Author Archives: zulkarnainh

Estimating the design flood based on design storm rainfall intensity/depth

rainfall-runoff transformation (image from

For Malaysian, we have a procedure (manual) to design flood hydrograph based on the design storm rainfall intensity, such as DID ((1976; 2010). Those manual are explained very well on the corrected procedures and methods to estimate the design flood hydrograph on the gauged and ungauged catchments.

The following procedure is recommended by DID (1976) for estimating the design storm:

  1. the design recurrence interval is selected on the basis of the guidelines suggested by Heiler and Tan (1974).
  2. the design storm depth for the required recurrence interval is calculated from the procedure by DID (1982). The rain depth or intensity is obtained from Intensity-Duration-Frequency curve.
  3. The areal reduction factors recommended by DID (1982) are used to convert point rainfall to catchment mean rainfall.
  4. The temporal pattern of the design storm is not considered.
  5. the design storm duration is taken as that duration which gives the highest peak discharge.

Note: the design storm duration is usually adopted as that duration gives the maximum discharge. this critical duration is found by trial and error by calculating the design flood for a range of storm duration. From the experience, the duration within the catchment lag (time concentration) gives the maximum discharge.


DID (1982), Estimation of the Design Rainstorm in Peninsular Malaysia. Hydrological Procedure No. 1.
DID ( (1976). Design Flood Hydrograph Estimation for Rural Catchments in Peninsular Malaysia. Hydrological Procedure No. 11.
DID (2010). Estimation of design flood hydrograph using clark method for rural catchments in Peninsular Malaysia. Hydrological Procedure No. 27
Heiler T.D and Tan H.T (1974). Hydrological Design Return Periods, Provisional Hydrological Procedure.

Mencari Parameter dan Simulasi Model Neyman-Scott

Assalamualaikum & Salam Sejahtera,

Berikut adalah tutorial untuk mencari parameter untuk model Neyman-Scott, serta cara simulasi bagi mendapat data hujan (skala sejam). File sokongan dan source code untuk tutorial boleh dimuat-turn disini (Link).

PART 1: Mencari ciri-ciri hujan setiap bulan

PART 2: Mencari parameter Nyeman-Scott menggunakan ABC optimization (MATLAB code)

PART 3: Simulasi hujan skala sejam menggunakan model.

Normalize values in a matrix to be between 0 and 1 (Matlab Tips)

I’m run a function in Matlab and it requires a matrix of variables within 0 and 1. The way to normalize the values to be between 0 and 1, and transform back to the original matrix as follows:

b = [10; 0; 1; 1];

%% normalized matrix B to 0 and 1
normB = b - min(b(:));
normB = normB ./ max(normB(:))

%% transform normalized matrix B to the original matrix
B_sim = normB_sim .* max(b(:))

Make sure, when transforming normalized matrix to the original matrix, you provided the maximum value of the original matrix. It not, the code cannot be run.

Original source: (Link) 

Multiple colors to features within a single shapefile

I have received one shape file from a friend, who has a lot of features and attributes. However, it is within a single shapefile. So, it is difficult to me to recognise their features, since QGIS is only displayed one colour.

There is actually a way to display multiple colours of features although you have a single shape file. You can change the styles of the shape file in the layer properties. Double click the layer and select style. Select Categorized style and choose a field you want to visualize. Remember to classify your values before leaving the dialogue.


Import “starred places” into a My Map

There is a situation, you have saved several places in Google Maps and you want to display all those places in one map in Google Maps. How to do it? It is a way to do it, by using My Maps. However, there is no way to add them through My Maps directly. Here the tips from this link to do it:

  1. Export them using Google Takeout
  2. Export them from “Google Maps (My Places)”, not from “Bookmarks”. They will be downloaded as a GeoJSON file.
  3. Use this site to convert the file to KML GeoJSON
  4. Once download the KML file, can import it into the custom map.

Using HEC-GeoRAS for the HEC-RAS modelling (Videos Expired!)

Note: All video tutorials have been expired!. I will make the videos to replaced expired videos soon. Sorry for the inconvenience caused. – zulkarnain

If you do HEC-RAS for the flood or water quality modeling, HEC-GeoRAS may help you. In general, HEC-GeoRAS is a plugin in ArcGIS, to help to process geospatial data from the raster image. 1) It is very helpful that allows the preparation of geometric data for import into HEC-RAS and 2) helps to display the GIS outcome, based on the outcome of HEC-RAS. This software can be download from this link.

Preparation of geometric data for import into HEC-RAS

To create the import file, the user must have an existing digital terrain model (DTM) of the river system in the ArcInfo TIN format. The user creates a series of line themes pertinent to developing geometric data for HEC-RAS. The themes created are the Stream Centerline, Flow Path Centerlines (optional), Main Channel Banks (optional), and Cross Section Cut Lines referred to as the RAS Themes.

These are the best tutorial that I obtained from youtube:

Part 1

Part 2

Part 3

Part 4

Helps to display the GIS outcome

Water surface profile data and velocity data exported from HEC-RAS simulations may be processed by HEC-GeoRAS for GIS analysis for floodplain mapping, flood damage computations, ecosystem restoration, and flood warning response and preparedness.

The tutorial to export the data from HEC-RAS to GeoRAS as follows:

Credit: Yasir A. for the good tutorials.