there still exist a number of
challenges created by these industries. For example, chemical industries have widely contributed
to the contamination of water sources. Fertilizer manufacturing-plants quite often release harmful
waste gases like Nitrogen and Phosphorous into the atmosphere. When these gases get to the
atmosphere, they form chemical compounds such as Nitrates and Phosphates (Mills et al., 2014).
The nitrates formed increases the process of eutrophication which in turn facilitates the growth of
algae and macrophytes thereby contaminating water sources quality. This is a dangerous health-
hazard for the human population since it results in cancer cases. Phosphates, on the other hand,
are harmful to the growth of aquatic-plants which is as an atmospheric-nitrogen fixer.
Phosphates, therefore, become a limiting-agent to the growth of algae and macrophytes.
Biological-water pollution
Bacteria are single-celled micro-organisms that are considered to be dangerous water pollutants.
Because of their tiny sizes, they can transmit several diseases through contaminated underground
water-systems. The main problem with bacterial-pollution is should biological-hazard occur in a
particular region, then through water circulation processes, it is likely to be transmitted to many
kilometers spreading to several regions across the world. It is therefore important to note that

sewerage-systems that carry human wastes and piped-water should be constructed far away from
a water source to avoid this kind of contamination (Qiao et al., 2015).
Chemical-Weathering
Weathering refers to the process by which chemical and physical processes breaks-down the
rock-structures that are found on the earth surface. Weathering occurs when there is direct
exposure of the earth's rock-material to water and air. Disintegration normally occurs at the
submicroscopic surface due to the weathering processes hence making pores of exposed rock-
materials and the fractured surfaces to allow chemical-weathering to take place (Gericke and
Smithers, 2014). This process of chemical weathering is accelerated by increased concentration
of chemicals that are subjected to the earth's atmosphere.
The rate of chemical weathering is influenced by three key elements; temperature, amount of the
earth's surface area and the available water sources or natural-acid. This is the reason why the
environment in the tropics does experience a high and acute level of weathering processes.
During these chemical processes, water is used as a solvent material that will make several
chemicals dissolve to form chemical compounds.
Methods of measuring flow rates in natural watercourses
Measurement of flow-rates in natural watercourses is a very important exercise that should be
carried to determine the quantity of earth surface-outflow of a given basin, its temporary
variation and the features of outflow. The measurement should be simple, reliable and accurate.
For this to work out, the hydrometric-station should be well equipped with the necessary
facilities and adequate staff. Below are some of the methods used to measure the flow-rates of
natural watercourses

Velocity-area-stationary Meter method
Velocity-area-stationary Meter method is used to measure the velocity of moving water at
vertical points within a transverse-section of a natural watercourse. This method is simple, easy
to use and highly accurate if the natural watercourse is not that deep (Chandler et al., 2014). It
comprises of current meters that are widely used worldwide. It is applicable in places where
there are relatively constant flow and proper distribution channels that must be in uniform
situations.
Velocity-area-ADCP (Acoustic-Doppler Current-Profiler) Moving-boat method
It uses ADCP-instrument that is always mounted on the moving boat. Equally, this method is
also common and used extensively across the world. This method is faster and uses a lot of
information that must be detailed. In comparison to the Velocity-area-stationary meter method,
this method gives a lot of information which is detailed hence quick and efficient (Watral,
Jakubowski and Michalski, 2015). Further, to give the location, GPS is used alongside the
moving-boat. It is used to measure the depth of water, velocity-profiles of water and velocity of a
moving boat.
Volumetric-Method
This type of method records water flow in specialized containers called volume and a
measurement of time is captured from the beginning to when the container is completely filled
up. The volumetric method is suitable for small water-flows. Its main purpose is to record the
time is taken and the volume of water-flows.

Tracer dilution method
This method involves the addition of a known quantity of a concentrated-tracer at a uniform rate
to the water-flows (Watral, Jakubowski and Michalski, 2015). Chemical-analysis is then
performed to ascertain the level of dilution of constantly mixed-concentrate at the downstream-
point. This method is beneficial in the sense that it does not require the measurements of the
flow-channel geometry.
There exist two kinds of Tracer dilution; a Color dilution or Salt dilution. Color dilution is
normally used to measure relatively small flows to relatively large flows whereas Salt dilution is
best suited for measuring turbulent-streams that vary in size that is from small size to medium
size. This method is generally costly as compared to rest since it uses a special type of equipment
and requires a high level of experienced persons to operate it. On the same note, its level of
accuracy is not constant based on the equipment used as well as the level of experience by the
operator.
Hydraulic-Structures
These are important equipment that can be used to channel, block and control the flow of open-
water channels. It is a device of fixed-geometry (Maradei et al., 2015). Normally, it is placed into
the flow area to enable all the flows to be channeled to the device. It is categorized into two;
flumes and weirs. This method is a little bit expensive to set up as compared to other methods.
Indirect-discharge method: This method is commonly used to measure flood-flows. It is
appropriate in taking the measurement of peak-water levels along the water channels; surveying
of structures after the flood has taken place and approximating the hydraulic-parameters for the
water channels (Maradei et al., 2015).

Separation of base flow from the hydrograph of a stream’s discharge
A hydrograph is a graphical representation that shows the flow-rate (discharge) against time
beyond a specific part in a river, channel-flow or conduit that carries the flow. The flow rate can
be measured and expressed in cubic meters per second (m3s-1) or cubic feet per second (CFC).
Therefore, the analysis of this process is very necessary because of the increasing needs of water
by the human population (Rimmer and Hartmann, 2014). It is for these increased needs that have
made it possible for people to embark on ways of storing water during rainy seasons that could
be used in dry spell seasons.
The analysis of hydrograph is extremely important to approach that is suitable for investigating
several water resources. Separation of stream-flow hydrographs into base flows and the surface
run-off parts is generally suitable approximate the influence of groundwater to stream-flows
(Rimmer and Hartmann, 2014). Further, this technique has facilitated the drafting of the
hydrologic budget that is useful in coming up with estimates of recharge rates.
Separation of base flow from the hydrograph of a stream’s discharge uses the records of time
series analysis of stream-flow to generate base flow marks. The graphical-separation method can,
therefore, be used to give the points for the intersection between base flow and rising or falling-
limbs of the quick-flow response. This will facilitate the filtration of the whole stream-
hydrograph to generate a baseflow-hydrograph (Mills et al., 2014). Using the analysis of digital-
signal tools especially the recursive digital filters, a frequency-quick flow signal can be
eliminated to generate a low-level frequency baseflow-signal. These filters are considered to be
very strong and simple but the outcomes seem to be extremely sensitive to the filter-parameters.
For the possible outcomes to be considered justifiable, then calibration should be made on this
filter-parameter before the base flow separation.

During the process of base flow separation, frequency-analysis uses different techniques to
establish the interrelation between magnitude and frequency-rate of stream-flow discharges. As a
result, a Flow Duration Curved (FDC) is established. This curve shows the percentage of time
taken by a particular flow-rate to be in equilibrium status (stable condition) or unstable condition
(Mills, et al., 2014).
The analysis of base flow comprises of extensive methodologies that have been made available
to provide an important strategy to enhance the unique understanding of how underground water
is discharged to stream flows. This approach is quite beneficial since the statistical data derived
from it or that has been routinely recorded is made available for the consumption of the general
public. From this perspective, the process of base flow analysis is taken to be the desktop study
before carrying out the actual and comprehensive investigation in the field (Lott and Stewart,
2016). The following are some of the techniques that are available for separation of base flow
from hydrograph stream’s discharge;
Use of smoothed-minimum method-This is the simplest procedure of separating base flow from
hydrographs in that it is based on the assumption that base flow is made up of regular line-shape
and free from factors that which are produced due to changes from hydrograph stream-flows
(Gore & Banning, 2017).
Half linear-minimum or half linear-maximum methods: This procedure resembles the use of a
smoothed-minimum method but the unique feature is that it is based on the assumption that the
figure of base flow is just below the stream-flows hydrograph's peak. In the end, baseflow-rate is
given either by the minimum figure of base flow depicted in the curve of past recession or the
maximum figure of base flow depicted by the continuing recession.

Efficient sub-surface method: This method takes into account the seepage from precipitation
during several recession periods thus dividing the stream-flow hydrograph in three layers. That
is, influenced surface, sub-surface and groundwater-flows. This gives rise to the reversed
recession curve drawn from the efficient point of base flow to the inefficient of base flow (Gore
and Banning, 2017).
Conclusion
The process of base flow separation from the stream's discharge of hydrograph is an inaccurate
science. Therefore, the separation of base flow from the hydrograph stream's discharge is an
arbitrary-exercise. Due to such nature of separation, several graphical and empirical methods
have been generated to facilitate the separation of these base flows from the hydrograph stream's
discharge.

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