Runoff and Streamflow Measurement Questions and Answers

Answer: A

The direct runoff volume is 1500 m³.

The φ-index is the constant loss rate; rainfall above it becomes direct runoff, hour by hour:

\[ \begin{aligned} \text{excess} &= (2-1) + 0 + (1.5-1) + 0 \\ &= 1.5\ \text{cm} = 0.015\ \text{m} \\ V &= 0.015 \times 10 \times 10^{4}\ \text{m}^{2} = 1500\ \text{m}^{3} \end{aligned} \]

Hours in which the intensity equals φ (1 cm/h) contribute nothing. 15000 m³ misplaces the hectare conversion by a factor of 10, and 4500 or 5500 m³ subtract the loss from the total rainfall (5.5 cm) carelessly or not at all.

Answer: B

The plot described is the area elevation curve.

The curve that shows how the area of a catchment is distributed with elevation, the area lying above (or below) each elevation plotted against that elevation, is the hypsometric curve, also called the area-elevation curve. The paper prints the name as 'hydrometric', in both its English and Hindi text, but the plot it describes is this one. It is used to describe the relief of a watershed and its stage of geomorphic development.

Rainfall values and isohyets on a basin map make an isohyetal map. Time of concentration and depth of rainfall against elevation are not what this curve plots.

Answer: A

The keyed answer is the shape index.

The shape of a watershed governs how quickly its runoff reaches the outlet: a compact, nearly circular watershed gives a sharper flood peak than a long narrow one. Its shape is expressed by shape indices, the general name for dimensionless ratios such as the form factor (area divided by the square of length) and the compactness coefficient (perimeter compared with that of a circle of the same area).

The form factor and compactness coefficient are particular shape indices, so the general term covers them. The bifurcation ratio describes the branching of the stream network, not the shape of the watershed.

Answer: D

The linear aspects are analysed through all three, so the answer is All of above.

In morphometric analysis, a watershed is studied in linear, areal and relief aspects. The linear aspects deal with the stream network in one dimension: stream order (the Strahler hierarchy), stream length of each order, the bifurcation ratio, and the length of overland flow, the distance water travels over the ground before reaching a channel.

Each of the three options is one linear parameter, so all of them are included.

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.

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.

Answer: D

A flow mass curve is also called a Rippl diagram, printed in the paper as 'Ripple diagram'.

The mass curve plots cumulative inflow to a reservoir against time. W. Rippl introduced it in 1883 for finding the storage needed to meet a given demand, which is why it carries his name.

A hyetograph plots rainfall intensity against time, and a hydrograph plots river discharge against time. A bar chart is a general graph, not a name for the mass curve.

Answer: D

It results in Runoff.

Runoff is the part of precipitation that, after interception, infiltration and evaporation losses, flows to streams, lakes, channels and rivers, either over the surface (surface runoff) or just below it (interflow or subsurface runoff), together with base flow from groundwater.

Transpiration and evaporation return water to the atmosphere. The hydrologic cycle is the whole circulation of water, not the particular portion that moves to streams.

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.