a) Water stored in the rocks below ground 1. Throughflow b) Water moving downhill within rivers 2. Channel Flow c) Water moving across the surface of the ground. This may happen when the rain cannot soak into the ground, for example where there are tarmac surfaces or even during heavy rainfall. 3. Surface Runoff 4. Soil Moisture d) Water moving downhill through the soil layers. It will generally flow slowly unless concentrated in natural pipes in the soil. 5. Groundwater e) Water held within the soil, the quantity of which will vary.

What is a storm (flood) hdrograph? 21 October 2013 What is a storm (flood) hdrograph? Learning Objectives: To understand the components of a storm hydrograph. Learning Outcomes: C Essential – you will know the variables of the storm hydrograph. Stretch – you will examine and explain the relationships between the variables of the storm hydrograph. B A* Challenge – you will investigate factors which influence the storm hydrograph.

RIVERS 3: Flood Hydrographs Rivers provide a rapid surface route from the drainage basin and their flow can vary, there are three main types of flow: permanent/perennial; intermittent or ephemeral

The routes that the water will take to reach the channel are varied and will be different in every drainage basin..

The amount of water flowing in a channel is called the discharge and is calculated by multiplying velocity by cross sectional area of the river: Q (discharge) = V (velocity)  A (cross sectional area)

1 - Working in groups add these labels to your hydrograph where you think they belong (Don’t stick them down yet!!) ·    Most of the discharge at this point is from baseflow ·    This represents the lag time between the peak in rainfall and the peak in discharge ·    The discharge takes longer to fall as water is being released relatively slowly from the channel ·    Here the rapid rise in discharge reflects significant throughflow from the soil ·    Beyond this point water will spill onto the floodplain ·    This part of the curve is often the result of rapid overland flow 2 – Define and/or explain the original labels on the Hydrograph. For example: What does lag time mean?

The discharge of a river at any point can be plotted on a STORM HYDROGRPH. This shows the rivers response to a single rainfall event The time from peak rainfall to peak discharge is the LAG TIME. The soil becomes saturated and overland flow and through flow reach the river and discharge increases. Overland flow arrives first. The discharge starts to fall slowly as water is added from through flow and groundwater flows which are much slower. The base flow supplies the river with water between storms and keeps it flowing in summer. Rainfall is intercepted or infiltrated into the soil moisture store Start of the storm there is a slow rise in discharge, as only a small amount of water falls into the channel

FACTORS WHICH INFLUENCE STORM HYDROGRAPHS VEGETATION COVER This varies seasonally. The type and amount will affect interception and stemflow/throughfall. Overland flow is reduced. Lag time will be increased. ROCK TYPE Impermeable rocks prevent groundwater flow and encourage through flow and overland flow. These rocks will decrease lag time. Permeable rock will have the opposite effect. Lag time will . . . CLIMATE The distribution of rainfall over the year and the temperatures change. Lag time will . . . LAKES & RESERVOIRS These will store floodwater and thus reduce lag time and control river response to heavy rainfall. Lag time will . . . FACTORS WHICH INFLUENCE STORM HYDROGRAPHS SLOPES Steep slopes will encourage overland flow and gentle slope will slow run off down. Lag time will . . . LAND USE Impermeable surfaces created by urbanisation will reduce infiltration and encourage overland flow. Different types of crops affect interception rates e.g. cereals 7-15%. Lag time will . . . SOIL TYPE & DEPTH Deep soils store more water, pipes in the soil encourage through flow. Soils with small pore spaces will reduce infiltration and increase overland flow. Lag time will . . . RAINFALL INTENSITY & DURATION Intense rain will increase overland flow and reduce lag times. Gentle rain over a longer time will allow more infiltration. Lag time will . . .

What’s Flash got to do with it?

"Flashy" To say that a hydrograph is flashy means that the graph depicts sharp vertical jumps and equally steep vertical declines. What this means for the actual stream represented by the graph is that a flashy stream is one that exhibits significantly increased flows immediately following the onset of a precipitation event and a rapid return to pre-rain conditions shortly after the end of the precipitation. That is to say, water that precipitates within a flashy stream's watershed will make its way quickly from the land into the stream and be flushed through the system rapidly. On the other hand, in watersheds supplying a stream that is not flashy, the transport of water will be slowed through absorption into and seepage through soils, containment on the surface in lakes, and retention in the soil as moisture.

Memory test! surplus Recharge Deficit Utilisation 1 – What are the four terms used to describe the different shades? 2 – Where should they be? surplus Recharge Deficit Utilisation

Jan 2010

Jan 2010 1 (b)(i) Sketch hydrograph for 4/5/6.7.07 should show much lower peak (1) and longer time lag (1) in contrast to 19/20/21. 2 × 1 for each element. Peak should be much higher (approx 3 times) for third mark or much more steeply rising limb for 19 – 21. If dissimilar start point on Y axis/or does not begin at Y axis – maximum 2. (3 marks) 1 (b)(ii) High rainfall total over the two days of 19/20 suggests high intensity which would lead to a steep rising limb (1). The higher amount on the first day would reduce lag time and increase the peak as stores would be fuller (1) saturation or lack of infiltration (1). Rainfall would flow overland (1) so faster transfer (1). Must relate back to hydrographs and make links.