Skip to main content

Unit Hydrograph Derivation: The Instantaneous Unit Hydrograph (IUH) and Clark’s Model

 An Instantaneous Unit Hydrograph (IUH) represents the direct runoff hydrograph resulting from an instantaneous discharge of 1$\text{ cm}$ of effective rainfall applied uniformly over a catchment at time t = 0. Because rainfall duration approaches zero, the IUH reflects pure catchment routing characteristics without the influence of storm duration. Clark’s Method derives the IUH by routing incremental time-area histograms through a single linear reservoir:

$$S = K \cdot O$$

​Where $S$ is storage, $K$ is storage attenuation constant, and $O$ is outflow. The routing process follows the Muskingum-based finite difference equation:

$$O_2 = C_0 \cdot I_2 + C_1 \cdot O_1$$

​Where $I_2$ is area of the time-area segment, and routing coefficients are defined as $C_0 = \frac{\Delta t}{2K + \Delta t}$ and $C_1 = \frac{2K - \Delta t}{2K + \Delta t}.$

​In steep Himalayan catchments subject to intense cloudburst events, traditional constant-duration unit hydrographs fail to capture peak attenuation and time-lag variations.

​Modern flood warning systems implemented by the Central Water Commission (CWC) rely on GIS-based Clark’s IUH modeling. By extracting catchment time-area curves directly from high-resolution Digital Elevation Models (DEMs), hydrologists dynamically calibrate $K$ and time of concentration $(t_c)$ to predict real-time peak discharges during flash floods.

​Note: This technical content was curated and structured with AI assistance to support technical education.

Labels:

Comments

Post a Comment

Popular posts from this blog

RIVER INTAKE STRUCTURE

  RIVER INTAKE As we know intake should be located at the upstream side of the city so pollution is minimum and this river intake should be sufficiently inside the river water so need of water can be supplied at every seasons of the year. Some river intakes are constructed near the bank of river when sufficient depth is available, some are created away from the bank of river when river bed is soft or unstable near bank, sometimes water level raised by constructing weir on the river and sometimes channel created and water led to the intake tower. This all situations divides river intake into two major types: (1) Single well type intake and (2) Twin well type intake. Parts of river intake are Intake well, Intake pipe and Jack well. River intake well has two parts, lower part is Jack well and upper part is surves pump house. SINGLE WELL TYPE RIVER INTAKE In single well type intakes water is directly enter into jack well through the penstockes (openings) created at different level. As ...
Post a Comment
Read more

CANAL INTAKE STRUCTURE

  CANAL INTAKE Canal intake structure An irrigation canal used as the source of water when other source are far from the city. Intake structure constructed near the bank of canal. An intake chamber created inside the canal using concrete or masonry having one bell mouth entry pipe inside it. Intake chamber has opening guarded with coarse screen and bell mouth entry protected with fine screen or mesh. Bell mouth entry located at expected low water level of the canal. Water enters from this bell mouth entry and conveyed through withdrawal conduits to sump well or city.
Post a Comment
Read more

RESERVOIR INTAKE STRUCTURE

  RESERVOIR INTAKE All rivers has not sufficient depth of flow throughout the year and hence dam constructed across the river to form a reservoir having sufficient depth for intake. This intake structure built upstream side near the dam and it is similar to the river intake. A typical reservoir intake well consists number of water entry ports located at various elevations so that relatively clear top water is only drawn at all seasons. All control on this entry ports is at topnof the well. Dry intakes and wet intakes formed according to the position of entry valves outer and inner of the well respectively.
Post a Comment
Read more