Your Answer : (Not Answered)

Correct Answer : D

It is the Unit hydrograph.

Sherman's unit hydrograph (1932) is the direct runoff hydrograph resulting from one unit (1 cm, or 1 mm) of excess rainfall falling uniformly over the watershed at a uniform rate during a specified duration. Assuming the watershed responds linearly, it represents the runoff process and is scaled and superposed to predict runoff from other storms.

A natural hydrograph is the observed one, a synthetic hydrograph is built from watershed characteristics where no records exist, and a dimensionless hydrograph expresses flow and time as ratios.

Your Answer : (Not Answered)

Correct Answer : C

They are called Natural hydrographs.

A natural hydrograph is plotted directly from the observed discharge of a stream, by measuring runoff rates at the outlet of a watershed over time during and after a storm.

Unit, dimensionless and synthetic hydrographs are derived ones. A unit hydrograph is computed from natural hydrographs for 1 cm of excess rainfall, and a dimensionless hydrograph expresses discharge and time as ratios to their peak values. 'Basic hydrograph' is not a standard type.

Your Answer : (Not Answered)

Correct Answer : B

The correct match is a-III, b-I, c-IV, d-II.

• Unconfined aquifer: the water table aquifer, whose upper surface is the free water table (III).
• Confined aquifer: the artesian aquifer, held under pressure between impermeable layers (I).
• Semi-confined aquifer: the leaky aquifer, whose confining layer is only semi-pervious, so water leaks through (IV).
• A body of rock or sediment that holds and yields groundwater is the definition of an aquifer (II).

Every other option breaks at least one of these pairs; the commonest slip is to call the confined aquifer the leaky one.

Your Answer : (Not Answered)

Correct Answer : A

The science is Hydrology.

Hydrology is the science of the waters of the Earth: their occurrence, circulation and distribution, their chemical and physical properties and their relation to the environment. The hydrologic cycle of evaporation, precipitation, infiltration and runoff is its central concept.

Hydroponics is growing plants in nutrient solution without soil. A hydrophyte is a plant that grows in water. 'Hydril technology' is not a branch of science.

Your Answer : (Not Answered)

Correct Answer : B

They are Channel characteristics.

Among the factors that affect runoff, channel characteristics are the hydraulic properties of the stream channels: their size, cross-section, slope, roughness and storage capacity. They govern how fast water flows and how the runoff from a watershed is routed to the outlet.

Interception is rain caught by vegetation, climatic factors are rainfall intensity and duration, temperature and wind, and watershed characteristics are the area, shape, slope and land use of the whole catchment.

Your Answer : (Not Answered)

Correct Answer : C

The mass curve ordinate is \(V = \int_{0}^{T} Q \cdot dt\).

The mass curve plots the cumulative volume of flow against time. The volume that passes in a short interval is \(Q\,dt\), so the cumulative volume from the start up to time T is the integral of the discharge:

\[ V = \int_{0}^{T} Q\, dt \]

Its slope at any point is therefore the discharge, \(dV/dt = Q\), which is how storage is found from it. Integrating \(Q^{2}\), \(Q^{3}\) or \(1/Q\) gives quantities without the dimensions of volume.

Your Answer : (Not Answered)

Correct Answer : B

The runoff is 7.5 cm.

The φ index is the uniform rate of loss above which rainfall becomes runoff. From the first storm:

\[ \begin{aligned} \phi &= \frac{9 - 6}{6} = 0.5\ \text{cm/h} \\ \text{loss in 9 h} &= 0.5 \times 9 = 4.5\ \text{cm} \\ R &= 12 - 4.5 = 7.5\ \text{cm} \end{aligned} \]

4.5 cm is the loss, not the runoff. 6.0 cm repeats the first storm's runoff, and 9.0 cm keeps the first storm's total loss of 3 cm without allowing for the longer duration.

Your Answer : (Not Answered)

Correct Answer : C

A lysimeter is used to measure Evapotranspiration.

A lysimeter is a tank of soil with growing vegetation, set in the field so that its conditions match the surroundings. By measuring the water added (rain and irrigation) and the water draining out, and weighing the tank, the water lost by evaporation and transpiration is found.

Humidity is measured with a hygrometer or psychrometer, infiltration with an infiltrometer, and wind speed with an anemometer.

Your Answer : (Not Answered)

Correct Answer : C

The term is Precipitation.

Precipitation is all forms of water that condense from atmospheric vapour and fall or are deposited on the Earth's surface: rain, drizzle, snow, sleet, hail, and also dew and frost. It is the input to the land phase of the hydrologic cycle.

Runoff is water flowing over the land after precipitation, and infiltration is water entering the soil. Both happen after precipitation. 'Interaction' is not a hydrological term at all; the related term interception means rain caught by vegetation, which never reaches the ground.

Your Answer : (Not Answered)

Correct Answer : C

The optimal number of rain gauges is \((C_{v} / \epsilon)^{2}\).

The standard error of the mean of N stations is proportional to \(C_v/\sqrt{N}\). Setting it equal to the permitted percentage error \(\epsilon\) and solving:

\[ \begin{aligned} \epsilon &= \frac{C_v}{\sqrt{N}} \\ N &= \left(\frac{C_v}{\epsilon}\right)^{2} \end{aligned} \]

So halving the allowable error needs four times as many stations. The other options square only one of the two quantities, or neither, so they do not follow from the \(\sqrt{N}\) law.

Your Answer : (Not Answered)

Correct Answer : A

The average depth is 50 cm.

In the isohyetal method each area between two isohyets is given the mean of their values, and the results are weighted by area.

\[ \begin{aligned} P_1 &= \tfrac{40 + 60}{2} = 50,\ P_2 = \tfrac{55 + 45}{2} = 50 \\ P &= \frac{100 \times 50 + 100 \times 50}{200} = 50\ \text{cm} \end{aligned} \]

500 and 550 come from adding without dividing by the area properly, and 5 cm from a slip of a decimal place.

Your Answer : (Not Answered)

Correct Answer : A

The keyed term is Watershed.

A watershed is the area bounded by the ridge line or drainage divide, from which all runoff drains to a common outlet. It is the basic unit for planning soil and water conservation, so it is the term this definition is written for in soil conservation texts.

'Catchment' is used in much the same sense, especially in hydrology and for the area draining to a river gauging point or a reservoir, but the paper's soil conservation wording follows the watershed definition. A basin usually means the whole drainage area of a large river, made up of many watersheds.

Your Answer : (Not Answered)

Correct Answer : A

20 ha-m is \(2 \times 10^{11}\) cm³.

A hectare-metre is the volume of water covering one hectare to a depth of one metre.

\[ \begin{aligned} 1 \text{ ha} &= 10^{4} \text{ m}^{2} \\ 20 \text{ ha-m} &= 20 \times 10^{4} \times 1 = 2 \times 10^{5} \text{ m}^{3} \\ 1 \text{ m}^{3} &= 10^{6} \text{ cm}^{3} \\ 2 \times 10^{5} \text{ m}^{3} &= 2 \times 10^{11} \text{ cm}^{3} \end{aligned} \]

\(2 \times 10^{9}\) and \(2 \times 10^{13}\) cm³ are each out by a factor of 100, the error made by using \(10^{4}\) or \(10^{8}\) cm³ per cubic metre.

Your Answer : (Not Answered)

Correct Answer : A

The dominance of overland flow is identified by the drainage density.

Drainage density is the total length of streams divided by the watershed area. It controls how far water must travel over the ground before it meets a channel: the length of overland flow is roughly half the reciprocal of drainage density. A low drainage density means long overland flow paths, so overland flow dominates the runoff; a high density means water reaches channels quickly.

Stream order and stream length describe the channel network itself, and the bifurcation ratio describes its branching. None of them alone tells how much of the watershed's runoff travels as overland flow.

Your Answer : (Not Answered)

Correct Answer : B

A recording rain gauge records rainfall in terms of depth and time.

Recording (self-recording) gauges, such as the tipping bucket, weighing bucket and natural siphon types, draw a continuous record of accumulated rainfall depth against time on a chart or a data logger. This mass curve shows when the rain fell and how fast, so rainfall intensity can be worked out from its slope.

Depth alone is what a non-recording gauge gives. Rainfall is not reported as a volume or as a specific weight.

Your Answer : (Not Answered)

Correct Answer : C

A plot of rainfall intensity against time is a hyetograph.

A hyetograph is usually drawn as a bar chart of rainfall intensity (or depth) in successive time intervals during a storm. It shows how the storm developed and is the input from which runoff hydrographs are computed.

A hydrograph plots river discharge against time, the output of the catchment rather than the rain. Isohyets are lines of equal rainfall drawn on a map, showing distribution in space, not time. A mass curve plots cumulative rainfall against time; 'Man curve' as printed is not a standard term.

Your Answer : (Not Answered)

Correct Answer : C

The correct matching is P-3, Q-4, R-1, S-5, T-2.

An isohyet joins points of equal rainfall (R-1), and an isobar joins points of equal pressure (T-2). An isobath joins points of equal depth, used in groundwater maps for equal depth to the water table (Q-4). An isochrone joins points of equal travel time to the outlet of a catchment and is used to route surface runoff (S-5). That leaves the isopleth, a general line of equal value of any variable, for evapotranspiration (P-3).

The first option swaps isopleth and isobath, the second pairs isochrone with evapotranspiration and isopleth with runoff, and the last swaps rainfall and pressure between the isohyet and the isobar.

Your Answer : (Not Answered)

Correct Answer : C

Infiltration takes place at capacity when rainfall intensity is equal to or more than the infiltration capacity of soil.

The infiltration capacity is the maximum rate at which a soil can absorb water. The actual infiltration rate equals the smaller of the rainfall intensity and the infiltration capacity. So infiltration proceeds at its full capacity only when rain falls at least that fast; any excess then becomes surface runoff.

If the intensity is less than the infiltration capacity, all the rain soaks in and infiltration proceeds at the rainfall rate, below capacity. So both 'less than' options are wrong.

Your Answer : (Not Answered)

Correct Answer : C

The infiltration in the last hour is about 20 mm.

The depth infiltrated is the area under the infiltration capacity curve between t = 1 h and t = 2 h:

\[ \begin{aligned} F &= \int_{1}^{2} (2 + e^{-3t})\, dt \\ &= 2 + \frac{e^{-3} - e^{-6}}{3} \\ &= 2 + 0.016 = 2.016\ \text{cm} \approx 20\ \text{mm} \end{aligned} \]

By the second hour the decaying term has almost vanished, so the rate is essentially the final capacity of 2 cm/h. 10 mm and 5 mm are what a rate of 1 cm/h or 0.5 cm/h would give, and 25 mm is more than the 2 cm/h final rate plus the small decaying term can supply in one hour.

Your Answer : (Not Answered)

Correct Answer : C

The falling limb depends on basin characteristics only.

The falling (recession) limb of a hydrograph begins after the peak, once rainfall has stopped adding to the flow. From then on the discharge is the catchment draining its stored water, from surface, channel and groundwater storage, and its shape is set by the properties of the basin: its size, shape, slope, drainage density, soils and geology. This is why a recession curve can be described by a basin constant and is independent of the storm that produced it.

The rising limb and the peak are the parts that depend on both basin and storm characteristics, such as rainfall intensity, duration and its movement across the basin. Storm characteristics alone, or the direction of the rainfall, do not govern the recession.