Water Resources Planning Branch, WRA, MOEAWater Resources Planning Branch, WRA, MOEA

Tools related to water resources development and planning, which are listed as five major projects:1. topographic index model, 2.MODFLOW, 3. Tank model, 4. WRASIM, 5. Water Resources Integration Database Platform, contents are as follows:

1. Topographic Index Model

   Model category：rainfall-runoff model

   1. Development Background：

      “Topographic index model”(TOPMODEL) which proposed by Beven and Kirkby (1979),the model derives the distance between the surface and the saturated aquifer and simulates the hydrograph of the catchment area by the relationship between the topography and the soil characteristics of the catchment area.

      Started by Professor Kwan-Tun Lee of National Taiwan Ocean University in 1997, this model can simulate the river runoff through the project achievement of ”Development of the Surveying and Planning Information System for Possible Dam Sites in Taiwan” in 2014 by the Water Resources Planning Institute.

   2. Functions:

      When the river observation discharge data is insufficient, this model can simulate the catchment behavior of the catchment area by using rainfall ,discharge record data ,topographic and geologic characteristics of the catchment area, and estimate the hydrograph at the exit of the catchment area. The system operation screen is shown in Figure 1：

      

      Figure.1 System operation screen

   3. Input and output data

      Inputs data include the Digital Terrain Model (DTM), rainfall, rainfall station location, temperature and discharge records. The parameters that have been set include, ”hydraulic conductivity Ko”, ”dry/wet season model parameter m”, “dry/wet season maximum storage capacity of root layer SRZmax” and “initial groundwater depth”. The output data is the hydrograph of the catchment area exit, and the simulation results are shown in Figure 2.

      

      Figure.2 hydrograph of the catchment area exit

      (source：2015, Water Resources Planning Institute, Development of the Surveying and Planning Information System for Possible Dam Sites in Taiwan)

   4. Applicability and Limitations

      This mode is suitable for catchment areas with Digital Terrain Model. Due to the model parameters must be verified during the mode establishment process, the runoff cannot be properly simulated where there is not enough hydrological record for model parameters verification.

      This model assumes that the flow of the saturated zone is approximately successive steady state. In the long-distance runoff simulation (such as day, month, and a period of ten days), the above assumptions are reasonable. However, if the model is applied to short-distance cases (such as hours, minutes, etc.), the assumption of saturated sone flow near continuous steady state cannot be fully satisfied, so whether it is applicable or not is open to question.

      This model is built in the ”Development of the Surveying and Planning Information System for Possible Dam Sites in Taiwan”, which provide Water Resources Planning Institute for internal planning, the model and manual are not open to the public.

2. MODFLOW

   Proper nouns and planning tools - planning tools
   Model category：Groundwater numerical model
   Model name：MODFLOW(Modular Three-dimensional Finite-difference Groundwater Flow Model)

   1. Background

      MODFLOW is a numerical model developed by the US Geological Survey (USGS) to solve two-dimensional and three-dimensional groundwater changes. USGS proposed the first version in 1983, and updated it to MODFLOW 88 in 1987. In 1996, it updated to MODFLOW 96, and the latest version was MODFLOW-OWHM. MODFLOW-OWHM is the latest version, OWHM is the abbreviation of One Water Hydrologic Flow Model, the main purpose is to establish a full hydrological numerical model, not only limited to the groundwater itself.

      In recent years, due to the wide application of the MODFLOW model, many data input pre-processing and simulation result post-processing systems specially designed for the MODFLOW model have also flourished, such as MODELCAD, Processing Modflow (PMWIN), and Groundwater Modeling System (GMS)(shown in Figure 3). MODFLOW model makes data input and result output work faster and more conveniently from the graphical interface.

      

      Figure.3 GMS operation interface

   2. Theoretical summary

      MODFLOW uses the Block Centered Finite Difference Approach to solve the groundwater flow control equation. The node uses the Block Centered method (shown in Figure 4) to calculate the volume flow rate of the six faces in the three-dimensional space and approximate the groundwater flow control equation by the second-order difference method. About the three-dimensional flow of fixed-density groundwater flowing through pore medium in saturated soil in MODFLOW model, the partial differential equation is expressed as follows：

      `∂/(∂x) (K_(x x) (∂h)/(∂x))+∂/(∂y) (K_(yy) (∂h)/(∂y))+∂/(∂z) (K_(zz) (∂h)/(∂z))-W=S_s (∂h)/(∂t)`

      Where `K_(x x)` , `K_(yy)` and `K_(zz)` are the hydraulic conductivity (L/T) along the x, y, and z coordinate axes; `h` is the pressure head (L); `W` is the volume flow rate per unit volume (1/T) ; `S_s` is the specific reserve of the porous medium (1/L); is the time (T). In the groundwater flow, the partial differential equation is generally approximated by the finite difference method. The simulation system is represented by a block of grid elements (Cell), which can be divided into columns (Row), each column spacing is `Δc_i` ; row (Column ), the spacing of each row is `Δr_j` ; Layer, the distance between each layer is `Δv_k` . Assuming that the density of the groundwater flow is constant, then for an element (i, j, k), the water exchange behavior between the six aquifer elements[(i-1, j, k), (i+1, j, k), (i, j-1, k), (i, j+1, k), (i, j, k-1), (i, j, k+1)] that are themselves adjacent to it must be considered.

      

      Figure.4 Block center method

   3. Model function

      The type of aquifer in the MODFLOW application can be a free, compressed, semi-compressed aquifer, and can also be classified into homogeneous, heterogeneous and isotropic, anisotropic aquifers according to geological characteristics. MODFLOW can simulate the groundwater flow conditions of multi-layer aquifers and irregular grids, river infiltration, natural and artificial recharge, groundwater evaporation, rainfall infiltration and pumping at the same time. The output results include the groundwater level, inflow, outflow, mass balance and numerical method numerical solution convergence of each simulated grid in every aquifer.

   4. Applicability and Limitations

      1. Open resource: The USGS official documents are extremely detailed, transparent and open. Documents must be reviewed by internal peers before they can be made public. It is very beneficial for researchers to understand the meaning of the model. However, there are a large number of documents. For less experienced users, a large number of documents need to be read in detail, the threshold for entry is much higher.
      2. Source code publish: Researchers can research the source code themselves and have the right to change the source code to expand the simulation category. However, there are many versions. For less experienced users, how to choose the appropriate version according to the required questions, the entry threshold is higher.
      3. Numerous simulation scenarios: From the original trap and unconfined aquifer flow simulation, the various modules gradually expand to the unsaturated layer water flow, river exchange simulation, catchment overland flow simulation, solute transport and formation subsidence. On the topic of partial functional expansion, the problem simulation may be simplified because of computational efficiency considerations. However, the problem of subsidence of the ground layer is simplified to the vertical one-dimensional. If the problem is to consider three-dimensional deformation, there will be limitations for the problem of unsaturated layer. MODFLOW adopts the UZF module simulation, which adopts the one-dimensional vertical equation. The lateral reaction of the saturated layer has limitations in use.
      Model link：http://water.usgs.gov/nrp/gwsoftware/ModelMuse/ModelMuse.html

3. Tank model

   Proper nouns and planning tools - planning tools
   Model category：Rainfall runoff model
   Model name：Tank model

   1. Background

      The Tank model is the result of a study by the Water Resources Planning Institute of the Ministry of Economic Affairs in 2002 through the "Research on the Automatic Calculation of the Parameter of the tank model". This model was developed by Professor Chen Rongsong of National Chung Hsing University, with reference to the water tank model developed by Sugawara in 1971, and solved the problem of automatic parameterization of the model parameters through the MultiStart-Powell algorithm. It has been applied to river runoff estimation in major river basins in Taiwan.

   2. Function

      This model can estimate the rainfall amount and discharge through the upstream observation when the river observation data is insufficient. The tank model is an important model for estimating river flow through rainfall. The tank model is composed of four layers of buckets. The parameters include 16 parameters of the four-layer bucket (A1~A5, B1~B3, Z1~Z4 and S1~S4). The accuracy of the model depends on the accuracy of the parameters. In the past, it was not only time-consuming but also based on extensive experience to determine the parameters of the tank model by trial and error. It is not easy for non-hydrological professionals to use this model. This model is established by the MultiStart-Powell method automatic parameter rate, which effectively solves the huge calculation of the rate parameter process.

   3. Theory

      The Tank Model is a general hydrological model initiated by Masatoshi Kuwahara of the Japanese Academy of Science and Technology in 1971. The concept is to replace the runoff mechanism of the basin with a number of storage model containers. In the in-line storage container shown in Figure 5, part of the surface soil layer (ie, the uppermost water tank) is wetted by rain (ie, stored) during rainfall, and part of it penetrates below the `Q_2` to the first aquifer (ie, the second water tank). When the rainfall is getting larger and the moisture content of the surface layer exceeds a certain level (when the storage height of the upper water tank exceeds the height `h_1` of the outlet hole at the lower right side), the water flows through the surface layer (surface) and becomes the surface diameter retention flow `Q_1` . If the rain continues and increases, the water content of the surface layer also increases, so the surface runoff `Q_1` also increases sharply. This situation is equivalent to the storage height of the upper water tank exceeding the outflow hole above the right side. When the uppermost water pipe continues to infiltrate into the second water pipe by `Q_2` , and exceeds a certain limit (that is, the storage height of the second water tank exceeds the height of the outflow hole at the lower right side thereof), the aquifer will generate a runoff `Q_3` , that is, if the mountain waist is poured out spring water. So on and so forth.

      

      Figure.5 Principle of the tank model

      (Taken from the second volume of Applied Hydrology, edited by Wang Ruyi and Yi Ren)

   4. Input and output data

      Input data includes: catchment area, observed rainfall amount, river observation discharge and evaporation. Before use, it is necessary to determine the parameters of the tank model (ie, 16 parameters such as A1~A5, B1~B3, Z1~Z4, and S1~S4) with a period of observation data (ie, rainfall, flow rate). After the parameters of the simulation effect meets the demand, the discharge can be estimated with the known rainfall amount. The output data includes the 16 parameters and the simulated discharge generated by the mode.

   5. Applicability and Limitations

      The tank model graphically maps the conditions of the catchment area, rainfall, discharge, etc., and the process of inputting the data. The graphical interface of the program is shown in Figure 6. The hydrological simulation effect and the various evaluation indexes (percentage of runoff volume error, efficiency coefficient, root mean square error, and objective function value) of the parameters after the rate determination and the rate determination period can be automatically calculated.

      

      Figure.6 The tank model graphic interface

      The hydrological model can be applied to flood forecasting, climate change research, water resources planning, and so on. Due to different application fields, the emphasis is different. For example, the river flood control plan focuses on the event-type maximum peak flow and peak arrival time. The commonly used objective functions are root mean square error, flood peak error percentage, flood peak arrival time error. Water resources planning focuses on the accuracy of low flow, and the commonly used objective function is the relative error of the root mean square.

      This model uses different objective functions to determine the automation parameters, thereby changing the prediction performance of the mode.

      It is not suitable to use this model if the simulated area lacks sufficient long-term known data (rainfall, discharge) or catchment topography and land use type change, which will make the mode parameter difficult to obtain and can not get good simulation results.

4. Water Resources Agency Simulation Model

   Proper nouns and planning tools - planning tools
   Model category：Water source calculation model
   Model name：WRASIM(Water Resources Agency Simulation Model)

   1. Background

      WRASIM is the result of the “General Regional Water Resources Dispatching and Supply and Demand Analysis Model” between 2004 and 2005 for the Water Resources Planning Institute of the Ministry of Economic Affairs. WRASIM was developed by Professor Zhou Naijun of the National Cheng Kung University which refer to the MODSIM model developed by the University of Colorado State University.

   2. Theory

      WRASIM is a general-purpose wide-area water supply and demand utilization simulation model based on the minimum cost network flow planning method. The so-called network flow refers to the network pattern composed of many nodes and arrows. The node represents a position, and the arrow line is a directional connection between the nodes, which has water flow. The main limitation of the mode is that the discharge into and out of the node should be conserved, and the arrow line has the upper and lower limits of the discharge, and each arrow is given a cost or weight coefficient of one unit of water flow. The minimum cost network flow planning is to find the overall flow mode of minimum cost in the case that the water flow in and out of the nodes is conserved and the flow rate on each arrow line meets the upper and lower limits. If a network stream has m nodes, the network flow proposition of its minimum flow cost is as follows:

      Minimize` sum_(i=1)^m sum_(j=1)^m C_(ij) * X_(ij)`(1)

      Subject to

      `sum_(j=1)^m X_(ji)- sum_(j=1)^m X_(ij)=0`      `i=1,...m;   j≠i`(2)

      `l_(ij) ≤ x_(ij) ≤ u_(ij)`                  `i,j=1,...m`(3)

      Where m = total number of nodes, i, j = node number, `x_(ij)` = discharge from node i to node j, `c_(ij)` = discharge cost or weight per unit of water from arrow i to node j, `i_(ij)` = The lower limit of the discharge on the arrow line from node i to node j, `u_(ij)` = the upper limit of the arrow flow between node i and node j. In the above formulas, the formula (2) represents a limit of conservation of the discharge entry and exit node, and the equation (3) represents a limit of the magnitude of the arrow discharge.

      Figure 7 shows a network flow diagram of a general water resources system. The diagram divides the composition of the water resources system into: inflows, reservoirs, hydropower plants, water purification plants, confluence points or water diversion points, water demand and terminals, etc. Each arrows connecting the nodes may be: rivers, reservoirs, water pipes, water diversion tunnels, and water pipelines. According to the mathematical propositions of equations (1) to (3), the network flow mode can obtain the water distribution result that meets the priority order.

      The biggest advantage of WRASIM is that its water distribution concept is clear. By appropriately setting the demand or the order of reservoir water storage, the model can effectively solve the complex wide-area system water allocation problem.

      

      Figure.7 Recurring network flow diagram of physical system and virtual nodes and arrows

   3. Function

      In order to analyze the wide-area application of various types of water resources in Taiwan, the WRASIM model includes a series of modules to provide various functional options, see Table 1.

      Table 1: WRASIM mode module function list

      Item	Model analysis function	Applicable analytical topics
      E	Wide-area water resources simulation analysis. Simulate the operation and operation of the water resources system on a time-by-cycle basis according to the rules or principles of the reservoir regulation line, the water rights priority order, the standard water use agreement, the hydropower generation, the raw water turbidity limit water intake or the clean water.	Planning and evaluation of multi-water resources development plans: (1). Assess the remaining flow of the river system (2). Evaluate system supply and demand situation
      Y	According to the set target water supply area and water shortage criterion, the water supply potential or water supply capacity of the water resources system under the water shortage criterion is automatically iteratively calculated.	Assess the water supply potential or water supply capacity of the new facility.
      M	Simulation of water use in multi-reservoir systems. According to the rules of multiple reservoirs combined with the regulation line and the water storage balance curve, the operation of the multi-reservoir combined operation system is simulated on a time-by-hour basis.	For the multi-reservoir system, the results of different joint application strategies for water resource utilization can be evaluated as a simulation tool for the joint application of the regulation line.
      G	Ground water and groundwater combined application simulation. Using WRASIM to simulate the water allocation and utilization of surface water system, determine the pumping and refilling of groundwater by groundwater system, further combine the groundwater level variation in MODLOW simulation aquifer, and modify the pumping strategy of surface water system based on the simulated groundwater level.	Ground water and groundwater normal use combined simulation. Feasibility review using groundwater as a backup source.
      D	Optimal scheduling analysis of water resources in the absence of water. According to the system discharge predicted in the future period, the optimal application strategy of the system water source during this period is optimized dynamically. During the analysis, the reservoir discharge is not subject to any rules, and is completely oriented to meet the stable demand of each period.	The best scheduling analysis of water resources across time, cross-standard and cross-region during water shortage period. Estimate the maximum water supply potential of the water resources system.
      L	Consider the water use simulation of water flow prolongation. Iteratively calculates the time delay effect of the arrow line water delivery, and simulates the effect of uneven water flow on water during the day.	Supply water resources systems with spiked power generation for management deployment analysis. The optimal development capacity assessment of the river dams downstream of the reservoir.

   4. Input and output data

      The WRASIM model divides the physical system nodes into: reservoirs (separate or combined use of reservoirs), general demand (consumptive or non-consumptive demand), spiked power generation requirements (considering nonlinear relationships with reservoir storage), and specific Agricultural water demand (considering return water), inflow (natural inflow or hydrological model simulated flow), river storage, pumping area, water purification field, general confluence, diversion and system terminal.

   5. Applicability and Limitations

      1. The model provides a graphical towed node and an arrow network network interface to facilitate the establishment of a water resource system, which can quickly establish a system that is not the same.
      2. According to the network structure, the defined inflow hydrograph, reservoir storage capacity, water demand, water distribution order, etc. The model automatically converts the water distribution in the network into the proposition of the network flow planning every day. And the algorithm of network flow planning solves the water distribution result, and the obtained result can ensure the compliance with water conservation and consider the capacity limitation of water purification and water delivery facilities.
      3. By setting the priority order of water allocation, it is possible to simulate the order of water rights, prioritize the uncontrolled flow of water, allocate water according to the application line, the water storage and discharge sequence of multiple reservoirs, and the different water route preferences in the water resources system.

5. Water Resources Integration Database Platform

   Model category：Hydrology
   Model name：Water Resources Integration Database Platform

   1. Back ground

      The domestic hydrology and water resources related information has been established and managed by various water conservancy authorities for business purposes for a long time, which makes information transmission and application difficult. The application of value added still needs to be handled manually or semi-automatically. In order to respond to the application and challenges of the new state, strengthen the feedback and reuse of value-added data and project data, and build an integrated data platform to strengthen data management and application.

   2. Function

      The platform system functions can be divided into "water environment", "water use", "water supply and demand", "cloud computing", "knowledge base", "space information", "data query", "data management", "system management", etc. Feature category. Among them, water environment, water use, water supply and demand, can provide future information on the overall outline of Taiwan's water resources with reliability and reference; cloud computing, knowledge base to provide assistance and information for internal water resources planning operations as the main appeal. Other functions target the management and supply of basic data. The platform architecture diagram is shown in Figure 8. The contour map after integrating the data is shown in Figure 9.

      

      Figure.8 The platform architecture diagram

      

      Figure.9 he contour map after integrating the data

      Platform layout design considers the use of mobile devices and screens of different specifications, and adopts Responsive Web Design. Through CSS and JQuery web technology, when different devices, such as mobile phones, tablets, and computers, use the graphic content and database of the same website, on different sizes or resolutions of devices or screens, according to the user's device, A style that matches the size of the page to display the content of the page.

   3. Theory

      The needs of the water resources integration database platform, considering the current situation of the system and the future development direction. Divide the use level, the bottom layer is the computer hardware and software, network and database infrastructure, and then to improve the efficiency of the automation system, to help handle the daily routine data system, and then to provide management, staff and strategy development.

      The platform system is aimed at the collection and supply of data required for water resources planning operations, and organizes and analyzes the information to develop systems that support higher-level applications. It can improve the system function level, expand the scope of use and improve system efficiency.

   4. Input and output data

      The information collected on this platform is divided into seven categories, including Meteorological Hydrology, Facilities Management, Water Information, Environmental Ecology, Engineering Hydrology, Earthquake Observation and Mode Parameters.

   5. Applicability and Limitations

      The system is aimed at the collection and supply of information required for water resources planning operations, and users are set to other information systems and applications. In the future, information on the overall profile of Taiwan's water resources with reliability and reference can be provided.