Irrigation method for coastal regions

An irrigation method for coastal regions, comprising:

• (S1) selecting coastal region and collecting natural and environmental data of the coastal region;
• and building a basic database of the coastal region based on high-precision map of the coastal region;
• (S2) establishing a water demand calculation model for coastal crops and a multi-source water supply model, wherein the multi-source water supply model comprises a multi-source water of mixed salt-fresh water calculation model and a freshwater source calculation model;
• and the multi-source water supply model is configured for calculation and controlling of a salt content of mixed irrigation water;
• the multi-source water of mixed salt-fresh water calculation model is expressed as follows:
• S
• mixed
• =
• S
• 1
• ·
• Q
• 1
• +
• S
• 2
• ·
• Q
• 2
• +
• S
• 3
• ·
• Q
• 3
• +
• …
• +
• S
• n
• ·
• Q
• n
• Q
• 1
• +
• Q
• 2
• +
• Q
• 3
• +
• …
• +
• Q
• n
• ×
• 1
• ⁢
• 00
• ⁢
• %
• ;
• wherein Qi=Zi×vi, where i is 1, 2, 3, . . . , n;
• Smixed is a salt content of mixed salt-fresh water;
• S1, S2, . . . , Sn are salt contents of different salt-fresh water sources;
• Q1, Q2, Q3, . . . , Qn are the amounts of different salt-fresh water sources;
• Zi is a flow cross-section of an i-th irrigation-drainage canal;
• and vi is a flow speed of the i-th irrigation-drainage canal;
• and
• (S3) calculating a water demand Qdemand during a forecast period according to the water demand calculation model for coastal crops;
• calculating a water supply amount Qsupply in the coastal region during the forecast period according to the multi-source water of mixed salt-fresh water calculation model;
• and comparing the Qdemand and the Qsupply to accordingly regulate irrigation operation;
• the water demand calculation model for coastal crops comprises:
• Qdemand=Kc·ET0Qdemand=Kc·ET0, wherein ET0 is a reference crop water demand, and is calculated by Penman-Monteith equation;
• and Kc is a crop coefficient;
• or Qdemand=h·ZQdemand=h·Z, wherein Z is crop acreage in a field;
• h=h1+P−S−α·E0h=h1+P−S−α·E0, wherein h1 is a depth of storage water in the field at beginning of the forecast period, and h is a depth of the storage water in the field at end of the forecast period;
• P is the amount of rainfall;
• S is the amount of water leakage in the field;
• α·E0 is the amount of evaporation of the field;
• E0 is the amount of evaporation from water surface;
• and a is a coefficient of crop water demand in each growth period;
• or Qdemand=h·ZQdemand=h·Z, wherein Z is the crop acreage in the field;
• h=h1+P−E h=h1+P−E, wherein P is the amount of rainfall;
• and E is the amount of evaporation from land surface;
• the freshwater source calculation model is expressed as follows:
• Qfreshwater=Qrainfall+Qreclaimed water+Qdiversion water+Qgroundwater;Qfreshwater=Qrainfall+Qreclaimed water+Qdiversion water+Qgroundwater
• wherein Qrainfall=α·I·A, is a runoff coefficient;
• I is the amount of rainfall during the forecast period;
• A is a runoff gathering area, Qreclaimed water is the amount of reclaimed water;
• Qdiversion water is the amount of freshwater by water diversion project;
• and Qgroundwater is the amount of groundwater supply;
• an irrigation process comprises the following modes:
• when Qsupply=Qfreshwater=Qrainfall≤Qdemand Qsupply=Qfreshwater=Qrainfall≤Qdemand, the freshwater is sufficient to meet requirements of crop growth during the forecast period, and hupper or θupper is taken as limit index for stage crop;
• when a water level in field and a water content in soil are higher than hupper or θupper, excess rainwater is drained into ditch, pond and water course around the field to be stored for use;
• when Qsupply=Qfreshwater=Qrainfall Qreclaimed water≥Qdemand Qsupply=Qfreshwater=Qrainfall+Qreclaimed water≥Qdemand, the freshwater is sufficient to meet the requirements of crop growth during the forecast period, and hupper and hlower or θupper and θlower are taken as control indexes according to crop growth stages;
• when the water level in field and the water content in soil are higher than hupper or θupper, excess freshwater is drained into ditch, pond and water course around the field to be stored for use;
• when the water level in field and the water content in soil are lower than hlower or θlower, the field is irrigated according to water demand calculated by the water demand calculation model for coastal crops;
• when Qfreshwater=Qrainfall+Qreclaimed water<Qdemand Qfreshwater=Qrainfall+Qreclaimed water<Qdemand, a minimum amount Qminimum diversion water of the freshwater by water diversion project is calculated by the freshwater source calculation model and the multi-source water of mixed salt-fresh water calculation model;
• the Qminimum diversion water is no more than (Qdemand−Qrainfall−Qreclaimed water)+Qdemand−Qrainfall−Qreclaimed water);
• hlower or θlower is taken as limit index for stage crop;
• and when the water level in field and the water content in soil are lower than hlower or θlower, the field is irrigated according to the water demand calculated by the water demand calculation model for coastal crops;
• and
• when Qfreshwater=Qrainfall+Qreclaimed water+Qdiversion water<Qdemand Qfreshwater=Qrainfall+Qreclaimed water+Qdiversion water<Qdemand, a minimum amount Qminimum groundwater of freshwater by groundwater supply is calculated according to the multi-source water of mixed salt-fresh water calculation model;
• hlower or θlower is taken as limit index for stage crop;
• and when the water level in field and the water content in soil are lower than hlower or θlower, the field is irrigated according to the water demand calculated by the water demand calculation model for coastal crops;
• wherein hupper is an upper threshold of the water level in field;
• θupper is an upper threshold of the water content in soil;
• hlower is a lower threshold of the water level in field;
• and
• θlower is a lower threshold of the water content in soil.