HYDRAULICS AND HYDROLOGY LABORATORY
LABORATORY INSTRUCTION SHEETS
COURSE CODE BNP 20103
EXPERIMENT NO. 2
EXPERIMENT TITLE BASIC HYDROLOGY
DATE 27/9/2016
GROUP NO. 2
LECTURER/ INSTRUCTOR/ TUTOR
1) MADAM ZARINA BINTI MD ALI
2) DR NOR HASLINA BT MOHD HASHIM DATE OF REPORT
SUBMISSION 4/10/2016
DISTRIBUTION OF MARKS FOR LABORATORY REPORT
ATTENDANCE/PARTICIPATION/DISPLINE /5%
INTRODUCTION: /5%
PROCEDURE: /5%
RESULTS & CALCULATIONS /15%
ANALYSIS /15%
DISCUSSIONS: /20%
ADDITIONAL QUESTIONS: /15%
CONCLUSION: /10%
SUGGESTION & RECOMENDATIONS /5%
REFERENCES: /5%
TOTAL: /100%
STUDENT CODE OF ETHICS
DEPARTMENT OF CIVIL ENGINEERING TECHNOLOGY
FACULTY OF ENGINEERING TECHNOLOGY
I hereby declare that I have prepared this report with my own efforts. I also admit to not accept or provide any assistance in preparing this report and anything that is in it is true.
1) Group Leader __________________________________________(Signature) Name : HARDIAM SYAM BIN JAMALUDDIN
Matrix No : AN150288
2) Group Member 1 __________________________________________(Signature) Name : INA SYAZWANI BINTI HAMZAH
Matrix No : AN150020
3) Group Member 2 __________________________________________(Signature) Name : IZZATI BINTI ABDUL MANAF
Matrix No : AN150115
4) Group Member 3 __________________________________________(Signature) Name : KU NUR FARZANA BINTI KU ADZMAN
1.0 OBJECTIVE
To identify the relationship between rainfall and runof.
2.0 LEARNING OUTCOMES
At the end of the course, students should be able to apply the knowledge and skills they have learned to:
a. Understand the basic terms in hydrology.
b. Understand the concept of watershed area including time of concentration (tc) and outlet or concentration point.
3.0 INTRODUCTION / THEORY
3.1 Runoff is generated by rainstorms and its occurrence and quantity are dependent on the characteristics of the rainfall event, i.e. intensity, duration and distribution. The rainfall-runoff process is extremely complex, making it difficult to model accurately. There are, in addition, other important factors which influence the runoff generating process like natural surface detention, soil infiltration characteristics and the drainage pattern formed by natural flow paths. The soil type, vegetative cover and topography play as important roles. Rainfall and runoff are very important hydrologic components because of their direct relations with water resources quantity, flood, streamflow and design of dam and hydraulic structure.
4.0 EQUIPMENTS
4.1 Basic hydrological instrument 4.2 Stop watch
5.0 PROCEDURES
a) Case 1: Flat and sandy soils surface with 1:100 slope profile
The rail at side of the catchment area was adjusted to justify according the requirement for case 1 (from upstream to downstream).
The steel ruler was used to measure the depth (mm) of the sandy soils.
The pump was switched on and the stop watch was started when the water level reading equal to 0.
The water level every 30 seconds (during the rainfall) and the reading from the rain gauge (mm) were recorded at the same time.
When the peak level achieved (after 6 water level readings with same values obtained), switched off the pump to stop the rainfall. The time were recorded while stop of rainfall.
At the same time, the water level readings must be recorded for each 30 seconds until the values reach nearly zero.
Table 6.1 was filled. The discharge (m3/s) were calculated by referring to the provided graph attached to the equipment.
6.0 RESULTS AND CALCULATIONS
TABLE 6.1 Basic hydrological experiment results Time,
t
(s)
Case 1
Water Level Discharge Rain gaugereading
(cm) (mm) (liter/min) (m³/s) (mm) 40 0 0 0 0 22 80 0.5 5 0.3 0.000005 22 120 2.5 25 8.8 0.000150 24 160 2.9 29 12.5 0.000210 24 200 3.1 31 15.0 0.000250 26 240 3.1 31 15.0 0.000250 26 280 3.1 31 15.0 0.000250 26 320 3.1 31 15.0 0.000250 24 360 3.1 31 15.0 0.000250 23 400 2.1 21 5.5 0.000092 0 440 1.6 16 2.8 0.000047 0 480 1.2 12 1.4 0.000023 0 520 1.2 12 1.4 0.000023 0 560 0.9 9 0.8 0.000013 0 600 0.8 8 0.7 0.000012 0 640 0.8 8 0.7 0.000012 0 680 0.8 8 0.7 0.000012 0 720 0.7 7 0.5 0.000008 0 760 0.7 7 0.5 0.000008 0 800 0.7 7 0.5 0.000008 0 840 0.6 6 0.4 0.000007 0 880 0.6 6 0.4 0.000007 0 920 0.6 6 0.4 0.000007 0 960 0.6 6 0.4 0.000007 0 1000 0.6 6 0.4 0.000007 0 1040 0.6 6 0.4 0.000007 0 Total 217 Example of calculation At t= 80 s , discharge = 0.3litre min× 0.001 m3 1 litre × 1 min 60 s =0.000005 m3 s
7.0 QUESTIONS
7.1 Plot the discharge (unit m3/s) versus time (second) graph separately from the above values for each cases (case 1 and case 2).
0 40 80 120 160 200 240 280 320 360 400 440 480 520 560 600 640 680 720 760 800 840 880 920 960 1000 1040
Discharge, Q (m³/s) vs Time, t (s)
Time, t (s) Disharge, Q (m³/s)1.1 From the graph plotted, determine: (a) Time concentration
When the discharge is constant, the value is between 200 and 360 seconds. So, 200 < tc < 360 seconds.
(b) Rainfall duration
The constant value of discharge dropped at 360 seconds, meaning that the water in the soil had decreased from the maximum volume of water the soil can hold, which means the rain had stopped. Therefore, the rainfall duration is 360 seconds.
(c) Peak discharge
Peak discharge is the highest point on the hydrograph when the rate of discharge is the greatest, so peak discharge is 0.00025 m³/s.
(d) Runoff volume
Discharge, Q (m³/s) vs Time, t (s)
Time, t (s) Disharge, Q (m³/s)
Calculation for areas:
A = 12(40) (0.000005) = 1 × 10-4 m3 B = 1 2(0.000005 + 0.00015)(40) = 3.1 × 10 -3 m3 C = 12(0.00015 + 0.00021)(40) = 7.2 × 10-3 m3 D = 1 2 (0.00021 + 0.00025)(40) = 9.2 × 10 -3 m3 E = (160)(0.00025) = 0.04 m3 F = 12(0.00025 + 0.000092)(40) = 6.84 × 10-3 m3 G = 1 2 (0.000092 + 0.000047)(40) = 2.78 × 10 -3 m3
H = 12 (0.000047 + 0.000023)(40) = 1.4 × 10-3 m3 I = (40)(0.000023) = 9.2 × 10-4 m3 J = 12 (0.000023 + 0.000013)(40) = 7.2 × 10-4 m3 K = 1 2 (0.000013 + 0.000012) (40) = 5 × 10 -4 m3 L = (80)( 0.000012) = 9.6 × 10-4 m3 M = 12 (0.000012 + 0.000008)(40) = 4 × 10-4 m3 N = (80)( 0.000008) = 6.4 × 10-4 m3 O = 12 (0.000008 + 0.000007)(40) = 3 × 10-4 m3 P = (200)(0.000007 ) = 1.4 × 10-3 m3
Total Area = A+B+C+D+E+F+G+H+I+J+K+L+M+N+O+P = 7.65 × 10-2
m3 Runoff volume = 7.65 × 10-2
(a) Rainfall intensity
Rainfall intensity = Maximum rain gaugeRain duration = 26 mm
360 s = 0.0722 m/s (b) Storage volume
Storage volume = Total rainfall – Total runoff
= (Total rain gauge reading × Catchment area) – Total runoff = (Total rain gauge reading × [0.6 × 1.8] m²) – Total runoff = ([217 × 10−3
¿ m × 1.08 m²) - 7.65 × 10-2 m³
= 0.1579 m³
7.2 Provide a table for all the results obtained from (2).
Time concentration (s) 200 < tc < 360 Rainfall duration (s) 360 Peak discharge (m³/s) 0.00025 Rainfall intensity (mm/s) 0.0722 Storage volume (m³) 0.1579 7.3
Prepared by / Disediakan oleh:
Signature/Tandatangan:
Name/Nama: DR. NOR HASLINA HASHIM Date/Tarikh : AUGUST 2016
Approved by / Disahkan oleh :
Signature / Tandatangan :
Name / Nama : ASSOC. PROF. DR. ISHAK BABA
Date / Tarikh : AUGUST 2016
DATA ANALYSIS
From the experiment, we can see that water can absorb fast because inside the soil, they have a lot of void. Also from the experiment, we consider that the soil is dry, after plot a graph of infiltration rate versus time. The process of infiltration is quite fast because they can easily absorbed water inside the soil. So, the water rapidly absorbed inside the soil during the experiment was carried out.
The infiltration capacity of the soil depends on its texture and structure, as well as on the antecedent soil moisture content. The initial capacity of a dry soil is high but, as the storm continues, it decreases until it reaches a steady value termed as final infiltration rate.
Based on our results, the water level in the beginning of the experiment is increase rapidly with just per second. In other words, it took several seconds just to achieve the peak level. However, the water level that is continued to be record from the peak level as soon as the rainfall began to stop take much more times rather than when its start to rain.
Up until several constant of water level reading, we decided to stop recording the data. The full depiction of our results for this experiment can be seen more clearly with the graph included in the report.
DISCUSSION
Runoff is generated by rainstorms and its occurrence and quantity are dependent on the characteristics of the rainfall event, i.e. intensity, duration and distribution. There are, in addition, other important factors which influence the runoff generating process. The rainfall-runoff process is extremely complex, making it difficult to model accurately. There are, in addition, other important factors which influence the runoff generating process like natural surface detention, soil infiltration characteristics and the drainage pattern formed by natural flow paths.
Factors affecting runoff are: Soil type
The infiltration capacity is among others dependent on the porosity of a soil which determines the water storage capacity and affects the resistance of water to flow into deeper layers. Porosity differs from one soil type to the other. The highest infiltration capacities are observed in loose, sandy soils while heavy clay or loamy soils have considerable smaller infiltration capacities. The infiltration capacity depends further more on the moisture content prevailing in a soil at the onset of a rainstorm. The initial high capacity decreases with time (provided the rain does not stop) until it reaches a constant value as the soil profile becomes saturated.
Vegetation
The amount of rain lost to interception storage on the foliage depends on the kind of vegetation and its growth stage. Values of interception are between 1 and 4 mm. A cereal crop, for example, has a smaller storage capacity than a dense grass cover. More significant is the effect the vegetation has on the infiltration capacity of the soil. A dense vegetation cover shields the soil from the raindrop impact and reduces the crusting effect as described earlier. In addition, the root system as well as organic matter in the soil will increase the soil porosity thus allowing more water to infiltrate. Vegetation also retards the surface flow particularly on gentle slopes, giving the water more time to infiltrate and to evaporate. In conclusion, an area densely covered with vegetation, yields less runoff than bare ground.
Slope and catchment size
Investigations on experimental runoff plots have shown that steep slope plots yield more runoff than those with gentle slopes. In addition, it was observed that the quantity of runoff decreased with increasing slope length. This is mainly due to lower flow velocities and subsequently a longer time of concentration (defined as the time needed for a drop of water to reach the outlet of a catchment from the most remote location in the catchment).This means that the water is exposed for a longer duration to infiltration and evaporation before it reaches the measuring point. The same applies when catchment areas of different sizes are compared. The runoff efficiency (volume of runoff per unit of area) increases with the decreasing size of the catchment i.e. the larger the size of the catchment the larger the time of concentration and the smaller the runoff efficiency.
Rainfall-runoff processes
Apart from recording and forecasting rainfall itself, the next most important problem is understand and forecasting the runoff generated by the rainfall. This difficult problem has attracted enormous amounts of attention and effort around the world. There are possibly as many models for calculating rainfall-runoff, as there are people who have a direct interest in the subject. Runoff generation from rainfall over a catchment can be assumed to depend on factors such as:
Atmospheric conditions over the catchment (wind speed, direction, temperature, humidity)
The surface cover (type, distribution, interception, take up, evapotranspiration)
Surface soil (type, permeability, porosity)
Terrain (slope, surface texture)
Geology (structure distribution, permeability, porosity, groundwater levels)Generally the following processes are usually identified as taking place:
Evapotranspiration at the surface Surface infiltration
Overland flow
Unsaturated zone flow
Rainfall and runoff are very important hydrologic components because of their direct relations with water resources quantity, flood, stream flow and design of dam and hydraulic structure. To convert discharge volume in liter/min to m3/s, we use this formula:
Q , Liter min × 1 m3 1000 liter× min 60 s
Based on the graph discharge versus time, we get the bell shape graph. The value of discharge increase when the time increases.
SUGGESTION& RECOMMENDATION
During the experiment some errors existed which a little bit affects the result of the test. Some of the errors detected are:
1. Readings taken was not very accurate 2. The soil was still wet before the test started 3. Instrument drift
To avoid the errors some precaution steps can be used in order to achieve better results. The list of the precaution steps are as follows:
1. Avoid parallax error when taking measurements by making sure the eye of the observer is perpendicular to the scale.
2. Make sure that the readings were taken at the meniscus.
CONCLUSION
As the conclusion of this experiment, we clearly understand the basic terms in hydrology which is how to relate the relationship between the process of runoff and rainfall event. Based on the experiment results, we can prove that when the rainfall increased, the runoff will also increases. The result occurs after the runoff reached the time of maximum discharge.
It shows that the watershed is important to increase the infiltration of rainwater. In hydrology, time of concentration is a concept to measure the response of a watershed to a rain event. It is defined as the time needed for water to flow from the most remote point in a watershed to the watershed outlet. In addition, runoff is one of the most important hydrology component because of it connection with the water source quantity, flood and others hydraulic control structure. This occurs when the rate of rainfall on a surface exceeds the rate at which water can infiltrate the ground.
From the experiment conducted, we can apply this to control the flood using the applications of the basic hydrology system. Other than that, we can design a dam and drain by applying this knowledge. Then, we also can determine all factors that effected runoff such as rain fall intensity, type of surfaces, rainfall duration and others.
REFERENCES
1. https://www.scribd.com/doc/174047240/BASIC-HYDROLOGY-INFILTRATION-TEST. 2. https://en.wikipedia.org/wiki/Time_of_concentration
